High-strength and high-toughness bulletproof steel and its preparation method and application

Abstract

The present invention provides a tempered high-strength and high-toughness bulletproof steel, the chemical composition and mass fraction of which include: carbon 0.08-0.12%, silicon 0.15-0.25%, manganese 1.7-1.9%, phosphorus ≤0.015%, sulfur ≤0.003%, acid-soluble aluminum 0.025-0.060%, niobium 0.050-0.060%, titanium 0.135-0.170%, molybdenum 0.22-0.32%, chromium 0.23-0.30%, nitrogen ≤0.0045%. The present invention solves the defects of high difficulty in cutting and welding of bulletproof steel in the processing process, has remarkable effect, and is worthy of promotion.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and specifically relates to a tempered high-strength and high-toughness bulletproof steel and a preparation method and application thereof. Background Art

[0002] Cash transport vehicles are vehicles used to transport cash, gold, silver, jewelry, securities, important certificates and other important items in the financial and security service industries. With the progress of society and the rapid development of the economy, they have been widely used, and bulletproof is one of their most critical functions. According to the People's Republic of China Public Security Industry Standard GA164-2005 "Technical Conditions for Protection of Special Cash Transport Vehicles", cash transport vehicles are divided into three levels from low to high: A, B, and C, based on their bulletproof and riot-proof capabilities.

[0003] According to research in recent years, the anti-bullet performance of bulletproof steel depends on the purity, hardness, strength, toughness and thickness of the steel. The higher the strength and hardness, the better the bullet resistance. However, in addition to paying attention to the performance of bulletproof steel, special vehicle manufacturers also have high requirements for its process performance, surface quality, weldability and manufacturing cost. For example, as a bulletproof steel for automobiles, bulletproof steel is usually required to have good cold stamping and easy bending, sheet metal formability and excellent flatness (especially high-hardness bulletproof steel). However, most bulletproof steels have defects in cutting and welding difficulties during processing, which poses a huge challenge to the processing performance of bulletproof steel.

[0004] However, in the commonly used technologies, A and B grade bulletproof steels often have the technical problem of being difficult to simultaneously take into account the strength, toughness and excellent processing performance of bulletproof steel. Summary of the invention

[0005] The invention aims to solve the technical problem that the above-mentioned common technologies cannot take into account strength, toughness and excellent processing performance of bullet-proof steel at the same time. The present invention proposes a tempered high-strength and high-toughness bullet-proof steel, whose chemical composition and mass fraction include: carbon 0.08-0.12%, silicon 0.15-0.25%, manganese 1.7-1.9%, phosphorus ≤0.015%, sulfur ≤0.003%, acid-soluble aluminum 0.025-0.060%, niobium 0.050-0.060%, titanium 0.135-0.170%, molybdenum 0.22-0.32%, chromium 0.23-0.30%, nitrogen ≤0.0045%.

[0006] Furthermore, the metallographic structure of the bulletproof steel is a dual-phase structure of ferrite and carbide, and the carbide includes titanium and molybdenum composite microalloyed carbides.

[0007] Furthermore, in the metallographic structure, the grain size grade is not less than grade 12;

[0008] The present invention provides a method for preparing tempered high-strength and high-toughness bullet-proof steel, comprising the steps of:

[0009] S1. Heating the steel billet;

[0010] The chemical composition and mass fraction of the steel billet include: carbon 0.08-0.12%, silicon 0.15-0.25%, manganese 1.7-1.9%, phosphorus ≤0.015%, sulfur ≤0.003%, acid-soluble aluminum 0.025-0.060%, niobium 0.050-0.060%, titanium 0.135-0.170%, molybdenum 0.22-0.32%, chromium 0.23-0.30%, nitrogen ≤0.0045%;

[0011] S2. The heated steel billet is subjected to rough rolling and finish rolling in sequence to obtain a steel strip;

[0012] Wherein, the final rolling temperature of the rough rolling is 1050-1100°C, and the final rolling temperature of the fine rolling is 825-895°C;

[0013] S3. After the steel strip is cooled to 540-580°C, it is coiled to obtain a steel coil;

[0014] S4. Wait until the steel coil is cooled to room temperature;

[0015] S5. The steel coil is cut transversely to obtain a flat plate, and the flat plate is tempered to obtain a tempered high-strength and high-toughness bulletproof steel.

