A 750mpa grade high-strength corrosion-resistant steel plate and a preparation method thereof

Abstract

The application discloses a 750MPa-grade high-strength corrosion-resistant steel plate and a preparation method thereof, and belongs to the field of alloy steel metallurgy and new materials. The steel plate is composed of the following components in percentage by mass: C: 0.05-0.09%, Si: 0.10-0.25%, Mn: 0.40-0.70%, Cr: 1.40-1.70%, Ni: 2.00-2.80%, Mo: 0.40-0.60%, Cu: 0.30-0.50%, Nb: 0.03-0.06%, Ti: 0.008-0.02%, Sb: 0.03-0.07%, Ca: 0.002-0.005%, N: not more than 0.004%, P: not more than 0.008%, S: not more than 0.002%, and the balance of Fe and impurities. The production process comprises BOF smelting, LF+RH refining, continuous casting, slow cooling, slab heating, controlled rolling and controlled cooling, and quenching and tempering heat treatment. The steel plate disclosed by the application has a thickness of 16-80 mm, is high-strength and high-corrosion-resistant, is suitable for island reef facilities and marine engineering, and can realize large-scale stable supply.

Description

Technical Field

[0001] This invention belongs to the field of alloy steel metallurgy and new materials, specifically relating to a 750MPa-grade high-strength corrosion-resistant steel plate and its preparation method. The steel plate uses a 370mm thick continuously cast billet as raw material, with a finished product thickness ranging from 16 to 80mm, and possesses a 750MPa-grade yield strength and excellent corrosion resistance. Background Technology

[0002] With the deepening of my country's maritime power strategy, the demand for island and reef construction, offshore energy development, and long-range support facilities in the South China Sea is increasing. However, island and reef and near-shore engineering structures, which operate in extreme marine environments such as high salt spray, high temperature and humidity, and strong ultraviolet radiation for extended periods, face severe material corrosion problems. Studies have shown that Cl in the tropical marine atmosphere... - The sediment load can be dozens of times higher than that in inland areas. Coupled with high temperature, high humidity, and alternating wet and dry conditions, the corrosion rate of steel can reach over 0.3 mm / a, far exceeding that of ordinary marine environments (0.1 mm / a). In addition, steel used in island and reef engineering must withstand dynamic stresses such as wave impact and typhoon loads, which can easily induce stress corrosion cracking (SCC) and corrosion fatigue, seriously threatening structural safety and service life.

[0003] Currently, island and reef facilities mainly use traditional high-strength steels for ships (such as EH36 and DH36) or low-alloy steels. While these possess good mechanical properties and weldability, they are insufficient in long-term corrosive environments. For example, Q355B steel showed extensive pitting corrosion after only one year of exposure on islands and reefs in the South China Sea, with the maximum pit depth exceeding 1.5 mm. While S355J2W weathering steel improves atmospheric corrosion resistance through Cu-P-Cr alloying, its resistance to pitting corrosion in high-Cl⁻ media is limited. More importantly, the strength and corrosion resistance of traditional steels often exhibit an inverse relationship: increasing strength requires increasing carbon equivalent, leading to deterioration in weldability. To address the aforementioned contradictions, scholars both domestically and internationally have proposed three technical pathways: first, developing new coating technologies, but these still have shortcomings in protecting against localized corrosion after mechanical damage; second, developing stainless steel composite plates, but the yield rate of explosive rolling processes is less than 60%; and third, optimizing alloy design to enhance intrinsic corrosion resistance through multi-element synergy. Japan's JFE-CORTEN series, using a Cu-Cr-Ni-Mo system, achieves a two-fold increase in corrosion resistance at 0.1%C. Ansteel's patent application CN202311302422.X, "A 560MPa Grade High-Strength Corrosion-Resistant Steel Plate for Marine Engineering and Its Production Method," discloses a high-strength corrosion-resistant steel plate that improves strength, low-temperature toughness, and corrosion resistance by employing an ultra-low carbon design and incorporating multi-element alloying strengthening elements such as Cr and Ni. However, increasing the Ni content (>5%) to enhance corrosion resistance results in Pcm >0.30%, requiring preheating to over 150℃ for welding, significantly increasing costs. Balancing alloy cost, weldability, and adaptability to extreme environments remains a core challenge that urgently needs to be overcome.

