Ultra-high strength high toughness steel material, method for preparing same and use thereof

Abstract

The application discloses a kind of ultra-high strength high toughness steel material and its preparation method and application, according to mass percentage, its chemical composition is: C 0.40~0.50%, Si≤0.15%, Mn≤0.15%, P≤0.005%, S≤0.003%, Cr 0.6~0.8%, Ni 1.0~2.0%, Mo 0.1~0.4%, Nb 0.065~0.085%, Ti 0.06~0.12%, V 0.04~0.10%, Al 0.015~0.030%, N 0.005~0.01%, B 0.0020~0.0035%, the rest is Fe and inevitable impurities.Improve the toughness of protective steel, fully meet the forming requirement of room temperature bending;Under the working condition of bulletproof, the steel plate can occur stable plastic deformation, effectively avoid brittle fracture phenomenon, improve its comprehensive protection performance.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and more specifically, to an ultra-high strength and high toughness steel material, its preparation method, and its application. Background Technology

[0002] With the rapid development of modern military and protection technologies, armor protection materials play a crucial role in resisting various ballistic threats. The current mainstream design concept for protective steel materials is primarily based on high hardness. The high hardness of martensitic steel allows for the initial fragmentation of the projectile upon impact, effectively defending against the penetration of soft projectiles such as lead-core or ordinary steel-core projectiles. Benefiting from mature metal smelting and rolling processes, these materials exhibit uniform microstructure and stable mechanical properties, thus possessing reliable repeatability of ballistic performance.

[0003] Traditional protective steel is applied in the form of flat sheets. Because its hardness is usually above HB500, its cold workability is significantly reduced, making it difficult to meet the requirements of complex shape processing such as cold bending and stamping. At the same time, the increase in material hardness is accompanied by a decrease in toughness and plasticity. When facing hard alloy projectiles (such as armor-piercing projectiles), microcracks are prone to occur in the contact area between the projectile and the armor surface. The inherent brittleness of high-hardness steel will promote the rapid propagation of cracks, weakening the material's ability to absorb impact energy through plastic deformation. Ultimately, this leads to a significant decrease in protective effectiveness in high-threat scenarios.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide an ultra-high strength and high toughness steel material, its preparation method and application, in order to improve the above-mentioned technical problems.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides an ultra-high strength and high toughness steel material, the chemical composition of which, by mass percentage, is: C 0.40%~0.50%, Si≤0.15%, Mn≤0.15%, P≤0.005%, S≤0.003%, Cr 0.6%~0.8%, Ni 1.0%~1.6%, Mo 0.1%~0.4%, Nb 0.065%~0.085%, Ti 0.06%~0.12%, V 0.04%~0.10%, Al 0.015%~0.030%, N 0.005%~0.01%, B 0.0020%~0.0035%, with the remainder being Fe and unavoidable impurities.

[0007] In an optional embodiment, the chemical composition, by mass percentage, is: C 0.40%~0.470%, Si≤0.15%, Mn≤0.15%, P≤0.005%, S≤0.003%, Cr 0.6%~0.8%, Ni 1.0%~1.6%, Mo 0.1%~0.4%, Nb 0.065%~0.085%, Ti 0.06%~0.12%, V 0.04%~0.10%, Al 0.015%~0.030%, N 0.005%~0.01%, B 0.0020%~0.0035%, with the remainder being Fe and unavoidable impurities.

[0008] In an optional embodiment, the microstructure of the ultra-high strength and high toughness steel material is fine martensite and austenite, with the austenite volume accounting for 1% to 5%.

[0009] In an optional embodiment, the ultra-high strength and high toughness steel material has a strength of 2100MPa~2400MPa, an elongation after fracture of 8%~11%, and a fracture toughness KIC≥120MPa / m. 2 .

[0010] Secondly, the present invention provides a method for preparing ultra-high strength and high toughness steel material as described in any of the foregoing embodiments, comprising: smelting, continuous casting, hot rolling and heat treatment of raw materials according to their chemical composition.

[0011] In an optional embodiment, the smelting is carried out by refining the chemical composition using two or more of the following methods: converter, electric furnace, VD furnace, and LF furnace.

