A high-strength extra-thick steel plate and its preparation method

Abstract

This invention discloses a high-strength, extra-thick steel plate and its preparation method, comprising the following steps: S1, obtaining an extra-thick steel ingot through smelting and casting; S2, subjecting the extra-thick steel ingot to homogenization heat treatment; S3, subjecting the extra-thick steel ingot to forging, normalizing, and tempering treatments to obtain an extra-thick steel plate billet with a thickness of 300mm-500mm; S4, subjecting the extra-thick steel plate billet to quenching and tempering treatment, followed by waterjet cutting and surface polishing treatment to obtain a finished extra-thick steel plate of a defined size; in step S1, the purification of the molten steel is achieved by a combination of diffusion deoxidation and precipitation deoxidation, and ladle refining is performed in a ladle refining furnace; casting is carried out using a cryogenic casting method, during which the molten steel in the cryogenic ingot mold is electromagnetically stirred. This invention uses a cryogenic ingot mold and electromagnetic stirring to solve the problem of difficult synergistic control among the strength characteristics, internal microstructure uniformity, and performance consistency in all directions of extra-thick steel plates.

Description

Technical Field

[0001] This invention relates to the technical field of alloy steel plates, specifically a high-strength extra-thick steel plate and its preparation method. Background Technology

[0002] Extra-thick homogeneous steel plates are the basic material for the processing and fabrication of large engineering components. They are an important part of ensuring the country's rapid development in special and critical fields. With my country's major breakthroughs in deep sea, aerospace, polar regions, and power in recent years, there are even higher requirements for the uniformity of microstructure and the consistency of performance of extra-thick steel plates.

[0003] Factors affecting the uniformity of microstructure and properties across different sections of extra-thick homogeneous steel plates mainly include defects such as compositional segregation, porosity, and shrinkage cavities during the solidification process of molten steel, as well as differences in grain morphology; differences in surface and core deformation, grain refinement, and defect welding during forging; and asynchronous phase transformation, microstructure inhomogeneity, and uneven residual stress caused by temperature gradients in all directions during heat treatment. When the steel plate thickness reaches 300 mm or more, it is difficult to effectively control the uniformity of composition, microstructure, and properties in all directions within the steel plate. Currently, most common extra-thick steel plates achieve their uniformity and consistency at the expense of steel plate strength.

[0004] Furthermore, in the field of casting technology, cryogenic casting combined with electromagnetic stirring, as an advanced solidification control method, has been widely applied in the forming process of light alloys such as aluminum alloys and magnesium alloys. This process significantly increases the supercooling of the melt by pouring the molten metal into a cryogenic mold (usually cooled to tens of degrees below zero Celsius using liquid nitrogen), thereby promoting nucleation and refining grains. Simultaneously, the electromagnetic field induces forced convection in the melt, effectively breaking up dendrites, reducing compositional segregation, and improving microstructure uniformity. Existing technologies (such as patent CN116748475 B) have demonstrated that this process has a significant grain refinement effect on light alloy castings such as AZ91D magnesium alloy and 7075 aluminum alloy, eliminating columnar crystals and coarse dendrites, and improving mechanical properties.

[0005] Applying cryogenic casting and electromagnetic stirring processes to the preparation of extra-thick steel ingots (thickness ≥ 300 mm) faces numerous unresolved major technical challenges. First, molten steel has a high melting point (approximately 1500℃), high density, and high viscosity, resulting in solidification characteristics drastically different from light alloys. The extremely high casting temperature places extreme demands on the thermal shock resistance, cooling stability, and lifespan of the cryogenic ingot mold. Directly applying the low-temperature mold scheme used for light alloys can lead to problems such as thermal shock cracking and uneven cooling. Furthermore, the long solidification time of extra-thick steel ingots and the significant temperature difference between the core and surface make them highly susceptible to macroscopic segregation and shrinkage cavities. While simple cryogenic cooling can increase undercooling, if it is not precisely matched with the temperature and flow fields of the entire cross-section, it can exacerbate the inconsistency in solidification between the internal and external layers, leading to deterioration of the core microstructure. Finally, extra-thick steel plates require prolonged high-temperature diffusion, multi-stage forging, and complex heat treatment; the initial microstructure of the ingot (such as dendrite morphology and inclusion distribution) directly affects the subsequent processing results. If the cryogenic electromagnetic stirring process cannot provide uniform, defect-free billets for subsequent forging, or introduces new abnormal structures, then the entire technical route will lose its application value.

[0006] Therefore, it is essential to propose a method for preparing ultra-thick steel plates that is suitable for ultra-thick dimensions and meets the requirements of high strength, high uniformity and high consistency. Summary of the Invention

[0007] This application provides a high-strength ultra-thick steel plate and its preparation method, which solves the problem of the difficulty in synergistic control of the strength characteristics, internal microstructure uniformity, and performance consistency in all directions of ultra-thick steel plates.

[0008] On one hand, this application provides a method for preparing a high-strength, extra-thick steel plate, comprising the following steps: S1, obtaining an extra-thick steel ingot through smelting and casting; S2, subjecting the extra-thick steel ingot obtained in step S1 to homogenization heat treatment; S3, subjecting the extra-thick steel ingot obtained in step S2 to forging, normalizing, and tempering treatments to obtain an extra-thick steel plate billet with a thickness of 300mm-500mm; S4, subjecting the extra-thick steel plate billet obtained in step S3 to quenching and tempering treatment, and performing water jet cutting and surface polishing treatments to obtain a finished extra-thick steel plate of a defined size; in step S1, the purification of the molten steel is achieved by a combination of diffusion deoxidation and precipitation deoxidation, and ladle refining is performed in a ladle refining furnace; casting is carried out using a cryogenic casting method, during which the molten steel in the cryogenic ingot mold is electromagnetically stirred.

[0009] Preferably, in step S1, the ingot film is frozen with liquid nitrogen during the casting process, and the ingot mold temperature is controlled at -60℃ to 0℃; the electromagnetic stirring during the casting process adopts crystallizer electromagnetic stirring, with a current range of 300A to 500A and a frequency range of 2Hz to 5Hz; the electromagnetic stirring mode during the casting process is intermittent rotary stirring, rotating forward for 10s to 30s, stopping for 2 to 6s, and rotating backward for 10s to 30s.

