Bulletproof steel plate and manufacturing method

Abstract

The invention relates to the technical field of protective steel, in particular to a bulletproof steel plate and a manufacturing method. The bulletproof steel plate comprises the following chemical components in percentage by mass: 0.22%-0.30% of C, less than or equal to 1.00% of Mn, less than or equal to 0.40% of Si, 0.50%-1.50% of Cr, 0.50%-1.50% of Ni, 0.15%-0.50% of Mo, 0.01%-0.10% of Nb, 0.03%-0.15% of V, 0.01%-0.10% of Ti, 0.03%-0.25% of Cu, less than or equal to 0.020% of P, less than or equal to 0.010% of S and the balance of Fe and inevitable impurity elements, and the carbon equivalent CEIIW is 0.6-0.8. Compared with the prior art, the thin bulletproof steel plate with protection and processing properties is high in tensile strength, high in yield strength and good in cold bending processing property, can meet more stringent use requirements, is a necessary guarantee condition for high-efficiency and low-cost manufacturing of equipment and quick repair in wartime, and has wide application prospects. The invention is also one of the core technologies for the development of modern armored vehicles.

Description

Technical Field

[0001] The present invention relates to the technical field of steel for protection, and in particular to a bulletproof steel plate and a manufacturing method thereof. Background Art

[0002] In response to the further improvement requirements for the lightweight level and protection performance of the new generation of weaponry and equipment, the comprehensive performance requirements for protective steel materials are also getting higher and higher. Taking armored vehicles as an example, currently, most of their vehicle bodies are made of 500HBW-grade thin-specification bulletproof steel plates, and many components need cold bending forming and welding. To ensure their protection performance, the carbon equivalent of bulletproof steel plates of this strength level is usually relatively high. Therefore, there are problems such as poor toughness and plasticity, difficult welding to ensure, and bending cracking. Among the current military standards for bulletproof steel plates, the standards for 500HBW-grade and thin-specification armor steels with a supply thickness of less than 10 mm mainly include GJB 8223, GJB8486, GJB 3019A, and GJB 3166A. Among them, only GJB 8486 has cold bending requirements for 6211 bulletproof steel, and mainly refers to GB / T 232-2024 "Test Method for Bending of Metallic Materials". The maximum width of the specimen is 50 mm. During the actual manufacturing process of armored vehicles, the cold forming cracking rate of large-size wide-plate high-strength armor steel is relatively high, and its weldability is poor, resulting in low material utilization rate and increased manufacturing cost. Therefore, inventing a thin-specification bulletproof steel plate with both protection and process performance is a necessary guarantee condition for the efficient and low-cost manufacturing of equipment and rapid repair during wartime, and is also one of the core technologies for the development of modern armored vehicles.

[0003] The adaptation of high bulletproof performance and good process performance is a contradiction. Internationally, only SSAB and Arcelormittal in Sweden can produce armored steel plates with both good bulletproof performance and process performance. At present, many 500HBW-grade bulletproof steel plates have been invented in China. For example, Patent Publication No. CN102181795A discloses a high-strength bulletproof plate and its manufacturing process. The yield strength of the 2.2 mm B-grade steel plate prepared by this invention is ≥1350 MPa, and the tensile strength is ≥1700 MPa. However, the carbon content of this bulletproof plate is relatively large, between 0.3% and 0.4%, and its cold bending, welding and other process performances are questionable.

