A 2000mpa-grade high-strength high-toughness alloy steel plate for protection and a manufacturing method thereof

Abstract

This invention discloses a high-strength, high-toughness alloy steel plate for 2000MPa grade protection and its manufacturing method. Its chemical composition, by mass percentage, is: C 0.35%–0.42%, Si 0.2%–0.6%, Mn 0.5%–1.2%, Cr 0.2%–0.8%, Ni 1.0%–3.0%, Mo 0.2%–0.8%, Nb 0.05%–0.2%, P ≤0.003%, S ≤0.003%, and the total content of other impurity elements ≤0.01%, with the balance being Fe and unavoidable impurities. After quenching and low-temperature tempering, the alloy steel plate has a microstructure consisting of tempered martensite, a small amount of retained austenite, and dispersed ε-carbides, with a grain size of 2μm–5μm. It exhibits excellent mechanical properties, with a yield strength R... p0.2 Tensile strength R reaches 1800MPa~1900MPa. m It achieves a strength of 2000MPa to 2100MPa, an elongation of 9% to 11%, and a Charpy impact energy of >16J at 25℃. The manufacturing process involves smelting, continuous casting, heating, two-stage temperature-controlled hot rolling, and quenching and tempering, resulting in a simple process suitable for mass production. This invention achieves a balance between high strength and high toughness, with low alloy cost, and can be widely used in high-security protection fields such as armored vehicles, explosion-proof structures, and bulletproof plates.

Description

Technical Field

[0001] This invention relates to the field of alloy steel technology, and more specifically, to a 2000MPa grade high-strength and high-toughness alloy steel plate for protection and its manufacturing method, which is particularly suitable for high-safety protective equipment such as armored vehicles, explosion-proof structures, and bulletproof plates. Background Technology

[0002] With the increasing demands on the performance of protective equipment in modern military, counter-terrorism, and security fields, protective steel must possess excellent toughness, ductility, and machinability while ensuring ultra-high strength. Traditional high-strength steel plates often sacrifice plasticity and toughness when increasing strength, making it difficult to meet the requirements of use under complex load conditions.

[0003] Currently, high-strength steel plates with tensile strengths exceeding 2000 MPa are mainly used in armored vehicles, bulletproof plates, and explosion-proof structures. To improve their protective performance, various alloy designs have been proposed. For example, Chinese patent application CN202110680952.2 discloses a 2000 MPa-grade protective steel plate with the following chemical composition by weight percentage: C 0.51%–0.56%, Si 2.20%–2.60%, Mn 0.10%–0.18%, Ni 2.7%–3.3%, Cr 1.10%–1.50%, Nb 0.045%–0.065%, B 0.0025%–0.0035%, with the remainder being Fe and unavoidable impurities. This steel plate, through a design with high carbon, high silicon, high nickel, and high chromium components, combined with rolling, laminar flow cooling, quenching, and tempering processes, achieves a tensile strength exceeding 2000 MPa. However, this technical solution has a high carbon content (0.51%–0.56%), which is detrimental to welding performance, and also contains a high content of nickel (2.7%–3.3%) and chromium (1.10%–1.50%), resulting in a high alloy cost.

[0004] Chinese patent application CN202011186691.0 discloses a low yield strength ratio 2000MPa grade ultra-high strength steel with the following chemical composition by mass percentage: C 0.2%–0.4%, Mn 5%–9%, ​​Si 1%–2%, V 0.1%–0.3%, with the balance being Fe and unavoidable impurities. This technical solution uses low-alloy steel with moderate manganese content, and through controlled forging and tempering processes, obtains a martensitic and retained austenitic microstructure. The retained austenite volume fraction is 25%–45%, the tensile strength is greater than 2000MPa, and the elongation after fracture is greater than 10%. However, the high manganese content (5%–9%) in this technical solution easily leads to billet segregation and uneven microstructure. Furthermore, the use of forging technology results in low production efficiency, making large-scale industrial production difficult.

