Ocean atmosphere corrosion resistant 690MPa-grade steel for ocean engineering and preparation method of ocean atmosphere corrosion resistant 690MPa-grade steel

Abstract

The invention relates to the technical field of ocean engineering steel preparation, in particular to ocean atmospheric corrosion resistant 690MPa-grade ocean engineering steel and a preparation method thereof. The proportion of strengthening elements such as C, Nb, V, Ti and Mo is accurately controlled, elements such as Zr, Mg and RE (La and Ce) are introduced for inclusion modification, and meanwhile the corrosion resistance of a matrix is improved through elements such as Cr, Ni and Cu; and a full-flow production process of controlled rolling, ultrafast cooling and optimized quenched-tempered heat treatment is adopted, and finally the steel plate with the strength, toughness and corrosion resistance perfectly matched is obtained. The steel plate has FH690-grade high strength and excellent low-temperature toughness, more importantly, the steel plate shows excellent corrosion resistance in a harsh marine atmospheric environment, meanwhile, the production process is stable, and the steel plate is suitable for industrial large-scale production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel preparation for ocean engineering, and particularly relates to a 690MPa-grade ocean engineering steel resistant to marine atmospheric corrosion and a preparation method thereof. BACKGROUND

[0002] With the deepening of the strategy of building a strong marine country in China, the ocean engineering equipment puts forward higher requirements for the key structural material, i.e. the ocean engineering steel. The ocean engineering steel is long-term served in the harsh marine environment with high salt, high humidity and strong radiation, and faces the severe challenges of chloride ion corrosion and stress corrosion cracking. The corrosion resistance of the ocean engineering steel is directly related to the service safety and life of the marine equipment. At present, the ocean engineering steels developed at home and abroad are often difficult to simultaneously consider high strength, high toughness and excellent corrosion resistance. Although some steel materials perform well in corrosion resistance, the strength does not reach the requirement of 690MPa grade. Some steel materials reach the strength requirement, but sacrifice the low-temperature toughness (impact energy at-60 ℃ is less than 100 J) or corrosion resistance. In addition, the production process of some advanced steel materials is complex, and it is difficult to realize large-scale industrial application. In view of the current situation that the domestic rate of high-end ocean engineering steel is insufficient, it is an urgent need to develop the ocean engineering steel with ultra-high strength (yield strength ≥690 MPa), excellent low-temperature toughness (impact energy at-60 ℃ ≥100 J) and excellent corrosion resistance (weight gain after 250 hours of salt spray corrosion ≤0.021 mg / mm²), which supports the national marine strategy and breaks through the technical bottleneck.

[0003] In recent years, researchers have obtained a series of excellent performance of marine engineering steels by designing or regulating the microstructure of steel materials through chemical composition. For example, the Chinese patent documents with invention patents CN113584398A and CN109136752A disclose “Corrosion-resistant steel plate and production method of corrosion-resistant steel plate” and “420 MPa grade low yield ratio marine atmosphere corrosion resistant bridge steel and production method thereof”, which produce steel plates with high salt mist corrosion resistance, but the yield strength is far lower than the strength requirement of HF690 MPa marine steel; the Chinese patent document with invention patent CN112342352A discloses “Corrosion-resistant high-manganese austenitic steel plate and preparation method thereof”, which greatly improves the corrosion resistance of the steel, but uses a cold rolling process, which puts high requirements on the production equipment of marine steel and is not conducive to industrial production. The Chinese patent document with invention patent CN114959443A discloses “Marine corrosion-resistant high-strength steel material, round steel and manufacturing method thereof”, which greatly improves the strength and corrosion resistance of the steel material, but the room temperature impact toughness is only 80 J, which limits its use in marine environments; the Chinese patent document with invention patent CN111057965B discloses “Low yield ratio marine engineering steel and preparation method thereof”, which greatly improves the corrosion resistance of the steel, but the heat treatment process is extremely complex and not easy to use in industrial production; the Chinese patent documents with invention patents CN116179970A and CN112746224A disclose “900 MPa grade steel plate for extremely cold marine environments and manufacturing method thereof” and “690 MPa grade marine engineering steel plate and manufacturing method thereof”, which improve the strength and toughness, but the corrosion resistance needs to be further verified; the Chinese patent document with invention patent CN112095052B discloses “Corrosion-resistant steel material and preparation method and application thereof, and corrosion-resistant steel plate and preparation method thereof”, which greatly improves the corrosion resistance of the steel, but whether the strength and toughness meet the development needs needs to be further detected.

