2GPa-grade ultrahigh-strength steel plate as well as preparation method and application thereof

Abstract

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

Description

Technical Field

[0001] The present invention relates to the technical field of alloy steel, and in particular to a 2GPa-level ultra-high-strength steel plate and a preparation method and application thereof. Background Art

[0002] Alloy steel refers to an iron-carbon alloy formed by adding an appropriate amount of one or more alloying elements to ordinary carbon steel. Depending on the added elements and the appropriate processing technology, 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] In addition to being widely used in the military field, high-strength protective steel is also widely used in the civilian field, such as money transport vehicles, escort vehicles, armed police explosion-proof vehicles and civilian vehicle shields. When the yield strength of the required material is greater than 1300MPa and the tensile strength is greater than 1500MPa, it is ultra-high strength protective steel.

[0004] However, the existing ultra-high strength protective steel meets the hardness and strength requirements, but the comprehensive performance matching of strength, plasticity and toughness is lacking, which makes cold cracks very sensitive and cannot meet the bending processing requirements of steel plates. With the increasing demand for the integrated development of protective equipment, more and more protective fields require bending processing to reduce welds as much as possible, thereby avoiding the reduction of protectiveness caused by welding softening. Therefore, how to improve the toughness and plasticity of protective steel, improve its bending processing performance and thus improve protective performance is still an important direction of current protective material research. Summary of the invention

[0005] Based on this, the present invention provides an alloy steel having high strength, high plasticity and high toughness, which is a 2GPa-level ultra-high-strength steel plate. In addition, a preparation method and application of the 2GPa-level ultra-high-strength steel plate are provided.

[0006] The technical solution is as follows:

[0007] A 2GPa-level ultra-high-strength steel plate, whose chemical composition, measured 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%, and the balance is Fe and unavoidable impurities.

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

[0009] In one of the embodiments, the Si content of the 2 GPa grade ultra-high strength steel plate is 0.20% to 0.40% by weight.

[0010] In one of the embodiments, the Mn content of the 2 GPa grade ultra-high strength steel plate is 0.40% to 0.55% by weight.

[0011] In one of the embodiments, the Cr content of the 2 GPa grade ultra-high strength steel plate is 0.90% to 1.20% by weight.

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

[0013] In one of the embodiments, the Mo content of the 2 GPa grade ultra-high strength steel plate is 0.40% to 0.60% by weight.

[0014] In one of the embodiments, the V content of the 2 GPa grade ultra-high strength steel plate is 0.10% to 0.15% by weight.

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

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

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

[0018] In one of the embodiments, under the test conditions of using a bending mold with an upper mold R≥6a and a lower mold 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 of the embodiments, 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 expansion, heating in a heating furnace, rolling, coiling, cooling, cross-cutting, quenching and tempering.

[0021] In one embodiment, in the hydrogen expansion step, the hydrogen expansion time is ≥ 24h.

[0022] In one of the embodiments, in the step of heating in the heating furnace, the heating temperature is 1200° C. to 1280° C., and the heating time is ≥180 min.

[0023] In one embodiment, cooling comprises the steps of:

[0024] The coiled steel coil is placed in an insulation box for slow cooling, wherein the cooling rate is 6°C / h to 10°C / h and the cooling time is 72h to 96h.

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

[0026] After being kept at 870-920℃ for 20-40min, it is taken out of the furnace and quenched by roller quenching.

[0027] In one of the embodiments, in the tempering step, the temperature is 180°C to 240°C.

[0028] In one of the embodiments, in the tempering step, the tempering holding time = 3.5×the thickness of the steel plate, wherein the unit of the tempering holding time is min, and the unit of the steel plate thickness is mm.

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

[0030] A protective steel comprises the 2 GPa grade ultra-high strength steel plate as described above.