[0004] Patent Publication No. CN109628835A discloses a cold-rollable high-performance bulletproof steel plate and its manufacturing process. The 2.5-mm and 4.0-mm steel plates prepared by this invention can meet the protection requirements of Class B and Class C of GA164 standard respectively, and can be bent to 90° without cracks when the cold bending punch radius ≤ 4 times the plate thickness. However, the small-sized cold bending specimens with a width ≤ 50 mm in the "Test Method for Bending of Metallic Materials" of GB / T 232-2024 are still used in this invention, and only one microalloying element, Nb, is adopted. To ensure the protection performance, the designed maximum carbon content of the steel plate in this invention can reach 0.45%. During the rolling or heat treatment process of large-sized wide plates, greater residual stresses may accumulate. During cold bending, these internal stresses will be superimposed on the processing stresses, resulting in local areas exceeding the yield strength of the material and causing cracking. Therefore, when processing large-sized wide plate components, the improvement of the process performance matching of this steel plate is limited. Patent Publication No. CN111455289A discloses a high-strength hot-rolled bulletproof steel plate and its manufacturing method. The 4-6 mm steel plate prepared by this invention can meet the protection requirements of GJB59.18 standard and has good weldability. Although the designed carbon content of this invention is relatively low, only one microalloying element, V, is adopted. Therefore, to improve the strength and toughness, its nickel content is increased to 1.00-1.80%, which increases the cost during the production process, and the actual carbon content in the examples is all ≥ 0.28%, and the performance when the carbon content < 0.28% cannot be verified. In addition, the cold bending performance test part in this invention does not indicate the cold bending test and the cold bending radius of the finished steel plate, so its cold bending performance characteristics cannot be reflected. Patent Publication No. CN104674121A discloses a manufacturing method of a steel plate for high anti-ballistic armor. The 5-60 mm armor steel manufactured by this invention adopts a low carbon equivalent design, with the carbon content between 0.2 and 0.28 and the carbon equivalent less than or equal to 0.65, but it only adopts one microalloying element, Ti, and does not mention its process performance. Patent Publication No. CN102181795A discloses an ultra-high-strength bulletproof steel plate and its manufacturing process. The 2.2-mm-thick 500HB-level bulletproof steel plate prepared by this invention is microalloyed with 1-2 elements selected from Nb, V, and Ti. However, since the steel contains element B, it may lead to insufficient toughness and poor process performance, and the toughness and process performance are not mentioned in this invention. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects existing in the above-mentioned prior art, and provide a bulletproof steel plate and its manufacturing method, so as to obtain a thin-specification bulletproof steel plate with both protection and process performance, high tensile strength, high yield strength, good cold bending process performance at the same time, which can meet more stringent use requirements, is a necessary guarantee condition for the efficient and low-cost manufacturing of equipment and rapid repair during wartime, and is also one of the core technologies for the development of modern armored vehicles.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] In one aspect, the present invention provides a bulletproof steel plate. The chemical composition of the bulletproof steel plate by mass percentage is as follows: C: 0.22% - 0.30%, Mn ≤ 1.00%, Si ≤ 0.40%, Cr: 0.50% - 1.50%, Ni: 0.50% - 1.50%, Mo: 0.15% - 0.50%, Nb: 0.01% - 0.10%, V: 0.03% - 0.15%, Ti: 0.01% - 0.10%, Cu: 0.03% - 0.25%, P ≤ 0.020%, S ≤ 0.010%, and the balance is Fe and inevitable impurity elements. The carbon equivalent CE IIW = 0.6 - 0.8.

[0008] The design principle of the alloy composition of the present invention:

[0009] C: As a strong solution strengthening element of the body-centered cubic structure phase, C not only increases the strength of the steel plate but also reduces the difficulty of smelting control. However, when the C content is high, it will inevitably affect the process performance of the steel plate. Therefore, the C content is controlled at 0.22 - 0.30%.

[0010] Mn: By adding Mn, Ar3 can be reduced, the coarsening of carbides such as cementite can be inhibited, and in addition, it can act synergistically with the C element to improve the low-temperature toughness of the steel plate. The Mn content is set at 0.50 - 1.00%.

[0011] Si: Si can not only remove the O element in the steel plate but also significantly increase the strength of the body-centered cubic structure phase through solution strengthening without causing a decrease in the toughness of the steel plate. However, when the Si content is too high, the surface quality of the steel plate will be significantly deteriorated. Therefore, the Si content is controlled at ≤ 0.40%.

[0012] Ni: It improves the hardenability of the steel and the low-temperature toughness of the steel plate without causing deterioration of the toughness in the heat-affected zone of welding. However, due to high cost and lack of domestic resources, the content is set at 0.50 - 1.50%.

[0013] Cr: It improves the hardenability and hydrogen embrittlement resistance of the steel, can replace part of Mn and Mo, has a lower segregation tendency than Mn, and does not reduce the impact toughness of the steel plate.

[0014] Mo: It refines the microstructure, promotes the formation of martensite / bainite, and increases the yield strength of the steel. It can also act synergistically with B to improve the hardenability of the steel plate. Therefore, the Mo content is controlled at 0.15 - 0.50%.

[0015] V, Ti: V and Ti are mainly used for precipitation strengthening and also play a role in fixing nitrogen. Therefore, the contents of V and Ti are controlled at 0.03 - 0.15% and 0.01 - 0.10% respectively.

[0016] P: P is prone to segregate at grain boundaries. When a load is applied, brittle fracture along the grain boundaries is likely to occur, significantly deteriorating the toughness of the steel plate. Therefore, the content of P is strictly controlled, P ≤ 0.020%.

[0017] S: During the solidification process of molten steel, S will segregate to form sulfide inclusions, which will reduce the low-temperature toughness of the steel plate. Therefore, the S content of the steel plate is strictly controlled, S ≤ 0.010%.

[0018] Cu: Cu mainly functions in solid-solution strengthening and fine-grain strengthening. Cu can inhibit the growth of austenite grains and promote nucleation, thereby refining the grains. Therefore, the Cu content is controlled at 0.03% - 0.25%.

[0019] Furthermore, the yield strength of the bulletproof steel plate is ≥ 1300 MPa, the tensile strength is ≥ 1500 MPa, the elongation after fracture is ≥ 8%, the impact energy KV2 of the V-notch impact specimen at -40 °C is ≥ 30 J, the Brinell hardness from the surface to the core is 480 - 520 HBW, and the thickness of the steel plate is 2.5 - 10 mm.

[0020] Furthermore, under the condition that the bending radius is 2.5 times the plate thickness, the bulletproof steel plate can be bent 90° along the rolling direction and the transverse direction without cracks.