[0004] Currently, there is a technical problem in the prior art that existing marine steel plates cannot simultaneously meet the requirements of high strength of 690 MPa or more, excellent low temperature toughness of 100 J or more, and ultra-low salt mist corrosion weight gain in a hot and humid marine atmosphere environment. SUMMARY

[0005] The purpose of the present application is to overcome the above-mentioned deficiencies of the prior art, and to provide a 690 MPa grade marine engineering steel with ultra-high strength, excellent low temperature toughness and excellent marine atmospheric corrosion resistance, and a production method thereof.

[0006] The first object of the present application is to provide a 690 MPa grade marine engineering steel resistant to marine atmospheric corrosion, said marine engineering steel comprising the following chemical composition in mass percentage: C: 0.12-0.16%, Si: 0.38-0.46%, Mn: 1.20-1.70%, P: ≤ 0.003%, S: ≤ 0.0015%, Al: 0.02-0.06%, Nb: 0.040-0.055%, V: 0.040-0.070%, Ti: 0.080-0.120%, Ni: 0.96-1.80%, Cr: 0.30-0.85%, Cu: 0.30-0.46%, Mo: 0.30-0.50%, Mg: 0.0005-0.0010%, Ca: 0.0010-0.0018%, N: 0.0030-0.0070%, Zr: 0.008-0.020%, RE: 0.001-0.010%, the balance being Fe and inevitable impurities; and the above element contents must simultaneously satisfy the following relationships: 1.20 ≤ (Mn+Cr) / Mn ≤ 1.60; 0.25 ≤ Nb+V+Mo ≤ 0.55, and 0.12 ≤ (V+Nb) / Mo ≤ 0.40; 12 ≤ (Mn+Si) / (Ti+RE) ≤ 20; 0.025 ≤ Zr+Ti+RE) / (Cr+Cu+Ni) ≤ 0.072.

[0007] Further, the marine engineering steel has a saturation current density less than or equal to 6.0 mA under the condition that the constant electrode potential is equal to -300 mV.

[0008] Further, the marine engineering steel has a salt spray corrosion weight gain of the marine engineering steel of ≤ 0.021 mg / mm 2 .

[0009] Further, the marine engineering steel has a microstructure type of tempered martensite.

[0010] Further, the marine engineering steel has a corrosion active inclusion density less than or equal to 8 pieces / mm 2 .

[0011] Further, the marine engineering steel has a yield strength ≥ 690 Mpa.

[0012] Further, the steel has a Charpy V-notch impact energy ≥ 100 J under a low temperature environment of -60℃.