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

[0032] The present invention regulates the chemical composition of the alloy steel, especially the type of elements and the percentage of content, to provide a 2GPa-level ultra-high-strength steel plate with a tensile strength of more than 2000MPa (2GPa), a yield strength of more than 1500MPa, good plasticity, and an elongation after fracture of more than 10%. The 2GPa-level ultra-high-strength steel plate can be bent at 70° without cracks or breakage using a bending die with an upper die R ≥ 6a and a lower die opening ≥ 18a (a is the plate thickness), which can meet the requirements of complex protective equipment for material strength indicators and plasticity indicators. At the same time, since the Mn and Ni contents of the 2GPa-level ultra-high-strength steel plate of the present invention are relatively low, the alloy cost is greatly reduced. In addition, the preparation method of the 2GPa-level ultra-high-strength steel plate of the present invention has the advantages of simple operation, high efficiency, good repeatability, low green and environmental protection energy consumption, and low production cost, and is suitable for industrialization and market (especially protective steel plates) promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a tensile performance diagram of a 2 GPa grade ultra-high strength steel plate prepared in Example 1 of the present invention;

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

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

[0036] Figure 4 This is the target test result of preparing 2GPa grade ultra-high strength steel plate according to Example 3 of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described in detail below in conjunction with specific embodiments and accompanying drawings. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0039] Where “including,” “having,” and “comprising” are used herein, it is intended to cover a non-exclusive inclusion, and another component may also be added unless explicit limiting terms such as “only,” “consisting of,” etc. are used.

[0040] The words "preferably", "more preferably", "preferably", "better", etc. in the present invention refer to embodiments of the present invention that can provide certain beneficial effects in certain circumstances. However, other embodiments may also be preferred under the same circumstances or other circumstances. In addition, the statement of one or more preferred embodiments does not imply that other embodiments are not applicable, nor is it intended to exclude other embodiments from the scope of the present invention. That is, in the present invention, "preferably", "more preferably", "preferably", "better", etc. are only used to describe implementation methods or examples with better effects, but do not constitute a limitation on the scope of protection of the present invention.

[0041] In the present invention, “further”, “furthermore”, “particularly”, etc. are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of the present invention.

[0042] In the present invention, "at least one" means more than one, such as one, two and more than two. "Multiple" or "several" means at least two, such as two, three, etc., and "multilayer" means at least two layers, such as two layers, three layers, etc., unless otherwise clearly and specifically defined. In the description of the present invention, "several" means at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0043] When a numerical range is disclosed in the present invention, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when the range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the range can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges included therein. And only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range, and any upper limit can also be combined with any other upper limit to form an unambiguous range. In addition, each individually disclosed point or single value itself can be combined with any other point or single value as a lower limit or upper limit or with other lower limits or upper limits to form an unambiguous range.

[0044] If not otherwise specified, all steps of the present invention may be performed sequentially or randomly. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0045] Unless mentioned to the contrary, terms in the singular may include plural forms and should not be construed as being one in number.

[0046] The temperature parameters in the present invention, if not specifically limited, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows the temperature to fluctuate within the precision range controlled by the instrument.

[0047] The weights of the relevant components mentioned in the embodiments of the present invention description may not only refer to the specific content of each component, but also indicate the weight ratio between the components. Therefore, as long as the content of the relevant components in the embodiments of the present invention description is proportionally enlarged or reduced, it is within the scope disclosed in the embodiments of the present invention description. Specifically, the weights described in the embodiments of the present invention description may be mass units known in the chemical industry such as μg, mg, g, and kg.

[0048] In the present invention, when referring to the unit of the data range, if there is a unit only after the right endpoint, it means that the units of the left endpoint and the right endpoint 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 the present 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 the present 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 mentioned to the contrary, terms in the singular may include plural forms and should not be construed as being one in number.

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

[0053] A 2GPa-level ultra-high-strength steel plate, whose chemical composition, measured 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%, and the balance is Fe and unavoidable impurities.

[0054] Carbon (C): C is an effective economic element for improving the strength of steel, but if the C content is too high, a brittle structure will be formed, which will reduce the low-temperature impact toughness of the alloy steel, deteriorate the welding performance and corrosion resistance. An appropriate amount of C and Ti can form a stable nano-scale precipitate TiC, and the TiC nano-scale precipitate can produce a strong precipitation strengthening effect and a fine grain strengthening effect, greatly improving the strength of the steel plate. In order to achieve ultra-high yield strength (>1300MPa), ultra-high tensile strength (>1500MPa) and comprehensively consider high plasticity and high toughness, the present invention controls the C content in the steel to 0.35% to 0.45%. It can be understood that it 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 of the embodiments, the C content of the 2 GPa grade ultra-high strength steel plate is 0.36% to 0.42% by weight.

