A hot-pressed ultra-high strength steel for battery casing and its preparation method

Abstract

This invention discloses a hot-pressed ultra-high-strength steel for battery casings and its preparation method, belonging to the technical field of steel for battery casings. The hot-pressed ultra-high-strength steel employs a high-manganese, low-carbon composition system and a specific Nb, V composite microalloying design in its chemical composition design. This effectively reduces component segregation and stress concentration, improves the uniformity and purity of the steel structure, and achieves high mechanical strength. Through process optimization, a self-healing regulator and organically modified zinc oxide nanospheres are introduced into the passivation solution, improving the uniformity and adhesion of the passivation film. This effectively avoids the problem of easy cracking or peeling of the passivation film in traditional processes, enabling the steel to maintain high strength while also possessing excellent corrosion resistance, significantly extending the service life of the battery casing and providing a solid guarantee for the safety and reliability of new energy vehicle batteries.

Description

Technical Field

[0001] This invention belongs to the technical field of steel for battery casings, specifically relating to a hot-pressed ultra-high strength steel for battery casings and its preparation method. Background Technology

[0002] As a crucial component of the battery structure, the quality of the materials used in the battery casing directly affects the battery's safety and lifespan. With the rapid development of the new energy vehicle industry, the requirements for battery casing materials are becoming increasingly stringent. They not only need to possess high strength and good formability, but also need to maintain stable performance under extreme conditions.

[0003] Battery casing steel has good plasticity and formability, but generally has low carbon content and low strength. In the prior art, the battery casing steel in patent application CN 120830041 A incorporates a high content of manganese into the iron matrix, producing a "solid solution strengthening" effect and achieving high mechanical strength. However, this design is a double-edged sword; Mn is an easily oxidized element, and after oxidation, it forms granular oxides on the steel surface, resulting in poor corrosion resistance and stress defects, affecting the mechanical strength of the steel and the overall safety of the battery. Passivation is a common method to improve the corrosion resistance of battery steel casings. It is low-cost and simple to process; however, due to the numerous tiny manganese corrosion sites on the steel surface and the low bonding strength with traditional passivation films, the passivation film cracks or peels off, making it difficult to achieve ideal corrosion resistance.

[0004] Therefore, how to improve the corrosion resistance and service life of battery casing steel while ensuring high strength has become an urgent technical problem to be solved in the field of battery casing steel technology. Summary of the Invention

[0005] To address the problems existing in the background art, the present invention provides a hot-pressed ultra-high strength steel for battery casings and its preparation method, which enables the steel to maintain high strength while also having excellent corrosion resistance, thus significantly extending the service life of the battery casing.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A hot-pressed ultra-high strength steel for battery casings contains the following chemical composition by mass percentage: C: 0.002~0.004%, Si: 0.01~0.02%, Mn: 0.48~0.52%, Als: 0.02~0.04%, V: 0.10~0.20%, Nb: 0.02~0.03%, Ti: 0.005~0.015%, B: 0.0012~0.0020%, P: ≤0.015%, S: ≤0.08%, while satisfying 0.60%≤Mn+V≤0.68%, Nb / (C+N)≥2, with the balance being Fe and unavoidable impurities.

[0007] This invention features a specially designed Mn content to ensure the mechanical strength of the steel. Higher manganese content increases the likelihood of component segregation and cracking during smelting and continuous casting. The use of Nb and V composite microalloying ensures an appropriate amount of Nb in the steel, effectively fixing C and N content, inhibiting austenite recrystallization, refining austenite grains, and mitigating the adverse effects of excessive Mn on the casting performance of molten steel. Simultaneously, V, as a strong carbide-forming element, preferentially combines with carbon and nitrogen in the steel to form stable nanoscale carbonitrides, reducing the carbon content in the matrix, refining the original high-manganese austenite grains, and improving the mechanical strength of the steel. Furthermore, the dispersed distribution of nitrides reduces the initiation of cracks and stress defects, enhancing the corrosion resistance and stability of the steel.

[0008] The present invention also provides a method for preparing hot-pressed ultra-high strength steel for battery casings, which includes the following steps: smelting molten iron, continuous casting, hot rolling, coiling, pickling, cold rolling, annealing, leveling and passivation.

[0009] Furthermore, the preparation method of the passivation solution in the passivation treatment includes the following: by weight percentage, 2-3% sodium bisulfite, 3-5% titanium oxynitrate, 4-6% citric acid, 3.5-4.5% potassium phosphate, 1.5-2.5% organically modified zinc oxide nanospheres, 3-5% self-healing regulator and 0.5-2% tetraethyl orthosilicate are added to the balance water, heated to 50-60℃, and stirred for 5-10 minutes to obtain the passivation solution.