[0016] Furthermore, the thickness of the steel billet is 210-250 mm, and the thickness of the tempered high-strength and high-toughness bulletproof steel is 2-8 mm.

[0017] Furthermore, the preparation of the steel billet includes: the molten steel is sequentially subjected to KR desulfurization, converter smelting, LF refining, and RH vacuum treatment, and then continuously cast to obtain the steel billet; wherein the continuous casting speed is ≥0.85m / min.

[0018] Furthermore, the heating temperature of the steel billet is 1270-1300° C., the heating time of the steel billet is 180-480 min, and the solution treatment time of the steel billet is 30 min.

[0019] Furthermore, in step S3, the cooling method of the steel strip includes laminar cooling, and the cooling rate of the steel strip is 20-30° C. / s.

[0020] Furthermore, in step S5, the temperature of the tempering treatment is 640-660° C., and the insulation time of the tempering treatment is 16-27 min.

[0021] The present invention provides a use of any of the above-described tempered high-strength and high-toughness bullet-proof steels and / or any of the above-described preparation methods prepared by the tempered high-strength and high-toughness bullet-proof steels in bullet-proof equipment.

[0022] Compared with the prior art, the present invention strictly controls the element content in the bulletproof steel (i.e., tempered high-strength and high-toughness bulletproof steel, the same below), wherein:

[0023] Carbon: The present invention controls the carbon content to 0.08-0.12%. Carbon plays a major role in solid solution strengthening in bulletproof steel. When the carbon content is higher than 0.12%, lath martensite will be formed, which will reduce the low temperature toughness of the bulletproof steel and deteriorate the processing properties such as welding performance.

[0024] Silicon: The present invention controls the silicon content to 0.15-0.25%. As a commonly used deoxidizer, when the silicon content is higher than 0.25%, the welding performance and toughness of bulletproof steel are simultaneously limited, and it will also make it difficult to remove the iron oxide scale during the steel rolling process, affecting the surface quality.

[0025] Manganese: The present invention controls the manganese content to 1.7-1.9%. Manganese has the highest hardenability factor and can achieve a two-way improvement in the strength and toughness of bulletproof steel.

[0026] Phosphorus and sulfur: The present invention controls the phosphorus content to below 0.015% and the sulfur content to below 0.003%. As harmful inclusion elements in steel, phosphorus and sulfur are prone to forming defects such as inclusions and segregation. When the phosphorus and sulfur content is too high, it is very easy to affect the impact toughness, elongation, welding performance and performance directional difference of bulletproof steel.

[0027] Aluminum: The present invention controls the content of acid-soluble aluminum to 0.025-0.060%. An appropriate amount of aluminum acid solution can fix the free [N] in the bulletproof steel, reduce the free [N] in the welding heat affected zone (HAZ), and improve the low-temperature toughness of the welding HAZ. However, when the acid-soluble aluminum content in the steel is greater than 0.060%, it will not only cause casting difficulties, but also form a large number of dispersed needle-shaped Al2O3 inclusions in the bulletproof steel, which will damage the low-temperature toughness and welding performance of the bulletproof steel.

[0028] Niobium: The present invention controls the niobium content to 0.050-0.060%. Niobium is a carbide-forming element that can increase the recrystallization temperature of austenite, allowing austenite to be rolled at a higher rolling temperature. In addition, Nb can control the precipitation strengthening effect during the subsequent cooling process of the rolling treatment. The strain-induced precipitation of Nb carbonitrides can pin austenite grains, refine austenite grains, and improve strength and low-temperature toughness. However, due to the limitation of carbon content and the influence of heating temperature, when the niobium content is higher than 0.060%, it cannot be dissolved, and it will also lead to deterioration of welding performance.

[0029] Titanium: The present invention controls the titanium content to 0.135-0.170%. Ti has a strong nitrogen fixation effect. The TiC formed by titanium and carbon is relatively stable and can inhibit the growth of grains. The combination of titanium and nitrogen to form TiN can inhibit the coarsening of grains in the heat-affected zone of welding.