[0005] Chinese patent application CN200710045335.5 discloses a 2000MPa grade ultra-high strength and high toughness steel plate. Its chemical composition includes: C 0.20%–0.60%, Si 1.0%–3.0%, Mn 1.0%–5.0%, Mo 0.10%–0.60%, with the balance being Fe and unavoidable impurities. This steel plate uses a Mn-Si-Mo system composition and achieves a bainitic + martensite multiphase structure through controlled rolling and cooling technology, resulting in a tensile strength exceeding 2000MPa. However, this technical solution does not include nickel, so its low-temperature toughness needs further improvement, and its relatively high final rolling temperature (1000℃–1050℃) limits the grain refinement effect.

[0006] In summary, the existing technologies still have the following shortcomings: First, in order to obtain ultra-high strength of 2000MPa, high carbon, high manganese or high nickel content is usually used in the design, which leads to poor welding performance or high alloy cost; second, the manufacturing process is complicated, and some technologies require forging or offline heat treatment, which results in low production efficiency and makes it difficult to achieve large-scale production; third, it is difficult to balance strength and toughness, and some technical solutions achieve ultra-high strength but lack low-temperature toughness and cold forming performance.

[0007] Therefore, developing a high-strength, high-toughness alloy steel with excellent comprehensive mechanical properties, suitable for protective applications, with a strength level of 2000MPa, low alloy cost, simple process, and easy industrial production has important engineering application value. Summary of the Invention

[0008] The present invention aims to solve the technical problems of existing protective alloy steel plates, such as difficulty in achieving both strength and toughness, high alloy cost, and complex manufacturing process. It provides a 2000MPa grade high-strength and high-toughness alloy steel plate for protection and its manufacturing method. The alloy steel plate has high strength, high toughness and good elongation performance, and the alloy cost is low, the process is simple and easy to industrialize.

[0009] To achieve the above objectives, on the one hand, the present invention provides a 2000MPa grade protective high-strength and high-toughness alloy steel plate, which comprises the following chemical composition by mass percentage: C 0.35%~0.42%, Si 0.2%~0.6%, Mn 0.5%~1.2%, Cr 0.2%~0.8%, Ni 1.0%~3.0%, Mo 0.2%~0.8%, Nb 0.05%~0.2%, P≤0.003%, S≤0.003%, and the total content of other impurity elements ≤0.01%, with the balance being Fe and unavoidable impurities.

[0010] In this invention, the functions of each chemical component are as follows:

[0011] C: Carbon is the main element for improving strength, significantly enhancing the strength of steel through solid solution strengthening and precipitation strengthening. When the carbon content is below 0.35%, it is difficult to achieve a tensile strength exceeding 1800 MPa; above 0.42%, it reduces plasticity and toughness, affecting weldability. Therefore, the carbon content is controlled between 0.35% and 0.42%. Compared to the high carbon design of 0.51% to 0.56% in the prior art CN202110680952.2, the carbon content of this invention is lower, which is beneficial for improving weldability.

[0012] Si: Silicon has a certain solid solution strengthening effect and helps with deoxidation. However, excessive content will reduce toughness, so it is controlled at 0.2% to 0.6%. Compared with the high silicon content of 2.20% to 2.60% in the prior art CN202110680952.2 and the silicon content of 1.0% to 3.0% in CN200710045335.5, the silicon content of this invention is moderate, avoiding the adverse effects of high silicon on toughness.

[0013] Mn: Manganese can improve hardenability and strength, but excessive content can easily cause segregation and affect toughness. It should be controlled at 0.5% to 1.2%. Compared with the high manganese design of 5% to 9% in the existing technology CN202011186691.0 and the manganese content of 1.0% to 5.0% in CN200710045335.5, the manganese content of this invention is lower, which can effectively reduce the segregation of the billet and improve the uniformity of the microstructure.

[0014] Cr: Chromium improves hardenability and corrosion resistance, and helps form fine martensitic structure. Its content is controlled at 0.2% to 0.8%. Compared with the high chromium design of 1.10% to 1.50% in the prior art CN202110680952.2, the chromium content of this invention is lower, which is beneficial to cost control.