[0021] Furthermore, the 2.5-mm thick bulletproof steel plate can defend against 51B type 7.62-mm pistol bullets at a shooting distance of 10 m, the 4.1-mm thick bulletproof steel plate can defend against ordinary bullets fired by a 56 type 7.62-mm light submachine gun at a shooting distance of 15 m, and the 6.5-mm thick bulletproof steel plate can defend against M16 rifle 5.56×45 mm SS109 bullets at a shooting distance of 30 m.

[0022] On the other hand, the present invention also provides a manufacturing method of a bulletproof steel plate, including the following steps:

[0023] S1. Smelt the raw materials to obtain molten steel. The raw materials are configured according to the following mass formula: C: 0.22% - 0.30%, Mn ≤ 1.00%, Si ≤ 0.40%, Cr: 0.50% - 1.50%, Ni: 0.50% - 1.50%, Mo: 0.15% - 0.50%, Nb: 0.01% - 0.10%, V: 0.03% - 0.15%, Ti: 0.01% - 0.10%, Cu: 0.03% - 0.25%, P ≤ 0.020%, S ≤ 0.010%, and the balance is Fe and inevitable impurity elements. The carbon equivalent CE IIW = 0.6 - 0.8;

[0024] S2. Cast the molten steel into slab billets;

[0025] S3. Subject the slab billets to controlled rolling, coiling, leveling, and heat treatment to obtain bulletproof steel plates.

[0026] Further, in step S1, the smelting process includes primary smelting and LF refining. The tapping temperature of the primary smelting is 1600 - 1650 °C, and the ending temperature of LF refining is 1570 - 1620 °C.

[0027] Furthermore, the primary smelting uses a primary smelting furnace, and LF refining is carried out using an LF refining furnace.

[0028] Furthermore, before raw material smelting, KR hot metal pretreatment is carried out. The smelted hot metal undergoes KR desulfurization to make the S content ≤ 0.050%.

[0029] Further, in step S2, casting the molten steel into slab billets adopts the method of continuous slab casting. During the continuous casting stage, the tundish superheat is controlled at 10 - 30 °C, and the overall temperature fluctuation range ≤ 10 °C;

[0030] The cooling method of the casting is stack cooling.

[0031] Furthermore, the time of the stack cooling is 24 - 72 h, and the termination temperature of slow cooling is 20 - 30 °C.

[0032] Further, in step S3, the specific process of the controlled rolling: the slab billets are subjected to rough rolling and finish rolling in sequence to obtain controlled-rolled slab billets. By subjecting the slab billets to rough rolling and finish rolling in sequence, the casting structure of the slab billets can be destroyed, the grains of the steel can be refined, and the defects of the microstructure can be eliminated, so that the steel structure is dense and the mechanical properties are improved;

[0033] Among them, the starting rolling temperature of the rough rolling is 1100 - 1150 °C, the ending rolling temperature is 1000 - 1050 °C, the starting rolling temperature of the finish rolling is 950 - 1000 °C, the ending rolling temperature is 800 - 850 °C, and the thickness of the obtained controlled-rolled slab billets is 2.5 - 10 mm.

[0034] Furthermore, the slab billets are heated and then continue to be controlled rolled. The heating temperature is 1150 - 1250 °C, and the heating time is 4 - 10 h, so that the internal and external temperatures of the slab billets are consistent, laying a foundation for subsequent controlled rolling.

[0035] Further, in step S3, the coiling temperature is 750 - 650 °C, and slow cooling treatment is carried out after coiling.

[0036] Further, in step S3, the specific process of the heat treatment is: the leveled slab billets are quenched and heat treated at 800 - 900 °C for insulation. The insulation time is determined according to the slab thickness to obtain quenched slab billets, and then the quenched slab billets are subjected to low-temperature tempering treatment at 180 - 280 °C to obtain bulletproof steel plates.

[0037] Furthermore, water quenching is used for the quenching heat treatment, and the water temperature is 20 - 50°C; in the low-temperature tempering treatment, it is held at 180 - 280°C and then air-cooled. Low-temperature tempering can ensure the strength of the slab, and air-cooling can reduce the internal stress in the slab and improve the ductility and toughness of the slab.

[0038] Principle of the bulletproof steel plate in the present invention: Low-carbon equivalent microalloying composition design: Microalloying elements Nb, V, and Ti combine with carbon in the bulletproof steel to form nano-scale precipitation phases (such as Nb(C,N), V(C,N)), pin the grain boundaries, prevent austenite recrystallization and grain growth, thereby producing fine grain strengthening to improve the strength and toughness of the bulletproof steel. The precipitation of dispersed phases such as Nb(C,N) and V(C,N) enhances the matrix to produce precipitation strengthening to improve strength and toughness. The microalloying elements are directly dissolved in martensite to increase the strength of the matrix. The low-carbon equivalent reduces the aggregation of carbon atoms in martensite, thereby reducing brittleness and improving plasticity and toughness, providing a basis for deformation during the cold bending process. The strength loss caused by the reduction of carbon content is compensated by microalloying.