[0010] Preferably, in step S2, the homogenization heat treatment is carried out using a gradient heating method, with the furnace loading temperature ≤400℃. In the low-temperature preheating stage, the temperature is heated to 750℃~800℃ at a rate of 60℃ / h~80℃ / h. In the medium-temperature preheating stage, the temperature is heated to 950℃~1000℃ at a rate of 90℃ / h~100℃ / h. In the high-temperature heating stage, the temperature is heated to 1180℃~1220℃ at a rate of 30℃ / h~50℃ / h. In the homogenization heat preservation stage, the heat preservation time is determined by increasing the heat preservation time by 5h~7h for every 100mm of cross-sectional thickness.

[0011] Preferably, in step S3, the forging process requires the surface temperature of the extra-thick steel ingot to be higher than 950°C; when the surface temperature of the extra-thick steel ingot is lower than 950°C, it is returned to heat treatment and reheated to 1180°C to 1220°C at a rate of 30°C / h to 50°C / h, and held at that temperature for 1h to 2h before being taken out and forging process continued.

[0012] Preferably, in step S3, the forging process includes chamfering, pressing the handle, cutting the bottom, drawing, and upsetting.

[0013] Preferably, in step S3, the reduction rate of each upsetting operation is 20% to 30%, and the feed rate / anvil width is 0.7 to 0.9.

[0014] Preferably, in step S3, the extra-thick steel plate after forging is subjected to normalizing and tempering treatment after its surface temperature is air-cooled to 400℃~500℃. The normalizing process involves heating at a rate of 30℃ / h~50℃ / h to a normalizing temperature of 890℃~910℃, holding at that temperature for 6h~10h, and then cooling with forced air. The tempering process involves heating at a rate of 30℃ / h~50℃ / h to a tempering temperature of 600℃~680℃, holding at that temperature for 12h~16h, and then cooling with the furnace.

[0015] Preferably, in step S4, the extra-thick steel plate billet is subjected to quenching and tempering treatment, with a quenching temperature of 890℃~910℃, a holding time of 6~10h, and a cooling method of circulating cooling oil quenching; the tempering temperature is 600℃~680℃, a holding time of 12~16h, and furnace cooling.

[0016] On the other hand, this application provides a high-strength extra-thick steel plate, which is prepared by a method for preparing high-strength extra-thick steel plates. The chemical composition of the extra-thick steel plate includes C: 0.40%~0.60%; N: 0.05%~0.15%; B: 0.001%~0.006%; Cr: 3.00%~5.00%; Ni: 1.00%~2.00%; Al: 0.010%~0.040%; Mn: 1.00%~2.00%; Si: 0.20%~0.70%; Mo: 0.10%~0.50%; P≤0.010%; S≤0.004%, with the balance being Fe and non-essential impurity elements.

[0017] One or more technical solutions provided in this application have at least the following technical effects or advantages:

[0018] 1. This application employs 0.40%~0.60% C to ensure the high strength of the extra-thick steel plate, while controlling B at 0.001%~0.006%, P≤0.010%, S≤0.004%, and Cr at 3.00%~5.00% to ensure the hardenability and uniformity of the extra-thick steel plate. During the smelting process, a combination of diffusion deoxidation and precipitation deoxidation is used to purify the molten steel, followed by ladle refining in a ladle refining furnace. This significantly reduces the content of oxide inclusions and harmful elements, minimizing the possibility of large inclusions becoming heterogeneous nucleation sites.

[0019] 2. This application employs a cryogenic casting method for solidification control of the ingot. During casting, the molten steel in the cryogenic ingot mold is electromagnetically stirred, and the ingot mold is cooled with liquid nitrogen. This results in greater supercooling of the molten steel within the ingot mold, significantly increasing the nucleation rate, rapidly passing through the grain growth temperature range, and inhibiting grain growth. During the casting process, electromagnetic stirring is used on the outer ring of the ingot mold to break the branch tips and form new fine crystal nuclei, greatly increasing the number of equiaxed crystal nuclei, achieving grain refinement, and improving the uniformity between the surface and core of the ingot.

[0020] 3. In the homogenization heat treatment of steel ingots, this application adopts a gradient heating method. A low heating rate is used at the temperature where cracking and overheating are likely to occur, while a high heating rate is used in the safe temperature range. This reduces the risk of cracking of steel ingots caused by thermal stress, avoids overheating of steel ingots, and ensures that the segregation region inside the steel ingot has sufficient driving force and time for homogenization and diffusion.

[0021] 4. In this application, the upsetting reduction rate of the steel ingot is controlled at 20%~30% per forging, and the feed rate / anvil width is 0.7~0.9, which can ensure uniform deformation of the steel ingot during forging and effectively forge away core defects. The quenching and tempering treatment after forging adopts circulating cooling oil quenching, which can significantly improve the uniformity and consistency of cooling, reduce the vapor film stage, eliminate local hot spots, ensure process stability and repeatability, and reduce the tendency of quenching cracking.

[0022] 5. The present invention utilizes a frozen ingot mold and electromagnetic stirring to greatly improve the uniformity of the steel ingot structure, reduce internal defects in the steel ingot, and reduce the time and difficulty of subsequent homogenization heat treatment, forging and other processes. It can shorten the preparation and processing time of extra-thick steel plates while ensuring high strength, high uniformity and high consistency performance requirements. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The image shows the microstructure of the 300mm thick steel plate prepared in Example 1 of this invention, specifically at 1 / 2 of the thickness direction of the thick steel plate.

[0025] Figure 2 The image shows the microstructure of the 300mm thick steel plate prepared in Example 1 of this invention, specifically at 1 / 4 of the thickness direction of the thick steel plate.

[0026] Figure 3 The image shows the microstructure of the 400mm thick steel plate prepared in Example 2 of this invention, specifically at 1 / 2 of the thickness direction of the thick steel plate.

[0027] Figure 4 The image shows the microstructure of the 400mm thick steel plate prepared in Example 2 of this invention, specifically at 1 / 4 of the thickness direction of the thick steel plate.

[0028] Figure 5 The image shows the microstructure of the 500mm thick steel plate prepared in Example 3 of this invention, specifically at 1 / 2 of the thickness direction of the thick steel plate.