[0012] In an optional embodiment, the continuous casting is the continuous casting of molten steel obtained from refining into slabs; In an optional embodiment, the hot rolling temperature is 1150℃~1250℃, the number of rolling passes is 5~8, and the reduction of the first three rolling passes is 10%~25%.

[0013] In an optional embodiment, the heat treatment adopts a quenching and tempering heat treatment process, with a quenching temperature of 890~930℃ and a quenching time of 60min~120min, and a tempering temperature of 170℃~200℃ and a tempering time of 60min~120min.

[0014] Thirdly, the present invention provides the application of ultra-high strength and high toughness steel materials as described in any of the foregoing embodiments as protective steel materials.

[0015] Fourthly, the present invention provides a protective steel component with a bending portion, which is made of the ultra-high strength and high toughness steel material described in any of the foregoing embodiments.

[0016] This invention offers the following advantages: By scientifically proportioning various alloying elements such as manganese, chromium, nickel, and boron, it effectively enhances the hardenability of the material, thereby solving the technical challenge of poor surface and core microstructure uniformity in thick plate materials during heat treatment. Simultaneously, by optimizing the synergistic mechanism of elements such as carbon, molybdenum, niobium, titanium, vanadium, aluminum, and nitrogen, it promotes the precipitation of second-phase particles such as carbides and nitrides during steel production, fully leveraging their grain boundary pinning effect. This technical solution achieves precise control over the entire process of austenite and martensite grain size, significantly improving material strength while effectively maintaining its excellent toughness, successfully overcoming the technical bottleneck of the difficulty in synergistically optimizing the strength and toughness of traditional protective steel. Through this technology, the toughness of protective steel is significantly improved, fully meeting the formability requirements for room temperature bending; under ballistic protection conditions, the steel plate can undergo stable plastic deformation, effectively avoiding brittle fracture, thereby significantly improving its energy absorption capacity and overall protective performance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The image shows the metallographic structure of the ultra-high strength and high toughness steel material of Embodiment 1 of the present invention. Figure 2 This is a metallographic diagram of the ultra-high strength and high toughness steel material of Embodiment 2 of the present invention; Figure 3 This is a metallographic diagram of the ultra-high strength and high toughness steel material of Embodiment 3 of the present invention; Figure 4 This is a metallographic diagram of the ultra-high strength and high toughness steel material of Comparative Example 1 of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0020] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0021] In the description of this invention, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships may exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0022] The following is a detailed description of an ultra-high strength and high toughness steel material, its preparation method, and its applications provided by the present invention.

[0023] In a first aspect, the present invention provides an ultra-high strength and high toughness steel material, the chemical composition of which, by mass percentage, is: C 0.40%~0.50%, Si≤0.15%, Mn≤0.15%, P≤0.005%, S≤0.003%, Cr 0.6%~0.8%, Ni 1.0%~1.6%, Mo 0.1%~0.4%, Nb 0.065%~0.085%, Ti 0.06%~0.12%, V 0.04%~0.10%, Al 0.015%~0.030%, N 0.005%~0.01%, B 0.0020%~0.0035%, with the remainder being Fe and unavoidable impurities.

[0024] By comprehensively employing elements such as manganese, chromium, nickel, and boron, the hardenability of materials is improved, solving the problem of uneven microstructure on the surface and in the core of thick plates. The comprehensive use of elements such as carbon, molybdenum, niobium, titanium, vanadium, aluminum, and nitrogen promotes the formation of carbides and nitrides during the steel production process, fully utilizing the "pinning" effect to refine the grain size of austenite and martensite throughout the entire process, comprehensively improving strength and toughness, resolving the contradiction of the inability to synergistically improve strength and toughness, and fundamentally enhancing the protective performance of protective steel at the microstructural level.

[0025] Specifically, the carbon (C) content determines the martensitic structure and hardness of the steel plate. To obtain a uniform and fine martensitic structure while achieving a hardness of 500 HBW to 650 HBW, a high-carbon steel design is adopted. However, excessively high carbon content can affect the weldability of the steel plate. Therefore, in this embodiment of the invention, the carbon content is controlled at 0.40% to 0.50%, for example, 0.4%, 0.41%, 0.42%, 0.43%, 0.44%, 0.45%, 0.46%, 0.47%, 0.48%, 0.49%, or 0.5%.