[0004] Against this backdrop, the development of high-strength corrosion-resistant steel with both 750MPa strength and excellent Cl⁻ corrosion resistance is of great strategic significance for ensuring the long-term safe service of my country's offshore infrastructure and is also a key research direction in the field of marine engineering materials. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a 750MPa high-strength corrosion-resistant steel plate and its preparation method, addressing the shortcomings of the prior art. By optimizing the alloy composition design and combining controlled rolling, controlled cooling, and heat treatment processes, the strength and corrosion resistance of the steel plate are comprehensively controlled, enabling mass production using existing industrial equipment. The resulting steel plate has a yield strength ≥750MPa, tensile strength ≥820MPa, elongation after fracture of 18-25%, and reduction of area ≥65%. Its corrosion resistance is significantly better than that of 10CrNi3MoV steel, making it widely applicable in applications requiring high corrosion resistance, while effectively reducing production costs and enhancing product competitiveness.

[0006] The technical solution adopted by this invention to solve the above problems is as follows: a 750MPa grade high-strength corrosion-resistant steel plate, the chemical composition of which is designed by mass percentage as follows: C: 0.05~0.09%, Si: 0.10~0.25%, Mn: 0.40~0.70%, Cr: 1.40~1.70%, Ni: 2.00~2.80%, Mo: 0.40~0.60%, Cu: 0.30~0.50%, Nb: 0.03~0.06%, Ti: 0.008~0.02%, Sb: 0.03~0.07%, Ca: 0.002~0.005%, N≤0.004%, P≤0.008%, S≤0.002%, with the remainder being iron and unavoidable impurities. This composition system requires that the fine inclusions A, B, C, and D in the steel be ≤1.5 grade and the coarse inclusions be ≤1.0 grade.

[0007] The rationale for using a Ni-Cu-Sb corrosion-resistant alloy for the steel composition in this invention is explained below: C: C is the most basic and effective strengthening and hardenability element in steel. However, excessive C content reduces ductility and decreases the steel's corrosion resistance. The C content should be controlled between 0.05% and 0.09%.

[0008] Si: Si is a significant strengthening element in steel, replacing Fe atoms in the crystal lattice to produce solid solution strengthening. A notable characteristic of solid solution strengthening is that as the number of solute atoms increases, strength and hardness rise, while plasticity and toughness decrease; the greater the strengthening effect, the greater the decrease in plasticity and toughness. Simultaneously, research shows that in atmospheric corrosion environments, a high Si content can increase the paramagnetic α-FeO(OH) content in the protective rust layer, refining α-FeO(OH) and thus reducing the corrosion rate of the material. The corrosion rate of carbon steel is related to the properties of α-Fe₂O₃ and α-FeO(OH). Large α-FeO(OH) particles and magnetic α-Fe₂O₃ hinder the complete formation of the protective rust layer, leading to an increased corrosion rate. Superparamagnetic α-FeO(OH) can refine α-FeO(OH) particles, thereby reducing the corrosion rate of carbon steel. This invention selects a Si mass percentage of 0.10%-0.25%.

[0009] Mn (Mn) forms a solid solution with Fe, increasing the hardness and strength of ferrite and austenite in steel. Mn also improves the stability of the austenite structure, significantly enhancing the hardenability of the steel. However, excessive Mn can reduce the plasticity of the steel. The addition of Mn also helps form a rust layer on the steel surface, improving its corrosion resistance. Excessive Mn can lead to the growth of corrosion product particles, increasing the corrosion rate. The Mn content should be controlled between 0.40% and 0.70%.

[0010] Cr: Cr is an element that greatly affects the corrosion resistance of steel. It can form a dense and complete oxide film between the rust layer and the steel substrate on the steel surface, refine the α-FeO(OH) grains in the rust layer, and effectively inhibit the intrusion of corrosive anions, especially Cl- ions. Simultaneously, it can prevent the reduction of the rust layer during the drying process of alternating wet and dry conditions, thus improving the corrosion resistance of the steel. The Cr content should be controlled between 1.4% and 1.7%.