[0029] Figure 6 This is a microstructure diagram of the 500mm thick steel plate prepared in Example 3 of this application, specifically at 1 / 4 of the thickness direction of the thick steel plate;

[0030] Figure 7 The image shows the microstructure of the 300mm thick steel plate prepared in Comparative Example 1 of this invention, specifically at 1 / 2 of the thickness direction of the thick steel plate.

[0031] Figure 8 The image shows the microstructure of the 300mm thick steel plate prepared in Comparative Example 1 of this invention, specifically at 1 / 4 of the thickness direction of the thick steel plate. Detailed Implementation

[0032] This application provides a high-strength ultra-thick steel plate and its preparation method, which solves the problem of the difficulty in synergistic control of the strength characteristics, internal microstructure uniformity, and performance consistency in all directions of ultra-thick steel plates.

[0033] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0034] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or server that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or modules not explicitly listed or inherent to such processes, methods, products, or devices.

[0035] The chemical composition range of the extra-thick steel ingots used in the embodiments of this application is C: 0.40%~0.60%; N: 0.05%~0.15%; B: 0.001%~0.006%; Cr: 3.00%~5.00%; Ni: 1.00%~2.00%; Al: 0.010%~0.040%; Mn: 1.00%~2.00%; Si: 0.20%~0.70%; Mo: 0.10%~0.50%; P≤0.010%; S≤0.004%, with the balance being Fe and other non-essential impurity elements.

[0036] Generally, when preparing steel plates with a certain composition, the steel mill is provided with a range of chemical compositions, such as "N: 0.05%~0.15%", rather than a fixed value. This is because it is extremely difficult for steel mills to comprehensively control the composition of various alloying elements to a specific value. Furthermore, once the molten steel solidifies, the chemical composition ratio of the resulting ingot, as well as the chemical composition ratio of the finished products such as "steel plates" and "steel bars" after processing such as "forging" and "rolling," remains consistent and does not change. However, localized compositional inconsistencies may occur due to the segregation of certain chemical elements within the steel. This problem can be solved by homogenization heat treatment, allowing the segregated elements to diffuse evenly within the steel without reducing or increasing the overall chemical composition ratio of the ingot or plate. Therefore, the chemical composition ratio of the extra-thick steel ingot used in this application is consistent with the ratio of the extra-thick steel plate obtained by the method described in this application.

[0037] Specifically, carbon (C) is the most crucial strengthening element. The strength of extra-thick steel plates relies primarily on C. However, excessively high C content can reduce weldability and increase segregation, easily forming banded structures in the core of the extra-thick steel plate, leading to insufficient uniformity. Furthermore, high C content also reduces the toughness of extra-thick steel plates. Therefore, a C content of 0.40% to 0.60% is considered optimal for extra-thick steel plates. Specifically, the C content can be, for example, but not limited to, any one or any combination of 0.40%, 0.45%, 0.50%, 0.55%, and 0.60%.

[0038] The nitrogen (N) content needs to be precisely matched with the al (Al) content to form aluminum nitride, pinning grain boundaries and preventing austenite grain growth, thus improving the strength and toughness of extra-thick steel plates. However, excessive N, if it forms free-state N, can easily lead to age embrittlement. Therefore, an N content of 0.05% to 0.15% is generally considered suitable for extra-thick steel plates. Specifically, the N content can be, for example, but not limited to, any one of 0.05%, 0.08%, 0.11%, 0.13%, and 0.15%, or any combination thereof.

[0039] The main role of boron (B) is to significantly improve the hardenability of extra-thick steel plates, that is, to delay ferrite nucleation at grain boundaries. Furthermore, the use of boron can reduce the use of precious metals such as chromium (Cr) and molybdenum (Mo), thus lowering costs. Therefore, a boron content of 0.001% to 0.006% is considered suitable for extra-thick steel plates. Specifically, the boron content can be, for example, but not limited to, any one or any combination of 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, and 0.006%.

[0040] Cr is a fundamental alloying element in high-strength steel, primarily used to improve hardenability, ensure the uniformity of performance in thick sections, and, when combined with Mo, effectively suppress temper brittleness. Therefore, a Cr content of 3.00% to 5.00% is generally suitable for extra-thick steel plates. Specifically, the Cr content can be, for example, but not limited to, any one or any combination of 3.00%, 3.50%, 4.00%, 4.50%, and 5.00%.

[0041] The primary role of Ni (Ni) is to improve the toughness of extra-thick steel plates, and it is a key element in ensuring the low-temperature toughness of the core. In addition, Ni also plays a role in improving hardenability and strength. Therefore, a Ni content of 1.00% to 2.00% is generally suitable for extra-thick steel plates. Specifically, the Ni content can be, for example, but not limited to, any one or any combination of 1.00%, 1.20%, 1.40%, 1.60%, 1.80%, and 2.00%.

[0042] The main role of Al is deoxidation and grain refinement. During crystallization, it forms fine Al₂O₃ inclusions, promoting intragranular nucleation and refining the grains. This not only improves strength and toughness but also reduces the anisotropy of extra-thick steel plates. Therefore, an Al content of 0.010% to 0.040% is considered suitable for extra-thick steel plates. Specifically, the Al content can be, for example, but not limited to, any one or any combination of 0.010%, 0.015%, 0.020%, 0.025%, 0.030%, 0.035%, and 0.040%.

[0043] The most important role of manganese (Mn) in extra-thick steel plates is to improve hardenability, strongly delaying the transformation of austenite to ferrite and pearlite, and ensuring that the core can be hardened through in the thickness direction. In addition, Mn can also form MnS with sulfur (S), eliminating the harmful hot brittleness of sulfur. However, excessively high Mn levels can also increase the tendency for temper brittleness. Therefore, an Mn content of 1.00% to 2.00% is generally considered suitable for extra-thick steel plates. Specifically, the Mn content can be, for example, but not limited to, any one or any combination of 1.00%, 1.20%, 1.40%, 1.60%, 1.80%, and 2.00%.

[0044] The main functions of silicon (Si) are to reduce oxide inclusions in steel, improve purity, and enhance the fluidity of molten steel. Additionally, it can delay the precipitation and growth of carbides, improving resistance to tempering softening. However, excessive Si content can negatively impact surface quality and weldability. Therefore, a Si content of 0.20% to 0.70% is generally considered suitable for extra-thick steel plates. Specifically, the Si content can be, for example, but not limited to, any one or any combination of 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, and 0.70%.

