Seawater-corrosion-resistant low-alloy high-strength steel plate and preparation method thereof

Abstract

The invention relates to the technical field of steel for ocean engineering, in particular to a seawater-corrosion-resistant low-alloy high-strength steel plate and a preparation method thereof. A proportioning system of strengthening elements such as C, Nb, V, Ti and Mo is innovatively optimized, meanwhile, Zr, Mg and rare earth elements (La and Ce) are introduced for inclusion modification treatment, and elements such as Cr, Ni and Cu are cooperatively utilized for improving the corrosion-resisting intrinsic performance of a matrix; in the aspect of a production process, a whole-process precise regulation and control technology of controlled rolling, ultrafast cooling and optimized quenching and tempering heat treatment is adopted, and finally the high-performance steel plate with the strength, the toughness and the corrosion resistance cooperatively matched is prepared. According to the steel plate, the excellent mechanical properties that the yield strength is larger than or equal to 690 MPa and the low-temperature impact energy at the temperature of-60 DEG C is larger than or equal to 100 J can be achieved, the excellent corrosion resistance is shown in the harsh seawater environment, the stability of the production process is high, and the steel plate is suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention relates to the field of steel technology for marine engineering, and in particular to a low-alloy high-strength steel plate resistant to seawater corrosion and its preparation method. Background Technology

[0002] Although China has made some progress in the development of steel for offshore platforms, it still relies on imports for certain high-end materials, such as high-toughness, corrosion-resistant, and easily weldable steel for offshore platforms with good comprehensive mechanical properties, a thickness of over 120mm, a yield strength of over 690MPa, and other characteristics. The complex marine environment, including high humidity and high salinity, causes severe corrosion to steel, and these factors are significant constraints on the development of such materials.

[0003] In recent years, researchers have obtained a series of high-performance marine engineering steels by designing or controlling the microstructure of steel through chemical composition. For example, Chinese patent document CN117210766A discloses "A marine engineering steel resistant to seawater corrosion and its preparation method," which significantly improves corrosion resistance. However, its yield strength and plate thickness are not reflected, failing to meet the requirements of modern countries for thick and wide marine engineering steel plates. Chinese patent documents CN117660836A and CN116377343B disclose "High-strength marine engineering steel with high ductility and resistant to marine atmospheric corrosion and its manufacturing method" and "A marine engineering steel plate for service in polar marine environments and its manufacturing method." These patents obtain high-strength marine engineering steel with high ductility and resistant to marine atmospheric corrosion through the design of reasonable chemical composition and the control of microstructure, but their yield strength is relatively low; similarly, they cannot provide a theoretical basis for the design and manufacture of thick and wide plates with a strength greater than 690 MPa. Chinese patent documents with patent numbers CN115094322A, CN115354240B, CN102392192B, CN102965592B, CN117802403A, CN116288064B, CN112746224A, and CN117026090A disclose "An 80mm thick 690MPa grade ultra-high strength and toughness marine engineering steel plate and its preparation method", "An economical seawater erosion resistant steel plate and its manufacturing method", and "An 80mm thick low compression ratio marine engineering steel". Patents such as "A Steel Plate with Low Compressibility Ratio and its Manufacturing Method," "A Production Method for a Thick, Ultra-High Strength Marine Engineering Steel Plate with Low Compressibility Ratio," "Ultra-High Strength Marine Engineering Steel with High Ductility and Resistance to Marine Atmospheric Corrosion and its Manufacturing Method," "An Ultra-High Strength Corrosion-Resistant Low-Temperature Marine Engineering Steel Plate and its Manufacturing Method," "A 690MPa Grade Marine Engineering Steel Plate and its Manufacturing Method," and "A 690MPa Grade Bridge Steel Plate with Heavy Industrial Atmospheric Corrosion Resistance and its Manufacturing Method" improve the corrosion resistance or strength of marine engineering steel through special component ratios and heat treatment processes. However, their processes are complex and not conducive to industrial production. Chinese patent document CN111057965B discloses "A Marine Engineering Steel with Low Yield-to-Strength Ratio and its Preparation Method," which significantly improves corrosion resistance, but the heat treatment process is complex and difficult to implement in industrial production. Chinese patent document CN112095052B discloses "Corrosion-Resistant Steel and its Preparation Method and Application, Corrosion-Resistant Steel Plate and its Preparation Method," which significantly improves corrosion resistance, but mechanical properties are not reflected.