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] (1) The bulletproof steel plate of the present invention combines protection and process performance, has high tensile strength and yield strength, and at the same time has good cold bending process performance, can meet more stringent use requirements, is a necessary guarantee condition for the efficient and low-cost manufacturing of equipment and rapid repair during wartime, and is also one of the core technologies for the development of modern armored vehicles.

[0041] (2) Through the alloy composition design of low-carbon equivalent, the present invention improves the cold bending performance of the steel plate, and makes up for the strength loss caused by low carbon through grain refinement and microalloying, realizing a 500HBW-level bulletproof plate with both protection and process performance. Description of the Drawings

[0042] Figure 1 Microstructure diagram of the bulletproof steel plate prepared for Example 1, (a) original austenite grain structure, (b) scanning electron microscope structure;

[0043] Figure 2 Large-size cold bending specimen of the bulletproof steel plate prepared for Example 1;

[0044] Figure 3 Target test specimens of the bulletproof steel plates prepared for Examples 1 - 3, where (a) front situation of the target test specimen of Example 1, (b) front and back situations of the target test specimen of Example 1, (c) front situation of the target test specimen of Example 2, (d) back situation of the target test specimen of Example 2, (e) front situation of the target test specimen of Example 3, (f) back situation of the target test specimen of Example 3. Detailed Description of the Invention

[0045] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments. Based on the given embodiments, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

[0046] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art.

[0047] Example 1

[0048] An anti-ballistic steel plate, the chemical composition of the anti-ballistic steel plate is by mass percentage: C: 0.25%; Mn: 0.79%; Si: 0.16%; Cr: 0.90%; Ni: 0.92%; Mo: 0.21%; V: 0.074%; Ti: 0.020%; Al: 0.039%; Cu: 0.040%; P≤0.020%; S≤0.005% and the balance of iron and inevitable impurity elements, carbon equivalent CE IIW = 0.65.

[0049] A manufacturing method of an anti-ballistic steel plate, the production process flow is: hot metal → primary refining → LF refining → slab continuous casting → slow cooling → slab heating → controlled rolling → coiling → leveling → heat treatment, specifically including the following steps:

[0050] (1) Smelt the raw materials to obtain molten steel.

[0051] The raw materials are configured according to the following mass formula: 0.25%; Mn: 0.79%; Si: 0.16%; Cr: 0.90%; Ni: 0.92%; Mo: 0.21%; V: 0.074%; Ti: 0.020%; Cu: 0.040%; Al: 0.039%; P≤0.020%; S≤0.005% and the balance of iron and inevitable impurity elements, carbon equivalent CE IIW = 0.65.

[0052] Perform KR hot metal pretreatment on the raw materials, and smelt the hot metal to make the S content ≤ 0.050% through KR pre-desulfurization

[0053] First, preliminarily refine the hot metal in a preliminary refining furnace, and then perform LF refining in an LF refining furnace to obtain molten steel. Among them, the tapping temperature of the preliminary refining is 1600°C, and the end temperature of the LF refining is 1570°C.

[0054] (2) Pour the molten steel into slabs.

[0055] The molten steel is cast into slabs by continuous slab casting. During continuous casting, the superheat of the tundish is controlled at about 10°C, and the temperature fluctuation range throughout the process is ≤10°C. The cooling method during casting is stacking slow cooling. The time of stacking slow cooling is 40 h, and the termination temperature of slow cooling is 25°C.

[0056] (3) The slab is subjected to controlled rolling, coiling, leveling, and heat treatment to obtain a bulletproof steel plate.

[0057] The slab is heated to 1150°C for 5 h to make the internal and external temperatures of the slab uniform. The slab is subjected to rough rolling and finish rolling in sequence to obtain a controlled-rolled slab. Among them, the starting rolling temperature of rough rolling is 1100°C, the finishing rolling temperature is 1000°C, the starting rolling temperature of finish rolling is 1000°C, and the finishing rolling temperature is 800°C. The thickness of the obtained controlled-rolled slab is 6.5 mm. The slab is coiled at 650°C, and after coiling, it is subjected to slow cooling treatment, and then the slab is leveled. The leveled slab is quenched and heat-treated at 880°C for 15 min to obtain a quenched slab, and then the quenched slab is subjected to low-temperature tempering treatment at 200°C for 2 h to obtain a bulletproof steel plate. Among them, water quenching is used for quenching and heat treatment, and the water temperature is 20°C.

[0058] Figure 1 It is the microstructure diagram of the bulletproof steel plate prepared in Example 1. Figure 1 (a) It is the original austenite grain structure of Example 1. It can be seen from the figure that its grain size is fine, and it has a strong effect of fine grain strengthening. After statistics, its grain size is 5.7 μm, and the grain fineness reaches grade 12. Figure 1 (b) It is the scanning electron microscope structure of Example 1, and its structure is composed of lath martensite. It can be seen from this that the microstructure of the bulletproof steel plate prepared in Example 1 is composed of martensite, the original austenite grain size is fine, which provides guarantee for the strength and toughness of the high-strength steel plate.

