2 gpa-grade ultrahigh-strength steel plate, and preparation method therefor and use thereof

Abstract

The present invention relates to a 2 GPa-grade ultrahigh-strength steel plate and a manufacturing method therefor. The 2 GPa-grade ultrahigh-strength steel plate comprises the following chemical components in percentages by weight: C: 0.35-0.45%, Si: 0.10-0.40%, Mn: 0.30-0.60%, Cr: 0.80-1.20%, Ni: 1.20-1.80%, Mo: 0.30-0.60%, V: 0.05-0.15%, Ti: 0.01-0.04%, P:≤0.006%, S:≤0.003%, H:≤0.00015%, N:≤0.006%, and the balance of Fe and inevitable impurities. The 2 GPa-grade ultrahigh-strength steel plate has a tensile strength of greater than or equal to 2000 MPa, a yield strength of greater than or equal to 1500 MPa, good plasticity and a percentage elongation after fracture of greater than or equal to 10%, can be bent to 70° without cracking or breaking, and is applicable as protective steel.

Description

2GPa grade ultra-high strength steel plate, its preparation method and application Technical Field

[0001] This invention relates to the field of alloy steel technology, and in particular to a 2GPa grade ultra-high strength steel plate, its preparation method, and its application. Background Technology

[0002] Alloy steel refers to iron-carbon alloys formed by adding appropriate amounts of one or more alloying elements to ordinary carbon steel. Depending on the added elements and the adoption of appropriate processing techniques, special properties such as high strength, high toughness, wear resistance, corrosion resistance, low-temperature resistance, high-temperature resistance, and non-magnetic properties can be obtained.

[0003] High-strength protective steel is widely used not only in the military field but also in the civilian sector, including armored cash transport vehicles, security vehicles, armed police explosive-proof vehicles, and protective covers for civilian vehicles. When the required material has a yield strength greater than 1300 MPa and a tensile strength greater than 1500 MPa, it is classified as ultra-high-strength protective steel.

[0004] However, while existing ultra-high strength protective steels meet the requirements for hardness and strength, their overall performance in terms of strength, plasticity, and toughness is lacking, making them highly susceptible to cold cracking and unable to meet the requirements for bending processing. With the increasing demand for integrated protective equipment, bending processing is increasingly needed in protective applications to minimize welds and avoid the reduction in protective performance caused by weld softening. Therefore, improving the toughness and plasticity of protective steels and enhancing their bending performance to improve protective capabilities remains an important direction in current protective material research. Summary of the Invention

[0005] Based on this, the present invention provides an alloy steel with high strength, high plasticity and high toughness, belonging to the 2GPa grade ultra-high strength steel plate. In addition, the present invention also provides a method for preparing the 2GPa grade ultra-high strength steel plate and its application.

[0006] The technical solution is as follows:

[0007] A 2GPa grade ultra-high strength steel plate, by weight percentage, has the following chemical composition: C: 0.35%~0.45%, Si: 0.10%~0.40%, Mn: 0.30%~0.60%, Cr: 0.80%~1.20%, Ni: 1.20%~1.80%, Mo: 0.30%~0.60%, V: 0.05%~0.15%, Ti: 0.01%~0.04%, P: ≤0.006%, S: ≤0.003%, H: ≤0.00015%, N: ≤0.006%, with the balance being Fe and unavoidable impurities.

[0008] In one embodiment, the carbon content of the 2GPa grade ultra-high strength steel plate is 0.36% to 0.42% by weight.

[0009] In one embodiment, the 2GPa grade ultra-high strength steel plate contains 0.20% to 0.40% Si by weight percentage.

[0010] In one embodiment, the 2GPa grade ultra-high strength steel plate contains 0.40% to 0.55% Mn by weight percentage.

[0011] In one embodiment, the 2GPa grade ultra-high strength steel plate contains 0.90% to 1.20% Cr by weight percentage.

[0012] In one embodiment, the Ni content of the 2GPa grade ultra-high strength steel plate is 1.40% to 1.70% by weight.

[0013] In one embodiment, the 2GPa grade ultra-high strength steel plate contains 0.40% to 0.60% Mo by weight percentage.