[0055] Silicon (Si): Si is dissolved in alloy steel, which can improve the strength of alloy steel and reduce the corrosion rate of steel. However, too high Si content will deteriorate the welding performance of steel and reduce the toughness of the material. Taking all factors into consideration, the present invention controls the Si content in the 2GPa-level ultra-high strength steel plate to be 0.10% to 0.40%, which can be understood to include but 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%. In one embodiment, the Si content of the 2GPa-level ultra-high strength steel plate is 0.20% to 0.40% by weight.

[0056] Manganese (Mn): Mn has a strong solid solution strengthening effect and an obvious fine grain effect. It can improve the strength of alloy steel and the toughness at the same time. However, too high Mn content can easily lead to segregation of core components, affect the processing performance and increase the alloy cost. Therefore, in order to make the steel plate have good strength and toughness, avoid segregation of core components and reduce the cost of alloy steel, the present invention controls the Mn content in the 2GPa grade ultra-high strength steel plate to be 0.30% to 0.60%, which can be understood to include but 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 of the embodiments, the Mn content of the 2 GPa grade ultra-high strength steel plate is 0.40% to 0.55% by weight.

[0057] Chromium (Cr): Cr can improve the corrosion resistance of alloy steel, and can significantly increase the strength and hardness of alloy steel, as well as hardenability, but can also increase the temper brittleness tendency of alloy steel, that is, an appropriate amount of Cr can improve the mechanical properties, but excessive Cr will lead to poor toughness of alloy steel. Comprehensively considered, in the present invention, the Cr content in the 2GPa grade ultra-high strength steel plate is controlled to be 0.80% to 1.20%, which can be understood to include but 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. Moreover, Ni can change the phase transition temperature and heat treatment characteristics of steel, making it more stable and uniform during the heat treatment process. In addition, Ni can also improve the strength, hardness, plasticity and toughness of steel, making it better able to resist tensile, bending and torsion. However, Ni is a precious metal, and high dosage will increase production costs, and excessive nickel will easily cause intergranular corrosion tendency and reduce corrosion resistance. In addition, excessive nickel content will also lead to an increase in the precipitation phase of stainless steel at high temperatures, further reducing the mechanical properties. Taking all factors into consideration, in the present invention, the Ni content in the 2GPa grade ultra-high strength steel plate is controlled to be 1.20% to 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): Mo in steel can improve hardenability and heat strength, prevent temper brittleness, and increase corrosion resistance, plasticity, and wear resistance. However, the addition of Mo will produce molybdenum oxide gas when the steel is heated, promote decarburization, prevent graphitization, and reduce the thermal conductivity of the steel. When the Mo content is too high, the oxidation resistance of the steel will decrease. Comprehensively considered, the present invention controls the Mo content in the 2GPa-level ultra-high-strength steel plate to be 0.30% to 0.60%, which can be understood to include but 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 Mo content of the 2GPa-level ultra-high-strength steel plate is 0.40% to 0.60% by weight.

[0060] Vanadium (V): V has a strong affinity with C and O, and forms corresponding stable compounds with them. V exists mainly in the form of carbides in steel. It is a typical carbide with high melting point, high hardness and high dispersion. It is an element that strongly improves wear resistance. The main function of V is to refine the structure and grain of steel, improve the strength and toughness of steel, and improve the 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, the present invention controls the V content in the 2GPa grade ultra-high strength steel plate 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 and N form TiN at high temperature. When the slab is heated and austenitized, TiN will inhibit the growth of austenite grains. During hot rolling, Ti and C form nano-scale TiC in a lower temperature range. The fine TiC particles have significant precipitation strengthening and fine grain 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 precipitation will be formed. When the steel plate is subjected to stress, the stress will be concentrated near the TiN particles, becoming the nucleation and growth source of microcracks, reducing the fatigue performance of the steel plate. On the other hand, due to the small solubility product of TiC, it is difficult for Ti to dissolve during the heating process of the continuous casting billet, and it does not play a corresponding role. Taking all factors into consideration, the present invention controls the Ti content in the 2GPa-level ultra-high strength steel plate to be 0.01% to 0.04%, which can be understood to include but not limited to 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035% or 0.04%. In one of the embodiments, the Ti content of the 2 GPa grade ultra-high strength steel plate is 0.03% to 0.04% by weight.