[0026] Silicon (Si) can dissolve in austenite, improving the strength, hardness, and thermal stability of steel. Simultaneously, silicon forms an oxide film in high-temperature oxidizing atmospheres, enhancing the steel plate's oxidation and rust resistance. However, excessive silicon content increases temper brittleness, complicates heat treatment processes, and reduces the steel plate's plasticity. Therefore, in this embodiment of the invention, the silicon (Si) content is controlled at ≤0.15%, for example, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, or 0.15%, etc.

[0027] Manganese (Mn) is beneficial for improving the hardenability and strength of martensitic steel. However, manganese (Mn) and sulfur (S) have a very high affinity, easily forming manganese sulfide inclusions that are distributed at the grain boundaries of the steel. This is especially true for thick plates like protective steel, where the presence of manganese sulfide inclusions in the core of the plate significantly reduces its protective performance. Therefore, it is necessary to control the content of both elements. In this embodiment of the invention, the manganese (Mn) content is controlled at ≤0.15%, for example, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, or 0.15%.

[0028] Phosphorus (P) is a harmful element in steel plate materials, which can significantly reduce the plasticity and toughness of steel. Protective steel needs to strictly control the phosphorus (P) content. In the embodiments of the present invention, the phosphorus (P) content is controlled at ≤0.005%.

[0029] Sulfur (S) is also a harmful element in steel plate materials. Sulfides formed by the alloying of sulfur (S) with manganese (Mn) and other elements will reduce the strength of the material. The sulfur (S) content of protective steel also needs to be strictly controlled. The sulfur (S) content in the embodiments of the present invention is controlled at ≤0.003%.

[0030] Chromium (Cr) significantly improves the hardenability of steel, which is especially important for protective steels, particularly thick plates. Insufficient hardenability leads to uneven microstructure on the surface and in the core of the steel plate, resulting in a severe decrease in hardness, strength, and protective performance. According to the International Institute of Welding (IIW) carbon equivalent CE formula: CE = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15, chromium (Cr) has a greater effect on increasing the carbon equivalent of steel plates than other alloying elements. Therefore, in alloy composition design, other alloying elements can be appropriately increased while controlling the amount of chromium (Cr). In the embodiments of this invention, the chromium (Cr) content is controlled at 0.6%~0.8%, for example, 0.6%, 0.65%, 0.7%, 0.75%, or 0.8%.

[0031] Nickel (Ni) can significantly improve the hardenability of steel, ensure uniform microstructure, and enhance material strength and hardness. Simultaneously, nickel (Ni) can form intermetallic compounds with other alloying elements, resulting in precipitation strengthening. Therefore, in the design of protective steel compositions, the nickel (Ni) content is higher than that of other alloying elements. In the embodiments of this invention, the nickel (Ni) content is controlled at 1.0% to 1.6%, for example, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%.

[0032] Molybdenum (Mo) has a solid solution strengthening effect and can also form tiny carbides with carbon (C), acting as a "pinning" element to hinder grain growth and achieve grain refinement in steel. Grain refinement is a key technology for controlling and improving the toughness of the protective steel of this invention. Therefore, in addition to molybdenum (Mo), other alloys such as vanadium (V), titanium (Ti), and niobium (Nb) are also added. The molybdenum (Mo) content in the embodiments of this invention is controlled at 0.1%~0.4%, for example, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, or 0.4%.

[0033] Niobium (Nb) has a strong affinity for carbon (C) and nitrogen (N), forming carbides (NbC) and nitrides (NbN), which also act as "pinning" elements, hindering grain growth and achieving grain refinement in the steel. Therefore, the protective steel of this invention increases both niobium (Nb) and nitrogen (N) content. The niobium (Nb) content in the embodiments of this invention is controlled at 0.065%~0.085%, for example, 0.065%, 0.07%, 0.075%, 0.08%, or 0.085%.

[0034] Titanium (Ti) has a strong affinity for carbon (C), and the resulting carbide (TiC) exhibits extremely high stability, especially at high temperatures (above 1000℃). It effectively suppresses grain growth during hot rolling and heat treatment, achieving finer grains and comprehensively improving strength, toughness, and protective properties. In this invention, the titanium (Ti) content is controlled at 0.06%~0.12%, for example, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, or 0.12%.