[0030] Molybdenum: The present invention controls the titanium content to 0.22-0.32%. As a medium-strong carbide-forming element, an appropriate amount of molybdenum can improve the thermal stability of microalloy carbonitrides and reduce the problem of uneven organization during thermal processing, thereby avoiding deformation caused by uneven heating of bulletproof steel during flame cutting and welding, thereby ensuring the accuracy of product components.

[0031] Chromium: The present invention controls the chromium content to 0.23-0.30%. An appropriate amount of chromium has a great strengthening effect on steel and can improve the strength, hardness and wear resistance of bulletproof steel. A chromium content greater than 0.2% will increase the difficulty of welding.

[0032] Nitrogen: The present invention controls the nitrogen content to be below 0.0045%. However, when the nitrogen content is higher than 0.0045%, it is not only not conducive to the toughness of the steel, but also consumes titanium and weakens the strengthening effect of titanium.

[0033] The present invention strengthens the synergistic effect of each element by regulating the type and content of each element in the high-strength and high-toughness bullet-proof steel. While ensuring that the strength and toughness of the bullet-proof steel meet industry standards, it effectively improves the processing performance of the bullet-proof steel and solves the defects of high difficulty in cutting and welding of the bullet-proof steel during the processing, thereby improving the cutting and bending efficiency of the bullet-proof steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0035] Figure 1 This is the microstructure diagram of the tempered high-strength and high-toughness bullet-proof steel prepared in Example 1 of the present invention.

[0036] Figure 2 This is the microstructure diagram of the tempered high-strength and high-toughness bullet-proof steel prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Furthermore, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in the field. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0039] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention are familiar to those skilled in the art and the description of the present invention, and any methods, equipment and materials of the prior art similar or equivalent to the methods, equipment and materials described in the embodiments of the present invention can also be used to implement the present invention.

[0040] The invention provides a tempered high-strength and high-toughness bulletproof steel, the chemical composition and mass fraction of which include: carbon 0.08-0.12%, silicon 0.15-0.25%, manganese 1.7-1.9%, phosphorus ≤0.015%, sulfur ≤0.003%, acid-soluble aluminum 0.025-0.060%, niobium 0.050-0.060%, titanium 0.135-0.170%, molybdenum 0.22-0.32%, chromium 0.23-0.30%, and nitrogen ≤0.0045%.

[0041] Compared with the prior art, the present invention strictly controls the element content in the bulletproof steel (i.e., tempered high-strength and high-toughness bulletproof steel, the same below), wherein:

[0042] Carbon: The present invention controls the carbon content to 0.08-0.12%. Carbon plays a major role in solid solution strengthening in bulletproof steel. When the carbon content is higher than 0.12%, lath martensite will be formed, which will reduce the low temperature toughness of the bulletproof steel and deteriorate the processing properties such as welding performance.

[0043] Silicon: The present invention controls the silicon content to 0.15-0.25%. As a commonly used deoxidizer, when the silicon content is higher than 0.25%, the welding performance and toughness of bulletproof steel are simultaneously limited, and it will also make it difficult to remove the iron oxide scale during the steel rolling process, affecting the surface quality.

[0044] Manganese: The present invention controls the manganese content to 1.7-1.9%. Manganese has the highest hardenability factor and can achieve a two-way improvement in the strength and toughness of bulletproof steel.

[0045] Phosphorus and sulfur: The present invention controls the phosphorus content to below 0.015% and the sulfur content to below 0.003%. As harmful inclusion elements in steel, phosphorus and sulfur are prone to forming defects such as inclusions and segregation. When the phosphorus and sulfur content is too high, it is very easy to affect the impact toughness, elongation, welding performance and performance directional difference of bulletproof steel.

[0046] Aluminum: The present invention controls the content of acid-soluble aluminum to 0.025-0.060%. An appropriate amount of aluminum acid solution can fix the free [N] in the bulletproof steel, reduce the free [N] in the welding heat affected zone (HAZ), and improve the low-temperature toughness of the welding HAZ. However, when the acid-soluble aluminum content in the steel is greater than 0.060%, it will not only cause casting difficulties, but also form a large number of dispersed needle-shaped Al2O3 inclusions in the bulletproof steel, which will damage the low-temperature toughness and welding performance of the bulletproof steel.