[0013] The second object of the present application is to provide a preparation method of the marine atmosphere corrosion resistant 690 MPa grade marine engineering steel. S1, smelting and refining: Hot metal pretreatment: the content of S in hot metal is ≤ 0.001%, and the front slag and rear slag are completely removed; Converter steelmaking: argon stirring is used throughout the process, and bottom argon blowing is used in the ladle after tapping; metal manganese and ferrosilicon are added for deoxidation when tapping, and the trace alloying elements according to claim 1 are added after the content of P is qualified; LF furnace refining: calcium carbide, ferrosilicon and manganese iron are added for deoxidation after entering the station, Zr, RE and Mg are added for deep deoxidation and alloying when the oxygen content is lower than 40 ppm, and the oxygen content is required to be lower than 5 ppm after refining for 10-15 min; RH vacuum treatment: the pressure in the vacuum chamber is ≤ 50 Pa, the limit vacuum holding time is ≥ 25 min, and calcium treatment is performed after vacuum treatment; S2, continuous casting: constant speed casting is used, the liquidus temperature is 1531-1563 ℃, the superheat is controlled at 12-26 ℃, and the casting speed is controlled at 0.50-0.62 m / min; S3, rolling: the continuous casting billet is rolled, the opening rolling temperature is controlled at 1079-1215 ℃, and the final rolling temperature is controlled at 900-930 ℃; after rolling, laminar cooling is immediately performed, and the steel plate is cooled to room temperature after air cooling to 350-420 ℃; S4, quenching: the rolled steel plate is heated to 839-886 ℃, and the holding time is 1-2 min / mm (calculated according to the thickness), and then water quenching is performed to room temperature; S5, tempering: the quenched steel plate is reheated to 600-620 ℃, and the holding time is 1-1.5 h, and finally water quenching is performed to room temperature.

[0014] The present application precisely controls the proportion of C, Nb, V, Ti, Mo and other strengthening elements through innovative component design, and introduces Zr, Mg, RE (La, Ce) and other elements for inclusion modification, while using Cr, Ni, Cu and other elements to improve the corrosion resistance of the matrix; and the whole process production process of "controlled rolling + ultra-fast cooling + optimized quenching and tempering heat treatment" is adopted, and finally the steel plate with perfect matching of strength, toughness and corrosion resistance is obtained. The steel plate not only has high strength (yield strength ≥ 690 MPa) and excellent low temperature toughness (impact energy ≥ 100 J at -60 ℃) of FH690 grade, but more importantly, it shows excellent corrosion resistance (weight gain ≤ 0.021 mg / mm² after 250 hours of salt spray corrosion) in severe marine atmospheric environment, and the production process is stable and suitable for large-scale industrial production.

[0015] The significant advantage of this invention lies in its effective solution to the problem of micro-galvanic cells formed by MnCr2O4 spinel and MnS inclusions in steel during salt spray corrosion. These micro-galvanic cells readily become corrosion initiation points, thereby accelerating the corrosion of the steel matrix. By precisely controlling the ratio of Mn to Cr, i.e., 1.20 ≤ (Mn+Cr) / Mn ≤ 1.60, this phenomenon can be significantly suppressed. Furthermore, by adjusting the contents of Al, Ca, Mg, and RE, easily corroded inclusions can be modified to reduce their size. For example, Mn-Si-O-MnS inclusions can be modified into Ti-Zr-O inclusions, and MgO-Al2O3 spinel can be transformed into MgO-Al2O3-TiO. x Inclusions, and Al2O3-SiO2-MnO-TiO x The composite inclusions transform into TiO x These modified inclusions are significantly smaller in size and have reduced surrounding stress, thus effectively inhibiting corrosion. To achieve effective modification of inclusions, the following condition must be met: 12 ≤ (Mn+Si) / (Ti+RE) ≤ 20. This precise control of chemical composition not only optimizes the composition and structure of inclusions but also significantly improves the overall corrosion resistance of the steel.

[0016] The main corrosion products generated during salt spray corrosion include α-FeOOH, γ-FeOOH, α-Fe₂O₃, and Fe₃O₄. Under specific conditions, γ-FeOOH can easily transform into α-FeOOH, and α-FeOOH, as one of the most stable corrosion products, provides a certain degree of protection to the steel surface. Adding RE (Ce, La) can promote the conversion of γ-FeOOH to α-FeOOH, thereby improving the density and protective properties of the rust layer. Furthermore, RE... 3+ The presence of Cr facilitates the existence of Cr in the rust layer as elemental or in the form of Cr₂O₃, which not only enhances the density of the surface rust layer but also effectively inhibits the propagation rate of localized corrosion. Furthermore, increasing the content of alloying elements such as Cr, Cu, and Ni also improves the density of the rust layer. Considering these factors, we determined the optimal ratio range of alloying element content: 0.025 ≤ (Zr+Ti+RE) / (Cr+Cu+Ni) ≤ 0.072. By modifying inclusions to delay the initiation of corrosion and by adjusting the density of the corrosion layer to suppress the corrosion rate, excellent corrosion resistance is ultimately achieved. Under a neutral salt spray corrosion environment of 40 ℃ and 70% relative humidity for 250 hours, the weight gain of the steel did not exceed 0.021 mg / mm², a result that fully demonstrates the significant effect of this invention in improving the corrosion resistance of steel.