[0045] The main functions of molybdenum (Mo) include significantly improving hardenability to ensure the core properties of thick sections, and suppressing temper brittleness to ensure that extra-thick steel plates maintain excellent toughness even after prolonged heat treatment. Furthermore, it can refine grains by forming fine carbides, thereby improving strength and toughness. Therefore, a Mo content of 0.10% to 0.50% is generally suitable for extra-thick steel plates. Specifically, the Mo content can be, for example, but not limited to, any one or any combination of 0.10%, 0.20%, 0.30%, 0.40%, and 0.50%.

[0046] Phosphorus (P) is a harmful element, primarily causing it to easily accumulate at grain boundaries during solidification, leading to uneven composition in the core of extra-thick steel plates. Furthermore, it causes a sharp decrease in toughness and an increase in the ductile-brittle transition temperature. Therefore, the P content in extra-thick steel plates needs to be controlled to ≤0.010%.

[0047] Sulfur (S) is a harmful element, primarily forming MnS inclusions, leading to anisotropy in steel. Furthermore, sulfides are the initiation points for hydrogen-induced cracking and stress corrosion. Therefore, the S content in extra-thick steel plates needs to be controlled to ≤0.004%.

[0048] The present invention will be described in further detail, specifically including the following operational steps:

[0049] S1. The extra-thick steel ingots are smelted in an electric furnace, where purification is achieved by a combination of diffusion deoxidation and precipitation deoxidation, and ladle refining is carried out in a ladle refining furnace (LF furnace).

[0050] During steel ingot casting, the casting temperature is 1550℃~1580℃, with superheat controlled at 20℃~25℃ to reduce component segregation. To meet the requirements for extra-thick steel plates of 300mm~500mm, both the melting furnace and ingot mold are selected to be 25 tons or larger. Liquid nitrogen-frozen ingot molds are used during casting, and the ingot mold temperature is controlled between -60℃ and 0℃. Depending on the size of the steel ingot, the ingot mold temperature can be, for example, but not limited to, any one or any two of -60℃, -50℃, -40℃, -30℃, -20℃, -10℃, and 0℃. Electromagnetic stirring during casting is performed using a crystallizer with a current range of 300A~500A. Depending on the size of the steel ingot, the current can be, for example, but not limited to, any one or any two of 300A, 350A, 400A, 450A, and 500A. The electromagnetic stirring frequency range is 2Hz~5Hz. Depending on the size of the steel ingot, the frequency can be any one or any two of 2Hz, 3Hz, 4Hz, and 5Hz. The electromagnetic stirring mode is intermittent rotary stirring, rotating forward for 10s~30s, stopping for 2~6s, and rotating backward for 10s~30s. The forward rotation time can be any one or any two of 10s, 15s, 20s, 25s, and 30s, the stopping time can be any one or any two of 2s, 3s, 4s, 5s, and 6s, and the reverse rotation time can be any one or any two of 10s, 15s, 20s, 25s, and 30s.

[0051] S2: Homogenization heat treatment is performed on extra-thick steel ingots, wherein the homogenization heat treatment is carried out by gradient heating method, and the furnace charging temperature is ≤400℃.

[0052] The low-temperature preheating stage involves heating to 750℃~800℃ at a rate of 60℃ / h~80℃ / h. For example, it can be, but is not limited to, heating to 750℃ at a rate of 60℃ / h; heating to 775℃ at a rate of 60℃ / h; heating to 800℃ at a rate of 60℃ / h; heating to 750℃ at a rate of 70℃ / h; heating to 775℃ at a rate of 70℃ / h; heating to 800℃ at a rate of 70℃ / h; heating to 750℃ at a rate of 80℃ / h; heating to 775℃ at a rate of 80℃ / h; heating to 800℃ at a rate of 80℃ / h, etc.

[0053] The intermediate-temperature preheating stage involves heating to 950℃~1000℃ at a rate of 90℃ / h~100℃ / h. For example, it can be, but is not limited to, heating to 950℃ at a rate of 90℃ / h; heating to 975℃ at a rate of 90℃ / h; heating to 1000℃ at a rate of 90℃ / h; heating to 950℃ at a rate of 95℃ / h; heating to 975℃ at a rate of 95℃ / h; heating to 1000℃ at a rate of 95℃ / h; heating to 950℃ at a rate of 100℃ / h; heating to 975℃ at a rate of 100℃ / h; heating to 1000℃ at a rate of 100℃ / h; etc.

[0054] The high-temperature heating stage involves heating at a rate of 30℃ / h to 50℃ / h to 1180℃ to 1220℃. For example, it can be, but is not limited to, heating at a rate of 30℃ / h to 1180℃; heating at a rate of 30℃ / h to 1200℃; heating at a rate of 30℃ / h to 1220℃; heating at a rate of 40℃ / h to 1180℃; heating at a rate of 40℃ / h to 1200℃; heating at a rate of 40℃ / h to 1220℃; heating at a rate of 50℃ / h to 1180℃; heating at a rate of 50℃ / h to 1200℃; heating at a rate of 50℃ / h to 1220℃, etc.

[0055] The insulation time during the homogenization stage is determined by increasing the insulation time by 5h to 7h for every 100mm of cross-sectional thickness. For example, it can be, but is not limited to, increasing the insulation time by 5h for every 100mm of cross-sectional thickness; increasing the insulation time by 6h for every 100mm of cross-sectional thickness; increasing the insulation time by 7h for every 100mm of cross-sectional thickness, etc.

[0056] S3: Take out the steel ingot from step S2 after the homogenization heat treatment holding time is over and forge it. All forging operations must be carried out at a surface temperature above 950℃. If the surface temperature of the steel ingot is below 950℃, the flattened steel ingot is returned to the furnace and heated to 1180℃~1220℃ at a rate of 30℃ / h~50℃ / h and held for 1h~2h before being taken out for forging. For example, it can be, but is not limited to, heating to 1180℃ at a rate of 30℃ / h and holding for 1 hour; heating to 1180℃ at a rate of 30℃ / h and holding for 2 hours; heating to 1220℃ at a rate of 30℃ / h and holding for 1 hour; heating to 1220℃ at a rate of 30℃ / h and holding for 2 hours; heating to 1180℃ at a rate of 50℃ / h and holding for 1 hour; heating to 1180℃ at a rate of 50℃ / h and holding for 2 hours; heating to 1220℃ at a rate of 50℃ / h and holding for 1 hour; heating to 1220℃ at a rate of 50℃ / h and holding for 2 hours, etc.