[0004] In summary, most marine engineering steels currently cannot simultaneously meet the requirements of high yield strength and high corrosion resistance. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by proposing a low-alloy high-strength steel plate resistant to seawater corrosion and its preparation method, which simultaneously achieves high strength of over 690MPa, excellent low-temperature toughness of over 100J at -60℃, and corrosion resistance in seawater environments.

[0006] The first objective of this invention is to provide a low-alloy high-strength steel plate resistant to seawater corrosion, wherein the steel plate comprises the following chemical composition in weight percentages: C:0.05-0.18%, Si:0.17-0.80%, Mn: 1.25-1.70%, P:≤0.008%, S:≤0.010%, Al: 0.018-0.050%, Nb: 0.02-0.06%, V: 0.001-0.006, Ti: 0.01-0.05%, Ni: 0.45-1.67%, Cr: 0.20-0.95%, Cu: 0.15-0.55%, Mo: 0.15-0.45%, Mg: 0.000 5-0.0050%, Ca: 0.0005-0.0020%, N: 0.0030-0.0070%, Zr: 0.008-0.020%, Ce: 0.0001-0.005%, La: 0.0001-0.005%, balance being Fe and unavoidable impurities; and the contents of the above elements must simultaneously satisfy the following relationships: 0.34≤C / Si≤0.50; 2.31≤Ni / Cu≤4.80; 5.1≤(Ce+Zr+La) / (Mg+Ca)≤9.5; 1.30≤(Mn+Cr) / Mn≤1.60; 0.35≤Nb+V+Ti+Mo≤0.60; 0.21≤(V+Ti+Nb) / Mo≤0.40; 22≤(Mn+Si) / (Ti+RE)≤30; 0.030≤(Zr+Ti+RE) / (Cr+Cu+Ni)≤0.063.

[0007] Furthermore, the density of corrosive inclusions in the steel plate is ≤8 inclusions / mm². 2 .

[0008] Furthermore, the average size of the corrosion-active inclusions in the steel plate is <4μm.

[0009] Furthermore, the microstructure of the steel plate is bainite + martensite.

[0010] Furthermore, the steel plate exhibits a maximum impedance ≥1200Ω at a 60-minute open-circuit potential, and a self-corrosion current density ≤2E-05A / cm² when scanned within the range of -0.3V to 0.3V. 2 .

[0011] Furthermore, the steel plate underwent a cyclic immersion wet-dry cycle test in a seawater solution at 35°C for 48 hours, with a weight loss rate of <400g / m. 2 ·h.

[0012] Furthermore, the steel plate has a yield strength ≥690MPa and a Charpy V-notch impact energy ≥100J at -60℃.

[0013] A second objective of this invention is to provide a method for preparing a low-alloy high-strength steel plate resistant to seawater corrosion as described above, comprising the following steps: S1, Smelting Hot metal pretreatment: S ≤ 0.001%; Converter steelmaking: When the oxygen content is <50ppm, add Zr-Mg alloy and rare earth elements in the mass percentages described in claim 1; Refining: Refine for 10-15 minutes until the oxygen content is <5ppm; Vacuum treatment: The vacuum chamber pressure is ≤50Pa, the ultimate vacuum is maintained, and then calcium treatment is performed; S2, Continuous Casting Constant casting speed, liquidus temperature 1531-1563℃; S3, Rolling The initial rolling temperature of the continuously cast billet is 1050-1105℃, and the final rolling temperature is 830-860℃; after rolling, it is cooled by laminar water to 450-580℃, and then air-cooled to room temperature; S4, tempering heat treatment Quenching: Heat to 823-859℃, hold at that temperature according to thickness, and then water quench. Tempering: Reheat to 625-668℃, hold at that temperature, and then quench in water.

