A method for producing low-density, high-strength, and high-toughness protective steel plates from continuously cast slabs

Abstract

This invention relates to a method for producing low-density, high-strength, and high-toughness protective steel plates from continuously cast billets, belonging to the field of metallurgy. The steel plate is an Fe-Mn-Al-C series austenitic low-density steel plate with an austenitic matrix supplemented by dispersed fine precipitated carbides, achieving high strength and high toughness, thus meeting the requirements for ballistic protection. The steel plate has a production thickness of 6-12 mm, a width of 1600-3000 mm, and a density of 6.75-7.05 g / cm³. 3 It has a density 7.85 g / cm³ higher than that of conventional steel. 3 The steel plate exhibits at least a 10% reduction in weight, good machinability and weldability, and excellent ballistic protection performance. A 6mm thick steel plate meets the NATO AEP STANAG 4569 standard Level I ballistic protection requirements, while a 12mm thick steel plate meets the NATO AEP STANAG 4569 standard Level II ballistic protection requirements. Production process: smelting—continuous casting—slow cooling—rolling—heat treatment—finishing—inspection—warehousing.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy, specifically relating to a low-density, high-strength, and high-toughness protective steel plate, which has good processing performance, welding performance, and ballistic protection performance. Background Technology

[0002] With rapid economic and industrial development, problems such as resource scarcity and environmental constraints are becoming increasingly apparent. Reducing energy consumption, minimizing environmental pollution, and conserving limited resources are crucial and urgent issues facing humanity today. Therefore, weight reduction is a key focus for various equipment manufacturers, especially those involved in steel applications such as automobiles, bridge engineering, offshore platforms, and shipbuilding.

[0003] There are two methods for reducing the weight of steel products: one is to reduce the weight of the material by increasing its strength. For example, the yield strength of high-strength steel plates, which are currently widely used, has increased from 690 MPa to a relatively stable 1100 MPa. While the strength of these high-strength steel plates has been improved, their impact toughness has decreased significantly. The other method is to add a certain proportion of alloying elements such as Al, Mn, and C to the steel to achieve weight reduction while ensuring strength and toughness. This type of steel is called low-density steel or lightweight steel, and it is still under development.

[0004] Low-density steel, based on its phase composition, includes Fe-Mn-Al-C type low-density steels such as ferritic steel, austenitic steel, ferritic-based dual-phase steel, and austenitic-based dual-phase steel. Compared with traditional high-strength steel, low-density high-strength steel has advantages such as good formability, fatigue resistance, and a higher work hardening rate. By controlling the microstructure, a multi-phase composite structure consisting of a hard matrix and austenite can be obtained, thus ensuring good strength and plasticity. The steel plates can be used in the manufacture of protective car bodies for special vehicles.

[0005] Currently, many research teams have conducted laboratory studies on low-density steel, mainly achieving improvements in material strength or toughness through different component ratios. Publication number CN112813356A discloses a 1500MPa ultra-high strength low-density steel and its preparation method. Ingots with a specific component ratio are obtained through a laboratory vacuum induction melting furnace. These ingots are then reheated and melted, cast into a steel plate mold of a certain thickness, and rapidly cooled to obtain a steel plate. The steel plate is then cold-rolled to obtain a 1500MPa ultra-high strength low-density steel plate. Publication number CN112760568A discloses a high-strength, high-toughness low-density steel and its preparation method. Ingots are obtained by smelting raw materials in a vacuum induction furnace at a certain mass percentage. These ingots are then forged to obtain smaller round bars or steel plates. At present, there are few reports on the large-scale production of low-density steel plates, and no reports have been found on the research or production of low-density, high-strength, and high-toughness protective steel plates. Summary of the Invention

[0006] In order to study the large-scale production of low-density / lightweight steel, this invention provides a method for producing low-density, high-strength, and high-toughness protective steel plates from continuously cast slabs. This method is of great significance for the lightweight development of special vehicles or equipment, especially special vehicles or equipment with bulletproof requirements.

[0007] The steel plate of this invention is preferably rolled on a heavy plate rolling mill and heat-treated in a continuous furnace, which is a mass production process for industrial applications.

