A ballistic steel plate and a method for producing the same

Abstract

This invention discloses a novel bulletproof steel plate with a thickness of 12-35mm, comprising the following chemical composition by weight percentage (unit: wt%): C: 0.25-0.28, Si: 1.20-1.40, Mn: 1.50-1.60, P: ≤0.007, S: ≤0.001, Cr: 0.50-0.60, B: 0.0015-0.0023, Ti: 0.03-0.04, with the remainder being Fe and residual elements; it eliminates the need for the addition of Ni, Mo, and rare earth elements, thus reducing alloy costs. In terms of production process, clean steel smelting is used to control the P and S content, thereby improving impact toughness; pressure quenching is employed with multi-point pressure application and reasonable distribution of water volume and pressure in each section of the high-pressure zone to achieve uniform cooling and flatness of the steel plate; furthermore, low-temperature tempering is used to effectively eliminate the influence of residual internal stress in the steel plate and improve the subsequent processing performance of the steel plate, such as cutting and welding. The resulting bulletproof steel has a tensile strength of 1700-1800MPa, a surface hardness of >500HBW, and an impact energy of >40J at -20℃, which fully meets the requirements for use of bulletproof steel plates.

Description

Technical Field

[0001] This invention belongs to the field of steel plate production, specifically relating to a bulletproof steel plate and its production method. Background Technology

[0002] Besides its widespread use in the military field, bulletproof steel plates are also used in the civilian sector for applications such as vehicle guards, police explosive-proof vehicles, and armored cash transport vehicles. Therefore, high-performance bulletproof steel has broad application prospects in the civilian field. Traditional bulletproof steel mainly relies on carbon content to control the hardness of the steel to achieve its bullet-resistant function. To achieve a highly homogeneous effect, expensive alloying elements must be added to the steel, especially large amounts of Cr, Mo, and Ni. Although this effectively improves hardenability, it results in high manufacturing costs. Furthermore, the addition of large amounts of alloying elements can easily lead to alloy segregation, deteriorating the steel's cold and hot working properties.

[0003] For example, Chinese patent CN109930075B discloses an armor-resistant steel plate with a tensile strength ranging from 1620 to 1730 MPa, containing 0.25–0.38% C, 0.10–0.38% Ni, 0.80–1.50% Cr, and 0.16–0.40% Mo, with a thickness ranging from 5 to 10 mm. Another example is Chinese patent CN111394652A, which discloses a rare-earth armor steel and its manufacturing method, containing 0.20–0.35% C, 0.50–2.00% Ni, 0.80–2.50% Cr, 0.30–0.80% Mo, and 0.005–0.080% rare-earth element REM, wherein REM is one or more of cerium (Ce), lanthanum (La), and yttrium (Y), with a thickness ranging from 1.8 to 20 mm.

[0004] However, in practical applications, the steel plates obtained by the above patents have the following problems: 1. The design uses a high carbon content, high alloy, and high carbon equivalent composition, which inevitably leads to hardening cracking during welding, resulting in poor weldability. Second, while increasing the hardness of steel increases its strength, its impact toughness and fracture toughness will decrease sharply, making the material brittle and unable to withstand the impact load of the huge energy of the shell, resulting in cracking and falling off. It is difficult to guarantee the ballistic resistance of armor steel. Third, the addition of large amounts of alloying elements such as Ni and Mo, as well as rare elements such as cerium (Ce), lanthanum (La), and yttrium (Y) to enhance the low-temperature toughness and plasticity of steel, inevitably leads to a complex composition system that brings disadvantages to smelting and production, such as a large number of alloying elements, high operational difficulty, easy cracking of steel billets, and high costs. Summary of the Invention

[0005] To address the aforementioned technical deficiencies, the present invention aims to provide a bulletproof steel plate that, in addition to ensuring the strength requirements of bulletproof steel plates, also possesses good ductility and toughness indicators, and does not require the addition of large amounts of alloying elements, thereby reducing production costs.