[0010] Furthermore, the preparation process of the self-healing regulator includes the following steps: A1. Mix secondary alcohol polyoxyethylene ether, polyethylene glycol, sodium dodecyl sulfonate and water in a mass ratio of 6~10:4~6:2~3:100 and stir for 8~12 min to obtain a premixed solution; A2. Add tetramethyldisiloxane dropwise to the premixed solution. The amount of tetramethyldisiloxane added is 8-12% of the mass of the premixed solution. The dropwise addition time is 3-10 min. After the dropwise addition is complete, adjust the pH to 6.0-7.0, heat to 40-50℃, react for 1.5-2.5 h, and cool to room temperature to obtain the self-healing regulator.

[0011] The preparation method of organically modified zinc oxide nanospheres includes the following steps: B1. Disperse nano zinc oxide in water, surface activate it with a tertiary aminosilane coupling agent, and then quaternize it with tetramethylammonium bromide. Remove the dispersant to obtain quaternized zinc oxide particles, wherein the mass ratio of nano zinc oxide, N,N-diethylaminopropyltrimethoxysilane and tetramethylammonium bromide is 100:1~2:4~6. B2. Quaternized zinc oxide particles are added to an aqueous solution of acrylate, with a mass ratio of quaternized zinc oxide particles to acrylate of 100:8~12. After heating and stirring to carry out the reaction, the mixture is centrifuged, dried, and sieved to obtain organically modified zinc oxide nanospheres.

[0012] Furthermore, in the molten iron smelting and continuous casting, the blast furnace molten iron KR is first stirred and desulfurized, and then it undergoes converter smelting, degassing treatment, LF furnace refining and billet casting, wherein the final temperature of the converter is 1640~1660℃.

[0013] Furthermore, the hot rolling heating temperature is 1200~1250℃, the hot rolling final rolling temperature is controlled at 860~900℃, and the coiling temperature is 580~620℃.

[0014] Furthermore, the reduction rate during cold rolling is 78-82%, and the surface roughness of the steel plate is controlled to be ≤0.6μm.

[0015] Furthermore, during the annealing process, a full hydrogen protective atmosphere is used, the annealing temperature range is 700~740℃, and the holding time is 100~200s.

[0016] Furthermore, the passivation process is as follows: after degreasing the steel plate, it is treated in a passivation solution at 50~60℃ for 90~150s, then rinsed clean with water and dried.

[0017] This application has the following beneficial effects: 1. This invention effectively reduces component segregation and stress concentration by designing the chemical composition and adjusting the production process, thereby improving the uniformity and purity of the steel structure and achieving high mechanical properties for battery casing steel. By introducing a self-healing regulator and organically modified zinc oxide nanospheres into the passivation solution, the uniformity and adhesion of the passivation film are improved, effectively avoiding the problem of easy cracking or peeling of the passivation film in traditional processes. This allows the steel to maintain high strength while also possessing excellent corrosion resistance and stability, thus meeting the performance requirements in high humidity and corrosive environments and significantly extending the service life of the battery casing.

[0018] 2. By adopting a high-manganese, low-carbon composition system and a specific Nb, V composite microalloying design, it can enhance mechanical strength while avoiding the formation of large and concentrated stress defects in corrosive environments, thus ensuring the mechanical strength and stability of the formed material. Sodium bisulfite and titanium oxynitrate in the passivation solution can promote the rapid formation of the passivation film, while citric acid and potassium phosphate enhance the stability and durability of the film. This multi-component passivation solution design can effectively avoid micro-dispersed stress defects.

[0019] 3. The self-healing regulator obtained by using a specific ratio of secondary alcohol polyoxyethylene ether, polyethylene glycol, and sodium dodecyl sulfonate can not only form a cross-linked structure with other components in the passivation film, improving the density and uniformity of the film, but also achieve local self-repair when subjected to external corrosion or minor damage. In the preparation of organically modified zinc oxide nanospheres, the activation treatment of tertiary amine silane coupling agent introduces tertiary amine groups, and the quaternization reaction of tetramethylammonium bromide ultimately introduces bisquaternary ammonium salt groups, giving the nano zinc oxide high polarity and dispersibility. At the same time, it makes the surface of the nano zinc oxide carry hydrophobic long-chain alkyl groups, avoiding the sedimentation of the nano zinc oxide and ensuring the suspension stability of the passivation solution. In addition, by grafting an active matrix, the bonding strength between the passivation film and the metal surface can be improved. After loading the self-healing regulator onto the organically modified zinc oxide nanospheres, it can target weak sites for directional repair, prevent and inhibit the formation of corrosion sites on the steel surface, and achieve targeted repair and long-term corrosion protection. Attached Figure Description