[0008] The steel plate produced by this invention is an Fe-Mn-Al-C series austenitic low-density steel plate with an austenitic matrix and finely dispersed precipitated carbides, achieving high strength and high toughness, thus meeting the requirements for ballistic protection. The steel plate has a thickness of 6-12 mm, a width of 1600-3000 mm, and a density of 6.75-7.05 g / cm³. 3 It has a density 7.85 g / cm³ higher than that of conventional steel. 3 The steel plate exhibits at least a 10% reduction in thickness, good processing and welding properties, and excellent ballistic protection performance. A 6mm thick steel plate meets the NATO AEP STANAG 4569 standard Level I ballistic protection requirements, while a 12mm thick steel plate meets the NATO AEP STANAG 4569 standard Level II ballistic protection requirements. Specifically, steel plates with a thickness ≤10mm have a tensile strength ≥1050MPa and a V-impact value ≥30J at -40℃; steel plates with a thickness >10-12mm have a tensile strength ≥1000MPa and a V-impact value ≥20J at -40℃.

[0009] This invention uses the following chemical composition by mass percentage: C: 0.80–1.50%, Si: 0.10–0.30%, Mn: 17.00–25.00%, P: ≤0.015%, S: ≤0.003%, Al: 7.00–10.00%, Ni: 4.00–8.00%, Nb+Ti: 0.02–0.20%, with the balance being iron and unavoidable impurities. Molten steel is continuously cast into low-density steel plate billets of 150 mm or more. The billets are graded according to the YB / T 4003-2016 standard, requiring low-magnification quality requirements of segregation not exceeding Class B, grade 1.0, and porosity not exceeding grade 1.0. After hydrogen diffusion slow cooling, rolling, and heat treatment, the continuously cast billets are finished and sampled for inspection. Those that pass inspection are then stored in the warehouse. The preferred production process is as follows: KR→BOF→LF→RH→CCM→slab slow cooling→rolling→heat treatment→finishing→inspection→warehousing.

[0010] The specific technical solution of the present invention is as follows:

[0011] Methods for producing low-density, high-strength, and high-toughness protective steel plates from continuously cast slabs, including

[0012] I. Billet Preparation

[0013] (1) Smelting: Steel is smelted according to the chemical composition: C: 0.80~1.50%, Si: 0.10~0.30%, Mn: 17.00~25.00%, P: ≤0.015%, S: ≤0.003%, Al: 7.00~10.00%, Ni: 4.00~8.00%, Nb+Ti: 0.02~0.20%, with the balance being iron and unavoidable impurity elements;

[0014] The steelmaking process employs a clean steelmaking method, fully utilizing the thermodynamic conditions of low-temperature dephosphorization in the early stages of converter steelmaking. Slag removal and re-slag formation are carried out in the later stages of converter smelting to control the phosphorus content of the molten steel to ≤0.01%. The molten steel is refined using high-basicity white slag, and a steel-slag mixing technology is used during the refining process. While controlling P ≤0.015% and S ≤0.003%, the content of other residual elements is controlled to ensure Sb ≤0.02%, Sn ≤0.02%, and As ≤0.02%, with Sb+Sn+As+Bi+Pb ≤0.04%. Inclusion content is strictly controlled, with the sum of the A, B, C, and D inclusion ratings in the molten steel ≤3.5. Vacuum degassing is used, and argon gas is employed to agitate the molten steel, promoting the flotation of light materials, resulting in H: ≤0.0002%, O: ≤0.0010%, and N: ≤0.0040% in the molten steel.

[0015] Strict control of harmful elements such as Sb, Sn, and As in molten steel helps improve the impact toughness of steel plates; strict control of the H content in the material prevents the formation of white spots and avoids the formation of micro-cracks in the core during the cooling process of thin plates; controlling the O content in the material aims to control the content of inclusions in the material, and reducing the content of inclusions can effectively improve the overall performance of the material; N is a strong element for Ti and Nb, and the N content needs to be controlled at a low level to reduce the precipitation of micron-sized carbon and nitrogen compounds, which helps to improve the processing performance of the material.

[0016] (2) Continuous casting: Billets with a thickness of 150mm or more are continuously cast using a straight-arc continuous casting machine. During casting, the gap between the rollers in the fan-shaped section of the continuous casting machine is ensured to be within ±0.5mm. Dynamic light reduction is used in the horizontal section of the fan-shaped section of the continuous casting machine, with a reduction of 5-10mm, effectively improving center segregation and porosity. Argon gas is used for the entire casting process, with a constant casting speed. Weak water cooling is used in the arc-shaped section after the billet exits the crystallizer, and strong water cooling is used after passing the arc-shaped section to avoid the precipitation of large amounts of carbides during the slow cooling process of the billet, thereby reducing the risk of billet cracking. After the billet is cut, it undergoes slow cooling in a hydrogen reactor.