[0059] Example 2

[0060] A bulletproof steel plate, the chemical composition of the bulletproof steel plate is by mass percentage: C: 0.22%; Mn: 0.73%; Si: 0.16%; Cr: 0.80%; Ni: 0.72%; Mo: 0.17%; V: 0.063%; Ti: 0.020%; Nb: 0.050%; Al: 0.031%; Cu: 0.040%; P≤0.020%; S≤0.005% and the balance of iron and inevitable impurity elements, the carbon equivalent CE IIW = 0.63.

[0061] A manufacturing method of a bulletproof steel plate, the production process flow is: hot metal → primary melting → LF refining → continuous slab casting → slow cooling → slab heating → controlled rolling → coiling → leveling → heat treatment, which specifically includes the following steps:

[0062] (1) Smelt the raw materials to obtain molten steel.

[0063] The raw materials are configured according to the following mass formula: C: 0.22%; Mn: 0.73%; Si: 0.16%; Cr: 0.80%; Ni: 0.72%; Mo: 0.17%; V: 0.063%; Ti: 0.020%; Nb: 0.050%; Cu: 0.040%; Al: 0.031%; P ≤ 0.020%; S ≤ 0.005% and the balance of iron and inevitable impurity elements, carbon equivalent CE IIW = 0.63.

[0064] Perform KR hot metal pretreatment on the raw materials. The smelted hot metal is pre - desulfurized by KR to make the S content ≤ 0.050%.

[0065] First, preliminarily smelt the hot metal in a primary melting furnace, and then perform LF refining in an LF refining furnace to obtain molten steel. The tapping temperature of the preliminary smelting is 1600 °C, and the ending temperature of LF refining is 1570 °C.

[0066] (2) Cast the molten steel into slabs.

[0067] Cast the molten steel into slabs by continuous slab casting. During the continuous casting process, the superheat of the tundish is controlled at 10 °C, and the overall temperature fluctuation range ≤ 10 °C. The cooling method for casting is stacking slow cooling. The time for stacking slow cooling is 40 h, and the termination temperature of slow cooling is 25 °C.

[0068] (3) Subject the slabs to controlled rolling, coiling, leveling, and heat treatment to obtain bullet - proof steel plates.

[0069] Heat the slabs to 1150 °C for 5 h to make the internal and external temperatures of the slabs consistent. Perform rough rolling and finish rolling on the slabs in sequence to obtain controlled - rolled slabs. The starting rolling temperature of rough rolling is 1100 °C, the ending rolling temperature is 1000 °C, the starting rolling temperature of finish rolling is 1000 °C, and the ending rolling temperature is 800 °C. The thickness of the obtained controlled - rolled slabs is 6.5 mm. Coil the slabs at 650 °C, perform slow cooling treatment after coiling, and then level the slabs. Heat - treat the leveled slabs at 860 °C for 15 min for quenching heat treatment to obtain quenched slabs, and then perform low - temperature tempering treatment on the quenched slabs at 200 °C for 2 h to obtain bullet - proof steel plates. The quenching heat treatment uses water quenching, and the water temperature is 20 °C.

[0070] Example 3

[0071] An anti - ballistic steel plate, the chemical composition of the anti - ballistic steel plate is by mass percentage: C: 0.30%; Mn: 0.77%; Si: 0.16%; Cr: 0.80%; Ni: 0.65%; Mo: 0.20%; V: 0.052%; Ti: 0.020%; Nb: 0.050%; Al: 0.030%; Cu: 0.040%; P≤0.020%; S≤0.005% and the balance of iron and inevitable impurity elements, the carbon equivalent CE IIW = 0.69.

[0072] A manufacturing method of an anti - ballistic steel plate, the production process flow is: hot metal → primary melting → LF refining → slab continuous casting → slow cooling → slab heating → controlled rolling → coiling → leveling → heat treatment, specifically including the following steps:

[0073] (1) Smelt the raw materials to obtain molten steel.

[0074] The raw materials are configured according to the following mass formula: C: 0.30%; Mn: 0.77%; Si: 0.16%; Cr: 0.80%; Ni: 0.65%; Mo: 0.20%; V: 0.052%; Ti: 0.020%; Nb: 0.050%; Al: 0.030%; Cu: 0.040%; P≤0.020%; S≤0.005% and the balance of iron and inevitable impurity elements, the carbon equivalent CE IIW = 0.69.

[0075] Perform KR hot metal pretreatment on the raw materials, and smelt the hot metal to make the S content ≤ 0.050% through KR pre - desulfurization

[0076] First, primary - melt the hot metal in a primary melting furnace, and then perform LF refining in an LF refining furnace to obtain molten steel. The tapping temperature of the primary melting is 1600 °C, and the end temperature of LF refining is 1570 °C.

[0077] (2) Pour the molten steel into slabs.