[0014] In one embodiment, the 2GPa grade ultra-high strength steel plate contains 0.10% to 0.15% V by weight percentage.

[0015] In one embodiment, the yield strength of the 2GPa grade ultra-high strength steel plate is ≥1500MPa.

[0016] In one embodiment, the tensile strength of the 2GPa grade ultra-high strength steel plate is ≥2000MPa.

[0017] In one embodiment, the elongation at break of the 2GPa grade ultra-high strength steel plate is ≥10%.

[0018] In one embodiment, under the test conditions of using a bending die with an upper die R≥6a and a lower die opening≥18a, the 2GPa grade ultra-high strength steel plate can be bent 70° without cracks or breakage, where a is the plate thickness.

[0019] In one embodiment, the thickness of the 2GPa grade ultra-high strength steel plate is 3mm to 14mm.

[0020] The present invention also provides a method for preparing the 2GPa grade ultra-high strength steel plate as described above, comprising the steps of: converter, refining, continuous casting, hydrogen diffusion, heating in a heating furnace, rolling, coiling, cooling, cross-cutting and leveling, quenching and tempering.

[0021] In one embodiment, the hydrogen diffusion step takes ≥24 hours.

[0022] In one embodiment, during the heating step in the heating furnace, the heating temperature is 1200℃~1280℃ and the heating time is ≥180min.

[0023] In one embodiment, cooling includes the following steps:

[0024] The coiled steel is placed in an insulated box for slow cooling, with a cooling rate of 6℃ / h to 10℃ / h and a cooling time of 72h to 96h.

[0025] In one embodiment, quenching includes the following steps:

[0026] After holding at 870–920℃ for 20–40 minutes, the product is removed from the furnace and quenched using a roller pressing method.

[0027] In one embodiment, the temperature during the tempering step is 180°C to 240°C.

[0028] In one embodiment, during the tempering step, the tempering holding time is 3.5 × steel plate thickness, where the tempering holding time is in minutes and the steel plate thickness is in millimeters.

[0029] This invention also provides an application of the 2GPa-level ultra-high strength steel plate described above, the technical solution of which is as follows:

[0030] A protective steel comprising, as described above, a 2GPa grade ultra-high strength steel plate.

[0031] The present invention has at least the following beneficial effects:

[0032] This invention provides a 2GPa-grade ultra-high-strength steel plate by controlling the chemical composition of alloy steel, particularly the types and percentages of elements. This control allows for tensile strength exceeding 2000 MPa (2 GPa), yield strength exceeding 1500 MPa, good plasticity, and elongation after fracture exceeding 10%. Using a bending die with an upper die radius (R≥6a) and a lower die opening ≥18a (a being the plate thickness), the plate can be bent 70° without cracking or breakage. This meets the strength and plasticity requirements of complex protective equipment. Furthermore, the low Mn and Ni content in this 2GPa-grade ultra-high-strength steel plate significantly reduces alloy costs. Additionally, the preparation method of this 2GPa-grade ultra-high-strength steel plate offers advantages such as simple operation, high efficiency, good repeatability, environmental friendliness, low energy consumption, and low production costs, making it suitable for industrialization and market application (especially for protective steel plates). Attached Figure Description

[0033] Figure 1 shows the tensile properties of the 2GPa grade ultra-high strength steel plate prepared in Example 1 of the present invention;

[0034] Figure 2 shows the bending results of the 2GPa grade ultra-high strength steel plate prepared in Example 1 of the present invention;

[0035] Figure 3 is a plate shape diagram of the 2GPa grade ultra-high strength steel plate prepared in Example 2 of the present invention;

[0036] Figure 4 shows the target test results of the 2GPa-level ultra-high strength steel plate prepared in Example 3 of the present invention. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0039] When using “including,” “having,” and “contains” as described herein, the intention is to cover non-exclusive inclusion, unless an explicit qualifying term such as “only,” “consisting of,” etc., is used, in which case another component may be added.