[0017] II. Heating and Rolling

[0018] (1) Heating: The temperature range of the preheating section is 650~950℃; the temperature range of the heating section is 1000~1210℃; the temperature range of the soaking section is 1200~1240℃; the heating time is ≥10×Hmin / mm, where H is the billet thickness in mm; and the billet is removed from the furnace.

[0019] (2) Rolling: According to the thickness specifications of the steel plates produced, Xunze steel rolling process;

[0020] For steel plates with a thickness of 6-8mm: the rolling process is adopted. The billet is descaled by high-pressure water and rolled a total of 8-16 times. The high-pressure water descaling is performed 2-3 times in the rolling passes before entering the coiling furnace. No descaling is performed in the rolling passes after entering the coiling furnace. The highest possible opening rolling temperature is adopted, with an opening rolling temperature ≥1100℃ and a final rolling temperature of 750-780℃ (below this final rolling temperature, the material will be difficult to deform during rolling). After rolling, the steel plate is straightened and then removed from the line. The removed steel plate is covered with other heated steel plates.

[0021] The rolling process for steel plates with a thickness greater than 8-12mm is as follows: A two-stage rolling process is adopted. The billet is descaled by high-pressure water. The roughing process is rolled 5-10 times to a thickness of 1.5-2.0 times that of the finished steel plate. The roughing process is descaled by high-pressure water 1-2 times. The initial rolling temperature of the roughing process is ≥1050℃, and the final rolling temperature is ≥850℃. After the roughing process, the steel plate is heated to 830-850℃ before the finish rolling process begins. The finish rolling process is rolled 3-8 times to a final rolling temperature of 750-780℃. The finish rolling process is descaled by high-pressure water 1 time. After the rolling, the steel plate is straightened and then slowly cooled on the line.

[0022] (2) Heat treatment: Hot-rolled steel plates are heat-treated to precipitate nano-scale carbides, thereby improving the strength of the material.

[0023] As one embodiment of the above method, the steel plate is produced with a thickness of 6-12 mm, a width of 1600-3000 mm, and a density of 6.75-7.05 g / cm³. 3 The microstructure of the steel plate is mainly austenite, supplemented by a small amount of precipitated carbides.

[0024] As one of the implementation methods described above, during the steel smelting stage, the vacuum treatment time is set to ≥20 min and the vacuum degree is set to 1 kPa-0.01 kPa to fully remove inclusions and light elements from the molten steel.

[0025] As one implementation of the above method, after the continuous casting billet is cut off, the billet temperature at the bottom of the line is ≥650℃ and the slow cooling time is ≥24h to complete the hydrogen diffusion slow cooling of the continuous casting billet.

[0026] As one of the implementation methods described above, the continuously cast billet is graded at low magnification according to the YB / T 4003-2016 standard, and the low magnification quality meets the requirements of segregation not exceeding Class B 1.0 grade and porosity not exceeding 1.0 grade.

[0027] As one implementation of the above method, in the heat treatment step, the heating temperature is set to 550-650℃, the holding time is 1-2 hours, and the steel plate is air-cooled to room temperature after being taken out of the furnace to promote the precipitation of nano-scale carbides in the microstructure.

[0028] As one implementation of the above method, in the smelting stage, the addition of Al blocks occurs after the molten steel undergoes silicon-calcium deoxidation, thereby reducing the presence of Al in the material as aluminum oxide.

[0029] As one implementation of the above method, the steel plate is straightened after the heat treatment to ensure that the flatness of the steel plate is ≤3mm / m. After straightening, the steel plate is plasma-trimmed and sampled for inspection, and then its appearance quality is checked and packaged according to product standards.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] This application discloses a method for producing low-density, high-strength, and high-toughness protective steel plates from continuously cast slabs. By using continuously cast slabs as the finished product, the production efficiency and yield of the material are improved. The quality of the finished steel plates is enhanced through strict control of harmful elements in the molten steel, control of the roll gap in the sector section of the continuous casting machine, and the adoption of light reduction operations.

[0032] This application discloses a method for producing low-density, high-strength, and high-toughness protective steel plates from continuously cast slabs. The continuous casting process employs a combination of constant casting speed, weak water cooling, and strong water cooling. The low-density steel in this invention is austenitic steel, which undergoes no significant microstructural transformation during continuous casting, ultimately resulting in a room-temperature austenitic structure. The alloy composition is designed to be austenitic, preventing phase transformation at room temperature and resulting in good slab plasticity. The strong water cooling process helps to slow down the segregation of alloying elements in the continuously cast slab, thereby improving the slab quality.