[0006] The second objective of this invention is to provide a method for producing bulletproof steel plates.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a bulletproof steel plate, wherein the thickness of the steel plate is 12-35mm, and the chemical composition comprises the following weight percentages: C: 0.25-0.28%, Si: 1.20-1.40%, Mn: 1.50-1.60%, P: ≤0.007%, S: ≤0.001%, Cr: 0.50-0.60%, B: 0.0015-0.0023%, Ti: 0.03-0.04%, and the remainder being Fe and residual elements; The steel plate has a tensile strength of 1700-1800MPa, a surface hardness of >500HBW, and an impact energy of >40J at -20℃.

[0008] Furthermore, the production method of the steel plate includes steel smelting, casting, heating, rolling, heat treatment, and heat treatment, wherein the heat treatment includes quenching + low-temperature tempering, specifically: The quenching process is carried out in a roller hearth quenching furnace, with a heating temperature of 880–900℃ and a holding time of 2.0–2.1 min / mm. After the holding time, the quenching is carried out in stages with controlled temperature until room temperature. The water pressure in the high-pressure section is controlled at 0.7–0.9 MPa. For the finished steel plate with a thickness of 12–15 mm, the roller speed of the quenching machine is 10–12 m / min, and the water flow rate in the high-pressure section is 400 m³ / min. 3 / h, water ratio 1.5, high-pressure second stage water volume 180m 3 / h, water ratio 1.65; for the finished steel plates with a thickness greater than 15mm and less than 35mm, the quenching machine roller speed is 6-9m / min, and the high-pressure first stage water flow is 450m³ / h. 3 / h, water ratio 1.3, high-pressure second stage water volume 160m³ 3 / h, water ratio 1.4, high-pressure three-stage water flow 200m³ 3 / h, water ratio 1.65; The tempering process controls the heating temperature to 200-230℃ and the holding time to 3.5 min / mm.

[0009] The steel plate production method includes steel smelting, casting, heating, rolling, and cooling, specifically as follows: a. Steelmaking: The converter adopts low-pulling carbonization and dephosphorization smelting, and the converter tapping temperature is controlled at 1590-1610℃, with P ≤ 0.005% at tapping; LF adopts large slag volume slag making, and the white slag holding time is controlled at 30-40min, with S content controlled at ≤ 0.001%; ​​VD refining controls the holding time at vacuum degree ≤ 67Pa for 15-18min, with H content controlled at ≤ 1.2ppm, and after breaking the vacuum, Ca treatment is carried out at 1.5-2.0m / t to modify inclusions, and the steel is hoisted after soft blowing for 5-7min; b. Casting: Argon sealing protection throughout the casting process, superheated by 5-20℃, and the billet cross section is 300mm thick; c. Heating: To ensure sufficient solid solution of alloying elements and prevent excessive growth of austenite grains, the first heating temperature is ≤950℃, the second heating temperature is 1210~1230℃, the soaking temperature is 1200~1220℃, and the heating time is 11~13min / cm.

[0010] d. Rolling: A two-stage rolling process is adopted. The first stage starts at a rolling temperature of 1000℃~1100℃, with a pass reduction of 12%~15%, and the steel is dried to a thickness of 2-3 times the finished product. The first stage of rolling is completed in the temperature range of the austenite recrystallization zone. In order to obtain fine and dispersed grains, the second stage is rolled in the temperature range of the non-recrystallization zone of austenite. The second stage starts at a rolling temperature of 820~880℃, with a pass reduction of ≥15%, which fully breaks down the grains and prevents grain growth. After rolling, the steel plate is naturally cooled to 500℃ on a cooling bed before being taken off the production line. e. Stacking cooling: After rolling, the temperature of the steel plate in the slow cooling pit is ≥400℃, the slow cooling time is 36 to 48 hours, the height of the slow cooling stack is controlled at 1.5 to 2m, and the upper and lower surfaces of the steel plate must not be exposed to the air.