[0017] 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 0.25 ≤ Nb + V + Mo ≤ 0.55 and 0.12 ≤ (V + 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 a low-temperature impact toughness exceeding 100 J at -60 °C. Attached Figure Description

[0018] Figure 1 This is a microstructure photograph of the marine engineering steel prepared in Example 1 of the present invention under an electron microscope; Figure 2 The constant potential polarization result of the marine engineering steel prepared in Example 1 of the present invention was measured in a chloride ion medium; Figure 3 The results of constant potential polarization of the marine engineering steel prepared in Comparative Example 1 of this invention were measured in a chloride ion medium. Figure 4 Photographs of corrosion-active inclusion elements in marine engineering steel prepared in Example 1 of this invention; Figure 5 This is a photograph of the corrosive inclusion elements in the marine engineering steel prepared in Comparative Example 1 of this invention. Detailed Implementation

[0019] To better explain the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to specific embodiments. The following embodiments are merely illustrative of the technical solution of the present invention and do not limit the present invention in any way. The sequence numbers of the following embodiments are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0020] 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 and corrosion properties of the embodiments and comparative examples of the present invention.

[0021] Examples 1-3 and Comparative Examples 1-2 The marine engineering steels in Examples 1-3 were all prepared using the following steps: (1) Smelting and refining: Hot metal pretreatment: The sulfur content of the hot metal leaving the station is ≤ 0.001%, and the front and rear slags are completely removed; Converter steelmaking: Argon blowing and stirring throughout the process, bottom blowing of argon into the ladle after tapping; metallic manganese and ferrosilicon are added for deoxidation during tapping, and trace alloying elements are added after the P content is qualified; LF furnace refining: After entering the station, calcium carbide, ferrosilicon and ferromanganese are added for deoxidation. When the oxygen content is lower than 40 ppm, Zr, RE and Mg are added for deep deoxidation and alloying. After refining for 10-15 minutes, the oxygen content is required to be lower than 5 ppm. RH vacuum treatment: vacuum chamber pressure ≤ 50 Pa, ultimate vacuum holding time ≥ 25 min, followed by calcium treatment; (2) Continuous casting: constant casting speed is adopted, liquidus temperature is 1531-1563 ℃, superheat is controlled at 12-26 ℃, and casting speed is controlled at 0.50-0.62 m / min; (3) Rolling: Roll the continuously cast billet, with the initial rolling temperature controlled at 1079-1215 ℃ and the final rolling temperature controlled at 900-930 ℃; immediately after rolling, laminar cooling is performed, and after cooling to 350-420 ℃, it is air-cooled to room temperature; (4) Quenching: Heat the rolled steel plate to 839-886 ℃, hold for 1-2 min / mm (calculated according to thickness), and then water quench to room temperature; (5) Tempering: Reheat the quenched steel plate to 600-620 ℃, hold for 1-1.5 h, and finally water quench to room temperature.

[0022] In this invention, the chemical composition design and related processes of the 690 MPa grade marine engineering steel in Examples 1-3 all meet the design specifications of this invention. The chemical composition design of the comparative steels in Examples 1-2 can be found in Tables 1 and 2 below.

[0023] 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.

[0024] The specific production process parameters of the 690 MPa grade marine engineering steel in Examples 1-3 are shown in Table 3.

[0025] Table 1. List of chemical components (wt%) of various embodiments and comparative examples of the present invention.

[0026] Table 2. Chemical composition (wt%) of each embodiment and comparative example of the present invention to the corresponding equations.