[0040] In this invention, the terms "preferredly," "more preferably," "better," and "even better" refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of the invention. That is, in this invention, "preferredly," "more preferably," "better," and "even better" are merely descriptions of more effective implementations or examples, but do not constitute a limitation on the scope of protection of the invention.

[0041] In this invention, terms such as "further," "even more," and "particularly" are used for descriptive purposes and to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0042] In this invention, "at least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two layers, three layers, etc., unless otherwise explicitly specified. In the description of this invention, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0043] When a numerical range is disclosed in this invention, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Further, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included. Only a few numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0044] Unless otherwise specified, all steps of this invention may be performed sequentially or randomly. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0045] Unless otherwise stated, a singular term may include a plural term and should not be understood as having a quantity of one.

[0046] Unless otherwise specified, the temperature parameters in this invention can be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument.

[0047] The weights of the relevant components mentioned in the embodiments of this invention can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this invention is within the scope disclosed in the embodiments of this invention. Specifically, the weights mentioned in the embodiments of this invention can be well-known units of mass in the chemical industry, such as μg, mg, g, and kg.

[0048] In this invention, if the unit of a data range is only followed by the right endpoint, it indicates that the units of the left and right endpoints are the same. For example, 800~850nm means that the units of the left endpoint "800" and the right endpoint "850" are both nm (nanometers).

[0049] In this invention, "above" or "below" both include the number itself. For example, "below 1" means less than or equal to 1 (≤1), and "above 1" means greater than or equal to 1 (≥1).

[0050] In this invention, "A and B are independently selected from x, y or z" means that A and B are independent events, and event A does not affect the occurrence of event B. Therefore, when A is selected from x, B can be selected from any one of x, y or z; when A is selected from y, B can be selected from any one of x, y or z; when A is selected from z, B can be selected from any one of x, y or z.

[0051] Unless otherwise stated, a singular term may include a plural term and should not be understood as having a quantity of one.

[0052] The technical solution of the present invention is as follows:

[0053] A 2GPa grade ultra-high strength steel plate, by weight percentage, has the following chemical composition: C: 0.35%~0.45%, Si: 0.10%~0.40%, Mn: 0.30%~0.60%, Cr: 0.80%~1.20%, Ni: 1.20%~1.80%, Mo: 0.30%~0.60%, V: 0.05%~0.15%, Ti: 0.01%~0.04%, P: ≤0.006%, S: ≤0.003%, H: ≤0.00015%, N: ≤0.006%, with the balance being Fe and unavoidable impurities.

[0054] Carbon (C): C is an effective and economical element for improving steel strength, but excessive C content will result in a brittle structure, reducing the low-temperature impact toughness of alloy steel, and deteriorating weldability and corrosion resistance. Appropriate amounts of C and Ti can form stable nanoscale precipitates, TiC. These TiC nanoscale precipitates can produce strong precipitation strengthening and grain refinement strengthening effects, significantly improving the strength of the steel plate. To achieve ultra-high yield strength (>1300MPa), ultra-high tensile strength (>1500MPa), and considering both high plasticity and high toughness, this invention controls the C content in the steel to 0.35%~0.45%. Understandably, this includes, but is not limited to, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.40%, 0.41%, 0.42%, 0.43%, 0.44%, or 0.45%. In one embodiment, the C content of the 2GPa grade ultra-high strength steel plate is 0.36%~0.42% by weight.

[0055] Silicon (Si): Si dissolved in alloy steel can improve its strength and reduce its corrosion rate. However, excessive Si content can worsen the weldability and reduce the toughness of the steel. Considering all factors, this invention controls the Si content in the 2GPa grade ultra-high strength steel plate to be 0.10%~0.40%, which can be understood to include, but is not limited to, 0.10%, 0.12%, 0.15%, 0.18%, 0.20%, 0.25%, 0.28%, 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, or 0.40% by weight. In one embodiment, the Si content of the 2GPa grade ultra-high strength steel plate is 0.20%~0.40% by weight.