[0062] Phosphorus (P): Although P can increase the corrosion resistance of alloy steel, it will significantly deteriorate the toughness of steel. Taking all factors into consideration, the present invention controls the P content in the 2GPa-level ultra-high strength steel plate to be ≤0.006%, which can be understood to include but 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, which is mainly due to the poor plasticity of iron sulfide formed by the combination of sulfur and iron. Taking all factors into consideration, the present invention controls the S content in the 2GPa grade ultra-high strength steel plate to be ≤0.003%, which can be understood to include but not limited to 0, 0.001%, 0.002%, and 0.003%.

[0064] Hydrogen (H): Metal materials have hydrogen embrittlement tendency to varying degrees. If the hydrogen content of high-strength steel is less than ppm, it may cause delayed failure. Taking all factors into consideration, the present invention controls the H content of 2GPa-level ultra-high-strength steel plate to be ≤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 will significantly reduce the plasticity, toughness and weldability of steel. Taking all factors into consideration, the present invention controls the N content of the 2GPa grade ultra-high strength steel plate to be ≤0.006%, including but not limited to 0, 0.001%, 0.002%, 0.003%, 0.004%, 0.005% or 0.006%.

[0066] In summary, the present invention provides an alloy steel with high strength, high plasticity and toughness by regulating the chemical composition of the alloy steel, especially regulating the types of elements and content percentages.

[0067] After testing, the 2GPa-level ultra-high-strength steel plate provided by the present invention has a strength of more than 2000MPa, a yield strength of more than 1500MPa, good plasticity, and an elongation after fracture of more than 10%. Under the test conditions of a bending mold with an upper mold R ≥ 6a and a lower mold opening ≥ 18a (a is the plate thickness), the 2GPa-level ultra-high-strength steel plate can be bent 70° without cracks or breakage, and can meet the requirements of complex protective equipment for material strength indicators and plasticity indicators. At the same time, due to the low Mn and Ni content of the 2GPa-level ultra-high-strength steel plate of the present invention, the alloy cost is greatly reduced. Compared with other ultra-high-strength alloy structural steels such as 4130, 4340, 300M, H13, etc., which have an elongation of only less than 5%, the steel plate provided by the present invention can meet the requirements of complex protective equipment for material strength indicators and plasticity indicators.

[0068] In one of the embodiments, 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-level ultra-high strength steel plate as described above, and the technical scheme is as follows:

[0070] A method for preparing the 2GPa-level ultra-high strength steel plate as described above comprises the steps of converter, refining, continuous casting, hydrogen expansion, heating in a heating furnace, rolling, coiling, cooling, cross-cutting, quenching and tempering.

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

[0072] S1: The continuous casting billet is obtained through the process of converter → refining (LF+RH) → continuous casting. The weight percentage of the chemical element composition of the continuous casting 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%, the balance is Fe and unavoidable impurities.

[0074] S2: Hydrogen expansion: After the slab is cut, it directly enters the insulation pit. The slab is surrounded by other high-temperature slabs on the top, bottom and both sides of the length direction for slow cooling and hydrogen expansion.

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

[0076] S3: Heating → Rolling → Coiling: Slowly cool the billet and heat it at a temperature of 1200°C to 1280°C (if the soaking temperature is 1230°C), the heating time is ≥180min, and then the billet is rolled to the target thickness and coiled.

[0077] S4: Slow cooling in the insulation box → cross-cutting and flattening: The hot-rolled coil is then hoisted into the insulation box for slow cooling to avoid the air-cooling quenching effect of the steel coil and reduce the difficulty of cross-cutting. The coil is then hoisted out for cross-cutting and flattening to form a hot-rolled steel plate.

[0078] In one embodiment, the coiled steel coil is placed in a heat preservation 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-type heating furnace is heated to 870℃~920℃. When the temperature is stable, the high-plasticity protective steel plate is transported to the roller-type heating furnace. The holding time (min) = 2.4×plate thickness (mm). Then it is taken out of the furnace and quenched by roller quenching. The quenching water volume is 500m 3 / h, water ratio 1.5, roller speed 0.4m / s. Roller quenching reduces the deformation of the steel plate during heat treatment and ensures that the steel plate has a good and flat shape; low-temperature tempering releases the internal stress of the steel plate to ensure that there is no brittle fracture or warping when cutting.