[0033] This application discloses a method for producing low-density, high-strength, and high-toughness protective steel plates from continuously cast slabs, representing the first industrial-scale mass production process for this type of high-strength steel. The steel plates have a density of 6.75–7.05 g / cm³, a thickness of 6–12 mm, and a width of 1600–3000 mm. The steel plates exhibit good machinability and weldability, and excellent ballistic protection performance. A 6 mm thick steel plate meets the Level I ballistic protection requirements of NATO AEP STANAG 4569 standard, while a 12 mm thick steel plate meets the Level II ballistic protection requirements of NATO AEP STANAG 4569 standard.

[0034] In the method for producing low-density, high-strength, and high-toughness protective steel plates from continuously cast slabs, different rolling processes are used for steel plates of different thicknesses. For steel plates with a thickness of 6-8 mm, a coil rolling process is used, with the highest possible initial rolling temperature and precise control of the final rolling temperature. For steel plates with a thickness of >8-30 mm, a two-stage rolling process is used. The roughing stage involves high-temperature initial rolling to improve the core density of the steel plate, while the finishing stage involves precise control of the initial rolling temperature, the initial rolling temperature, and the final rolling temperature, which is key to improving the material performance indicators.

[0035] In the manufacturing method of producing low-density, high-strength, and high-toughness protective steel plates from continuously cast slabs, the hot-rolled steel plates are heat-treated to effectively promote the precipitation of carbides (K-type carbides, which do not require slow cooling after rolling), thereby achieving precipitation strengthening. Attached Figure Description

[0036] Figure 1 This is the microstructure of a 12mm thick steel plate magnified 3000 times in an embodiment of the present invention. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to the embodiments. The embodiments are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0038] Low-density, high-strength, and high-toughness protective steel plates are produced using continuously cast slabs. The slabs are selected with Fe as the base element and contain the following components by mass percentage: C: 0.80–1.50%, Si: 0.10–0.30%, Mn: 17.00–25.00%, P: ≤0.015%, S: ≤0.003%, Al: 7.00–10.00%, Ni: 4.00–8.00%, Nb+Ti: 0.02–0.20%, and unavoidable impurities. Through a rational continuous casting process, slab heating regime, rolling process, and heat treatment regime, high-strength and high-toughness steel plates are obtained, exhibiting excellent processing and protective properties.

[0039] The present invention will be further described in detail below with reference to the embodiments.

[0040] Example 1

[0041] This embodiment uses a low-density, high-strength, and high-toughness protective steel plate with a thickness of 6mm and a width of 1900mm.

[0042] The raw materials were smelted and sequentially subjected to KR hot metal pretreatment, converter smelting, LF refining, and RH vacuum degassing to obtain high-purity molten steel. The RH ultimate vacuum time was 25 minutes. The molten steel was then continuously cast into 150*2000mm thick slabs using a straight-arc continuous casting machine. The superheat during continuous casting was 20-30℃, and a combination of constant casting speed, weak water cooling, and strong water cooling was employed, along with a light reduction technique. The slab composition was: H: 0.00008%, O: 0.0008%, N: 0.0021%, Sb: 0.0011%, Sn: 0.0017%, As: 0.0032%, and Sb+Sn+As+Bi+Pb: 0.0094%. The slab's low-magnification quality was: Class B, grade 0.5, with a central porosity grade of 0.5. The slab's final temperature was 705℃, and the cooling time was 28 hours.

[0043] The billet is heated in a walking beam furnace, with a preheating section temperature range of 650–950℃, a heating section temperature range of 1000–1210℃, and a soaking section temperature range of 1200–1240℃, for a total heating time of approximately 250 minutes. A rolling process is employed, with the billet undergoing high-pressure water descaling and a total of 15 rolling passes: 6 flat rolling passes and 9 coil rolling passes. The thickness of the rolled steel plate entering the coiling furnace is four times the finished product thickness. High-pressure water descaling is performed in the second and fifth rolling passes, with an initial rolling temperature of 1110℃ and a final rolling temperature of 756℃. After rolling, the steel plate is straightened by a hot straightener and then removed from the line. Other heated steel plates, with a temperature of approximately 150℃, are used as a cover. After cooling, the steel plate undergoes heat treatment in a continuous furnace at a heating temperature of 630℃ for 1.5 hours. After exiting the furnace, the steel plate is air-cooled to room temperature. After heat treatment, the steel plate is subjected to force straightening to ensure that the flatness of the steel plate is ≤3mm / m; after straightening, the steel plate is plasma-cut and sampled for inspection, and the appearance quality is checked and packaged according to product standards.