[0056] Manganese (Mn): Mn has a strong solid solution strengthening effect and a significant grain refinement effect. It can improve the strength and toughness of alloy steel. However, excessive Mn content can easily lead to core component segregation, affecting processing performance and increasing alloy cost. Therefore, in order to achieve good strength and toughness of the steel plate, avoid core component segregation, and reduce the cost of alloy steel, this invention controls the Mn content in 2GPa grade ultra-high strength steel plate to be 0.30%~0.60%, which can be understood to include, but is not limited to, 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.40%, 0.41%, 0.42%, 0.43%, 0.44%, 0.45%, 0.50%, 0.51%, 0.53%, 0.55%, 0.58%, or 0.60%. In one embodiment, the 2GPa grade ultra-high strength steel plate contains 0.40% to 0.55% Mn by weight percentage.

[0057] Chromium (Cr): Cr can improve the corrosion resistance of alloy steel and significantly increase its strength, hardness, and hardenability. However, it can also increase the temper brittleness tendency of alloy steel. That is, an appropriate amount of Cr can improve mechanical properties, but excessive Cr will lead to a decrease in the toughness of alloy steel. Taking all factors into consideration, in this invention, the Cr content in the 2GPa grade ultra-high strength steel plate is controlled at 0.80%~1.20%, which can be understood to include, but is not limited to, 0.80%, 0.82%, 0.84%, 0.85%, 0.88%, 0.90%, 0.92%, 0.94%, 0.95%, 0.98%, 1.0%, 1.05%, 1.10%, 1.15%, or 1.20%.

[0058] Nickel (Ni): Ni can form solid solutions or precipitates with other elements, increasing the lattice stability, strength, and corrosion resistance of steel. Furthermore, Ni can alter the phase transformation temperature and heat treatment characteristics of steel, making it more stable and uniform during heat treatment. Additionally, Ni can improve the strength, hardness, plasticity, and toughness of steel, giving it better tensile, bending, and torsional resistance. However, Ni is a precious metal, and high dosage increases production costs. Excessive nickel can also easily cause intergranular corrosion, reducing corrosion resistance. Moreover, excessively high nickel content can lead to an increase in precipitated phases in stainless steel at high temperatures, further reducing mechanical properties. Considering all factors, in this invention, the Ni content in the 2GPa grade ultra-high strength steel plate is controlled at 1.20%~1.80%, which can be understood to include, but is not limited to, 1.20%, 1.25%, 1.30%, 1.35%, 1.40%, 1.45%, 1.50%, 1.55%, 1.60%, 1.65%, 1.70%, 1.75%, or 1.80%.

[0059] Molybdenum (Mo): In steel, Mo improves hardenability and hot strength, prevents temper brittleness, and increases corrosion resistance, plasticity, and wear resistance. However, the addition of Mo causes the production of molybdenum oxide gas during steel heating, promotes decarburization, inhibits graphitization, reduces the thermal conductivity of the steel, and reduces the oxidation resistance of the steel when the Mo content is too high. Taking all factors into consideration, this invention controls the Mo content in 2GPa grade ultra-high strength steel plates to be 0.30%~0.60%, which can be understood to include, but is not limited to, 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.40%, 0.41%, 0.42%, 0.43%, 0.44%, 0.45%, 0.50%, 0.51%, 0.53%, 0.55%, 0.58%, or 0.60%. In one embodiment, the 2GPa grade ultra-high strength steel plate contains 0.40% to 0.60% Mo by weight percentage.

[0060] Vanadium (V): V has a strong affinity for C and O, forming corresponding stable compounds. In steel, V mainly exists in the form of carbides, which are typical high-melting-point, high-hardness, and highly dispersed carbides. It is an element that strongly improves wear resistance. The main function of V is to refine the microstructure and grain of steel, improve the strength and toughness of steel, and enhance its resistance to hydrogen corrosion under high temperature and high pressure. However, excessive V content will deteriorate the processing performance of steel. Taking all factors into consideration, this invention controls the V content in 2GPa grade ultra-high strength steel plates to be 0.05% to 0.15%, which can be understood to include, but is not limited to, 0.05%, 0.055%, 0.06%, 0.065%, 0.07%, 0.075%, 0.076%, 0.08%, 0.085%, 0.09%, 0.095%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, or 0.15%.