[0057] In step S3, the forging process involves the following steps: (1) chamfering; (2) pressing the clamp handle; (3) cutting the bottom; (4) drawing; and (5) upsetting. The upsetting reduction rate for each upsetting is 20% to 30%, and the feed rate / anvil width is 0.7 to 0.9.

[0058] This forging method allows for sufficient deformation of the steel ingot, ensuring adequate deformation in the core as well. Examples include, but are not limited to, upsetting reduction rates of 20% per pass with a feed / anvil width of 0.7; 20% upsetting reduction rate with a feed / anvil width of 0.8; 20% upsetting reduction rate with a feed / anvil width of 0.9; 25% upsetting reduction rate with a feed / anvil width of 0.7; 25% upsetting reduction rate with a feed / anvil width of 0.8; 25% upsetting reduction rate with a feed / anvil width of 0.9; 30% upsetting reduction rate with a feed / anvil width of 0.7; 30% upsetting reduction rate with a feed / anvil width of 0.8; and 30% upsetting reduction rate with a feed / anvil width of 0.9, etc.

[0059] In step S3, after the forged extra-thick steel plate is air-cooled to a surface temperature of 400℃~500℃, it undergoes normalizing and tempering treatment. The normalizing process involves heating at a rate of 30℃ / h~50℃ / h to a normalizing temperature of 890℃~910℃, holding at that temperature for 6h~10h, and then cooling with forced air. The tempering process involves heating at a rate of 30℃ / h~50℃ / h to a tempering temperature of 600℃~680℃, holding at that temperature for 12h~16h, and then cooling with the furnace.

[0060] During normalizing treatment, for example, but not limited to, air-cooling the extra-thick steel plate to 400°C, heating it to 890°C at a rate of 30°C / h, and holding it at that temperature for 6 hours; air-cooling the extra-thick steel plate to 450°C, heating it to 900°C at a rate of 40°C / h, and holding it at that temperature for 8 hours; air-cooling the extra-thick steel plate to 500°C, heating it to 910°C at a rate of 50°C / h, and holding it at that temperature for 10 hours, etc.

[0061] During tempering, for example, but not limited to, heating to 600°C at a rate of 30°C / h and holding for 12 hours; heating to 640°C at a rate of 40°C / h and holding for 14 hours; heating to 680°C at a rate of 50°C / h and holding for 16 hours, etc.

[0062] S4: The extra-thick steel plate after S3 tempering is subjected to quenching and tempering treatment. The quenching is carried out at a rate of 30℃ / h~50℃ / h to the quenching temperature of 890℃~910℃, held for 6~10h, and cooled by circulating cooling oil quenching. The tempering is carried out at a rate of 30℃ / h~50℃ / h to the tempering temperature of 600℃~680℃, held for 12~16h, and cooled in the furnace.

[0063] During quenching, for example, but not limited to, heating to 890℃ at a rate of 30℃ / h and holding for 6h; heating to 900℃ at a rate of 40℃ / h and holding for 8h; heating to 910℃ at a rate of 50℃ / h and holding for 10h, etc.

[0064] During tempering, for example, but not limited to, heating to 600°C at a rate of 30°C / h and holding for 12 hours; heating to 640°C at a rate of 40°C / h and holding for 14 hours; heating to 680°C at a rate of 50°C / h and holding for 16 hours, etc.

[0065] The heat-treated extra-thick steel plate is then water-jet cut and surface-polished according to the required dimensions to obtain the finished extra-thick steel plate.

[0066] Furthermore, this application provides a further description of the technical solution of the present invention in conjunction with specific embodiments.

[0067] Example 1

[0068] S1: The extra-thick steel ingots are smelted in an electric furnace, where purification is achieved through a combination of diffusion deoxidation and precipitation deoxidation, followed by ladle refining in a ladle refining furnace (LF furnace). Furthermore, both the smelting furnace and the ingot mold are selected for a capacity of 50 tons.

[0069] The casting temperature is 1550℃, the superheat is 25℃, the ingot mold temperature is -60℃, the electromagnetic stirring adopts crystallizer electromagnetic stirring, the current is 300A, the electromagnetic stirring frequency is 5Hz, and the stirring mode is intermittent rotary stirring, rotating forward for 15s, stopping for 4s, and rotating backward for 15s.

[0070] The chemical composition of the obtained steel ingot is C: 0.47%, N: 0.13%, B: 0.002%, Cr: 3.78%, Ni: 1.81%, Al: 0.022%, Mn: 1.66%, Si: 0.53%, Mo: 0.48%, P: 0.008%, S: 0.003%, with the balance being Fe and other non-essential impurity elements.

[0071] S2: The homogenization heat treatment of the steel ingot is carried out using a gradient heating method, with a furnace charging temperature of 380℃. In the low-temperature preheating stage, the ingot is heated to 750℃ at a rate of 60℃ / h; in the medium-temperature preheating stage, the ingot is heated to 950℃ at a rate of 90℃ / h; and in the high-temperature heating stage, the ingot is heated to 1180℃ at a rate of 50℃ / h, and held at that temperature for 25 hours.

[0072] S3: The homogenized heat-treated steel ingot is forged to obtain a 300mm thick extra-thick steel plate. First, chamfering is performed, then clamping is done, then the bottom is cut, and finally drawing and upsetting begin. The upsetting reduction rate is 20% each time, and the feed rate / anvil width is 0.8. When the surface temperature of the steel ingot during forging is close to 950℃, the flattened steel ingot is returned to the furnace and heated to 1180℃ at a rate of 50℃ / h and held for 1 hour. It is then taken out and forged again until a 300mm thick extra-thick steel plate forging is obtained. Subsequently, the forged extra-thick steel plate is air-cooled to 500℃, then heated to 890℃ at a rate of 30℃ / h, held for 6 hours, and then cooled to room temperature by forced air. Finally, it is heated to 600℃ at a rate of 30℃ / h, held for 12 hours, and then cooled in the furnace.