[0035] Vanadium (V) has a strong affinity for carbon (C), and the resulting carbide (VC) exhibits high stability. During high-temperature austenitization, it partially dissolves, and the undissolved carbide hinders austenite grain growth, thereby significantly refining the grain size. In this embodiment of the invention, the vanadium (V) content is controlled at 0.04% to 0.10%, for example, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, or 0.1%.

[0036] Aluminum (Al) has the effect of refining the inherent grain size of steel and increasing the temperature at which the steel grains coarsen. Simultaneously, aluminum (Al) and nitrogen (N) can form aluminum nitride compounds, further refining the grain size of the steel. The aluminum-nitrogen content ratio designed in this embodiment of the invention is approximately 3:1. The aluminum (Al) content in this embodiment of the invention is controlled at 0.015%~0.030%, for example, 0.015%, 0.016%, 0.017%, 0.018%, 0.019%, 0.020%, 0.021%, 0.022%, 0.023%, 0.024%, 0.025%, 0.026%, 0.027%, 0.028%, 0.029%, or 0.030%, etc.

[0037] Nitrogen (N) has solid solution strengthening properties, which can improve the hardenability of steel. Simultaneously, this invention, by designing the aluminum-nitrogen content ratio, promotes the formation of aluminum-nitrogen compounds from aluminum (Al) and nitrogen (N), effectively "pinning" and refining the grains. In this embodiment of the invention, the nitrogen (N) content is controlled between 0.005% and 0.010%, for example, 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, or 0.01%.

[0038] Boron (B) element improves hardenability, enhances the uniformity of microstructure in thick plate materials, and increases the strength and protective performance of protective steel. In this embodiment of the invention, the boron (B) content is controlled between 0.0020% and 0.0035%, for example, 0.0020%, 0.0021%, 0.0022%, 0.0023%, 0.0024%, 0.0025%, 0.0026%, 0.0027%, 0.0028%, 0.0029%, 0.0030%, 0.0031%, 0.0032%, 0.0033%, 0.0034%, or 0.0035%, etc.

[0039] In some embodiments, to achieve better performance, the chemical composition of the ultra-high strength and high toughness steel material is further optimized. Its chemical composition, by mass percentage, is: C 0.40%~0.470%, Si≤0.15%, Mn≤0.15%, P≤0.005%, S≤0.003%, Cr 0.6%~0.8%, Ni 1.0%~1.6%, Mo 0.1%~0.4%, Nb 0.065%~0.085%, Ti 0.06%~0.12%, V 0.04%~0.10%, Al 0.015%~0.030%, N 0.005%~0.01%, B 0.0020%~0.0035%, with the remainder being Fe and unavoidable impurities.

[0040] In some embodiments, the microstructure of the ultra-high strength and high toughness steel material consists of fine martensite and austenite, with the austenite volume accounting for 1% to 5%.

[0041] In some embodiments, the ultra-high strength and high toughness steel material has a strength of 2100MPa~2400MPa, an elongation after fracture of 8%~11%, and a fracture toughness KIC≥120MPa / m. 2 .

[0042] Furthermore, some embodiments of the present invention also provide a method for preparing ultra-high strength and high toughness steel material as described in any of the foregoing embodiments, which includes: smelting, continuous casting, hot rolling and heat treatment of raw materials according to their chemical composition.

[0043] In some embodiments, smelting is carried out using two or more of the following methods: converter, electric furnace, VD furnace, and LF furnace, to refine the chemical composition.

[0044] The core objective of smelting is to refine raw materials such as iron ore or scrap steel into molten steel with acceptable composition and controllable impurity content.

[0045] In some implementations, the converter uses molten iron as the main raw material (accounting for approximately 70%-90%), supplemented with a small amount of scrap steel to adjust temperature and composition; the electric arc furnace uses scrap steel as the main raw material, with pig iron added to adjust carbon content. The raw materials require pretreatment: molten iron undergoes desulfurization and dephosphorization pretreatment, and scrap steel is sorted to remove oil, non-ferrous metals, and other impurities. The raw materials are then loaded into the furnace using specialized equipment. In the converter, high-pressure oxygen is blown into the furnace to oxidize carbon, silicon, manganese, and other elements in the molten iron, and the resulting high temperature maintains the smelting process. In the electric arc furnace, electric arc heating is generated by electrode discharge, melting the scrap steel and initiating a smelting reaction. During smelting, the steel composition is monitored in real time using equipment such as a spectrometer. Slag-forming agents such as lime and fluorite are added to adsorb sulfur, phosphorus, and other impurities in the molten steel, forming slag separation. Once the composition meets the standards, the steel can be tapped. The tapping flow rate must be controlled to prevent slag from mixing with the molten steel. To further improve purity, molten steel is usually refined in LF refining furnaces, RH vacuum refining furnaces, etc. Through operations such as vacuum degassing and alloy fine-tuning, the composition and temperature of the molten steel are precisely controlled to finally obtain qualified molten steel.