[0011] Compared with the prior art, the beneficial effects of the present invention include: This invention does not add Ni, Mo, or rare elements such as cerium (Ce), lanthanum (La), and yttrium (Y), resulting in low production costs, simple operation, and high-quality steel billets that are less prone to cracking. By employing alloy composition ratios within a specific range, it ensures both the strength and good ductility of the steel plate.

[0012] In terms of production process, clean steel smelting is used to control P and S content and improve impact toughness; pressure quenching is used with multi-point pressure and water volume and pressure are reasonably distributed in each section of the high-pressure zone to achieve uniform cooling and flatness of the steel plate; then low-temperature tempering is used to effectively eliminate the influence of residual internal stress in the steel plate and improve the subsequent cutting, welding and other processing performance of the steel plate. Detailed Implementation

[0013] The present invention will be further described below with reference to the embodiments.

[0014] To produce a 12-35mm thick bulletproof steel plate, the chemical composition (wt%) is as shown in Table 1:

[0015] The production method of the bulletproof steel plate includes hot metal pretreatment → converter smelting → LF refining → VD refining → continuous casting → heating → rolling → slow cooling → heat treatment, as detailed below: a. Hot metal pretreatment: After KR hot metal pre-desulfurization treatment, the S content of the hot metal entering the converter is ≤0.010%, and the P content is ≤0.010%.

[0016] b. Converter smelting: A low-pulling, carbon-enhancing, and phosphorus-removing process is adopted. The total amount of lime added to a 120-ton converter is 2500-3000 kg. During the process, lime is added in small batches and multiple times to control the final slag basicity at 2.8-3.2. The converter tapping temperature is controlled at 1590-1610℃, and the phosphorus content at tapping is ≤0.005%. Carbon powder is added to the molten steel during tapping to increase carbon content. After tapping, a slag-blocking cone is used to block slag, and the slag thickness at the bottom of the converter is controlled below 20 mm to avoid phosphorus return. After the molten steel reaches the argon station, 200 kg of lime is added to the molten steel, and argon is blown for 5 minutes for stirring.

[0017] c. LF Refining: Large-volume slag production is employed for slag formation. During the first refining heating process, simultaneously with the lower electrode heating, 200-300 kg of lime and 50-100 kg of alumina balls are added to the ladle. The total slag added during the entire first heating process is: lime controlled at 500-600 kg, and alumina balls controlled at 150-200 kg. The deoxidizers during the first heating process consist of aluminum granules, calcium carbide, and ferrosilicon powder. The addition amounts are 15-20 kg of aluminum granules, 40-50 kg of calcium carbide, and 15-20 kg of ferrosilicon powder. The deoxidizers are added in multiple small batches. The steel temperature at the end of the first refining heating process should be controlled at 1565-1575℃. During the second heating process, based on the submerged arc effect, 10-30 kg of calcium carbide, 15-20 kg of aluminum granules, and 5-10 kg of ferrosilicon powder are added each time. The deoxidizer additions must be done in multiple small batches to ensure that white slag is maintained throughout the entire second heating process. Ferrochrome and ferroboron are added during the second heating process after the formation of white slag. The addition of the deoxidizer during the third heating process depends on the slag color; the goal is to maintain the white slag. The white slag retention time should be controlled at 30-40 minutes, with the sulfur content kept ≤0.001%.

[0018] d. VD refining: The holding time at ≤67Pa is controlled at 15-18min. After vacuuming, H content is controlled at ≤1.2ppm. After breaking the vacuum, soft blowing is performed for 3-5min, during which the molten steel must not be exposed. After breaking the vacuum, Ca treatment is performed at 1.5-2.0m / t to modify inclusions. After soft blowing for 5-7min, the steel is hoisted.

[0019] e. Continuous casting: 300mm thick section continuous casting is adopted, and argon sealing protection is used throughout the pouring process. The pouring superheat is controlled at 5-20℃.