[0044] The 6mm thick steel plate obtained by the above production process has excellent surface quality, and its performance is shown in Table 1.

[0045] Example 2

[0046] This embodiment uses a low-density, high-strength, and high-toughness protective steel plate with a thickness of 12mm and a width of 2000mm.

[0047] The raw materials were smelted and sequentially subjected to KR hot metal pretreatment, converter smelting, LF refining, and RH vacuum degassing to obtain high-purity molten steel. The RH ultimate vacuum time was 28 minutes. The molten steel was then continuously cast into 150*2100mm thick slabs using a straight-arc continuous casting machine. During the continuous casting process, the superheat was 20-30℃, constant casting speed was used, and a combination of weak and strong water cooling was employed, along with a light reduction technique. The slab composition was: H: 0.00009%, O: 0.0007%, N: 0.0023%, Sb: 0.0012%, Sn: 0.0018%, As: 0.0033%, and Sb+Sn+As+Bi+Pb: 0.0098%. The slab's low-magnification quality was: Class B, grade 0.5, with a central porosity of grade 1.0. The slab's final temperature was 680℃, and the cooling time was 30 hours.

[0048] The billet is heated in a walking beam furnace, with a preheating section temperature range of 650–950℃, a heating section temperature range of 1000–1210℃, and a soaking section temperature range of 1200–1240℃, for a total heating time of approximately 260 minutes. A two-stage rolling process is employed. The billet undergoes high-pressure water descaling, followed by seven passes in the roughing process, with a target thickness of 24 mm. The second and fourth passes of the roughing process involve high-pressure water descaling. The initial roughing temperature is 1080℃, and the final rolling temperature is 870℃. After roughing, the steel plate is allowed to cool to 840℃ before finish rolling, which involves six passes in the finish rolling process, with a final rolling temperature of 754℃. The first pass of the finish rolling process involves high-pressure water descaling. The rolled steel plate is then straightened by a hot straightener and slowly cooled in a stack at 200℃. After cooling, the steel plate undergoes heat treatment in a continuous furnace at 600℃ for 1.8 hours. After exiting the furnace, the steel plate is air-cooled to room temperature. After heat treatment, the steel plate is subjected to force straightening to ensure that the flatness of the steel plate is ≤3mm / m; after straightening, the steel plate is plasma-cut and sampled for inspection, and the appearance quality is checked and packaged according to product standards.

[0049] The 12mm thick steel plate obtained by the above production process has excellent surface quality, and its performance is shown in Table 1.

[0050] Table 1 Performance indicators of steel plates in Examples 1-2

[0051]

[0052]

[0053] Note: An auxiliary specimen was used for the impact performance test of the V-notch steel plate. The specimen size was 5mm×10mm×55mm.

[0054] In addition to the above embodiments, the present invention also includes other embodiments. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.

Claims

1. A method for producing low-density, high-strength, and high-toughness protective steel plates from continuously cast slabs, characterized in that: include Smelting: Steel is smelted according to the following chemical composition: C: 0.80-1.50%, Si: 0.10-0.30%, Mn: 17.00-25.00%, P: ≤0.015%, S: ≤0.003%, Al: 7.00-10.00%, Ni: 4.00-8.00%, Nb+Ti: 0.02-0.20%, with the balance being iron and unavoidable impurity elements. The steelmaking process employs a clean steelmaking method, fully utilizing the thermodynamic conditions of early-stage low-temperature dephosphorization during converter steelmaking. Slag removal and re-slag formation are performed in the later stages of converter smelting to control the phosphorus content of the molten steel to ≤0.01%. The molten steel is refined using high-basicity white slag, and a steel-slag mixing technique is used during tapping. While controlling P ≤0.015% and S ≤0.003%, the content of other residual elements is controlled to ensure Sb ≤0.02%, Sn ≤0.02%, and As ≤0.02%, with Sb+Sn+As+Bi+Pb ≤0.04%. Inclusion content is strictly controlled, with the sum of the A, B, C, and D inclusion ratings in the molten steel ≤3.