[0078] Pour the molten steel into slabs by means of slab continuous casting. During the continuous casting stage, the superheat of the tundish is controlled at 10 °C, and the whole - process temperature fluctuation range ≤ 10 °C. The cooling method for pouring is stacking slow cooling. The time of the stacking slow cooling is 40 h, and the slow - cooling termination temperature is 25 °C.

[0079] (3) Perform controlled rolling, coiling, leveling, and heat treatment on the slabs to obtain an anti - ballistic steel plate.

[0080] The slab is heated to 1150°C for 5 hours to make the temperature inside and outside the slab uniform. The slab is rough-rolled and then finish-rolled in sequence to obtain a controlled-rolled slab. The starting rolling temperature for rough rolling is 1100°C, the finishing rolling temperature is 1000°C, the starting rolling temperature for finish rolling is 1000°C, and the finishing rolling temperature is 800°C. The thickness of the obtained controlled-rolled slab is 2.5 mm. The slab is coiled at 650°C, followed by slow cooling treatment, and then the slab is leveled. The leveled slab is quenched and heat-treated at 860°C for 15 minutes to obtain a quenched slab, and then the quenched slab is subjected to low-temperature tempering treatment at 200°C for 2 hours to obtain a bulletproof steel plate. Water quenching is used for the quenching and heat treatment, and the water temperature is 20°C.

[0081] Comparative Example 1

[0082] A bulletproof steel plate, the chemical composition of the bulletproof steel plate is by mass percentage: C: 0.37%; Mn: 0.80%; Si: 0.16%; Cr: 0.80%; Ni: 0.50%; Mo: 0.20%; V: 0.05%; Ti: 0.020%; Nb: 0.052%; Al: 0.030%; Cu: 0.040%; P ≤ 0.020%; S ≤ 0.005% and the balance of iron and inevitable impurity elements, carbon equivalent CE IIW = 0.77.

[0083] A manufacturing method of a bulletproof steel plate, the production process flow is: hot metal → primary melting → LF refining → slab continuous casting → slow cooling → slab heating → controlled rolling → coiling → leveling → heat treatment, specifically including the following steps:

[0084] (1) Smelt the raw materials to obtain molten steel.

[0085] The raw materials are configured according to the following mass formula: C: 0.37%; Mn: 0.80%; Si: 0.16%; Cr: 0.80%; Ni: 0.50%; Mo: 0.20%; V: 0.05%; Ti: 0.020%; Nb: 0.052%; Al: 0.030%; Cu: 0.040%; P ≤ 0.020%; S ≤ 0.005% and the balance of iron and inevitable impurity elements, carbon equivalent CE IIW = 0.77.

[0086] The raw materials are subjected to KR hot metal pretreatment, and the smelted hot metal is pre-desulfurized by KR to make the S content ≤ 0.050%

[0087] The hot metal is first primary melted in a primary melting furnace and then LF refined in an LF refining furnace to obtain molten steel. The tapping temperature for the primary melting is 1600°C, and the ending temperature for LF refining is 1570°C.

[0088] (2) Cast the molten steel into a slab.

[0089] The molten steel is cast into slabs by slab continuous casting. During the continuous casting process, the superheat of the tundish is controlled at 10°C, and the temperature fluctuation range throughout the process is ≤10°C. The cooling method during casting is stacking slow cooling, and the time for stacking slow cooling is 40 h, and the termination temperature of slow cooling is 25°C.

[0090] (3) The slabs are subjected to controlled rolling, coiling, leveling, and heat treatment to obtain bulletproof steel plates.

[0091] The slabs are heated to 1150°C for 5 h to make the internal and external temperatures of the slabs uniform. The slabs are subjected to rough rolling and finish rolling in sequence to obtain controlled-rolled slabs. Among them, the starting rolling temperature of rough rolling is 1100°C, the finishing rolling temperature is 1000°C, the starting rolling temperature of finish rolling is 1000°C, and the finishing rolling temperature is 800°C. The thickness of the obtained controlled-rolled slabs is 4.5 mm. The slabs are coiled at 650°C, and after coiling, they are subjected to slow cooling treatment, and then the slabs are leveled. The leveled slabs are quenched and heat-treated at 860°C for 15 min to obtain quenched slabs, and then the quenched slabs are subjected to low-temperature tempering treatment at 200°C for 2 h to obtain bulletproof steel plates. Among them, water quenching is used for quenching and heat treatment, and the water temperature is 20°C.

[0092] Comparative Example 2

[0093] A bulletproof steel plate, the chemical composition of the bulletproof steel plate is by mass percentage: C: 0.25%; Mn: 0.38%; Si: 0.40%; Cr: 1.05%; Ni: 0.60%; Mo: 0.40%; Nb: 0.060%; Al: 0.030%; P≤0.020%; S≤0.005% and the balance of iron and inevitable impurity elements, carbon equivalent CE IIW = 0.63.

[0094] A manufacturing method of a bulletproof steel plate, the production process flow is: hot metal → primary refining → LF refining → slab continuous casting → slow cooling → slab heating → controlled rolling → coiling → leveling → heat treatment, specifically including the following steps:

[0095] (1) The raw materials are smelted to obtain molten steel.