[0027] Table 3. List of main process parameter values ​​for each embodiment and comparative example of the present invention.

[0028] The marine engineering steel obtained according to the above composition and preparation process has a microstructure of tempered martensite (e.g., ...). Figure 1 (As shown).

[0029] 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.

[0030] 1. Testing Method (1) Potentially constant polarization experiment The constant potential saturation current density was measured using a Princeton VersaSTAT 4A electrochemical workstation.

[0031] Test method: Refer to the corrosion standard CTO 00190242-003-2017 "Method for determining the corrosion stability of carbon steel and low alloy steel" formulated by the Central Research Institute of Ferrous Metallurgy of Russia. Test experiment: A constant anodic potential of -300 mV (saturated silver chloride electrode) was applied for 60 min.

[0032] The potentiostatic polarization experiment was conducted in a classic three-electrode system. The electrochemical sample to be tested served as the working electrode, the AgCl electrode as the reference electrode, and the platinum sheet as the counter electrode. The test temperature was 25°C. The sample was immersed in the etching solution to test the open circuit potential (OCP) for 40 minutes. After the open circuit potential stabilized, the potentiostatic polarization test was started.

[0033] Figure 2 The constant potential polarization result of the marine engineering steel prepared in Example 1 of the present invention was measured in a chloride ion medium.

[0034] Figure 3 The results of constant potential polarization of the marine engineering steel prepared in Comparative Example 1 of this invention were measured in a chloride ion medium.

[0035] from Figure 2 , 3 It can be seen that the saturated current density of the marine engineering steel prepared in Example 1 is lower than that of the marine engineering steel prepared in Comparative Example 1.

[0036] (2) Determination of density of corrosive inclusions Cut the sample into 10×10×10 mm pieces, mechanically grind the surface to 1500 mesh, and then polish it to a mirror finish. Prepare the etching reagent according to the following ratio: each 100 mL ethanol solution contains 4.5-5.5 mL concentrated hydrochloric acid, 0.08-0.15 g CuCl2, 0.03-0.08 g SnCl2, and 2.6-3.4 g FeCl3. Drop the etching reagent onto the sample surface and treat for 5-10 seconds. Then rinse the surface with alcohol and blow it dry. Place the sample under a metallographic microscope at 100× magnification and count the density of the corrosion-active inclusions.

[0037] Figure 4 Photographs of corrosion-active inclusion elements in marine engineering steel prepared in Example 1 of this invention; Figure 5 This is a photograph of the corrosive inclusion elements in the marine engineering steel prepared in Comparative Example 1 of this invention.

[0038] from Figure 4 , Figure 5 It can be seen that the inclusions are modified after deep deoxidation and alloying with Zr, RE, and Mg.

[0039] (3) Neutral salt spray test According to ASTM B117-e16 standard, a 3.5±0.1% (mass fraction) NaCl solution (pH=6.8) was prepared. The salt spray chamber (model YWX-250) was set to 35±1 ℃, and the spray rate was 1.5 mL / h / cm². The sample was fixed to the support at a 30° tilt angle to ensure uniform salt spray deposition. The weight was measured before and after 250 hours of corrosion, and the weight gain was calculated.

[0040] (4) Impact test Charpy V-notch impact tests were performed according to ASTM E23. The specimen dimensions were 10 mm × 10 mm × 55 mm, with a notch depth of 2 mm and a notch root radius of 0.25 mm. The test was conducted at -60°C, with the specimens cooled to the test temperature using liquid nitrogen and held at this temperature for at least 5 minutes to ensure temperature uniformity. The impact energy absorbed by the specimens was then measured using an impact testing machine. Three specimens were tested under each condition, and the average value was taken.

[0041] (5) Tensile test Tensile test: Samples were taken from marine steels of Examples 1-3 and Comparative Examples 1-2 according to national standard GB / T2975 to prepare tensile specimens. Tensile properties were tested according to national standard GB / T228.1 to determine the yield strength of marine steels of Examples 1-3 and Comparative Examples 1-2.