5. Vacuum degassing is used, and the molten steel is stirred with argon gas to ensure H: ≤0.0002%, O: ≤0.0010%, and N: ≤0.0040%. Continuous casting: Use a straight arc continuous casting machine to continuously cast billets with a thickness of 150mm or more. During casting, ensure that the gap between the arc rolls in the fan-shaped section of the continuous casting machine is within ±0.5mm. Use dynamic light pressure in the horizontal section of the fan-shaped section of the continuous casting machine, with a light pressure reduction of 5-10mm. Use argon gas protection for casting throughout the process and maintain a constant casting speed. Use weak water cooling in the arc section after the continuous casting billet exits the crystallizer, and use strong water cooling after passing the arc section. After the billet is cut off, use hydrogen reactor slow cooling. Heating: Preheating section temperature range 650~950℃; heating section temperature range 1000~1210℃; soaking section temperature range 1200~1240℃; heating time ≥10min / mm×H, where H is the billet thickness in mm; unloading; Rolling: The rolling process is set according to the thickness specifications of the steel plates to be produced; For steel plates with a thickness of 6-8mm: the rolling process is adopted. The billet is descaled by high pressure water and rolled a total of 8-16 times. The high pressure water descales 2-3 times in the rolling passes before entering the coiling furnace. No descaling is performed in the rolling passes after entering the coiling furnace. The initial rolling temperature is ≥1100℃ and the final rolling temperature is 750-780℃. After rolling, the steel plate is straightened and then removed from the line. The removed steel plate is covered with other heated steel plates. The rolling process for steel plates with a thickness greater than 8 mm and less than or equal to 12 mm is as follows: A two-stage rolling process is adopted. The billet is descaled by high-pressure water. The roughing process is rolled 5 to 10 times to a thickness of 1.5 to 2.0 times that of the finished steel plate. The roughing process is descaled by high-pressure water 1 to 2 times. The initial rolling temperature of the roughing process is ≥1050℃ and the final rolling temperature is ≥850℃. After the roughing process, the steel plate is heated to 830 to 850℃ before the finish rolling process begins. The finish rolling process is rolled 3 to 8 times to a final rolling temperature of 750 to 780℃. The finish rolling process is descaled by high-pressure water 1 time. After the rolling process, the steel plate is straightened and then slowly cooled on the line. Heat treatment: Hot-rolled steel plates undergo heat treatment to precipitate nano-sized carbides.

2. The method according to claim 1, characterized in that: The steel plates are produced with a thickness of 6-12mm, a width of 1600-3000mm, and a density of 6.75~7.05g / cm³. 3 The microstructure of the steel plate is mainly austenite, supplemented by a small amount of precipitated carbides.

3. The method according to claim 2, characterized in that: 6mm thick steel plates meet the NATO AEP STANAG 4569 standard Level I ballistic protection requirements, and 12mm thick steel plates meet the NATO AEP STANAG 4569 standard Level II ballistic protection requirements; among them, steel plates with a thickness of ≤10mm have a tensile strength ≥1050MPa and a V-shaped impact value ≥30J at -40℃; steel plates with a thickness greater than 10mm and less than or equal to 12mm have a tensile strength ≥1000MPa and a V-shaped impact value ≥20J at -40℃.

4. The method according to claim 1, characterized in that: During the steelmaking stage, the vacuum treatment time is set to ≥20 min during vacuum degassing, and the vacuum degree is set to 1 kPa-0.01 kPa.

5. The method according to claim 1, characterized in that: After the continuous casting billet is cut off, the billet temperature is ≥650℃ and the slow cooling time is ≥24h to complete the hydrogen diffusion slow cooling of the continuous casting billet.

6. The method according to claim 1, characterized in that: The continuously cast billets are graded at low magnification according to the YB / T 4003-2016 standard. The quality at low magnification meets the requirements that segregation is no greater than Class B 1.0 and porosity is no greater than 1.

0.

7. The method according to claim 1, characterized in that: In the heat treatment step, the heating temperature is set to 550-650℃, the holding time is 1-2 hours, and the steel plate is air-cooled to room temperature after being taken out of the furnace.

8. The method according to claim 1, characterized in that: In the smelting stage, the Al blocks are added after the molten steel has undergone silicon-calcium deoxidation.

9. The method according to claim 1, characterized in that: After the heat treatment, the steel plate is straightened to ensure that the flatness of the steel plate is ≤3mm / m.

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