[0047] Niobium: The present invention controls the niobium content to 0.050-0.060%. Niobium is a carbide-forming element that can increase the recrystallization temperature of austenite, allowing austenite to be rolled at a higher rolling temperature. In addition, Nb can control the precipitation strengthening effect during the subsequent cooling process of the rolling treatment. The strain-induced precipitation of Nb carbonitrides can pin austenite grains, refine austenite grains, and improve strength and low-temperature toughness. However, due to the limitation of carbon content and the influence of heating temperature, when the niobium content is higher than 0.060%, it cannot be dissolved, and it will also lead to deterioration of welding performance.

[0048] Titanium: The present invention controls the titanium content to 0.135-0.170%. Ti has a strong nitrogen fixation effect. The TiC formed by titanium and carbon is relatively stable and can inhibit the growth of grains. The combination of titanium and nitrogen to form TiN can inhibit the coarsening of grains in the heat-affected zone of welding.

[0049] Molybdenum: The present invention controls the titanium content to 0.22-0.32%. As a medium-strong carbide-forming element, an appropriate amount of molybdenum can improve the thermal stability of microalloy carbonitrides and reduce the problem of uneven organization during thermal processing, thereby avoiding deformation caused by uneven heating of bulletproof steel during flame cutting and welding, thereby ensuring the accuracy of product components.

[0050] Chromium: The present invention controls the chromium content to 0.23-0.30%. An appropriate amount of chromium has a great strengthening effect on steel and can improve the strength, hardness and wear resistance of bulletproof steel. A chromium content greater than 0.2% will increase the difficulty of welding.

[0051] Nitrogen: The present invention controls the nitrogen content to be below 0.0045%. However, when the nitrogen content is higher than 0.0045%, it is not only not conducive to the toughness of the steel, but also consumes titanium and weakens the strengthening effect of titanium.

[0052] The present invention strengthens the synergistic effect of each element by regulating the type and content of each element in the high-strength and high-toughness bullet-proof steel. While ensuring that the strength and toughness of the bullet-proof steel meet industry standards, it effectively improves the processing performance of the bullet-proof steel and solves the defects of high difficulty in cutting and welding of the bullet-proof steel during the processing, thereby improving the cutting and bending efficiency of the bullet-proof steel.

[0053] In some embodiments, the metallographic structure of the bulletproof steel is a dual-phase structure with ferrite as the matrix and carbides dispersed between the phases; wherein the carbides are titanium and molybdenum composite microalloyed carbides.

[0054] Ferrite is an interstitial solid solution of carbon dissolved in α-Fe, with a body-centered cubic lattice. Its carbon solubility is very low, and it can only dissolve 0.0008% of carbon at room temperature. Pure ferrite has good plasticity and toughness, but poor strength and hardness. Carbide is a micro-alloy compound formed by carbon, titanium and molybdenum. Carbide particles precipitate from the matrix, which plays a precipitation strengthening role.

[0055] The present invention controls the organizational morphology and distribution in the bullet-proof steel, thereby controlling the product performance of the bullet-proof steel, thereby obtaining a high-strength and high-toughness bullet-proof steel with a yield strength of ≥800MPa, a tensile strength of ≥900MPa, and an elongation of ≥12%.

[0056] The present invention also provides a method for preparing tempered high-strength and high-toughness bulletproof steel, comprising the steps of:

[0057] S1. Heating the steel billet; wherein the chemical composition and mass fraction of the steel billet include: carbon 0.08-0.12%, silicon 0.15-0.25%, manganese 1.7-1.9%, phosphorus ≤0.015%, sulfur ≤0.003%, acid-soluble aluminum 0.025-0.060%, niobium 0.050-0.060%, titanium 0.135-0.170%, molybdenum 0.22-0.32%, chromium 0.23-0.30%, nitrogen ≤0.0045%.

[0058] In some embodiments, the heating temperature of the steel billet is 1270-1300°C, the heating time of the steel billet is 180-480 minutes, and the solid solution time of the steel billet is 30 minutes. By strictly controlling the temperature and time of heating the steel billet, the plasticity of the steel can be improved, the deformation resistance can be reduced, and the internal structural defects of the steel billet can be eliminated or reduced to facilitate subsequent rolling processing.