[0073] S4: The extra-thick steel plate after S3 tempering is subjected to quenching and tempering treatment, heated to 890℃ at a rate of 30℃ / h, held for 6 hours, then quenched in oil with circulating cooling, and then heated to 600℃ at a rate of 30℃ / h, held for 12 hours, and then cooled in the furnace. Finally, the quenched and tempered 300mm thick extra-thick steel plate is water-jet cut and surface-polished according to the required dimensions to obtain the finished extra-thick steel plate.

[0074] Reference Figure 1 and Figure 2 The microstructure of the 300mm thick steel plate obtained in Example 1 was characterized.

[0075] Specifically, Figure 1 The microstructure is located at 1 / 2 of the thickness direction of the steel plate. Figure 2 The microstructure at 1 / 4 of the thickness direction of the steel plate is shown. Both the 1 / 2 and 1 / 4 sections show high-temperature tempered sorbite microstructure. In comparison, the microstructures at both locations are highly uniform and show no difference in thickness direction.

[0076] Furthermore, the C content, hardness, density, and tensile strength of the extra-thick steel plate at different locations in the thickness direction in Example 1 were tested, and the data are summarized in Table 1 below.

[0077] Table 1. Physical properties of the extra-thick steel plate in Example 1 at different locations along the thickness direction.

[0078]

[0079] Example 2

[0080] This embodiment of a high-strength, extra-thick steel plate and its preparation method includes the following steps:

[0081] S1: The extra-thick steel ingots are smelted in an electric furnace, where purification is achieved through a combination of diffusion deoxidation and precipitation deoxidation, followed by ladle refining in a ladle refining furnace (LF furnace). Furthermore, both the smelting furnace and the ingot mold are selected for a capacity of 50 tons.

[0082] Specifically, the casting temperature was 1560℃, the superheat was 23℃, the ingot mold temperature was -35℃, and the electromagnetic stirring was performed using a crystallizer with a current of 450A and a stirring frequency of 3Hz. The stirring mode was intermittent rotary stirring, rotating forward for 30 seconds, stopping for 6 seconds, and then rotating in reverse for 20 seconds. The chemical composition of the obtained steel ingot was: C: 0.52%, N: 0.10%, B: 0.003%, Cr: 4.22%, Ni: 1.54%, Al: 0.031%, Mn: 1.80%, Si: 0.45%, Mo: 0.38%, P: 0.007%, S: 0.003%, with the balance being Fe and other non-essential impurities.

[0083] S2: The homogenization heat treatment of the steel ingot is carried out using a gradient heating method, with a furnace charging temperature of 392℃. The low-temperature preheating stage is heated to 800℃ at a rate of 80℃ / h, the medium-temperature preheating stage is heated to 975℃ at a rate of 95℃ / h, and the high-temperature heating stage is heated to 1200℃ at a rate of 40℃ / h, and held at that temperature for 30h.

[0084] S3: The homogenized heat-treated steel ingot is forged to obtain a 400mm thick extra-thick steel plate. First, chamfering is performed, then clamping is done, then the bottom is cut, and finally drawing and upsetting begin. The upsetting reduction rate is 25% each time, and the feed rate / anvil width is 0.7. When the surface temperature of the steel ingot during forging is close to 950℃, the flattened steel ingot is returned to the furnace and heated to 1200℃ at a rate of 40℃ / h and held for 1 hour. It is then taken out and forged again until a 400mm thick extra-thick steel plate forging is obtained. Subsequently, the forged extra-thick steel plate is air-cooled to 450℃, then heated to 900℃ at a rate of 40℃ / h, held for 8 hours, and then cooled to room temperature by forced air. Finally, it is heated to 640℃ at a rate of 40℃ / h, held for 14 hours, and then cooled in the furnace.

[0085] S4: The extra-thick steel plate after S3 tempering is subjected to quenching and tempering treatment, heated to 900℃ at a rate of 40℃ / h, held for 8 hours, then quenched in oil with circulating cooling, and then heated to 640℃ at a rate of 40℃ / h, held for 14 hours, and then cooled in the furnace. Finally, the quenched and tempered 400mm thick extra-thick steel plate is water-jet cut and surface-polished according to the required dimensions to obtain the finished extra-thick steel plate.

[0086] Reference Figure 3 and Figure 4 The microstructure of the 400mm thick steel plate obtained in Example 2 was characterized.

[0087] Specifically, Figure 3 The microstructure is located at 1 / 2 of the thickness direction of the steel plate. Figure 4The microstructure at 1 / 4 of the thickness direction of the steel plate is shown. Similar to Example 1, the microstructure at 1 / 2 and 1 / 4 of the thickness direction in Example 2 is high-temperature tempered sorbite, and the microstructures at both locations are highly uniform with no difference in thickness direction.

[0088] Furthermore, the C content, hardness, density, and tensile strength of the extra-thick steel plate at different locations in the thickness direction in Example 2 were tested, and the data are summarized in Table 2 below.

[0089] Table 2. Physical properties of the extra-thick steel plate in Example 2 at different locations along the thickness direction.

[0090]

[0091] Example 3

[0092] This embodiment of a high-strength, extra-thick steel plate and its preparation method includes the following steps:

[0093] S1: The extra-thick steel ingots are smelted in an electric furnace, where purification is achieved through a combination of diffusion deoxidation and precipitation deoxidation, followed by ladle refining in a ladle refining furnace (LF furnace). Furthermore, both the smelting furnace and the ingot mold are selected for a capacity of 50 tons.

[0094] Specifically, the casting temperature is 1580℃, the superheat is 20℃, the ingot mold temperature is -10℃, the electromagnetic stirring is performed using a crystallizer with a current of 500A and a stirring frequency of 2Hz. The stirring mode is intermittent rotary stirring, rotating forward for 10 seconds, stopping for 2 seconds, and then rotating backward for 30 seconds. The chemical composition of the obtained steel ingot is: C: 0.45%, N: 0.12%, B: 0.005%, Cr: 4.56%, Ni: 1.24%, Al: 0.018%, Mn: 1.55%, Si: 0.29%, Mo: 0.41%, P: 0.009%, S: 0.004%, with the balance being Fe and other non-essential impurities.