[0015] Ni: Nickel is a key element for improving toughness, especially at low temperatures, and also enhances the hardenability of steel. Its content is controlled between 1.0% and 3.0%. Compared to the 2.7%–3.3% nickel content in the existing technology CN202110680952.2, the lower limit of nickel content in this invention is lower, allowing for flexible adjustment according to performance requirements, balancing cost and toughness.

[0016] Mo: Molybdenum can significantly improve hardenability, refine grains, and suppress temper brittleness. Its content is controlled at 0.2% to 0.8%. Compared with the 0.10% to 0.60% molybdenum content in the prior art CN200710045335.5, the molybdenum content of this invention is moderate, which is beneficial to obtaining a uniform and fine tempered martensite structure.

[0017] Nb: Niobium refines grains and improves strength and toughness by forming carbonitrides, and its content is controlled at 0.05% to 0.2%.

[0018] P, S and other impurities: Strictly control P content ≤ 0.003%, S content ≤ 0.003%, and total content of other impurity elements ≤ 0.01% to prevent adverse effects on toughness and weldability.

[0019] Furthermore, the microstructure of the alloy steel plate after heat treatment consists of martensite, austenite, and ε-carbide, wherein the volume fraction of martensite is 85%–93%, the volume fraction of austenite is 0.1%–0.5%, the volume fraction of ε-carbide is 7%–9%, ​​and the average grain size is 2μm–5μm.

[0020] Furthermore, the yield strength R of the alloy steel plate p0.2 The tensile strength is 1800MPa~1900MPa, R m Its strength ranges from 2000 MPa to 2100 MPa, its elongation is 9% to 11%, and its Charpy impact energy at 25℃ is >16 J.

[0021] On the other hand, the present invention also provides a method for manufacturing the above-mentioned 2000MPa grade high-strength and high-toughness alloy steel plate for protection, comprising the following steps: (a) smelting: molten iron is smelted in a blast furnace, smelted in a converter and double refined by LF+RH to obtain molten steel that conforms to the chemical composition; (b) continuous casting: the molten steel is continuously cast to obtain a continuous casting billet; (c) heating: the continuous casting billet is fed into a heating furnace for heating; (d) hot rolling: the heated continuous casting billet is subjected to two-stage rolling, including rough rolling and finish rolling, to obtain a hot-rolled steel plate; (e) heat treatment: the hot-rolled steel plate is quenched and tempered to obtain a 2000MPa grade high-strength and high-toughness alloy steel plate for protection.

[0022] Preferably, in step (c), the heating temperature is 1150℃~1250℃, and the ratio of heating time to continuous casting billet thickness is 2.0~4.0min / mm.

[0023] Preferably, in step (d), the initial rolling temperature of the roughing mill is 1100℃~1200℃, the final rolling temperature of the roughing mill is 1000℃~1100℃, and the cumulative reduction rate of the roughing mill is 70%~85%; the initial rolling temperature of the finishing mill is 950℃~1050℃, the final rolling temperature of the finishing mill is 850℃~950℃, and the cumulative reduction rate of the finishing mill is 40%~60%.

[0024] Preferably, in step (e), the quenching heating temperature is 800℃~920℃, the ratio of holding time to the thickness of the finished steel plate is 1.5~3.5min / mm, and the cooling method is water quenching; the tempering heating temperature is 100℃~170℃, the ratio of holding time to the thickness of the finished steel plate is 10~15min / mm, and the cooling method is air cooling.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention adopts a C-Si-Mn-Cr-Ni-Mo-Nb composite microalloying composition design, which avoids the problems of poor welding performance, billet segregation or high cost caused by high carbon (CN202110680952.2), high manganese (CN202011186691.0) or high nickel (CN202110680952.2) in the prior art. The alloy has a lower cost and better welding performance.