[0061] Titanium (Ti): Ti reacts with N at high temperatures to form TiN. During the austenitization of the slab during heating, TiN inhibits austenite grain growth. During hot rolling, Ti reacts with C at lower temperatures to form nanoscale TiC. The fine TiC particles have significant precipitation strengthening and grain refinement strengthening effects, which are beneficial to improving the strength and toughness of the steel plate. However, when the Ti content is too high, on the one hand, coarse square TiN precipitates will form. When the steel plate is under stress, the stress will concentrate near the TiN particles, becoming a nucleation and growth source for microcracks, reducing the fatigue performance of the steel plate. On the other hand, due to the small solid solubility product of TiC, Ti is difficult to dissolve during the heating process of continuously cast steel billets, thus failing to play its corresponding role. Taking all factors into consideration, this invention controls the Ti content in 2GPa grade ultra-high strength steel plates to be 0.01%~0.04%, which can be understood to include, but is not limited to, 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, or 0.04%. In one embodiment, the 2GPa grade ultra-high strength steel plate contains 0.03% to 0.04% Ti by weight percentage.

[0062] Phosphorus (P): While P can increase the corrosion resistance of alloy steel, it significantly deteriorates the toughness of the steel. Taking all factors into consideration, this invention controls the P content in 2GPa grade ultra-high strength steel plates to be ≤0.006%, which can be understood to include, but is not limited to, 0, 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, or 0.006%.

[0063] Sulfur (S): S deteriorates the corrosion resistance, plasticity, ductility, and toughness of steel, mainly due to the poor plasticity of iron sulfide formed by the combination of sulfur and iron. Taking all factors into consideration, this invention controls the S content in 2GPa grade ultra-high strength steel plates to ≤0.003%, which can be understood to include, but is not limited to, 0, 0.001%, 0.002%, and 0.003%.

[0064] Hydrogen (H): All metallic materials exhibit varying degrees of hydrogen embrittlement tendency. High-strength steel may experience delayed failure even with hydrogen content below the ppm level. Taking all factors into consideration, this invention controls the H content of 2GPa grade ultra-high-strength steel plates to ≤0.00015%, including but not limited to 0, 0.00001%, 0.00002%, 0.00003%, 0.00004%, 0.00005%, 0.00006%, 0.00007%, 0.00008%, 0.00009%, 0.0001%, or 0.00015%.

[0065] Nitrogen (N): N significantly reduces the plasticity, toughness, and weldability of steel. Taking all factors into consideration, this invention controls the N content of 2GPa grade ultra-high strength steel plates to ≤0.006%, including but not limited to 0, 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, or 0.006%.

[0066] In summary, this invention provides a high-strength, high-plasticity, and high-toughness alloy steel by controlling the chemical composition of the alloy steel, especially by controlling the types and percentages of elements.

[0067] Testing revealed that the 2GPa grade ultra-high strength steel plate provided by this invention exhibits a strength exceeding 2000MPa, a yield strength exceeding 1500MPa, good plasticity, and an elongation after fracture exceeding 10%. Under bending die conditions with an upper die R≥6a and a lower die opening ≥18a (a being the plate thickness), the 2GPa grade ultra-high strength steel plate can be bent 70° without cracking or breakage, meeting the requirements of complex protective equipment for material strength and plasticity. Furthermore, the low Mn and Ni content in the 2GPa grade ultra-high strength steel plate significantly reduces alloy costs. Compared to other ultra-high strength alloy structural steels such as 4130, 4340, 300M, and H13, which have elongation rates below 5%, the steel plate provided by this invention effectively meets the requirements of complex protective equipment for material strength and plasticity.

[0068] In one embodiment, the thickness of the 2GPa grade ultra-high strength steel plate is 3mm to 14mm.

[0069] The present invention also provides a method for preparing the 2GPa grade ultra-high strength steel plate as described above, the technical solution of which is as follows:

[0070] A method for preparing 2GPa grade ultra-high strength steel plate as described above includes the following steps: converter, refining, continuous casting, hydrogen diffusion, heating in a heating furnace, rolling, coiling, cooling, cross-cutting and leveling, quenching and tempering.