[0095] S2: The homogenization heat treatment of the steel ingot is carried out using a gradient heating method, with a furnace charging temperature of 385℃. In the low-temperature preheating stage, the ingot is heated to 775℃ at a rate of 70℃ / h; in the medium-temperature preheating stage, the ingot is heated to 1000℃ at a rate of 100℃ / h; and in the high-temperature heating stage, the ingot is heated to 1220℃ at a rate of 30℃ / h, and held at that temperature for 32 hours.

[0096] S3: The homogenized heat-treated steel ingot is forged to obtain a 500mm thick extra-thick steel plate. First, chamfering is performed, then clamping is done, then the bottom is cut, and finally, drawing and upsetting begin. The upsetting reduction rate is 30% each time, and the feed rate / anvil width is 0.9. When the surface temperature of the steel ingot during forging is close to 950℃, the flattened steel ingot is returned to the furnace and heated to 1220℃ at a rate of 30℃ / h and held for 1 hour. It is then taken out and forged again until a 500mm thick extra-thick steel plate forging is obtained. Subsequently, the forged extra-thick steel plate is air-cooled to 400℃, then heated to 910℃ at a rate of 50℃ / h, held for 10 hours, and then cooled to room temperature by forced air. Finally, it is heated to 680℃ at a rate of 50℃ / h, held for 16 hours, and then cooled in the furnace.

[0097] S4: The extra-thick steel plate after S3 tempering is subjected to quenching and tempering treatment, heated to 910℃ at a rate of 50℃ / h, held for 10h, then quenched in oil with circulating cooling, and then heated to 680℃ at a rate of 50℃ / h, held for 16h, and then cooled in the furnace. Finally, the 500mm thick extra-thick steel plate after quenching and tempering treatment is waterjet cut and surface polished according to the required dimensions to obtain the finished extra-thick steel plate.

[0098] Reference Figure 5 and Figure 6 The microstructure of the 500mm thick steel plate obtained in Example 3 was characterized.

[0099] Specifically, Figure 5 The microstructure is located at 1 / 2 of the thickness direction of the steel plate. Figure 6 The microstructure at 1 / 4 of the thickness direction of the steel plate is shown. Similar to Examples 1 and 2, the microstructure at 1 / 2 and 1 / 4 of the thickness direction in Example 3 is high-temperature tempered sorbite, and the microstructure at both locations is highly uniform with no difference in thickness direction.

[0100] Furthermore, the C content, hardness, density, and tensile strength of the extra-thick steel plate at different locations in the thickness direction in Example 3 were tested, and the data are summarized in Table 3 below.

[0101] Table 3. Physical properties of the extra-thick steel plate in Example 3 at different locations along the thickness direction.

[0102]

[0103] The physical properties of the extra-thick steel plates in Examples 1-3 at different locations along the thickness direction were analyzed. Table 1 shows the C content, hardness, density, and tensile strength at different locations along the thickness direction in Example 1. It can be seen that the 300mm thick extra-thick steel plate in Example 1 has high strength and toughness, and its physical and mechanical properties show little fluctuation along the thickness direction. The composition exhibits good uniformity at each location, and the mechanical properties show good consistency across all locations.

[0104] In addition, Table 2 shows the C content, hardness, density, and tensile strength at different locations along the thickness direction of Example 2. Compared with Example 1, the 400mm thick extra-thick steel plate of Example 2 has slightly lower overall hardness and strength. In terms of chemical composition, physical properties, and mechanical properties, Example 2 is basically the same as Example 1 in terms of uniformity and consistency.

[0105] In addition, Table 3 shows the C content, hardness, density, and tensile strength at different locations along the thickness direction of Example 3. Compared with Examples 1 and 2, the 500mm thick extra-thick steel plate of Example 3 has the lowest hardness and strength. However, in terms of chemical composition, physical properties, and mechanical properties, Example 3, like Examples 1 and 2, exhibits high uniformity and consistency.

[0106] Comparative Example 1

[0107] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 did not use the frozen ingot mold and electromagnetic stirring preparation methods, but instead used a prior art method for preparing extra-thick steel plates. The extra-thick steel plate and its preparation method in Comparative Example 1 include the following steps:

[0108] S1: The raw material extra-thick steel ingots are smelted in an electric furnace, purified by diffusion deoxidation, and then refined outside the ladle in a ladle refining furnace (LF furnace).

[0109] The casting temperature was 1550℃, and the ingot mold temperature was room temperature. The chemical composition of the obtained steel ingot was: C: 0.47%, N: 0.13%, B: 0.002%, Cr: 3.78%, Ni: 1.81%, Al: 0.022%, Mn: 1.66%, Si: 0.53%, Mo: 0.48%, P: 0.008%, S: 0.003%, with the balance being Fe and other non-essential impurities.

[0110] S2: The homogenization heat treatment of steel ingots is carried out by direct heating. The ingots are loaded into the furnace at room temperature and heated to 1550℃ at a rate of 60℃ / h, and held for 40h.

[0111] S3: The homogenized heat-treated steel ingot is forged to obtain a 300mm thick extra-thick steel plate. First, chamfering is performed, then clamping is done, the bottom is cut, and finally, drawing and upsetting begin. When the surface temperature of the steel ingot during forging is close to 950℃, the flattened steel ingot is returned to the furnace and heated to 1180℃ at a rate of 50℃ / h and held for 1 hour. It is then removed and forged again until a 300mm thick extra-thick steel plate forging is obtained. Subsequently, the forged extra-thick steel plate is air-cooled to room temperature, and finally heated to 600℃ at a rate of 50℃ / h, held for 20 hours, and then cooled in the furnace.

[0112] S4: The extra-thick steel plate after S3 tempering is subjected to quenching and tempering treatment, heated to 900℃ at a rate of 50℃ / h, held for 10h, then quenched in oil with circulating cooling, and then heated to 650℃ at a rate of 50℃ / h, held for 20h, and then cooled in the furnace. Finally, the quenched and tempered 300mm thick extra-thick steel plate is waterjet cut and surface polished according to the required dimensions to obtain the finished extra-thick steel plate.