[0020] f. Heating: To ensure sufficient solid solution of alloying elements and prevent excessive growth of austenite grains, the first heating temperature is ≤950℃, the second heating temperature is 1210~1230℃, the soaking temperature is 1200~1220℃, and the heating time is 11~13min / cm.

[0021] g. Rolling: A two-stage rolling process is adopted. The first stage of rolling is completed within the temperature range of the austenite recrystallization zone. The initial rolling temperature of the first stage is 1000℃~1100℃, and the reduction per pass is 12%~15%, with the steel being air-dried to a thickness of 2-3 times the finished product. To obtain fine and dispersed grains, the second stage of rolling is carried out within the temperature range of the non-recrystallization zone of the austenite. The initial rolling temperature of the second stage is 820~880℃, and the reduction per pass is ≥15%, which fully breaks down the grains and prevents grain growth. After rolling, the steel plate is naturally cooled to 500℃ on a cooling bed before being removed from the production line.

[0022] h. Slow Cooling: The temperature of the rolled steel plate in the slow cooling pit should be ≥400℃, and the slow cooling time should be 36-48 hours. The height of the slow cooling stack should be controlled at 1.5-2m, and the upper and lower surfaces of the steel plate must not be exposed to the air. Slow cooling after rolling can promote the diffusion of hydrogen in the steel plate, avoiding internal defects caused by "H traps". On the other hand, it can gradually release the residual stress caused by rolling through slow cooling, avoiding stress cracking.

[0023] i. Heat treatment: Offline tempering is adopted. The quenching process is carried out in a roller hearth quenching furnace. The heating temperature is 880-900℃, and the holding time is 2.0-2.1 min / mm. After the holding time, the temperature is controlled in stages to room temperature. The water pressure in the high-pressure section is controlled at 0.7-0.9 MPa. The process control is shown in Table 2 below:

[0024] Tempering process: Heat the steel plate to 200-230℃, hold for 3.5 min / mm, and after the holding time is up, remove it from the furnace and air cool it to room temperature.

[0025] The performance of the steel plates obtained in the example was tested, and the indicators are shown in Table 3 below:

[0026] Based on the above data, the steel plate has a yield strength of 1650-1720MPa, a tensile strength of 1700-1800MPa, a surface hardness of >500HBW, and an impact energy of >40J at -20℃, which fully meets the requirements for bulletproof steel plates.

[0027] External inspection and flaw detection: The external inspection pass rate of the developed steel plate is 100%, and the final flaw detection of the steel plate meets the Class I flaw detection requirements of GB / T 2970 "Inspection Method for Thick Steel Plates".

[0028] The above description is only a preferred embodiment of the present invention. The above specific embodiments are not intended to limit the present invention. Any modifications, alterations or equivalent substitutions made by those skilled in the art based on the above description shall fall within the protection scope of the present invention.

Claims

1. A bulletproof steel plate, characterized in that, The steel plate has a thickness of 12-35 mm and contains the following chemical composition by weight percentage: C: 0.25-0.28%, Si: 1.20-1.40%, Mn: 1.50-1.60%, P: ≤0.007%, S: ≤0.001%, Cr: 0.50-0.60%, B: 0.0015-0.0023%, Ti: 0.03-0.04%, with the remainder being Fe and residual elements; The steel plate has a tensile strength of 1700-1800MPa, a surface hardness of >500HBW, and an impact energy of >40J at -20℃. The steel plate production method includes steel smelting, casting, heating, rolling, heat treatment, and heat treatment, wherein the heat treatment includes quenching + low-temperature tempering, specifically: The quenching process is carried out in a roller hearth quenching furnace, with a heating temperature of 880–900℃ and a holding time of 2.0–2.1 min / mm. After the holding time, the quenching is carried out in stages with controlled temperature until room temperature. The water pressure in the high-pressure section is controlled at 0.7–0.9 MPa. For the finished steel plate with a thickness of 12–15 mm, the roller speed of the quenching machine is 10–12 m / min, and the water flow rate in the high-pressure section is 400 m³ / min. 3 / h, water ratio 1.5, high-pressure second stage water volume 180m 3 / h, water ratio 1.65; for the finished steel plates with a thickness greater than 15mm and less than 35mm, the quenching machine roller speed is 6-9m / min, and the high-pressure first stage water flow is 450m³ / h. 3 / h, water ratio 1.3, high-pressure second stage water volume 160m³ 3 / h, water ratio 1.4, high-pressure three-stage water flow 200m³ 3 / h, water ratio 1.65; The tempering process controls the heating temperature to 200-230℃ and the holding time to 3.5 min / mm.