[0046] In some implementations, continuous casting involves continuously casting the refined molten steel into slabs. The crystallizer is the core equipment in continuous casting; its inner wall must be cleaned beforehand, and lubricant or protective slag lubrication must be applied to prevent molten steel from sticking together. Simultaneously, the crystallizer size is adjusted according to the slab specifications, and the cooling water channels are checked for unobstructed flow to ensure stable cooling. Molten steel is smoothly injected into the crystallizer through a tundish, which diverts the molten steel and filters some inclusions. The molten steel cools rapidly within the crystallizer to form a partially solidified slab shell, which is then uniformly pulled out of the crystallizer by a leveling machine. The pulled-out slab enters a secondary cooling zone, where it is further forced to solidify by spray cooling water, ensuring complete solidification of the slab's interior. The fully solidified slab is then cut to fixed lengths according to subsequent hot rolling requirements using a flame cutter or plasma cutter. After cutting, the slabs are inspected for surface defects such as cracks, inclusions, and porosity; unqualified slabs are marked and further processed.

[0047] In some embodiments, the hot rolling temperature is 1150℃~1250℃, such as 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, 1210℃, 1220℃, 1230℃, 1240℃ or 1250℃, 1150℃, etc., and the number of rolling passes is 5 to 8, such as 5, 6, 7 or 8, and the reduction of the first three rolling passes is 10%~25%, such as 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%, etc.

[0048] Hot rolling is the process of heating a billet and rolling it into steel plates, sections, wire rods, and other products using rolling equipment. Steel exhibits good plasticity at high temperatures, and rolling can refine the grains, improving the steel's strength and toughness. Through high-temperature adaptation and gradient reduction, the billet undergoes initial shaping, microstructure optimization, and surface quality improvement. After heating the billet to 1150℃~1250℃, the internal microstructure is fully austenitized, resulting in excellent plasticity and low deformation resistance. Setting a reduction of 10%~25% for the first three rolling passes at this point efficiently achieves two major shaping objectives. Firstly, it rapidly reduces the billet thickness, narrowing the dimensional difference between the billet and the final product, preventing a surge in equipment load due to excessive reduction in subsequent passes. Secondly, by gradually adjusting the billet width and shape, it corrects minor defects such as warping and uneven thickness that may occur during continuous casting. Furthermore, the rolling temperature of 1150℃~1250℃ ensures the uniformity of austenite grains while avoiding abnormal grain growth caused by excessively high temperatures. The 10%~25% reduction in the first three passes is within a reasonable range, and the plastic deformation during rolling breaks up the coarse austenite grains in the billet, while generating a large number of grain boundaries, creating conditions for subsequent recrystallization. In addition, the stress and plastic deformation generated by rolling can also close the micropores and porosity inside the billet, reducing the risk of internal cracks. After these three rolling passes, the internal structure of the billet will change from a loose as-cast structure to a dense, finer-grained deformed austenite structure, laying a solid foundation for improving the strength, toughness, and other mechanical properties of the final product.

[0049] In some embodiments, the heat treatment employs a quenching followed by tempering process. The quenching temperature is 890~930℃, for example, 890℃, 900℃, 910℃, 920℃, or 930℃, and the quenching time is 60min~120min, for example, 60min, 70min, 80min, 90min, 100min, 110min, or 120min; the tempering temperature is 170℃~200℃, for example, 170℃, 180℃, 190℃, or 200℃, and the tempering time is 60min~120min, for example, 60min, 70min, 80min, 90min, 100min, 110min, or 120min.

[0050] The microstructure of the steel was adjusted through the above specific heat treatment process, thereby improving the steel's toughness and bendability.