[0011] Ni: Ni can lower the self-corrosion potential of steel, shifting it positively and increasing stability. Simultaneously, Ni readily accumulates in rust layers, which can, to some extent, resist Cl- erosion and promote the formation of a protective rust layer, thereby reducing the corrosion rate of the steel. Ni can also significantly improve the impact toughness of steel. Excessive Ni increases cost, and its effect becomes less pronounced. The Ni content should be controlled between 2.00% and 2.80%.

[0012] Mo: Mo has a strong carbide-forming ability, which can organize coarse austenitic grains and also cause a rightward shift of the C-curve, reducing undercooling and greatly improving hardenability, which is conducive to the formation of a full martensitic structure during quenching. When Mo and Nb are added simultaneously, Mo can increase the inhibition of austenite recrystallization during controlled rolling, thereby promoting the refinement of the austenite microstructure. Adding an appropriate amount of Mo is also beneficial to improving the atmospheric corrosion resistance of steel. However, excessive Mo will impair the toughness of the heat-affected zone formed during welding and reduce the weldability of steel. Therefore, the Mo content in this invention is controlled at 0.40-0.60%.

[0013] Cu: As a strengthening element in steel, Cu can effectively improve the strength of steel through solid solution strengthening; Cu can also improve the atmospheric corrosion resistance of steel. The Cu content should be controlled between 0.30% and 0.50%.

[0014] Nb: The main functions of Nb in steel are: at high temperatures, undissolved Nb(C,N) inhibits austenite grain growth; at rolling temperatures, undissolved or strain-induced precipitated Nb(C,N) inhibits recrystallized grain growth; at rolling temperatures, both dissolved Nb and strain-induced precipitated Nb, when the Nb content is less than 0.1 wt%, inhibit the recrystallization behavior of the matrix with increasing Nb content; dissolved Nb delays the γ→α phase transformation of the matrix, while the precipitation of Nb(C,N) promotes the γ→α phase transformation; at lower temperatures, the very fine-sized micro-alloyed carbonitrides produce a strong precipitation strengthening effect. Micro-Nb rolling technology further strengthens the steel during the rolling process. To reduce production costs, the Nb content is controlled at 0.03–0.06%.

[0015] Ti: Ti can combine with C and N atoms in steel to form Ti(C,N) particles, hindering austenite recrystallization and refining ferrite grains. Simultaneously, Ti(C,N) particles, as a second phase, can precipitate and strengthen the matrix. On the other hand, Ti can fix C and N atoms in the steel, reducing ferrite and purifying ferrite grain boundaries to enhance corrosion resistance. The Ti content is controlled at 0.008–0.02%.

[0016] Sb: Sb forms a protective oxide film on the surface of the material, effectively inhibiting the intrusion of Cl- ions and reducing the corrosion rate of steel. It also increases corrosion resistance in marine climates. Excessive Sb content can affect the surface quality of the cast billet; the Sb content should be controlled between 0.03% and 0.07%.

[0017] Wherein, the element simultaneously satisfies Pcm≤0.23%.

[0018] The preparation method of the above-mentioned 750MPa grade high-strength corrosion-resistant steel plate This method relies on existing industrial metallurgical equipment. The process flow is as follows: KR hot metal pretreatment → BOF converter steelmaking → LF refining → RH vacuum degassing → continuous casting → billet heating → rolling → straightening → online quenching → steel plate tempering → performance testing → warehousing. The specific steps are as follows: Iron and steelmaking refining: KR iron pretreatment, BOF converter steelmaking, LF refining, and RH vacuum degassing are carried out in sequence. The endpoint of the BOF-LF-RH triple smelting is strictly controlled to [S]≤10ppm, [O]≤12ppm, and [H]≤0.5ppm to minimize harmful impurities and inclusions in the steel and improve the purity of the steel.

[0019] Continuous casting: The refined molten steel is continuously cast into a 370mm thick continuous casting billet. The chemical composition of the continuous casting billet is consistent with that of the steel plate mentioned above. The continuous casting process adopts protective pouring to prevent secondary oxidation of the molten steel.