[0059] Specifically, the steel billet may be heated in a heating furnace.

[0060] In other embodiments, the preparation of the steel billet may include: the molten steel is sequentially subjected to KR desulfurization, converter smelting, LF refining, and RH vacuum treatment, and then continuously cast to obtain the steel billet; wherein the continuous casting speed is ≥0.85m / min.

[0061] To further refine, KR desulfurization: the sulfur content of the molten steel is reduced to below 0.01% before the molten steel enters the furnace.

[0062] Converter smelting: After converter smelting, argon is blown through the ladle, and the terminal temperature of the argon station is controlled to be greater than 1530℃.

[0063] For example, converter slag blocking steelmaking or double slag smelting may be adopted.

[0064] LF refining: LF outlet temperature is 1600-1630℃, and refining time is not less than 35 minutes. Refining is used to fine-tune the composition of molten steel to the target composition (carbon 0.08-0.12%, silicon 0.15-0.25%, manganese 1.7-1.9%, phosphorus ≤0.015%, sulfur ≤0.003%, acid-soluble aluminum 0.025-0.060%, niobium 0.050-0.060%, titanium 0.135-0.170%, molybdenum 0.22-0.32%, chromium 0.23-0.30%, nitrogen ≤0.0045%). During the argon blowing and stirring of molten steel in the LF furnace, the contact interface of slag is increased, further achieving deep desulfurization.

[0065] RH vacuum treatment: vacuum degree requirement ≤133MPa, RH cycle time 18-30min.

[0066] Continuous casting: The continuous casting speed is controlled at ≥0.85m / min, and the steel billet is continuously cast in a light pressure mode.

[0067] In some embodiments, the steel billet after continuous casting can be cooled to room temperature before being loaded into a furnace for heating, and the cooling method of the steel billet can be stack cooling.

[0068] S2. The heated steel billet is subjected to rough rolling and finish rolling in sequence to obtain a steel strip.

[0069] Wherein, the final rolling temperature of the rough rolling is 1050-1100°C, and the final rolling temperature of the fine rolling is 825-895°C.

[0070] The hot rolling treatment in the present invention is based on metal deformation, phase transformation and other processes, and completes hardening measures such as solid solution strengthening, precipitation strengthening, dislocation strengthening, and fine grain strengthening under specified deformation and temperature conditions, thereby obtaining bulletproof steel with excellent comprehensive performance.

[0071] Specifically, the heated steel billet can enter the single stand and undergo 5 passes of rough rolling, and then be rolled by a 7-pass rough rolling unit.

[0072] In some embodiments, the single reduction amount during the rough rolling process may be 44-48 mm, and the total reduction amount may be 195-199 mm; the single reduction amount during the finishing rolling process may be 13-15 mm, and the total reduction amount may be 29-31 mm.

[0073] The present invention controls the deformation amount during the rolling process to roll a steel billet with a thickness of 210-250 mm into a steel strip with a thickness of 2-8 mm, thereby achieving lightweight bulletproof steel, facilitating subsequent transportation and installation, and saving manpower and material costs.

[0074] S3. After the steel strip is cooled to 540-580° C., it is coiled to obtain a steel coil.

[0075] In some embodiments, the cooling method of the steel strip includes laminar cooling, and the cooling rate of the laminar cooling is 20-30° C. / s. In this process, ferrite grains nucleate and grow, and carbonitrides precipitate.

[0076] The present invention makes full use of the rolling and heat treatment control capabilities of the continuous rolling mill, adopts a production method of controlled rolling and accelerated cooling, and obtains grains of appropriate size through deformation recrystallization of the high-temperature austenite zone, deformation of the low-temperature austenite non-recrystallization zone, and accelerated cooling after rolling.

[0077] Specifically, the present invention controls the grain size of ferrite to 12 levels.

[0078] S4. Wait until the steel coil is cooled to room temperature;

[0079] In some embodiments, the steel coil may be cooled to room temperature by stack cooling.

[0080] S5. The steel coil is cut transversely to obtain a flat plate, and the flat plate is tempered to obtain a tempered high-strength and high-toughness bulletproof steel.