[0014] The following details the reasons for limiting the amounts of the main chemical components in this invention: Carbon: As an essential element in steel, C can not only play a role in solid solution strengthening in steel, but also form carbides to achieve precipitation strengthening, thereby improving the yield strength of steel. However, excessive C will deteriorate the impact toughness and lead to a significant deterioration in weldability and corrosion resistance. Therefore, the mass percentage of C in the steel of this invention is 0.05-0.18%.

[0015] Silicon (Si) is a deoxidizing element in steel and can also exist in steel in solid solution form, increasing the steel's strength. However, excessive Si prevents carbon (C) in the steel from combining with elements such as Nb, Ti, and V, resulting in the complete formation of carbides and thus causing the yield strength to fall short of the expected value. Therefore, the mass percentage of Si in the steel of this invention is 0.17-0.80%.

[0016] Manganese (Mn): Mn can improve the hardenability of steel, but excessive Mn can cause segregation and affect the toughness of the weld heat-affected zone. Therefore, the mass percentage of Mn in the steel of this invention is 1.25-1.70%.

[0017] Phosphorus and sulfur: P and S are impurity elements that are difficult to remove during steelmaking. They impair the toughness and weldability of steel, and the content of P and S should be controlled within a low range as much as possible. Therefore, the mass percentage of P and S in the steel of this invention is P: ≤0.008% and S: ≤0.010%.

[0018] Aluminum: Al can be used as a deoxidizing element in steel, but if its content is too high, the billet is prone to cracking and it affects the surface quality during the rolling process. Therefore, the mass percentage of Al in the steel of this invention is 0.018-0.050%.

[0019] Niobium, vanadium, titanium, and molybdenum: Nb effectively improves the hardenability of steel and forms fine carbides, but excessive Nb can affect the weldability of steel; therefore, the mass percentage of Nb should be 0.020-0.060%. V and Ti can form stable carbides / nitrides with C and N, improving the mechanical properties of steel; however, excessive V can affect the toughness of steel. Therefore, the mass percentages of V and Ti are V: 0.001-0.006 and Ti: 0.01-0.05%, respectively. Mo can significantly improve the hardenability of steel and also has the effect of stabilizing carbides, thus having a positive effect on strength. Therefore, the mass percentage of Mo should be 0.15-0.45%. To achieve the best effect from the combination of niobium, vanadium, titanium, and molybdenum, the following formulas must be satisfied: 0.35≤Nb+V+Ti+Mo≤0.60; 0.21≤(V+Ti+Nb) / Mo≤0.40.

[0020] Nickel and copper: Ni can improve the hardenability and low-temperature toughness of steel, while Cu can precipitate nano-scale carbides during heat treatment, enhancing the precipitation strengthening effect. However, excessive Cu will lead to a decrease in toughness. To ensure both toughness and maximize the precipitation of Cu carbides, the mass percentages of Ni and Cu are Ni: 0.45-1.67% and Cu: 0.15-0.55%, respectively.

[0021] Chromium (Cr): In marine environments, Cr can form a dense oxide film on the surface of steel, improving its corrosion resistance. However, excessive Cr will affect the mechanical properties of the tested steel. Therefore, the mass percentage of Cr is 0.20-0.95%, and it satisfies 1.30≤(Mn+Cr) / Mn≤1.60.

[0022] Boron: P has low solubility in steel, but it can significantly improve the hardenability of steel. Therefore, the mass percentage of P is ≤0.008%.