[0096] The raw materials are configured according to the following mass formula: C: 0.25%; Mn: 0.38%; Si: 0.40%; Cr: 1.05%; Ni: 0.60%; Mo: 0.40%; Nb: 0.060%; Al: 0.030%; P≤0.020%; S≤0.005% and the balance of iron and inevitable impurity elements, carbon equivalent CE IIW = 0.63.

[0097] The raw materials are subjected to KR hot metal pretreatment, and the smelted hot metal is pre-desulfurized by KR to make the S content ≤0.050%

[0098] The molten iron is first preliminarily refined in a primary melting furnace and then subjected to LF refining in an LF refining furnace to obtain molten steel. The tapping temperature of the preliminary refining is 1600 °C, and the ending temperature of the LF refining is 1570 °C.

[0099] (2) Pour the molten steel into a slab.

[0100] The molten steel is poured into a slab by continuous slab casting. During the continuous casting process, the superheat of the tundish is controlled at 10 °C, and the overall temperature fluctuation range ≤ 10 °C. The cooling method during pouring is stacking slow cooling. The time of the stacking slow cooling is 40 h, and the termination temperature of the slow cooling is 25 °C.

[0101] (3) Subject the slab to controlled rolling, coiling, leveling, and heat treatment to obtain a bulletproof steel plate.

[0102] Heat the slab to 1150 °C for 5 h to make the temperature inside and outside the slab uniform. Subject the slab to rough rolling and finish rolling in sequence to obtain a controlled-rolled slab. Among them, the starting rolling temperature of the rough rolling is 1100 °C, the ending rolling temperature is 1000 °C, the starting rolling temperature of the finish rolling is 1000 °C, and the ending rolling temperature is 800 °C. The thickness of the obtained controlled-rolled slab is 4.5 mm. Coil the slab at 650 °C, perform slow cooling treatment after coiling, and then level the slab. Heat-treat the leveled slab at 860 °C for 15 min to obtain a quenched slab, and then perform low-temperature tempering treatment on the quenched slab at 200 °C for 2 h to obtain a bulletproof steel plate. Among them, water quenching is used for the heat treatment of quenching, and the water temperature is 20 °C.

[0103] Perform room-temperature tensile and low-temperature impact tests on the bulletproof steel plates prepared in Examples 1 to 3 and Comparative Examples 1 and 2 respectively. The test methods are carried out in accordance with GB / T 228.1 and GB / T 229 respectively, and the results are shown in Table 1. It can be seen from Table 1 that the hardness ranges of Examples 1 to 3 and Comparative Examples 1 and 2 are 480 - 520 HBW, the yield strength ≥ 1400, the tensile strength ≥ 1650 MPa, and the elongation ≥ 9%; the impact energy of the steel plates prepared in Examples 1 to 3 and Comparative Example 1 at -40 °C converted to full-size specimens > 30 J, and the impact energy of the steel plate prepared in Comparative Example 2 at -40 °C converted to full-size specimens < 30 J.

[0104] The bulletproof steel plates prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were subjected to cold bending along the rolling direction (RD) and the transverse direction (TD) respectively. The width of the cold-bent specimen was > 1000 mm, and the results are shown in Table 2. It can be seen from Table 2 that the steel plates prepared in Examples 1 to 3 can be bent 90° along the rolling direction (RD) and the transverse direction (TD) with a bending radius R ≤ 2.5 times the plate thickness. The steel plate prepared in Comparative Example 1 can be bent 90° along the rolling direction (RD) and the transverse direction (TD) with a bending radius R ≤ 4 times the plate thickness. However, when the bending radius R ≤ 2.5 times the plate thickness, cracks occurred during the 90° bending. This is because the high carbon content reduces the plasticity and toughness of the steel plate, thus deteriorating its cold bending performance. The steel plate prepared in Comparative Example 2 can be bent 90° along the rolling direction (RD) and the transverse direction (TD) with a bending radius R ≤ 4 times the plate thickness. However, when the bending radius R ≤ 2.5 times the plate thickness, cracks occurred during the 90° transverse (TD) bending. For the large-size cold-bent specimens of the steel plates prepared in Examples 1 to 3, as Figure 2 shown, it can be seen from Figure 2 that the steel plates prepared in Examples 1 to 3 can achieve good cold bending performance at a plate width of 1500 mm.

[0105] The bulletproof steel plates prepared in Examples 1 to 3 were subjected to target tests. Example 1 was carried out according to the Class I bulletproof requirements in STANAG 4569 standard, Example 2 was carried out according to the Class C bulletproof standard in GA164 standard, and Example 3 was carried out according to the Class B bulletproof standard in GA164 standard. The results are shown in Table 3. The results show that Examples 1 to 3 all meet the corresponding bulletproof standards. The target test specimens are as Figure 3 shown, and it can be seen from Figure 3 that the target test bullets did not penetrate the target plates after hitting the target plates, but only formed back protrusions on the back.