[0020] Billet heating: The continuously cast billet is sent to the heating furnace for heating at a temperature of 1180℃~1260℃, and the heating time is calculated at 2.0min / mm. The heating process is divided into a preheating section (580~610℃), a first heating section (950~1020℃), and a high-temperature section (1240~1260℃). A gradient heating method is adopted to avoid thermal stress cracks caused by sudden temperature changes in the billet. When the billet is taken out of the furnace, the temperature deviation of the core, upper surface, and lower surface of the billet is ≤5℃ to ensure uniform heating of the billet.

[0021] Rolling: The heated billet is subjected to rough rolling and finish rolling in sequence. The rough rolling temperature is 950℃~1050℃, and multi-pass rolling is adopted with no less than 3 passes. The maximum reduction rate of a single pass is ≥10%, and the reduction rate of the last three passes is ≥50%. The large reduction rate rolling breaks up the as-cast structure and refines the grains. The finish rolling temperature is 800℃~880℃, and multi-pass rolling is adopted. The maximum reduction rate of a single pass is ≥10%, and the reduction rate of the last three passes is ≥30%. The preferred number of finish rolling passes is 13~15. The final rolling temperature is controlled at 730~790℃ to ensure that the austenitic structure of the steel is fully refined, laying the foundation for obtaining excellent performance in subsequent heat treatment.

[0022] Straightening: The rolled steel plate is immediately straightened by a straightening machine to eliminate rolling deformation, ensure the plate shape accuracy, and avoid stress caused by poor plate shape during subsequent cooling and heat treatment.

[0023] Online quenching: After straightening, the steel plate is first subjected to controlled cooling. The controlled cooling temperature is 760℃~800℃, the cooling medium is water, the cooling rate is 20~25℃ / s, the roller speed is 1.2~1.5m / s, and the red-hot temperature is controlled at 350℃~400℃. After controlled cooling, the steel plate is sent to the quenching furnace for quenching. The quenching temperature is 910℃~930℃, and the holding time is 2.0min / mm+30min to ensure uniform temperature inside and outside the steel plate. The quenching cooling method is water cooling, which makes the steel plate form a full martensitic structure and improves its strength.

[0024] Tempering: The quenched steel plate is sent to a continuous tempering furnace for tempering at a temperature of 610℃~630℃ and a holding time of 120min. After tempering, it is cooled by air cooling. The tempering process can eliminate quenching stress, refine the martensitic structure, and improve the plasticity, toughness and corrosion resistance of the steel plate while ensuring high strength, thus achieving a balance between strength and toughness.

[0025] Post-processing: After tempering, the steel plates undergo comprehensive performance testing, including mechanical property testing (tensile test) and corrosion resistance testing (salt spray corrosion test / marine atmospheric exposure test). At the same time, the inclusion level in the steel is tested. After all indicators meet the requirements of this invention, the steel plates are put into storage.

[0026] Compared with the prior art, the present invention has the following beneficial effects: 1. The steel plate obtained by this invention has a yield strength ≥750MPa, tensile strength ≥820MPa, elongation after fracture 18~25%, and reduction of area ≥65%. Its strength grade is far higher than that of the existing 560MPa grade marine engineering steel, and its corrosion resistance is significantly better than that of 10CrNi3MoV steel. It can withstand the extreme marine environment of high salt spray and high temperature and humidity in the South China Sea. At the same time, Pcm≤0.23%, it has excellent weldability and does not require preheating for welding, thus solving the common contradiction in the industry of mutual restriction between strength, corrosion resistance and weldability.

[0027] 2. This invention adopts a low-Ni design with Ni content of 2.00~2.80%, which significantly reduces the cost of alloy raw materials compared to existing high-Ni (>5%) corrosion-resistant steels; and welding does not require preheating, reducing the process cost of engineering construction. At the same time, all processes are implemented using existing industrial equipment, without the need for additional special equipment, resulting in low production costs.