[0081] In other embodiments, the temperature of the tempering treatment is 640-660° C., and the insulation time of the tempering treatment is 16-27 min.

[0082] Tempering refers to a metal heat treatment process in which the quenched steel is reheated to an appropriate temperature below the lower critical temperature Ac1 (the starting temperature of the transformation of pearlite to austenite during heating), kept warm for a period of time, and then cooled in air, water, oil or other media. Or the quenched steel is heated to an appropriate temperature, kept warm for a certain period of time, and then slowly or quickly cooled. The above-mentioned quenching refers to the entire cooling metallurgical process of cooling the rolled bulletproof steel to room temperature in the present invention.

[0083] Tempering is generally used to reduce or eliminate the internal stress in quenched steel, or to reduce its hardness and strength to improve its ductility or toughness. Through the combination of quenching and tempering, high-strength and high-toughness bulletproof steel with excellent mechanical properties can be obtained.

[0084] In the commonly used technology, the A and B grade bulletproof steels are usually delivered in a hot-rolled state. In comparison, the high-strength and high-toughness bulletproof steel in the present invention can reduce the performance differences in the length and width directions of the bulletproof steel, improve the performance uniformity, and significantly reduce the internal stress of the bulletproof steel while ensuring that the strength meets the anti-bullet performance. This can improve the efficiency of subsequent blanking and processing, and effectively optimize the processing performance of the bulletproof steel. Bulletproof steel with uniform performance and low internal stress can maintain good straightness after blanking, without the need for straightening; after bending, the workpiece can also maintain good straightness, without uneven bending rebound or lateral bending distortion.

[0085] The present invention also provides a use of any of the high-strength and high-toughness bulletproof steels described above in bulletproof equipment.

[0086] In order to facilitate those skilled in the art to further understand the present invention, examples are given below:

[0087] Example 1

[0088] The molten iron is desulfurized by KR and then smelted in a 210-ton converter. It is then argon blown in a ladle, refined in a LF furnace, vacuum treated in RH and continuously cast into 230 mm slabs. The chemical element composition of the slabs is shown in Table 1.

[0089] After the slab was pile-cooled for 48 hours, it was heated to 1285° C. The slab was rough-rolled for 5 passes and finished-rolled by a 7-stand 2250 continuous rolling mill to obtain a steel strip with a thickness of 2.85 mm.

[0090] After the steel strip is cooled to 560°C by laminar flow, it is coiled to obtain a steel coil. The microstructure diagram is as follows: Figure 1~Figure 2 The controlled rolling and controlled cooling process parameters of this embodiment are shown in Table 2.

[0091] After the steel coil is cooled to room temperature, it is cut horizontally and flattened. The flat plate is heated to 650°C and kept warm for 16 minutes to obtain tempered high-strength and high-toughness bullet-proof steel. Its mechanical properties are shown in Table 3, and the anti-ballistic performance test is shown in Table 4.

[0092] Example 2

[0093] The molten iron is desulfurized by KR and then smelted in a 210-ton converter. It is then argon blown in a ladle, refined in a LF furnace, vacuum treated in RH and continuously cast into 230 mm slabs. The chemical element composition of the slabs is shown in Table 1.

[0094] After the slab was pile-cooled for 48 hours, it was heated to 1270° C. The slab was rough-rolled for 5 passes and finished-rolled by a 7-stand 2250 continuous rolling mill to obtain a steel strip with a thickness of 2.85 mm.

[0095] After the steel strip is laminar-cooled to 560° C., it is coiled to obtain a steel coil. The controlled rolling and controlled cooling process parameters of this embodiment are shown in Table 2.

[0096] After the steel coil is cooled to room temperature, it is cut horizontally and flattened. The flat plate is heated to 650°C and kept warm for 16 minutes to obtain tempered high-strength and high-toughness bullet-proof steel. Its mechanical properties are shown in Table 3, and the anti-ballistic performance test is shown in Table 4.

[0097] Comparative Example 1

[0098] The molten iron is desulfurized by KR and then smelted in a 210-ton converter. It is then argon blown in a ladle, refined in a LF furnace, vacuum treated in RH and continuously cast into 230 mm slabs. The chemical element composition of the slabs is shown in Table 1.