[0042] 2. Test Results and Analysis As can be seen from the data in Table 4, the steels prepared in Examples 1-3 of this invention showed a weight gain of no more than 0.021 mg / mm² during a 250-hour neutral salt spray corrosion test (Example 1: 0.015 mg / mm², Example 2: 0.018 mg / mm², Example 3: 0.021 mg / mm²), which is significantly lower than that of Comparative Example 1 (0.086 mg / mm²) and Comparative Example 2 (0.073 mg / mm²). This excellent corrosion resistance is mainly attributed to two innovations: First, through careful composition design, the proportions of alloying elements were ensured to meet the following conditions: 1.20 ≤ (Mn+Cr) / Mn ≤ 1.60, 12 ≤ (Mn+Si) / (Ti+RE) ≤ 20. This controlled ratio effectively modifies inclusions, reducing corrosive inclusions such as MnCr2O4 spinel and MnS that easily cause lattice distortion, and replacing them with inactive inclusions such as MgO-Al2O3-TiOx and TiOx, thereby delaying the onset of corrosion. Regarding the density of corrosive inclusions, Examples 1-3 have a density of only 7.2-7.7 inclusions / mm², while Comparative Examples 1 and 2 have densities as high as 15.8 inclusions / mm² and 18.6 inclusions / mm², respectively, further demonstrating the advantages of this invention in inclusion modification. Secondly, by ensuring that the proportion of alloying elements in the steel is within the range of 0.025 ≤ (Zr+Ti+RE) / (Cr+Cu+Ni) ≤ 0.072, the density of the corrosion layer is enhanced, significantly reducing the corrosion rate. The addition of RE (Ce, La) promoted the conversion of γ-FeOOH to α-FeOOH, improving the protective properties of the rust layer. Simultaneously, it allowed Cr to exist in the rust layer as elemental or in the form of Cr₂O₃, further inhibiting the spread of localized corrosion. Saturation current density data also support this conclusion; the saturation current densities in Examples 1-3 were all below 6.0 mA / cm². 2 (Example 1: 5.455 mA / cm) 2 Example 2: 5.092 mA / cm 2 Example 3: 4.796 mA / cm 2 (), while comparative examples 1 and 2 reached as high as 7.433 mA / cm, respectively. 2 and 8.732 mA / cm 2 This indicates that the steel of the present invention has a lower tendency for electrochemical corrosion.

[0043] Through carefully designed synergistic effects of Nb, V, and Mo elements, we successfully formed a large number of micro- and nano-sized carbonitrides in marine engineering steel. In particular, when the contents of Nb, V, and Mo were controlled within the range of 0.25 ≤ Nb + V + Mo ≤ 0.55 and 0.12 ≤ (V + Nb) / Mo ≤ 0.40, the interaction of these elements significantly enhanced the formation of complex carbonitrides in the steel. These micro- and nano-sized precipitates greatly improved the material's properties, resulting in a yield strength exceeding 690 MPa and a low-temperature impact toughness exceeding 100 J at -60℃.

[0044] Comprehensive analysis shows that only when the element content and ratio requirements specified in this invention are met can the corrosion resistance and toughness of the steel reach their optimal state. Therefore, the key to this invention lies in precisely controlling the content and ratio of Nb, V, and Mo elements to achieve a comprehensive improvement in the performance of the steel.

[0045] Table 4. List of test and analysis results of mechanical and corrosion properties of various embodiments and comparative examples of the present invention.

[0046] For any points not covered above, existing technologies shall apply.