[0028] 3. This invention introduces Sb to form a ternary synergistic corrosion-resistant system with Ni and Cu for the first time. Sb forms a protective oxide film on the steel plate surface, Cr forms a dense oxide film, and Ni and Cu promote the formation of a protective rust layer. The synergistic effect of multiple elements can effectively inhibit the formation of Cl. - It exhibits excellent resistance to ion intrusion, pitting corrosion, stress corrosion cracking (SCC), and corrosion fatigue, making it suitable for dynamic stress conditions in island and reef engineering projects.

[0029] 4. The process parameters of this invention are clear and controllable. The parameters for billet heating, rolling, cooling and heat treatment are all matched to the 370mm thick continuous casting billet and the 16~80mm finished product thickness. Moreover, the purity of the smelting process is strictly controlled, with inclusion grades ≤1.5 (fine) / ≤1.0 (coarse). The steel plate quality is stable, and batch and large-scale production can be realized with a high yield. Attached Figure Description

[0030] Figure 1 This is a microstructure diagram of the 80mm steel plate obtained in Example 1 of the present invention.

[0031] Figure 2 This is a microstructure diagram of the 35mm steel plate obtained in Example 2 of the present invention. Detailed Implementation

[0032] The technical solution of the present invention will be described in more detail below with reference to preferred embodiments. However, these embodiments are merely descriptions of preferred implementations of the present invention and should not be construed as limiting the scope of the present invention.

[0033] Example 1: Production of 80mm thick 750MPa high-strength corrosion-resistant steel plates Steel composition: by mass percentage, C=0.05%, Si=0.10%, Mn=0.50%, P≤0.007%, S≤0.0008%, Cr=1.42%, Ni=2.2%, Mo=0.4%, Cu=0.3%, Nb=0.03%, Ti=0.01%, Sb=0.03%, Ca=0.0004%, N≤0.003%, with the balance being Fe and unavoidable impurities; inclusions in the steel: fine category A, B, C, D ≤1.5 grade, coarse category ≤1.0 grade, Pcm≤0.23%.

[0034] Preparation steps: (1) Hot metal and steelmaking refining: After KR hot metal pretreatment, it is subjected to BOF converter steelmaking, LF refining, and RH vacuum degassing. The smelting endpoint is controlled as [S]≤8ppm, [O]≤10ppm, and [H]≤0.4ppm; (2) Continuous casting: Protectively cast into a 370mm thick continuous casting billet with the same chemical composition as above; (3) Heating of billet: Preheating section temperature 608℃, heating time 225min; first heating section temperature 957℃, heating time 235min; high temperature section temperature 1242℃, heating time 174min; when exiting the furnace, the core temperature is 1180℃, the upper surface temperature is 1178℃, the lower surface temperature is 1182℃, and the temperature deviation is ≤2℃. (4) Rolling: The roughing rolling temperature is 1143℃, with a total of 7 passes. The reduction per pass is 21.85 mm, 22.56 mm, 24.41 mm, 31.24 mm, 31.17 mm, 31.52 mm, and 32.27 mm, respectively. The reduction rate of the last three passes is ≥50%. The finishing rolling temperature is 890℃, with a minimum thickness of 170 mm. It is rolled to the target thickness of 80 mm in 13 passes. The final rolling temperature is 784℃. The cumulative reduction rate of the last 3 finishing passes is 43.79% ≥30%. (5) Straightening: After rolling, the steel plate is straightened by a straightening machine to ensure the plate shape accuracy; (6) Online quenching: Cooling starts at 877℃, with a cooling water volume and water group of 65 / 144 m³ / h * 7 groups, roller speed of 1.5m / s, average cooling rate of 24.04℃ / s, and reddening temperature of 650℃; then quenching in a quenching furnace at 920℃±10℃ for 190min, followed by water cooling. (7) Tempering: After quenching, the steel plate is tempered in a tempering furnace at 650℃±10℃ for 120 minutes and then air-cooled. (8) Performance testing: After testing, the product is put into storage.

[0035] Performance indicators: tensile strength 912MPa, yield strength 860MPa≥750MPa, elongation after fracture 20.0%∈18~25%, reduction of area 70%≥65%, corrosion resistance significantly better than 10CrNi3MoV steel, Pcm≤0.23%, and excellent weldability.