[0023] Magnesium and calcium: Mg and Ca can reduce the content of S and O in steel, and the optimal ratio of the two can effectively change the shape of inclusions, thereby improving the corrosion resistance of steel. Therefore, the mass percentages of Mg and Ca are Mg: 0.0005-0.0050% and Ca: 0.0005-0.0020%.

[0024] Zirconium, cerium, and lanthanum: The addition of Zr, Ce, and La to steel can comprehensively improve its corrosion resistance. Under certain conditions, Zr, Ce, and La can adhere to easily corroded inclusions such as MnS and CaO, reducing the probability of pitting corrosion and significantly enhancing the steel's corrosion resistance. Therefore, the mass percentages of Zr, Ce, and La are: Zr: 0.008-0.020%, Ce: 0.0001-0.005%, and La: 0.0001-0.005%, respectively, and must satisfy the following conditions: 22≤(Mn+Si) / (Ti+RE)≤30, 0.030≤(Zr+Ti+RE) / (Cr+Cu+Ni)≤0.063, and 5.1≤(Ce+Zr+La) / (Mg+Ca)≤9.5.

[0025] Nitrogen: N can form fine and stable carbides with elements such as Ti, V, and Nb, increasing the yield strength of steel. However, excessive N can lead to the formation of small voids in the steel, becoming the origin of cracks and deteriorating the various mechanical properties of the steel. Therefore, the mass percentage of N is 0.0030-0.0070%.

[0026] In terms of composition design, this invention innovatively optimizes the ratio of strengthening elements such as C, Nb, V, Ti, and Mo, while introducing Zr, Mg, and rare earth elements (La, Ce) for inclusion modification treatment, and synergistically utilizing elements such as Cr, Ni, and Cu to enhance the intrinsic corrosion resistance of the matrix. In terms of production process, a precise control technology is adopted throughout the entire process, combining controlled rolling, ultra-rapid cooling, and optimized tempering heat treatment, ultimately producing a high-performance steel plate with a synergistic balance of strength, toughness, and corrosion resistance. This steel plate not only achieves excellent mechanical properties such as a yield strength ≥690MPa and a low-temperature impact energy ≥100J at -60℃, but also exhibits outstanding corrosion resistance in harsh seawater environments (weight loss rate <400g / m³ after 48 hours of wet and dry cycling). 2 It has strong production process stability and is suitable for large-scale industrial production.

[0027] The beneficial effects of this invention are as follows: the composition design, which combines Zr, Ce, La, Mg, and Ca elements (i.e., 5.1 ≤ (Ce + Zr + La) / (Mg + Ca) ≤ 9.5), improves the morphology, quantity, and size of inclusions, resulting in inclusion sizes smaller than 4 μm and inclusion densities ≤ 8 inclusions / mm². 2Furthermore, the addition of Zr, Ce, and La allows corrosion-resistant structures to adhere around traditionally easily corroded inclusions, and reduces stress concentration between the inclusions and the aggregate, ultimately leading to a significant improvement in corrosion resistance. Its weight loss rate after 48 hours of wet-dry cycling is <400 g / m³. 2 ·h.

[0028] By precisely controlling the interactions of Nb, V, and Mo, we successfully formed a large number of nanoscale carbonitrides in marine steel. In particular, by limiting the contents of Nb, V, and Mo to within the range of 0.35 ≤ Nb + V + Ti + Mo ≤ 0.60 and 0.21 ≤ (V + Ti + Nb) / Mo ≤ 0.40, we not only promoted the synergistic effect of these elements but also significantly improved the steel's properties. This precise control of chemical composition resulted in steel exhibiting superior mechanical properties: a yield strength exceeding 690 MPa and an impact toughness exceeding 100 J at -60℃. Attached Figure Description