[0071] The preparation method of the 2GPa grade ultra-high strength steel plate of the present invention will be described in detail below by step-by-step description.

[0072] S1: The continuously cast billet is obtained through a converter → refining (LF+RH) → continuous casting process. The weight percentage of the chemical element composition of the continuously cast billet is as follows:

[0073] C: 0.35%~0.45%, Si: 0.10%~0.40%, Mn: 0.30%~0.60%, Cr: 0.80%~1.20%, Ni: 1.20%~1.80%, Mo: 0.30%~0.60%, V: 0.05%~0.15%, Ti: 0.01%~0.04%, P: ≤0.006%, S: ≤0.003%, H: ≤0.00015%, N: ≤0.006%, with the balance being Fe and unavoidable impurities.

[0074] S2: Hydrogen diffusion: After the slab is cut, it is directly put into the heat preservation pit. The top, bottom and sides of the slab are surrounded by other high-temperature slabs for slow cooling and hydrogen diffusion.

[0075] In one embodiment, the hydrogen diffusion time is ≥24h.

[0076] S3: Heating → Rolling → Coiling: Slow-cooled billet is heated at a temperature of 1200℃~1280℃ (if a uniform heating temperature of 1230℃ is required), with a heating time of ≥180min. Then it is rolled to the target thickness and coiled.

[0077] S4: Slow cooling in the heat preservation box → cross-cutting and leveling: The hot-rolled coil is immediately hoisted into the heat preservation box for slow cooling to avoid the air-cooling quenching effect of the steel coil and reduce the difficulty of cross-cutting. Then it is hoisted out for cross-cutting and leveling to form hot-rolled steel plate.

[0078] In one embodiment, the coiled steel coil is placed in an insulated box for slow cooling, wherein the cooling rate is 6°C / h to 10°C / h and the cooling time is 72h to 96h.

[0079] S5: Quenching

[0080] The roller hearth furnace is heated to 870℃~920℃. After the temperature stabilizes, the high-plasticity protective steel plate is transported into the roller hearth furnace and held for 2.4 mins × plate thickness (mm). It is then removed from the furnace and immediately quenched using a roller press quenching method with a quenching water volume of 500m³. 3 / h, water ratio 1.5, roller speed 0.4m / s. Roller quenching reduces deformation of the steel plate during heat treatment, ensuring good plate shape and flatness; low-temperature tempering releases internal stress in the steel plate, ensuring no brittle fracture or warping during cutting.

[0081] S6: Tempering: Heat the roller hearth tempering furnace to 180℃~240℃ and keep the furnace temperature stable. Immediately transport the quenched steel plate into the tempering furnace for tempering treatment. Tempering time = 3.5 × steel plate thickness, where the unit of tempering holding time is min and the unit of steel plate thickness is mm.

[0082] In one embodiment, the tempering time is 30 min to 60 min.

[0083] This invention also provides an application of the 2GPa-level ultra-high strength steel plate described above, the technical solution of which is as follows:

[0084] A protective steel, comprising the aforementioned 2GPa grade ultra-high strength steel plate.

[0085] The invention will be further described below with reference to examples.

[0086] The mechanical properties of the steel are tested according to standard GB / T228.1-2010 (tensile test) and standard GB / T 232-2010 (bending test). Examples 1 to 3 and Comparative Examples 1 to 5

[0087] The process flow is as follows:

[0088] S1: The continuously cast billet is obtained through the converter → refining (LF+RH) → continuous casting process. The weight percentage of the chemical element composition of the continuously cast billet is shown in Table 1 below, with the balance being Fe and unavoidable impurities.

[0089] S2: Hydrogen diffusion: After the high-plasticity protective steel slab is cut, it is directly put into the heat preservation pit. The top, bottom and both sides of the slab are surrounded by other high-temperature slabs, and the hydrogen diffusion is slow-cooled for 24 hours or more.

[0090] S3: Heating → Rolling → Coiling: Slow-cooled billet is heated, requiring a uniform heating temperature of 1230℃ and a heating time of ≥180 min, then rolled to the target thickness and coiled.