[0036] Example 2: Production of 35mm thick 750MPa high-strength corrosion-resistant steel plates Steel composition: completely consistent with Example 1.

[0037] Preparation steps: (1) Iron refining and steelmaking: Same as in Example 1, with the smelting endpoint controlled as [S]≤8ppm, [O]≤10ppm, and [H]≤0.4ppm; (2) Continuous casting: Same as in Example 1, 370mm thick continuous casting billet; (3) Heating of billet: Preheating section temperature 587℃, heating time 68min; first heating section temperature 1014℃, heating time 49min; high temperature section temperature 1252℃, heating time 103min; when exiting the furnace, the core temperature is 1199℃, the upper surface temperature is 1193℃, the lower surface temperature is 1196℃, and the temperature deviation is ≤3℃. (4) Rolling: The roughing rolling temperature is 1180℃, with a total of 8 passes. The reduction per pass is 25.03mm, 34.86mm, 34.95mm, 35.08mm, 35.33mm, 35.93mm, 35.87mm, and 36.58mm respectively. The reduction rate of the last three passes is ≥50%. The finishing rolling temperature is 894℃, with a minimum thickness of 90mm. It is rolled to the target thickness of 35mm in 15 passes. The final rolling temperature is 737℃. The cumulative reduction rate of the last 3 finishing passes is 32.37% ≥30%. (5) Straightening: Same as in Example 1; (6) Online quenching: Cooling starts at 810℃, cooling water volume and water group are 65 / 120 m³ / h *9 groups, roller speed is 1.2m / s, average cooling rate is 30℃ / s, red temperature is 703℃; then quenching is carried out in a quenching furnace at 920℃±10℃, holding time is 100min, and water cooling is used. (7) Tempering: Same as in Example 1, tempering at 650℃±10℃ for 120 min, followed by air cooling; (8) Performance testing: After testing, the product is put into storage.

[0038] Performance indicators: tensile strength 920MPa, yield strength 880MPa≥750MPa, elongation after fracture 21.0%∈18~25%, reduction of area 72%≥65%, corrosion resistance significantly better than 10CrNi3MoV steel, Pcm≤0.23%, and excellent weldability.

[0039] The 750MPa grade high-strength corrosion-resistant steel plate and its preparation method of the present invention are all achieved by relying on existing industrial equipment for alloy steel metallurgy (KR molten iron pretreatment device, BOF converter, LF / RH refining furnace, continuous casting machine, hot rolling mill, quenching furnace, tempering furnace, etc.), without the need for additional special equipment; the process parameters are clear and controllable, and the parameters for billet heating, rolling, cooling and heat treatment have been optimized and matched, which can achieve stable production from 370mm thick continuous casting billets to 16~80mm finished steel plates. The steel plates have uniform quality, stable performance and high yield, and have significant industrial applicability.

[0040] In addition to the above embodiments, the present invention can also adjust parameters such as feeding thickness and vibration time according to the design requirements of alloy melting furnaces of different tonnages. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.

Claims

1. A 750MPa grade high-strength corrosion-resistant steel plate, characterized in that, The chemical composition, by mass percentage, includes: C: 0.05–0.09%, Si: 0.10–0.25%, Mn: 0.40–0.70%, Cr: 1.40–1.70%, Ni: 2.00–2.80%, Mo: 0.40–0.60%, Cu: 0.30–0.50%, Nb: 0.03–0.06%, Ti: 0.008–0.02%, Sb: 0.03–0.07%, Ca: 0.002–0.005%, N≤0.004%, P≤0.008%, S≤0.002%, with the balance being Fe and unavoidable impurities. The inclusions in the steel plate are of fine grade A, B, C, and D ≤ grade 1.5, coarse grade ≤ grade 1.0, and carbon equivalent Pcm ≤ 0.23%.

2. The 750MPa grade high-strength corrosion-resistant steel plate according to claim 1, characterized in that, The preferred chemical composition is: C=0.05%, Si=0.10%, Mn=0.50%, Cr=1.42%, Ni=2.2%, Mo=0.4%, Cu=0.3%, Nb=0.03%, Ti=0.01%, Sb=0.03%, Ca=0.0004%, N≤0.003%, P≤0.007%, S≤0.0008%, with the balance being Fe and unavoidable impurities.