[0051] Some embodiments of the present invention also provide the application of the ultra-high strength, high toughness steel material as described in any of the foregoing embodiments as a protective steel material. This steel material has a strength of 2100 MPa to 2400 MPa, an elongation after fracture of 8% to 11%, and a fracture toughness KIC ≥ 120 MPa / m. 2 It has good toughness, meets the formability requirements for room temperature bending, and can undergo plastic deformation when used for bulletproofing, avoiding brittle cracking and improving energy absorption and protective performance.

[0052] Some embodiments of the present invention also provide a protective steel member with a bending portion, which is made of the ultra-high strength and high toughness steel material described in any of the foregoing embodiments.

[0053] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0054] Example 1 This embodiment provides a method for preparing ultra-high strength and high toughness steel material, which specifically includes the following steps: The steel billets are prepared by converter smelting and VD furnace refining, and continuous casting and rolling. The hot rolling temperature is 1200℃~1250℃, and the rolling is carried out in 5 passes, with a reduction of 25% in the first three passes. The quenching temperature is 910℃~920℃, the heating time is 80min, the tempering temperature is 180℃, and the tempering time is 90min.

[0055] The elemental composition of the prepared ultra-high strength and high toughness steel material is shown in Table 1.

[0056] Table 1

[0057] The performance of the steel material was tested according to the standards GB / T 13298, GB / T 228.1, GB / T 232, GB / T231.1 and GB / T 4161.

[0058] The metallographic structure of this ultra-high strength and high toughness steel material is as follows: Figure 1 As shown, this ultra-high strength and high toughness steel material has a tensile strength of 2145 MPa, an elongation after fracture of 10.5%, a minimum cold bending radius of 4T (T is the thickness of the steel plate), a hardness of 621 HBW, and a fracture toughness KIC of 125 MPa / m. 2 .

[0059] Example 2 This embodiment provides a method for preparing ultra-high strength and high toughness steel material, which specifically includes the following steps: Steel billets are prepared by converter smelting and VD furnace refining, and continuous casting and rolling. The hot rolling temperature is 1150℃~1200℃, and the rolling is carried out in 8 passes, with a reduction of 22% in the first three passes. The quenching temperature is 920℃~930℃, the heating time is 70min, the tempering temperature is 160℃, and the tempering time is 100min.

[0060] The elemental composition of the prepared ultra-high strength and high toughness steel material is shown in Table 2.

[0061] Table 2

[0062] The properties of the steel material were tested, and the test method is described in Example 1.

[0063] The metallographic structure of this ultra-high strength and high toughness steel material is as follows: Figure 2 As shown, this ultra-high strength and high toughness steel material has a tensile strength of 2389 MPa, an elongation after fracture of 8.5%, a minimum cold bending radius of 5T (T is the thickness of the steel plate), a hardness of 637 HBW, and a fracture toughness KIC of 138 MPa / m. 2 .

[0064] Example 3 This embodiment provides a method for preparing ultra-high strength and high toughness steel material, which specifically includes the following steps: Steel billets are prepared by converter smelting and VD furnace refining, and continuous casting and rolling. The hot rolling temperature is 1150℃~1200℃, and the rolling is carried out in 6 passes, with a reduction of 20% in the first three passes. The quenching temperature is 920℃~930℃, the heating time is 70min, the tempering temperature is 160℃, and the tempering time is 100min.

[0065] The elemental composition of the prepared ultra-high strength and high toughness steel material is shown in Table 3.

[0066] Table 3

[0067] The properties of the steel material were tested, and the test method is described in Example 1.

[0068] The metallographic structure of this ultra-high strength and high toughness steel material is as follows: Figure 3 As shown, this ultra-high strength and high toughness steel material has a tensile strength of 2210 MPa, an elongation after fracture of 9.3%, a minimum cold bending radius of 5T (T is the thickness of the steel plate), a hardness of 628 HBW, and a fracture toughness KIC of 130 MPa / m. 2 .

[0069] Comparative Example 1 This embodiment provides a method for preparing ultra-high strength and high toughness steel material, which specifically includes the following steps: The steel billets are prepared by converter smelting and VD furnace refining, and continuous casting and rolling. The hot rolling temperature is 1200℃~1250℃, and the rolling is carried out in 5 passes, with a reduction of 25% in the first three passes. The quenching temperature is 910℃~920℃, the heating time is 80min, the tempering temperature is 180℃, and the tempering time is 90min.