[0091] S4: Slow cooling in the heat preservation box → cross-cutting and leveling: The hot-rolled coil is immediately hoisted into the heat preservation box for slow cooling for 72 hours to avoid the air-cooling quenching effect of the steel coil and reduce the difficulty of cross-cutting. Then it is hoisted out for cross-cutting and leveling to form hot-rolled steel plate.

[0092] S5: Quenching: Heat the roller hearth furnace to 870-920℃. After the temperature stabilizes, transport the high-plasticity protective steel plate into the roller hearth furnace. Hold for 2.4 mins × plate thickness (mm). Then remove the plate from the furnace and immediately quench it using a roller pressing method with a quenching water volume of 500 ml. 3 / h, water ratio 1.5, roller speed 0.4m / s.

[0093] S6: Tempering: Heat the roller hearth tempering furnace to 180~240℃ and keep the furnace temperature stable. Immediately transport the quenched steel plate into the tempering furnace for tempering treatment. Tempering time (min) = 3.5 × plate thickness (mm).

[0094] (1) The chemical composition of the billet is shown in Table 1, and the process parameters are shown in Table 2 below.

[0095] Table 1 Chemical composition of alloy steel plates in the comparative examples / wt%, balance being Fe and unavoidable impurities;

[0096]

[0097] Table 2. Heat treatment processes of alloy steel plates in the comparative examples.

[0098]

[0099] Table 3 Mechanical properties of alloy steel plates in the comparative examples

[0100]

[0101] As shown in Table 1, compared with Comparative Examples 1 to 5, the alloy steel plates prepared in Examples 1 to 3 of the present invention have superior comprehensive performance.

[0102] Figure 1 shows the tensile properties (gauge length 50 mm) of the alloy steel plate prepared in Example 1 of the present invention. As can be seen from Figure 1, the yield strength of Example 1 reaches 1585 MPa, the tensile strength reaches 2108 MPa, and the elongation after fracture reaches 13.4%. This indicates that the protective steel plate prepared under this composition and process has extremely high strength and good plasticity, and is a 2GPa grade ultra-high strength steel plate, which has achieved the design target. This shows that the composition and the production process are well matched.

[0103] Figure 2 shows the bending results of the 2GPa grade ultra-high strength steel plate prepared in Example 1 of the present invention. It can be seen that the protective steel plate prepared in Example 1 has excellent plasticity and bending performance, and does not crack when bent at 75°.

[0104] Figure 3 shows the plate shape of the alloy steel plate prepared in Example 2 of the present invention. It can be seen that even if the steel plate prepared under this composition and process has a strength of more than 2000MPa, its plate shape is still good in industrial production. No problem of poor plate shape caused by high strength and high internal stress has occurred, indicating that the process parameters and composition are well matched.

[0105] Figure 4 shows the target test results of the 2GPa grade ultra-high strength steel plate prepared in Example 3 of the present invention. It can be seen that the steel plate prepared by this composition and process has excellent protective performance.

[0106] In summary, this invention is simple to operate, employs an alloy composition ratio within a specific range, and produces alloy steel plates with fine internal structure, high strength, tensile strength exceeding 2000 MPa, yield strength exceeding 1500 MPa, good plasticity, elongation >10%, strong resistance to hydrogen-induced delayed cracking, and resistance to cracking. Furthermore, it can meet the processing requirements of bending ≤70° under test conditions of upper die R≥6a and lower die opening ≥18a (a is the plate thickness). Compared to other ultra-high strength alloy structural steels such as 4130, 4340, 300M, and H13, which have elongation rates below 5%, the steel plates provided by this invention can meet the requirements of complex protective equipment for material strength and plasticity indicators. In addition, roll quenching reduces deformation during heat treatment, ensuring good plate shape and flatness; low-temperature tempering releases internal stress, ensuring no brittle fracture or warping during cutting.