[0027] 2. This invention uses a two-stage rolling process to control the cumulative reduction rate of roughing and finishing rolling, refines the austenite grains, and provides good microstructure preparation for subsequent heat treatment; the final rolling temperature is controlled at 850℃~950℃, avoiding the problem of grain coarsening caused by excessively high final rolling temperature (1000℃~1050℃) in the prior art CN200710045335.5.

[0028] 3. This invention adopts a quenching and tempering heat treatment process. By controlling the quenching heating temperature, holding time and cooling method, a composite structure with tempered martensite as the matrix, containing a small amount of austenite and dispersed ε-carbides is obtained. The average grain size is small and uniform (2μm~5μm), achieving a match between high strength and good plasticity and toughness.

[0029] 4. The yield strength R of the alloy steel plate prepared by this invention p0.2 The tensile strength is 1800MPa~1900MPa, R m With a strength of 2000MPa to 2100MPa, an elongation of 9% to 11%, and a Charpy impact energy of >16J at 25℃, it exhibits excellent comprehensive mechanical properties and is suitable for high-safety protection applications such as armored vehicles, explosion-proof structures, and bulletproof plates.

[0030] 5. The manufacturing method of this invention has a simple process flow and can be produced using a conventional hot rolling production line. It does not require complex forging or offline heat treatment processes (such as CN202011186691.0), and is easy to achieve large-scale industrial production. Attached Figure Description

[0031] Figure 1 This is a SEM image of the microstructure of the continuously cast billet after rolling in Example 1.

[0032] Figure 2 This is a SEM image of the steel plate after heat treatment in Example 1.

[0033] Figure 3 This is an EBSD microstructure diagram of the steel plate after heat treatment in Example 1.

[0034] Figure 4 The graph shows the tensile properties of the steel plate in Example 1. Detailed Implementation

[0035] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0036] Example 1

[0037] A 2000MPa grade high-strength and high-toughness alloy steel plate for protective applications has the following chemical composition by mass percentage: C 0.41%, Si 0.25%, Mn 0.55%, Cr 0.22%, Ni 1.0%, Mo 0.22%, Nb 0.05%, P 0.002%, S 0.002%, with other impurity elements totaling 0.008%, and the balance being Fe and unavoidable impurities.

[0038] The manufacturing method is as follows: (a) Smelting: Molten iron is smelted in a blast furnace, smelted in a converter, and refined using an LF+RH double refining process to obtain molten steel with the above-mentioned chemical composition. (b) Continuous casting: Molten steel is continuously cast, with a billet thickness of 100 mm, and stacked for slow cooling for 24-48 hours. (c) Heating: The heating temperature is 1180℃, and the ratio of heating time to billet thickness is 2.5 min / mm. (d) Hot rolling: The roughing rolling start temperature is 1150℃, the roughing rolling finish temperature is 1050℃, and the cumulative reduction rate of roughing rolling is 85%; the finishing rolling start temperature is 1000℃, the finishing rolling finish temperature is 880℃, and the cumulative reduction rate of finishing rolling is 60%; the total reduction rate is 94%, resulting in a hot-rolled steel plate with a thickness of 6 mm. (e) Heat treatment: Quenching heating temperature is 860℃, holding time to finished steel plate thickness ratio is 2.0min / mm, water quenching to room temperature; tempering heating temperature is 150℃, holding time to finished steel plate thickness ratio is 10min / mm, air cooling to room temperature.

[0039] Example 2

[0040] A 2000MPa grade high-strength and high-toughness alloy steel plate for protective applications has the following chemical composition by mass percentage: C 0.38%, Si 0.45%, Mn 0.95%, Cr 0.60%, Ni 2.0%, Mo 0.50%, Nb 0.12%, P 0.002%, S 0.002%, with other impurity elements totaling 0.009%, and the balance being Fe and unavoidable impurities.