[0047] 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 marine engineering steel with a corrosion resistance of 690 MPa, characterized in that, The marine engineering steel comprises the following chemical composition by mass percentage: C: 0.12-0.16%, Si: 0.38-0.46%, Mn: 1.20-1.70%, P: ≤0.003%, S: ≤0.0015%, Al: 0.02-0.06%, Nb: 0.040-0.055%, V: 0.040-0.070%, Ti: 0.080-0.120%, Ni: 0.96-1.80%, Cr: 0.30-0.85%, Cu: 0.30-0.46%, Mo: 0.30-0.50%, Mg: 0.0005-0.0010%, Ca: 0.0010-0.0018%, N: 0.0030-0.0070%, Zr: 0.008-0.020%, RE: 0.001-0.010%, balance being Fe and unavoidable impurities; and the contents of the above elements must simultaneously satisfy the following relationships: 1.20 ≤ (Mn+Cr) / Mn ≤ 1.60; 0.25 ≤ Nb+V+Mo ≤ 0.55, and 0.12 ≤ (V+Nb) / Mo ≤ 0.40; 12 ≤ (Mn+Si) / (Ti+RE) ≤ 20; 0.025 ≤ (Zr+Ti+RE) / (Cr+Cu+Ni) ≤ 0.

072.

2. The marine engineering steel with a 690 MPa grade resistant to marine atmospheric corrosion according to claim 1, characterized in that, Under the condition that the constant electrode potential is -300 mV, the saturation current density of the steel is less than or equal to 6.0 mA.

3. The marine engineering steel with a 690 MPa grade resistant to marine atmospheric corrosion according to claim 1, characterized in that, Under neutral salt spray corrosion conditions in a NaCl solution with a temperature of 40 ℃, a relative humidity of 70%, and a mass fraction of 3.5%, the weight gain of the steel after 250 hours of salt spray corrosion is ≤ 0.021 mg / mm². 2 .

4. The marine engineering steel with a 690 MPa grade resistant to marine atmospheric corrosion according to claim 1, characterized in that, The microstructure of the steel used in marine engineering is tempered martensite.

5. The marine engineering steel with a 690 MPa grade resistant to marine atmospheric corrosion according to claim 1, characterized in that, The corrosion-active inclusion density of the marine engineering steel is less than or equal to 8 inclusions / mm². 2 .

6. The marine engineering steel with a 690 MPa grade resistant to marine atmospheric corrosion according to claim 1, characterized in that, The yield strength of the steel used in marine engineering is ≥ 690 MPa.

7. A marine engineering steel with a 690 MPa grade resistant to marine atmospheric corrosion according to claim 1, characterized in that, At a low temperature of -60℃, the Charpy V-notch impact energy of the marine engineering steel is ≥ 100 J.

8. A method for preparing a 690 MPa grade marine engineering steel resistant to marine atmospheric corrosion as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Smelting and Refining: Hot metal pretreatment: The sulfur content of the hot metal leaving the station is ≤ 0.001%, and the front and rear slags are completely removed; Converter steelmaking: Argon blowing and stirring throughout the process, bottom blowing of argon into the ladle after tapping; metallic manganese and ferrosilicon are added for deoxidation during tapping, and trace alloying elements as described in claim 1 are added after the P content is qualified. LF furnace refining: After entering the station, calcium carbide, ferrosilicon and ferromanganese are added for deoxidation. When the oxygen content is lower than 40 ppm, Zr, RE and Mg are added for deep deoxidation and alloying. After refining for 10-15 minutes, the oxygen content is required to be lower than 5 ppm. RH vacuum treatment: vacuum chamber pressure ≤ 50 Pa, ultimate vacuum holding time ≥ 25 min, followed by calcium treatment; S2, Continuous casting: Constant casting speed is used, liquidus temperature is 1531-1563 ℃, superheat is controlled at 12-26 ℃, and casting speed is controlled at 0.50-0.62 m / min; S3. Rolling: Roll the continuously cast billet, with the initial rolling temperature controlled at 1079-1215 ℃ and the final rolling temperature controlled at 900-930 ℃; immediately after rolling, perform laminar flow cooling, and after cooling to 350-420 ℃, air cool to room temperature; S4. Quenching: Heat the rolled steel plate to 839-886 ℃, hold for 1-2 min / mm (calculated according to thickness), and then water quench to room temperature; S5. Tempering: Reheat the quenched steel plate to 600-620 ℃, hold for 1-1.5 h, and finally water quench to room temperature.

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