[0107] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The embodiments described above merely illustrate several implementation methods of the present invention to facilitate a detailed understanding of the technical solutions of the present invention, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided by the present invention through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this invention patent should be determined by the content of the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A 2 GPa-grade ultra-high-strength steel sheet, characterized by, The chemical composition, by weight percentage, includes: C: 0.35%–0.45%, Si: 0.10%–0.40%, Mn: 0.30%–0.60%, Cr: 0.80%–1.20%, Ni: 1.20%–1.80%, Mo: 0.30%–0.60%, V: 0.05%–0.15%, Ti: 0.01%–0.04%, P: ≤0.006%, S: ≤0.003%, H: ≤0.00015%, N: ≤0.006%, with the balance being Fe and unavoidable impurities.

2. The 2 GPa grade ultra-high strength steel sheet according to claim 1, characterized by, The 2GPa grade ultra-high strength steel plate contains 0.40% to 0.55% Mn by weight percentage.

3. The 2 GPa grade ultra-high strength steel sheet according to claim 1, characterized by, The Ni content of the 2GPa grade ultra-high strength steel plate is 1.40%~1.70% by weight percentage.

4. The 2 GPa grade ultra-high strength steel sheet according to claim 1, characterized by, By weight percentage, it satisfies one or more of the following (1) to (3): (1) The carbon content of the 2GPa grade ultra-high strength steel plate is 0.36%~0.42%; (2) The Si content of the 2GPa grade ultra-high strength steel plate is 0.20%~0.40%; (3) The Cr content of the 2GPa grade ultra-high strength steel plate is 0.90%~1.20%; (4) The Mo content of the 2GPa grade ultra-high strength steel plate is 0.40%~0.60%; (5) The V content of the 2GPa grade ultra-high strength steel plate is 0.10%~0.15%.

5. The 2 GPa grade ultra-high strength steel sheet according to any one of claims 1 to 4, characterized by, Satisfy one or more of the following conditions (1) to (4): (1) The yield strength of the 2GPa grade ultra-high strength steel plate is ≥1500MPa; (2) The tensile strength of the 2GPa grade ultra-high strength steel plate is ≥2000MPa; (3) The elongation at break of the 2GPa grade ultra-high strength steel plate is ≥10%; (4) Under the test conditions of using a bending die with upper die R≥6a and lower die opening≥18a, the 2GPa grade ultra-high strength steel plate can be bent 70° without cracks or breakage, where a is the plate thickness; (5) The thickness of the 2GPa grade ultra-high strength steel plate is 3mm~14mm.

6. A method of producing the 2 GPa grade ultra-high strength steel sheet according to any one of claims 1 to 5, characterized by, include: The steps include converter, refining, continuous casting, hydrogen expansion, heating in a heating furnace, rolling, coiling, cooling, cross-cutting and leveling, quenching and tempering.

7. The method of producing a 2 GPa grade ultra-high strength steel plate according to claim 6, characterized by, Satisfy one or more of the following: (1) to (3) (1) In the hydrogen expansion step, the hydrogen expansion time is ≥24h; (2) In the heating step of the heating furnace, the heating temperature is 1200℃~1280℃ and the heating time is ≥180min; (3) Cooling includes the following steps: The coiled steel is placed in an insulated box for slow cooling, with a cooling rate of 6℃ / h to 10℃ / h and a cooling time of 72h to 96h.

8. The method of producing a 2 GPa grade ultra-high strength steel sheet according to any one of claims 6 to 7, characterized by, Quenching includes the following steps: After holding at 870–920℃ for 20–40 minutes, the product is removed from the furnace and quenched using a roller pressing method.

9. The method of producing a 2 GPa grade ultra-high strength steel sheet according to any one of claims 6 to 7, characterized by, In the tempering step, one or more of the following (1) to (2) are satisfied: (1) The tempering temperature is 180℃~240℃; (2) the tempering holding time = 3.5 x the thickness of the steel plate, wherein the tempering holding time is in min and the thickness of the steel plate is in mm.

10. A steel for armor characterized by, The 2GPa-grade ultra-high strength steel plate according to any one of claims 1 to 5, or the 2GPa-grade ultra-high strength steel plate prepared according to any one of claims 6 to 9.

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