2. The method for producing bulletproof steel plates according to claim 1, characterized in that, The steel plate production method includes steel smelting, casting, heating, rolling, heat treatment, and heat treatment, wherein the heat treatment includes quenching + low-temperature tempering, specifically: The quenching process is carried out in a roller hearth quenching furnace, with a heating temperature of 880–900℃ and a holding time of 2.0–2.1 min / mm. After the holding time, the quenching is carried out in stages with controlled temperature until room temperature. The water pressure in the high-pressure section is controlled at 0.7–0.9 MPa. For the finished steel plate with a thickness of 12–15 mm, the roller speed of the quenching machine is 10–12 m / min, and the water flow rate in the high-pressure section is 400 m³ / min. 3 / h, water ratio 1.5, high-pressure second stage water volume 180m 3 / h, water ratio 1.65; for the finished steel plates with a thickness greater than 15mm and less than 35mm, the quenching machine roller speed is 6-9m / min, and the high-pressure first stage water flow is 450m³ / h. 3 / h, water ratio 1.3, high-pressure second stage water volume 160m³ 3 / h, water ratio 1.4, high-pressure three-stage water flow 200m³ 3 / h, water ratio 1.65; The tempering process controls the heating temperature to 200-230℃ and the holding time to 3.5 min / mm.

3. The method for producing bulletproof steel plates according to claim 2, characterized in that, The steel plate production method includes steel smelting, casting, heating, rolling, and cooling, specifically as follows: a. Steelmaking: The converter adopts low-pulling carbonization and dephosphorization smelting, and the converter tapping temperature is controlled at 1590-1610℃, with P ≤ 0.005% at tapping; LF adopts large slag volume slag making, and the white slag holding time is controlled at 30-40min, with S content controlled at ≤ 0.001%; ​​VD refining controls the holding time at vacuum degree ≤ 67Pa for 15-18min, with H content controlled at ≤ 1.2ppm, and after breaking the vacuum, Ca treatment is carried out at 1.5-2.0m / t to modify inclusions, and the steel is hoisted after soft blowing for 5-7min; b. Casting: Argon sealing protection throughout the casting process, superheated by 5-20℃, and the billet cross section is 300mm thick; c. Heating: To ensure the full solid solution of alloying elements and prevent excessive growth of austenite grains, the first heating temperature is ≤950℃, the second heating temperature is 1210~1230℃, the soaking temperature is 1200~1220℃, and the heating time is 11~13min / cm. d. Rolling: A two-stage rolling process is adopted. The first stage starts at a rolling temperature of 1000℃~1100℃, with a pass reduction of 12%~15%, and the steel is dried to a thickness of 2-3 times the finished product. The first stage of rolling is completed in the temperature range of the austenite recrystallization zone. In order to obtain fine and dispersed grains, the second stage is rolled in the temperature range of the non-recrystallization zone of austenite. The second stage starts at a rolling temperature of 820~880℃, with a pass reduction of ≥15%, which fully breaks down the grains and prevents grain growth. After rolling, the steel plate is naturally cooled to 500℃ on a cooling bed before being taken off the production line. e. Stacking cooling: After rolling, the temperature of the steel plate in the slow cooling pit is ≥400℃, the slow cooling time is 36 to 48 hours, the height of the slow cooling stack is controlled at 1.5 to 2m, and the upper and lower surfaces of the steel plate must not be exposed to the air.

Images