[0029] Figure 1 The microstructure of the marine engineering steel of Embodiment 1 of the present invention is shown. Figure 2 The impedance results of the marine engineering steel prepared in Example 1 of this invention were measured in a chloride ion medium. Figure 3 The impedance results of the marine engineering steel prepared in Comparative Example 1 of this invention were measured in a chloride ion medium. Figure 4 The potentiodynamic polarization results of the marine engineering steel prepared in Example 1 of this invention were measured in a chloride ion medium. Figure 5 The potentiodynamic polarization results of the marine engineering steel prepared in Comparative Example 1 of this invention were measured in a chloride ion medium. Figure 6 Photographs of corrosion-active inclusion elements in marine engineering steel prepared in Example 1 of this invention; Figure 7 This is a photograph of the corrosive inclusion elements in the marine engineering steel prepared in Comparative Example 1 of this invention. Detailed Implementation

[0030] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0031] Table 1 below is a list of chemical composition values ​​for each embodiment and comparative example of the present invention; Table 2 below shows the numerical values ​​of the chemical composition of each embodiment and comparative example of the present invention in relation to the corresponding equations. Table 3 below lists the main process parameter values ​​for each embodiment and comparative example of the present invention; Table 4 below lists the test results of the main mechanical properties of the embodiments and comparative examples of the present invention.

[0032] The processing technology of the steel plate of this invention: (1) Smelting and refining: 1. Hot metal pretreatment: S < 0.001% 2. Converter steelmaking: Add Zr-Mg alloy and rare earth elements when oxygen content is <50ppm; 3. Refining: Refine for 10-15 minutes until the oxygen content is <5ppm; 4. Vacuum treatment: The vacuum chamber pressure is ≤50Pa, and the ultimate vacuum is maintained before calcium treatment.

[0033] (2) Continuous casting Constant casting speed, liquidus temperature 1531-1563℃.

[0034] (3) Rolling The initial rolling temperature of the continuously cast billet is 1050-1105℃, and the final rolling temperature is 830-860℃. After rolling, it is cooled by laminar water to 450-580℃, and then air-cooled to room temperature.

[0035] (4) Tempering and tempering heat treatment 1. Quenching: Heat to 823-859℃, hold at the specified temperature according to thickness, and then water quench; 2. Tempering: Reheat to 625-668℃, hold at the specified temperature, and then water quench.

[0036] In this invention, the chemical composition design and related processes of Examples 1-3 all meet the design specifications of this invention. The chemical composition design can be found in Tables 1 and 2 below.

[0037] In contrast to Comparative Examples 1-2, the marine engineering steel, although produced using the same process as described above—smelting and casting, rolling, quenching and tempering—has chemical composition and related process parameters that fail to meet the design requirements of this invention.

[0038] Table 1. List of chemical components (wt, %) of various embodiments and comparative examples of the present invention

[0039] Table 2. Chemical composition (wt, %) of each embodiment and comparative example of the present invention to the corresponding equations

[0040] Table 3. List of main process parameters for each embodiment and comparative example of the present invention

[0041] The microstructure of marine engineering steel obtained according to the above composition and preparation process is lath martensite. Figure 1)

[0042] The following analysis and testing of the corrosion resistance and mechanical properties of the ultra-high marine atmospheric corrosion resistant marine engineering steel prepared by the examples are presented below.

[0043] 1. Testing Method (1) Potential polarization experiment Electrochemical corrosion was performed using a 3.5% sodium chloride (NaCl) solution as the corrosive medium, creating a simulated corrosion environment at room temperature. The electrochemical testing employed a classic three-electrode system: the test sample as the working electrode, a platinum electrode as the auxiliary electrode, and a saturated calomel electrode (SCE) as the reference electrode. The testing equipment consisted of a Princeton VersaSTAT 4A electrochemical workstation. Test parameters were set and adjusted using Thales electrochemical analysis software. The workstation was connected to the computer system for real-time monitoring, data acquisition, and recording during the testing process.