[0041] The manufacturing method is as follows: (a) Smelting: Same as Example 1. (b) Continuous casting: Same as Example 1. (c) Heating: The heating temperature is 1200℃, and the ratio of heating time to the thickness of the continuously cast billet is 3.0 min / mm. (d) Hot rolling: The roughing rolling start temperature is 1160℃, the roughing rolling finish temperature is 1060℃, and the cumulative reduction rate of roughing rolling is 80%; the finishing rolling start temperature is 1020℃, the finishing rolling finish temperature is 890℃, and the cumulative reduction rate of finishing rolling is 55%; the total reduction rate is 91%, resulting in a hot-rolled steel plate with a thickness of 9 mm. (e) Heat treatment: The quenching heating temperature is 880℃, the holding time to the finished steel plate thickness is 2.5 min / mm, and the plate is water-quenched to room temperature; the tempering heating temperature is 160℃, the holding time to the finished steel plate thickness is 10 min / mm, and the plate is air-cooled to room temperature.

[0042] Example 3

[0043] A 2000MPa grade high-strength and high-toughness alloy steel plate for protective applications has the following chemical composition by mass percentage: C 0.37%, Si 0.55%, Mn 1.15%, Cr 0.75%, Ni 3.0%, Mo 0.75%, Nb 0.19%, P 0.002%, S 0.002%, with other impurity elements totaling 0.010%, and the balance being Fe and unavoidable impurities.

[0044] The manufacturing method is as follows: (a) Smelting: Same as Example 1. (b) Continuous casting: Same as Example 1. (c) Heating: The heating temperature is 1250℃, and the ratio of heating time to the thickness of the continuously cast billet is 3.8 min / mm. (d) Hot rolling: The roughing rolling start temperature is 1200℃, the roughing rolling finish temperature is 1100℃, and the cumulative reduction rate of roughing rolling is 75%; the finishing rolling start temperature is 1030℃, the finishing rolling finish temperature is 910℃, and the cumulative reduction rate of finishing rolling is 50%; the total reduction rate is 87.5%, resulting in a hot-rolled steel plate with a thickness of 12.5 mm. (e) Heat treatment: The quenching heating temperature is 920℃, the holding time to the finished steel plate thickness is 3.2 min / mm, and the plate is water-quenched to room temperature; the tempering heating temperature is 170℃, the holding time to the finished steel plate thickness is 13 min / mm, and the plate is air-cooled to room temperature.

[0045] Example 4

[0046] A 2000MPa grade high-strength and high-toughness alloy steel plate for protective applications has the following chemical composition by mass percentage: C 0.40%, Si 0.35%, Mn 0.85%, Cr 0.45%, Ni 2.5%, Mo 0.55%, Nb 0.15%, P 0.002%, S 0.002%, with other impurity elements totaling 0.008%, and the balance being Fe and unavoidable impurities.

[0047] The manufacturing method is as follows: (a) Smelting: Same as Example 1. (b) Continuous casting: Same as Example 1. (c) Heating: The heating temperature is 1220℃, and the ratio of heating time to the thickness of the continuously cast billet is 3.2 min / mm. (d) Hot rolling: The roughing rolling start temperature is 1180℃, the roughing rolling finish temperature is 1080℃, and the cumulative reduction rate of roughing rolling is 70%; the finishing rolling start temperature is 1040℃, the finishing rolling finish temperature is 900℃, and the cumulative reduction rate of finishing rolling is 40%; the total reduction rate is 82%, resulting in a hot-rolled steel plate with a thickness of 18 mm. (e) Heat treatment: The quenching heating temperature is 900℃, the holding time to the finished steel plate thickness is 2.8 min / mm, and the plate is water-quenched to room temperature; the tempering heating temperature is 165℃, the holding time to the finished steel plate thickness is 15 min / mm, and the plate is air-cooled to room temperature.

[0048] Performance testing

[0049] The steel plates obtained in Examples 1-4 above were subjected to mechanical property tests. The test results are shown in Table 1.