[0113] The C content, hardness, density, and tensile strength of the extra-thick steel plate in Comparative Example 1 at different locations along the thickness direction were tested, and the data are summarized in Table 4 below.

[0114] Table 4. Physical properties of the extra-thick steel plate in Comparative Example 1 at different locations along the thickness direction.

[0115]

[0116] Table 4 shows the C content, hardness, density, and tensile strength at different locations along the thickness direction of Comparative Example 1. Compared with Examples 1, 2, and 3, the 300mm thick extra-thick steel plate of Comparative Example 1 has lower hardness and strength, and exhibits greater fluctuations in chemical composition, physical properties, and mechanical properties along the thickness direction, resulting in poor uniformity and consistency.

[0117] Additionally, refer to Figure 7 and Figure 8 The microstructure of the 300mm thick steel plate obtained in Comparative Example 1 was characterized. Figure 7 This is a microstructure diagram of the steel plate at half its thickness. Figure 8 This is a microstructure diagram at 1 / 4 of the thickness of the steel plate. In Comparative Example 1, the microstructure at both 1 / 2 and 1 / 4 of the extra-thick steel plate is high-temperature tempered sorbite. However, compared to the microstructures of Examples 1-3, the sorbite at 1 / 2 and 1 / 4 of the microstructure in Comparative Example 1 is coarser. Furthermore, the sorbite at 1 / 2 of the extra-thick steel plate in Comparative Example 1 is coarser than the sorbite at 1 / 4, indicating microstructure inhomogeneity along the thickness direction.

[0118] It should be noted that the order of the embodiments described above is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. Furthermore, specific embodiments have been described above. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps described in the claims can be performed in a different order than that shown in the embodiments and still achieve the desired result. Additionally, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0119] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0120] This specification and accompanying drawings are merely illustrative examples of this application and are intended to cover any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from its scope. Therefore, if such modifications and modifications fall within the scope of this application and its equivalents, this application intends to include such modifications and modifications.

Claims

1. A method for producing a high-strength ultra-heavy steel plate, characterized by, It comprises the following steps: S1, obtaining a super-thick ingot by melting and casting, adopting a combination of diffusion deoxidization and sedimentation deoxidization for the purification of molten steel, and carrying out external refining in a ladle refining furnace; the casting is carried out by a frozen casting method, and electromagnetic stirring is carried out on the molten steel in the frozen ingot mold during casting; S2, homogenizing heat treatment is carried out on the super-thick ingot in step S1; S3, the super-thick ingot in step S2 is subjected to forging treatment and normalizing and tempering treatment to obtain a super-thick steel plate blank with a thickness of 300mm-500mm; S4, the super-thick steel plate blank in step S3 is subjected to quenching and tempering treatment, and is subjected to water jet cutting and surface polishing treatment to obtain a finished super-thick steel plate with a determined size; The chemical composition of the super-thick steel plate comprises C: 0.40%-0.60%; N：0.05%~0.15%； B: 0.001%-0.006%; Cr: 3.00%-5.00%; Ni: 1.00%-2.00%; Al: 0.010%-0.040%; Mn: 1.00%-2.00%; Si: 0.20%-0.70%; Mo: 0.10%-0.50%; P≤0.010%; S≤0.004%, the balance being Fe and optional impurity elements; In the S1 step, the ingot mold is frozen by liquid nitrogen during casting, and the temperature of the ingot mold is controlled at-60℃-0℃; the electromagnetic stirring during casting adopts mold electromagnetic stirring, the current range is 300A-500A, and the frequency range is 2Hz-5Hz; the electromagnetic stirring mode during casting is intermittent rotary stirring, forward rotation for 10s-30s, stop for 2-6s, and reverse rotation for 10s-30s.

2. The method of producing a high-strength ultra-heavy steel plate according to claim 1, wherein In the S2 step, the homogenizing heat treatment is carried out in a gradient heating mode, the furnace loading temperature is ≤400℃, the low-temperature preheating stage is heated at a rate of 60℃ / h-80℃ / h to 750℃-800℃, the medium-temperature preheating stage is heated at a rate of 90℃ / h-100℃ / h to 950℃-1000℃, the high-temperature heating stage is heated at a rate of 30℃ / h-50℃ / h to 1180℃-1220℃, and the homogenizing holding stage is determined by increasing the holding time by 5h-7h per 100mm of cross-sectional thickness.

3. The method for preparing a high-strength, extra-thick steel plate as described in claim 1, characterized in that, In the S3 step, the forging treatment needs the surface temperature of the super-thick ingot to be higher than 950℃; When the surface temperature of the super-thick ingot is lower than 950℃, it is returned to heat treatment, reheated to 1180℃-1220℃ at a rate of 30℃ / h-50℃ / h, and held for 1h-2h before being taken out for further forging treatment.

4. The method of producing a high-strength ultra-heavy steel plate according to claim 3, wherein The S3 step, the forging treatment includes chamfering, pressing the handle, cutting the bottom, lengthening, and upsetting.

5. The method of producing a high-strength ultra-heavy steel plate according to claim 4, wherein In the S3 step, the reduction rate of each upsetting operation is 20%-30%, and the feed amount / anvil width is 0.7-0.

9.

6. The method of producing a high-strength ultra-heavy steel plate according to claim 5, wherein In the S3 step, the thick steel plate after the forging treatment is subjected to normalizing and tempering treatment when the surface temperature is air-cooled to 400-500 DEG C, the normalizing is heated to the normalizing temperature 890-910 DEG C at the rate of 30-50 DEG C / h, the temperature is kept for 6-10 h, and air blast cooling is performed; the tempering is heated to the tempering temperature 600-680 DEG C at the rate of 30-50 DEG C / h, the temperature is kept for 12-16 h, and the furnace cooling is performed.

7. The method of producing a high-strength ultra-heavy steel plate according to claim 1, wherein In the S4 step, the thick steel plate is subjected to the quenching and tempering treatment, the quenching temperature is 890-910 DEG C, the temperature is kept for 6-10 h, the cooling mode is the circulating cooling oil quenching; the tempering temperature is 600-680 DEG C, the temperature is kept for 12-16 h, and the furnace cooling is performed.

8. A high-strength ultra-heavy steel plate, characterized by, The high-strength thick steel plate is prepared by the method according to any one of claims 1-7.

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