[0044] Electrochemical corrosion testing was conducted at room temperature, with the core tests being the potentiodynamic polarization curves (Tafel curves) and electrochemical impedance spectroscopy (EIS) of small sample pieces. Before starting the test, the open-circuit potential (OCP) of the system was measured for 1 hour. After reaching a stable state, the electrochemical impedance spectroscopy and potentiodynamic polarization tests were performed sequentially. The electrochemical impedance spectroscopy parameters were set as follows: a sinusoidal perturbation signal with an amplitude of 10 mV was applied, and the test frequency scan range was 10 mHz to 10 kHz; the potentiodynamic polarization test used a scan rate of 0.5 mV / s, and the potential scan range was -0.3 V to 0.3 V (relative to a saturated calomel reference electrode, SCE). After the tests, Origin and ZsimpWin software were used to perform fitting analysis and plotting of the potentiodynamic polarization curves and electrochemical impedance spectroscopy data.

[0045] All corrosion electrochemical tests were performed using a classic three-electrode system, with the following configuration: the test sample was used as the working electrode, a saturated calomel electrode (SCE) as the reference electrode, and a platinum sheet as the counter electrode. The entire test was conducted at room temperature (25°C). For weld metal samples in the weld state, the test procedure was as follows: First, the sample was immersed in the corrosion solution for open circuit potential (OCP) monitoring for 60 minutes. After the open circuit potential reached a stable state, the electrochemical impedance spectroscopy (EIS) test was initiated. The applied sinusoidal perturbation signal had an amplitude of 10 mV, the frequency scan range was set to 10 mHz–10 kHz, and the duration of a single scan was 60 minutes.

[0046] (2) Determination of inclusion density The sample was cut into 10×10×10mm blocks, and the surface was mechanically ground to 2000 grit and then polished to a mirror finish. It was then cleaned with deionized water, rinsed with alcohol, and dried. Surface stains and foreign matter were removed by wiping with a non-woven cloth. Inclusions were automatically identified under a scanning electron microscope, and those within a certain area were screened and statistically analyzed.

[0047] (3) Dry and wet cycle test According to the national standard GB / T19746-2018, artificial seawater (pH=8.2) was prepared, and the wet-dry cycle test chamber (model) was set to 37℃. A 48-hour wet-dry cycle test was conducted. The sample was weighed before corrosion and again after removing the rust layer. The rate of weight loss was calculated.

[0048] (4) Impact test Charpy V-notch impact testing was performed strictly according to ASTM E23 standard. The specimen dimensions used were 10mm × 10mm × 55mm, with notch design parameters of 2mm depth and root radius of curvature of 0.25mm. The test was conducted at a low temperature of -60℃, using liquid nitrogen to cool the specimens. After the specimens reached the set test temperature, they were held at that temperature for at least 5 minutes to ensure internal temperature uniformity. The impact absorbed energy of the specimens was then measured using an impact testing machine. To ensure the reliability of the test data, three specimens were prepared in parallel for each test condition and the tests were repeated. The final result was the arithmetic mean of the three test data.

[0049] (5) Tensile test In accordance with the provisions of the national standard GB / T2975, representative samples were selected from the marine engineering steel materials of Examples 1-3 and Comparative Examples 1-2, and standard tensile test specimens were prepared. Subsequently, tensile performance tests were carried out according to the test methods and procedures in the national standard GB / T228.1. The core objective was to accurately determine the yield strength index of each batch of marine engineering steel to provide basic data for the evaluation of the material's mechanical properties.

[0050] 2. Test Results and Analysis Table 4. List of performance test and analysis results for each embodiment and comparative example of the present invention

[0051] Based on the data in Table 4, we can see that the steel prepared by this invention exhibits excellent corrosion resistance: the density of corrosion-active inclusions is controlled to be less than 3 per square millimeter, the size of the inclusions is less than 4 μm, and the number of inclusions in the matrix is ​​less than 8 per mm. 2 In addition, this steel has excellent mechanical properties, with a yield strength exceeding 690 MPa and an impact toughness greater than 100 J even at extremely low temperatures of -60°C.