[0099] After the slab was pile-cooled for 48 hours, it was heated to 1270° C. The slab was rough-rolled for 5 passes and finished-rolled by a 7-stand 2250 continuous rolling mill to obtain a steel strip with a thickness of 2.85 mm.

[0100] After the steel strip is laminar-cooled to 560° C., it is coiled to obtain a steel coil. The controlled rolling and controlled cooling process parameters of this comparative example are shown in Table 2.

[0101] After the steel coil is cooled to room temperature, the hot-rolled high-strength and high-toughness bullet-proof steel is obtained. Its mechanical properties are shown in Table 3, and the anti-ballistic performance test is shown in Table 4.

[0102] Table 1 Chemical composition of the slabs in Examples 1-2 and Comparative Example 1

[0103]

[0104] Table 2 Rolling process parameters in Examples 1-2 and Comparative Example 1

[0105]

[0106] Table 3 Mechanical properties of high strength and high toughness steels obtained in Examples 1-2 and Comparative Example 1

[0107]

[0108] Table 3 Anti-ballistic properties of high-strength and high-toughness steels prepared in Examples 1-2 and Comparative Example 1

[0109]

[0110] The above technical solutions of the present invention are only preferred embodiments of the present invention, and the patent scope of the present invention is not limited thereto. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for preparing tempered high-strength and high-toughness bulletproof steel, characterized in that: Includes steps: S1. Heating the steel billet; The chemical composition and mass fraction of the steel billet are as follows: carbon 0.08-0.12%, silicon 0.15-0.25%, manganese 1.7-1.9%, phosphorus ≤0.015%, sulfur ≤0.003%, acid-soluble aluminum 0.025-0.060%, niobium 0.050-0.060%, titanium 0.135-0.170%, molybdenum 0.22-0.32%, chromium 0.23-0.30%, nitrogen ≤0.0045%, and the balance is iron; S2. The heated steel billet is subjected to rough rolling and finish rolling in sequence to obtain a steel strip; Wherein, the final rolling temperature of the rough rolling is 1050-1100°C, and the final rolling temperature of the fine rolling is 825-895°C; S3. After the steel strip is cooled to 540-580°C, it is coiled to obtain a steel coil; the cooling method of the steel strip is laminar cooling, and the cooling rate of the steel strip is 20-30°C / s; S4. Wait until the steel coil is cooled to room temperature; S5. The steel coil is cut horizontally to obtain a flat plate, and the flat plate is tempered to obtain a tempered high-strength and high-toughness bulletproof steel, wherein the tempering temperature is 640-660° C., and the holding time of the tempering is 16-27 min; The metallographic structure of the tempered high-strength and high-toughness bulletproof steel is a dual-phase structure with ferrite as the matrix and carbides dispersed between the phases; wherein the carbides are titanium and molybdenum composite microalloyed carbides; The yield strength of the tempered high-strength and high-toughness bullet-proof steel is ≥800MPa, the tensile strength is ≥900MPa, and the elongation is ≥12%.

2. The method for preparing tempered high-strength and high-toughness bullet-proof steel according to claim 1, characterized in that: In the metallographic structure, the grain size grade is not less than grade 12.

3. The method for preparing tempered high-strength and high-toughness bullet-proof steel according to claim 1, characterized in that: The thickness of the steel billet is 210-250 mm, and the thickness of the tempered high-strength and high-toughness bulletproof steel is 2-8 mm.

4. The method for preparing tempered high-strength and high-toughness bullet-proof steel according to claim 1, characterized in that: The preparation of the steel billet comprises: the molten steel is sequentially subjected to KR desulfurization, converter smelting, LF refining, and RH vacuum treatment, and then continuously cast to obtain the steel billet; wherein the continuous casting speed is ≥0.85 m / min.

5. The method for preparing tempered high-strength and high-toughness bullet-proof steel according to claim 1, characterized in that: The heating temperature of the steel billet is 1270-1300° C., the heating time of the steel billet is 180-480 min, and the solution treatment time of the steel billet is 30 min.

6. Application of the tempered high-strength and high-toughness bullet-proof steel prepared by the method for preparing the tempered high-strength and high-toughness bullet-proof steel as claimed in any one of claims 1 to 5 in bullet-proof equipment.

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