[0050] Table 1 shows the mechanical properties of Examples 1-4. No. Yield strength (MPa) Tensile strength (MPa) Elongation (%) Impact work J (25°C) Impact specimen size (7.5 x 10 x 55 mm) Example 1 1904 2107 9.2 16.9 Example 2 1850 2050 10.2 17.6 Example 3 1820 2015 11.2 18 Example 4 1870 2068 9.7 17.4

[0051] As can be seen from Table 1, the alloy steel plates prepared in Examples 1-4 of this invention all have a yield strength of over 1800 MPa, a tensile strength of over 2000 MPa, an elongation of 9% to 11%, and a Charpy impact energy of over 16 J at 25℃, exhibiting excellent strength, plasticity, and toughness matching.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-strength, high-toughness alloy steel plate for 2000MPa protection, characterized in that, The alloy steel plate comprises the following chemical composition by mass percentage: C 0.35%–0.42%, Si 0.2%–0.6%, Mn 0.5%–1.2%, Cr 0.2%–0.8%, Ni 1.0%–3.0%, Mo 0.2%–0.8%, Nb 0.05%–0.2%, P ≤ 0.003%, S ≤ 0.003%, and the total content of other impurity elements ≤ 0.01%, with the balance being Fe and unavoidable impurities.

2. The 2000MPa grade high-strength and high-toughness alloy steel plate for protective applications according to claim 1, characterized in that, The microstructure of the alloy steel plate after heat treatment consists of tempered martensite, a small amount of retained austenite, and dispersed ε-carbides, wherein the volume fraction of martensite is 85%–93%, the volume fraction of austenite is 0.1%–0.5%, and the volume fraction of ε-carbides is 7%–9%.

3. The 2000MPa grade high-strength, high-toughness alloy steel plate for protective applications according to claim 1 or 2, characterized in that, The average grain size of the alloy steel plate after heat treatment is 2μm to 5μm.

4. The 2000MPa grade high-strength and high-toughness alloy steel plate for protection according to any one of claims 1-3, characterized in that, The yield strength R of the alloy steel plate p0.2 The tensile strength is 1800MPa~1900MPa, R m Its strength ranges from 2000 MPa to 2100 MPa, its elongation is 9% to 11%, and its Charpy impact energy at 25℃ is >16 J.

5. A method for manufacturing a 2000MPa grade high-strength and high-toughness alloy steel plate for protective applications as described in any one of claims 1-4, characterized in that, The manufacturing method includes the following steps: (a) smelting: molten iron is smelted in a blast furnace, smelted in a converter, and double-refined by LF+RH to obtain molten steel with the chemical composition described in claim 1; (b) continuous casting: the molten steel is continuously cast to obtain a continuously cast billet; (c) heating: the continuously cast billet is fed into a heating furnace for heating; (d) hot rolling: the heated continuously cast billet is subjected to two-stage rolling, including rough rolling and finish rolling, to obtain a hot-rolled steel plate; (e) heat treatment: the hot-rolled steel plate is quenched and tempered to obtain a 2000MPa grade high-strength and high-toughness alloy steel plate for protection.

6. The manufacturing method according to claim 5, characterized in that, In step (c), the heating temperature is 1150℃~1250℃, and the ratio of heating time to continuous casting billet thickness is 2.0~4.0min / mm.

7. The manufacturing method according to claim 5 or 6, characterized in that, In step (d), the initial rolling temperature of the roughing mill is 1100℃~1200℃, the final rolling temperature of the roughing mill is 1000℃~1100℃, and the cumulative reduction rate of the roughing mill is 70%~85%.

8. The manufacturing method according to any one of claims 5-7, characterized in that, In step (d), the initial rolling temperature of the finishing mill is 950℃~1050℃, the final rolling temperature of the finishing mill is 850℃~950℃, and the cumulative reduction rate of the finishing mill is 40%~60%.

9. The manufacturing method according to any one of claims 5-8, characterized in that, In step (e), the quenching heating temperature is 800℃~920℃, the ratio of the holding time to the thickness of the finished steel plate is 1.5~3.5min / mm, and the cooling method is water quenching.

10. The manufacturing method according to any one of claims 5-9, characterized in that, In step (e), the heating temperature for tempering is 100℃~170℃, the ratio of the holding time to the thickness of the finished steel plate is 10~15min / mm, and the cooling method is air cooling.

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