3. The 750MPa grade high-strength corrosion-resistant steel plate according to claim 1, characterized in that, The steel plate is made from a 370mm continuous casting billet, with a finished thickness of 16~80mm. The performance indicators meet the following requirements: yield strength ≥750MPa, tensile strength ≥820MPa, elongation after fracture 18~25%, reduction of area ≥65%, and corrosion resistance superior to 10CrNi3MoV steel.

4. The 750MPa grade high-strength corrosion-resistant steel plate according to claim 1, characterized in that, The Sb element forms a protective oxide film on the steel plate surface, inhibiting Cl... - Ion intrusion causes Cr to form a dense oxide film between the rust layer and the substrate on the steel surface, while Ni and Cu elements work together to promote the formation of a protective rust layer.

5. A method for preparing a 750MPa grade high-strength corrosion-resistant steel plate as described in claim 1, characterized in that, Includes the following steps: S1 molten iron and steelmaking refining: KR molten iron pretreatment, BOF converter steelmaking, LF refining, and RH vacuum degassing are carried out in sequence. The endpoint control of BOF-LF-RH triple smelting is [S]≤10ppm, [O]≤12ppm, and [H]≤0.5ppm. S2 continuous casting: The refined molten steel is continuously cast into a 370mm thick continuous casting billet, and the chemical composition of the continuous casting billet is consistent with that of the steel plate described in claim 1; S3 billet heating: Heat the continuous casting billet to 1180℃~1260℃, with a heating time of 2.0min / mm; S4 rolling: Roughing and finishing are performed sequentially. The roughing temperature is 950℃~1050℃, with multiple passes and no less than 3 passes. The maximum reduction rate per pass is ≥10%, and the reduction rate of the last three passes is ≥50%. The finishing temperature is 800℃~880℃, with multiple passes. The maximum reduction rate per pass is ≥10%, and the reduction rate of the last three passes is ≥30%. S5 Online Quenching: The rolled steel plate is quenched after controlled cooling. The controlled cooling start temperature is 760℃~800℃, the cooling rate is 20~25℃ / s, the red-hot temperature is 350℃~400℃, the quenching temperature is 910℃~930℃, and the holding time is 2.0min / mm+30min. S6 tempering: Temper the quenched steel plate at 610℃~630℃ for 120 minutes, then air cool. S7 Post-processing: After tempering, the steel plates pass the performance test and are put into storage. The performance test indicators meet the requirements.

6. The method for preparing a 750MPa grade high-strength corrosion-resistant steel plate according to claim 5, characterized in that, In step S3, the billet heating process is divided into a preheating section, a first heating section, and a high-temperature section. The temperature of the preheating section is 580~610℃, the temperature of the first heating section is 950~1020℃, and the temperature of the high-temperature section is 1240~1260℃. When the billet is taken out of the furnace, the temperature deviation of the core, upper surface, and lower surface of the billet is ≤5℃.

7. The method for preparing a 750MPa grade high-strength corrosion-resistant steel plate according to claim 5, characterized in that, In step S4, the number of roughing passes is 7 to 8, the number of finishing passes is 13 to 15, and the final rolling temperature is 730 to 790℃.

8. The method for preparing a 750MPa grade high-strength corrosion-resistant steel plate according to claim 5, characterized in that, In step S5, the cooling medium for controlled cooling is water, the roller speed is 1.2~1.5m / s, and the cooling method for quenching is water cooling.

9. The method for preparing a 750MPa grade high-strength corrosion-resistant steel plate according to claim 5, characterized in that, The step between step S4 and step S5 includes a straightening step, in which the rolled steel plate is straightened by a straightening machine to ensure the accuracy of the steel plate shape.

10. The method for preparing a 750MPa grade high-strength corrosion-resistant steel plate according to claim 5, characterized in that, The performance testing in step S7 includes mechanical performance testing and corrosion resistance testing. Mechanical performance testing is performed using tensile testing, and corrosion resistance testing is performed using salt spray corrosion testing or marine atmospheric exposure testing.

Images