[0052] Figure 2 The impedance results of the marine engineering steel prepared in Example 1 of this invention were measured in a chloride ion medium. Figure 3 The impedance results of the marine engineering steel prepared in Comparative Example 1 of this invention were measured in a chloride ion medium. Figure 4 The potentiodynamic polarization results of the marine engineering steel prepared in Example 1 of this invention were measured in a chloride ion medium. Figure 5 The potentiodynamic polarization results of the marine engineering steel prepared in Comparative Example 1 of this invention were measured in a chloride ion medium. Figure 2-5 It can be seen that the impedance of Example 1 is much greater than that of Comparative Example 1, and it has a more positive potential and a smaller current density, which indicates that Example 1 has better corrosion resistance.

[0053] Figure 6 Photographs of corrosion-active inclusion elements in marine engineering steel prepared in Example 1 of this invention; Figure 7 This is a photograph of the corrosive inclusion elements in the marine engineering steel prepared in Comparative Example 1 of this invention. Figure 6 , 7 It can be seen that the inclusions dissolved in Example 1 form a relatively dense cavity with shallower pores, while the inclusions dissolved in Comparative Example 1 form deeper pores.

[0054] Further analysis of the data in Table 2 revealed that when Comparative Examples 1 and 2 did not meet the condition 5.1 ≤ (Ce + Zr + La) / (Mg + Ca) ≤ 9.5, the size and density of inclusions in the steel increased, leading to a significant decrease in corrosion resistance. The main reason for this phenomenon is that only when the above ratio condition is met can elements such as Ce, Zr, and La effectively inhibit the formation and growth of inclusions. These elements can also form a protective film around the inclusions, better integrating with the matrix, thereby slowing down the corrosion rate starting from the inclusions and significantly improving the corrosion resistance of the steel.

[0055] In the steels of Comparative Examples 1 and 2, although the proportions of Nb (niobium), V (vanadium), Ti (titanium), and Mo (molybdenum) met the requirement of 0.21 ≤ (V + Ti + Nb) / Mo ≤ 0.40, their total content did not meet the range of 0.35 ≤ Nb + V + Ti + Mo ≤ 0.60. This resulted in a significant reduction in the formation of complex carbonitrides in the steel. Since these carbonitrides play a crucial role in improving the strength of steel, their reduction to some extent lowered the yield strength of the steel plate. Specifically, the yield strength of both comparative steels was below 460 MPa, far below the performance requirements of 690 MPa grade steel.

[0056] In the steel of Comparative Example 1, the failure to meet the chemical composition ratio requirements of 2.31≤Ni / Cu≤4.80 and 0.34≤C / Si≤0.50 resulted in a significant decrease in its yield strength and impact toughness at -60℃. The addition of Ni can improve the hardenability and enhance low-temperature toughness of the steel, while Cu can precipitate nanoscale carbides during heat treatment, thereby enhancing precipitation strengthening. However, excessive Cu leads to a decrease in toughness. Si exists in the steel in solid solution form, which can increase the steel's strength, but excessive Si prevents C from combining with elements such as Nb, Ti, and V, thus inhibiting carbide formation and causing the yield strength to fail to reach the expected value.

[0057] While the steel in Comparative Example 2 met the ratio requirement of 2.31 ≤ Ni / Cu ≤ 4.80, it failed to meet the restriction of 0.34 ≤ C / Si ≤ 0.50. Therefore, its toughness and yield strength were somewhat affected, although it still exhibited better performance than Comparative Example 1. This indicates that only when the ratios of Ni, Cu, C, and Si simultaneously meet certain requirements can steel possess both high toughness and high strength. Therefore, precisely controlling the ratios of these elements is crucial for achieving high-performance steel.