[0070] The elemental composition of the prepared ultra-high strength and high toughness steel is shown in Table 5. This composition reduces the number of microalloying elements, which has the advantage of low cost, but the toughness of the material is significantly reduced.

[0071] Table 5

[0072] The performance of the steel material was tested according to standards GB / T 13298, GB / T 228.1, GB / T 232, GB / T231.1, and GB / T 4161.

[0073] The metallographic structure of this ultra-high strength and high toughness steel material is as follows: Figure 4 As shown, this ultra-high strength and high toughness steel material has a tensile strength of 2053 MPa, an elongation after fracture of 3%, a minimum cold bending radius of 10T (T is the thickness of the steel plate), a hardness of 613 HBW, and a fracture toughness KIC of 81 MPa / m. 2 .

[0074] In summary, the embodiments of this invention comprehensively utilize elements such as manganese, chromium, nickel, and boron to improve the hardenability of steel, and comprehensively utilize elements such as carbon, molybdenum, niobium, titanium, vanadium, aluminum, and nitrogen to generate various carbides and nitrides, refining the grain size of austenite and martensite throughout the entire process. The final result is a protective steel with high strength and high toughness.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-strength, high-toughness steel material, characterized in that, Its chemical composition by mass percentage is as follows: C 0.40%~0.50%, Si≤0.15%, Mn≤0.15%, P≤0.005%, S≤0.003%, Cr 0.6%~0.8%, Ni 1.0%~2.0%, Mo 0.1%~0.4%, Nb 0.065%~0.085%, Ti 0.06%~0.12%, V 0.04%~0.10%, Al 0.015%~0.030%, N 0.005%~0.01%, B 0.0020%~0.0035%, with the remainder being Fe and unavoidable impurities.

2. The ultra-high strength and high toughness steel material according to claim 1, characterized in that, Its chemical composition by mass percentage is as follows: C 0.40%~0.470%, Si≤0.15%, Mn≤0.15%, P≤0.005%, S≤0.003%, Cr 0.6%~0.8%, Ni 1.0%~1.6%, Mo 0.1%~0.4%, Nb 0.065%~0.085%, Ti 0.06%~0.12%, V 0.04%~0.10%, Al 0.015%~0.030%, N 0.005%~0.01%, B 0.0020%~0.0035%, with the remainder being Fe and unavoidable impurities.

3. The ultra-high strength and high toughness steel material according to claim 1, characterized in that, The microstructure of the ultra-high strength and high toughness steel material consists of fine martensite and austenite, with the austenite volume accounting for 1% to 5%.

4. The ultra-high strength and high toughness steel material according to any one of claims 1 to 3, characterized in that, The ultra-high strength and high toughness steel material has a strength of 2100MPa~2400MPa, an elongation after fracture of 8%~11%, and a fracture toughness KIC≥120MPa / m. 2 .

5. A method for preparing an ultra-high strength and high toughness steel material as described in any one of claims 1 to 4, characterized in that, It includes: The raw materials are smelted, continuously cast, hot rolled, and heat-treated according to their chemical composition.

6. The method for preparing ultra-high strength and high toughness steel material according to claim 5, characterized in that, The smelting process employs two or more of the following methods: converter, electric furnace, VD furnace, and LF furnace, to refine the chemical composition.

7. The method for preparing ultra-high strength and high toughness steel material according to claim 5, characterized in that, The continuous casting process involves continuously casting the refined molten steel into slabs. And / or, the hot rolling temperature is 1150℃~1250℃, the number of rolling passes is 5~8, and the reduction of the first three rolling passes is 10%~25%.

8. The method for preparing ultra-high strength and high toughness steel material according to claim 5, characterized in that, The heat treatment adopts a quenching and tempering process, with a quenching temperature of 890~930℃ and a quenching time of 60min~120min, and a tempering temperature of 170℃~200℃ and a tempering time of 60min~120min.

9. The application of the ultra-high strength and high toughness steel material as described in any one of claims 1 to 4 as a protective steel material.

10. A protective steel component with a bent portion, characterized in that, It is made of the ultra-high strength and high toughness steel material as described in any one of claims 1 to 4.

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