[0081] S6: Tempering: Heat the roller hearth tempering furnace to 180℃~240℃, keep the furnace temperature stable, and immediately transport the quenched steel plate to the tempering furnace for tempering treatment. The 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] The present invention also provides an application of the 2GPa-level ultra-high strength steel plate as described above, and the technical solution is as follows:

[0084] A protective steel comprises the 2GPa-level ultra-high strength steel plate.

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

[0086] The mechanical properties of steel are tested by tensile test according to standard GB / T228.1-2010, and by bending test according to standard GB / T232-2010.

[0087] Example 1 to Example 3 and Comparative Example 1 to Comparative Example 5

[0088] The process flow is as follows:

[0089] S1: A continuous casting billet is obtained through the process of converter → refining (LF+RH) → continuous casting. The weight percentage of the chemical element composition of the continuous casting billet is shown in Table 1 below, and the remainder is Fe and unavoidable impurities.

[0090] S2: Hydrogen expansion: After being cut, the high-plasticity protective steel slab directly enters the insulation pit. The slab is surrounded by other high-temperature slabs on the top, bottom and both sides of the length direction, and slowly cooled and hydrogen expanded for 24 hours or more.

[0091] S3: Heating → Rolling → Coiling: Slowly cool the billet for heating, with a required soaking temperature of 1230°C and a heating time of ≥180min, then roll to the target thickness and complete coiling.

[0092] S4: Slow cooling in an insulation box → cross-cutting: The hot-rolled coil is then hoisted into an insulation box and slowly cooled for 72 hours to avoid the air-cooling quenching effect of the steel coil and reduce the difficulty of cross-cutting. The coil is then hoisted out for cross-cutting to form a hot-rolled steel plate.

[0093] S5: Quenching: Heat the roller-bottom heating furnace to 870-920°C. When the temperature stabilizes, transport the high-plasticity protective steel plate to the roller-bottom heating furnace. Keep warm for a time (min) = 2.4 × plate thickness (mm). Then take it out of the furnace and quench it with roller quenching. The quenching water volume is 500m 3 / h, water ratio 1.5, roller speed 0.4m / s.

[0094] S6: Tempering: Heat the roller hearth tempering furnace to 180-240°C, keep the furnace temperature stable, and immediately transport the quenched steel plate to the tempering furnace for tempering treatment. The tempering time (min) = 3.5 × plate thickness (mm).

[0095] (1) The chemical composition of the steel billet is shown in Table 1, and the process parameters are shown in Table 2 below.

[0096] Table 1 Chemical composition of alloy steel plates in the comparative examples (wt%), the remainder being Fe and unavoidable impurities

[0097] serial number C Si Mn Cr P S V Ti Ni Mo H N Example 1 0.38 0.22 0.45 1.15 0.0055 0.0015 0.12 0.03 1.55 0.55 0.00013 0.0045 Example 2 0.40 0.30 0.51 1.08 0.0051 0.0010 0.11 0.04 1.46 0.53 0.00012 0.0051 Example 3 0.41 0.28 0.40 0.97 0.0046 0.0009 0.15 0.04 1.68 0.57 0.00015 0.0057 Comparative Example 1 0.08 0.24 0.47 1.01 0.0092 0.0021 0.12 0.03 1.50 0.52 0.00015 0.0059 Comparative Example 2 0.39 1.5 0.60 0.98 0.0088 0.0014 0.11 0.04 1.48 0.58 0.00014 0.0057 Comparative Example 3 0.41 0.27 1.8 1.05 0.0087 0.0024 0.13 0.02 1.42 0.48 0.00016 0.0052 Comparative Example 4 0.41 0.31 0.58 0.92 0.0068 0.0013 0.14 0.03 1.56 0.20 0.00014 0.0059 Comparative Example 5 0.39 0.32 0.47 1.10 0.0060 0.0012 0.11 0.02 0.50 0.55 0.00012 0.0050

[0098] Table 2 Heat treatment process of alloy steel plate in comparative example

[0099]

[0100]

[0101] Table 3 Mechanical properties of alloy steel plates in the examples and comparative examples

[0102]

[0103] It can be seen from Table 1 that, compared with Comparative Examples 1 to 5, the alloy steel plates prepared in Examples 1 to 3 of the present invention have more excellent comprehensive properties.