[0106] Table 1 Mechanical properties of high-strength thin plates prepared in Examples 1, 2, and 3

[0107]

[0108] * The size of the impact specimen for the 6.5 mm steel plate is 5 × 10 × 55 mm; the size of the impact specimens for the 4.1 mm, 4.5 mm, and 2.5 mm steel plates is 2.5 × 10 × 55 mm.

[0109] Table 2 Cold bending properties of high-strength thin plates prepared in Examples 1 and 2

[0110]

[0111] Table 3 Target test properties of high-strength thin plates prepared in Examples 1 to 3

[0112]

[0113] Although the present invention has been described in detail above with general descriptions, specific embodiments and experiments, modifications or improvements can be made thereto based on the present invention, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of the present invention claimed.

Claims

1. A bulletproof steel plate, characterized in that, The chemical composition of the bulletproof steel plate by mass percentage is as follows: C: 0.22% - 0.30%, Mn ≤ 1.00%, Si ≤ 0.40%, Cr: 0.50% - 1.50%, Ni: 0.50% - 1.50%, Mo: 0.15% - 0.50%, Nb: 0.01% - 0.10%, V: 0.03% - 0.15%, Ti: 0.01% - 0.10%, Cu: 0.03% - 0.25%, P ≤ 0.020%, S ≤ 0.010%, and the balance is Fe and inevitable impurity elements, and the carbon equivalent CE IIW = 0.6 - 0.

8.

2. A bulletproof steel plate according to claim 1, characterized in that The yield strength of the bulletproof steel plate is ≥1350 MPa, the tensile strength is ≥1600 MPa, the elongation after fracture is ≥8%, the impact energy KV2 of the V-notch impact specimen at -40 °C is ≥30 J, the Brinell hardness from the surface to the core is 480 - 520 HBW, and the thickness of the steel plate is 2.5 - 10 mm.

3. A bulletproof steel plate according to claim 1, characterized in that, Under the condition that the bending radius is 2.5 times the plate thickness, the bulletproof steel plate is bent 90° along the rolling direction and the transverse direction without cracks.

4. A bulletproof steel plate according to claim 1, characterized in that, The 2.5-mm-thick bulletproof steel plate can defend against 51B type 7.62-mm pistol bullets at a shooting distance of 10 m, the 4.1-mm-thick bulletproof steel plate can defend against ordinary bullets fired by a 56 type 7.62-mm light submachine gun at a shooting distance of 15 m, and the 6.5-mm-thick bulletproof steel plate can defend against M16 rifle 5.56×45-mm SS109 bullets at a shooting distance of 30 m.

5. A manufacturing method of a bulletproof steel plate according to any one of claims 1 to 4, characterized in that, It includes the following steps: S1. Smelt the raw materials to obtain molten steel. The raw materials are configured according to the following mass formula: C: 0.22% - 0.30%, Mn ≤ 1.00%, Si ≤ 0.40%, Cr: 0.50% - 1.50%, Ni: 0.50% - 1.50%, Mo: 0.15% - 0.50%, Nb: 0.01% - 0.10%, V: 0.03% - 0.15%, Ti: 0.01% - 0.10%, Cu: 0.03% - 0.25%, P ≤ 0.020%, S ≤ 0.010%, and the balance is Fe and inevitable impurity elements, and the carbon equivalent CE IIW = 0.6 - 0.8; S2. Pour the molten steel into a slab. S3. Subject the slab to controlled rolling, coiling, leveling, and heat treatment to obtain the bulletproof steel plate.

6. The manufacturing method of a bulletproof steel plate according to claim 5, characterized in that, In step S1, the smelting process includes primary melting and LF refining. The tapping temperature of the primary melting is 1600 - 1650 °C, and the ending temperature of the LF refining is 1570 - 1620 °C.

7. A manufacturing method of a bulletproof steel plate according to claim 5, characterized in that, In step S2, the molten steel is poured into a slab by means of slab continuous casting, and the superheat of the tundish in the continuous casting stage is controlled at 10 - 30 °C. The cooling method for the pouring is stacking slow cooling.

8. The manufacturing method of a bulletproof steel plate according to claim 5, characterized in that, In step S3, the specific process of the controlled rolling: Rough roll and finish roll the slab in sequence to obtain a controlled-rolled slab. Among them, the starting rolling temperature of the rough rolling is 1100 - 1150 °C, the ending rolling temperature is 1000 - 1050 °C, the starting rolling temperature of the finish rolling is 950 - 1000 °C, the ending rolling temperature is 800 - 850 °C, and the thickness of the obtained controlled-rolled slab is 2.5 - 10 mm.

9. The manufacturing method of a bulletproof steel plate according to claim 5, characterized in that, In step S3, the coiling temperature is 650 - 700 °C.

10. The manufacturing method of a bulletproof steel plate according to claim 5, characterized in that, In step S3, the specific process of the heat treatment is: Keep the leveled slab at 800 - 900 °C for quenching heat treatment to obtain a quenched slab, and then perform low-temperature tempering treatment on the quenched slab at 180 - 280 °C to obtain the bulletproof steel plate.

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