[0058] For any points not covered above, existing technologies shall apply.

[0059] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-alloy high-strength steel plate resistant to seawater corrosion, characterized in that: The steel plate contains the following chemical composition by weight percentage: C: 0.05-0.18%, Si: 0.17-0.80%, Mn: 1.25-1.70%, P: ≤0.008%, S: ≤0.010%, Al: 0.018-0.050%, Nb: 0.02-0.06%, V: 0.001-0.006%, Ti: 0.01-0.05%, Ni: 0.45-1.67%, Cr: 0.20-0.95%, Cu: 0.15-0.55%, Mo: 0.15-0.45%, Mg: 0.0005-0.0050%, Ca: 0.0005-0.0020%, N: 0.0030-0.0070%, Zr: 0.0 0.020%, Ce: 0.0001-0.005%, La: 0.0001-0.005%, balance being Fe and unavoidable impurities; and the contents of the above elements must simultaneously satisfy the following relationships: 0.34≤C / Si≤0.50; 2.31≤Ni / Cu≤4.80; 5.1≤(Ce+Zr+La) / (Mg+Ca)≤9.5; 1.30≤(Mn+Cr) / Mn≤1.60; 0.35≤Nb+V+Ti+Mo≤0.60; 0.21≤(V+Ti+Nb) / Mo≤0.40; 22≤(Mn+Si) / (Ti+RE)≤30; 0.030≤(Zr+Ti+RE) / (Cr+Cu+Ni)≤0.

063.

2. The low-alloy high-strength steel plate resistant to seawater corrosion according to claim 1, characterized in that: The density of corrosion-active inclusions in the steel plate is ≤8 inclusions / mm². 2 .

3. The low-alloy high-strength steel plate resistant to seawater corrosion according to claim 1, characterized in that: The average size of the corrosion-active inclusions in the steel plate is <4μm.

4. The low-alloy high-strength steel plate resistant to seawater corrosion according to claim 1, characterized in that: The microstructure of the steel plate is bainite + martensite.

5. A low-alloy high-strength steel plate resistant to seawater corrosion according to claims 1 to 3, characterized in that: The steel plate, under 60-minute open-circuit potential, has a maximum impedance ≥1200Ω, and a self-corrosion current density ≤2E-05A / cm² when scanned within the range of -0.3V to 0.3V. 2 .

6. A low-alloy high-strength steel plate resistant to seawater corrosion according to claims 1 to 3, characterized in that: The steel plate was subjected to a cyclic immersion dry-wet cycle test in a seawater solution at 35°C for 48 hours, with a weight loss rate of <400g / m². 2 ·h.

7. The low-alloy high-strength steel plate resistant to seawater corrosion according to claim 1, characterized in that, The steel plate has a yield strength ≥690MPa and a Charpy V-notch impact energy ≥100J at -60℃.

8. A method for preparing a low-alloy high-strength steel plate resistant to seawater corrosion as described in any one of claims 1-7, characterized in that, Includes the following steps: S1, Smelting Hot metal pretreatment: S ≤ 0.001%; Converter steelmaking: When the oxygen content is <50ppm, add Zr-Mg alloy and rare earth elements in the mass percentages described in claim 1; Refining: Refine for 10-15 minutes until the oxygen content is <5ppm; Vacuum treatment: The vacuum chamber pressure is ≤50Pa, the ultimate vacuum is maintained, and then calcium treatment is performed; S2, Continuous Casting Constant casting speed, liquidus temperature 1531-1563℃; S3, Rolling The initial rolling temperature of the continuously cast billet is 1050-1105℃, and the final rolling temperature is 830-860℃; after rolling, it is cooled by laminar water to 450-580℃, and then air-cooled to room temperature; S4, tempering heat treatment Quenching: Heat to 823-859℃, hold at that temperature according to thickness, and then water quench. Tempering: Reheat to 625-668℃, hold at that temperature, and then quench in water.

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