[0104] Figure 1 This is a tensile performance diagram of the alloy steel plate prepared in Example 1 of the present invention (gauge length 50 mm), Figure 1 It can be seen that the yield strength of Example 1 reaches 1585MPa, the tensile strength reaches 2108MPa, and the elongation after fracture reaches 13.4%, indicating that the protective steel plate prepared under this component and this process system has extremely high strength and good plasticity, and is a 2GPa-level ultra-high-strength steel plate, which has achieved the design goal, indicating that the component and the production process are well matched.

[0105] Figure 2 This is a diagram of the bending results of the 2 GPa-level 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 properties, and does not crack when bent at 75°.

[0106] Figure 3 This is the plate shape diagram 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 this process has a strength of more than 2000MPa, its industrial production plate shape is still good, and there is no problem of poor plate shape due to high strength and high internal stress, which shows that the process parameters and composition are well matched.

[0107] Figure 4 This is the target test result of preparing 2GPa grade ultra-high strength steel plate in Example 3 of the present invention. It can be seen that the steel plate prepared by this composition and this process has excellent protective performance.

[0108] In summary, the present invention is simple to operate, and adopts alloy component ratios within a specific range. The alloy steel plate produced has fine internal structure, high strength, tensile strength of more than 2000MPa, and yield strength of more than 1500MPa. At the same time, it has good plasticity, elongation>10%, strong resistance to hydrogen-induced delayed cracking, and the steel plate is not easy to crack. In addition, it can meet the processing requirements of bending ≤70° under the test conditions of upper die R≥6a and lower die opening ≥18a (a is the plate thickness). Compared with other ultra-high-strength alloy structural steels such as 4130, 4340, 300M, H13, etc., which have an elongation of only less than 5%, the steel plate provided by the present invention can meet the requirements of complex protective equipment for material strength indicators and plasticity indicators. In addition, roller quenching reduces the deformation of the steel plate during heat treatment, ensuring that the steel plate has a good and flat shape; low-temperature tempering releases the internal stress of the steel plate to ensure that there is no brittle fracture or warping during cutting.

[0109] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0110] The above-described embodiments only express several implementation methods of the present invention, which are convenient for understanding the technical solutions of the present invention in detail, but they cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided by the present invention are all within the protection scope of the claims attached to the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the contents of the attached claims, and the description and drawings can be used to interpret the contents of the claims.

Claims

1. A 2GPa grade ultra-high strength steel plate, characterized in that: The chemical composition includes, by weight percentage: 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 is Fe and unavoidable impurities.

2. The 2GPa grade ultra-high strength steel plate according to claim 1, characterized in that: Calculated by weight percentage, the Mn content of the 2GPa-level ultra-high-strength steel plate is 0.40% to 0.55%.

3. The 2GPa ultra-high strength steel plate according to claim 1, characterized in that: Calculated by weight percentage, the Ni content of the 2GPa-level ultra-high-strength steel plate is 1.40% to 1.70%.

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

5. The 2 GPa grade ultra-high strength steel plate according to any one of claims 1 to 4, characterized in that: Satisfy one or more of the following (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 2 GPa grade ultra-high strength steel plate is ≥ 10%; (4) Under the test conditions of using a bending die with an upper die R ≥ 6a and a lower die opening ≥ 18a, the 2 GPa 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 2 GPa grade ultra-high strength steel plate is 3 mm to 14 mm.

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

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

8. The method for preparing a 2 GPa grade ultra-high strength steel plate according to any one of claims 6 to 7, characterized in that: Quenching includes the following steps: After being kept at 870-920℃ for 20-40min, it is taken out of the furnace and quenched by roller quenching.

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

10. A protective steel, characterized in that: It comprises the 2 GPa grade ultra-high strength steel plate as described in any one of claims 1 to 5, or the 2 GPa grade ultra-high strength steel plate prepared by the preparation method as described in any one of claims 6 to 9.

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