[0020] Figure 1 This is a comparative trend chart showing the tensile strength retention rate of the hot-pressed ultra-high-strength steel used for battery casings prepared in Examples 1-5 and Comparative Examples 1-5 of the present invention. Detailed Implementation

[0021] The present application will be further described in detail below with reference to the embodiments.

[0022] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0023] Example 1 This embodiment provides a hot-pressed ultra-high strength steel for battery casings, the chemical composition and mass percentage of which are as follows: C: 0.003%, Si: 0.015%, Mn: 0.50%, Als: 0.03%, V: 0.14%, Nb: 0.02%, Ti: 0.009%, B: 0.0016%, P: 0.011%, S: 0.06%, N: 0.006%, with the balance being Fe and unavoidable impurities; It is prepared by the following steps: molten iron smelting, continuous casting, hot rolling, coiling, pickling, cold rolling, annealing, leveling and passivation; In the process of molten iron smelting and continuous casting, blast furnace molten iron is first desulfurized using the KR method, and then smelted in a converter, degassed, refined in an LF furnace, and cast into billets. The final temperature of the converter is 1650℃. In hot rolling, the heating temperature is 1230℃, and the final hot rolling temperature is 880℃; The winding temperature during winding is 600℃; During pickling, the pickling solution is 10% hydrochloric acid, and the pickling time is 8 minutes. During the cold rolling process, the reduction rate is 80%, and the surface roughness of the steel plate is controlled to be ≤0.6μm; During the annealing process, a full hydrogen protective atmosphere is used, the annealing temperature range is 720℃, and the holding time is 150s; During leveling, the leveling elongation rate is controlled at 0.8%; The passivation process is as follows: After degreasing the steel plate, it is treated in a passivation solution at 55℃ for 120 seconds, then rinsed with water and dried. The passivation solution is prepared by adding the following ingredients by weight percentage: 2.5% sodium bisulfite, 4% titanium oxynitrate, 5% citric acid, 4% potassium phosphate, 2% organic modified zinc oxide nanospheres, 4% self-healing regulator and 1% tetraethyl orthosilicate to the remaining water, heating to 55°C and stirring for 8 minutes to obtain the passivation solution. The preparation process of the self-healing regulator includes the following steps: A1. Mix secondary alcohol polyoxyethylene ether, polyethylene glycol, sodium dodecyl sulfonate and water in a mass ratio of 8:5:2.5:100 and stir for 10 min to obtain a premixed solution; A2. Tetramethyldisiloxane was added dropwise to the premixed solution at a rate of 10% of the mass of the premixed solution over a period of 5 minutes. After the addition was complete, the pH was adjusted to 6.0-7.0, the solution was heated to 45°C, and the reaction was carried out for 2 hours. The solution was then cooled to room temperature to obtain the self-healing regulator. The preparation method of organically modified zinc oxide nanospheres includes the following steps: B1. Disperse zinc oxide nanoparticles with a particle size range of 5~25nm in water, surface activate them with a tertiary aminosilane coupling agent, and then quaternize them with tetramethylammonium bromide. Remove the dispersant to obtain quaternized zinc oxide particles, wherein the mass ratio of zinc oxide nanoparticles, N,N-diethylaminopropyltrimethoxysilane and tetramethylammonium bromide is 100:1.5:5. B2. Quaternized zinc oxide particles were added to an aqueous solution of methacrylate, with a mass ratio of quaternized zinc oxide particles to methacrylate of 100:10. An initiator was added, and the mixture was heated to 60°C. The mixture was stirred and reacted, then centrifuged, dried, and sieved to obtain organically modified zinc oxide nanospheres.

[0024] Example 2 This embodiment provides a hot-pressed ultra-high strength steel for battery casings, the chemical composition and mass percentage of which are as follows: C: 0.004%, Si: 0.01%, Mn: 0.48%, Als: 0.04%, V: 0.14%, Nb: 0.025%, Ti: 0.015%, B: 0.0012%, P: 0.010%, S: 0.06%, N: 0.008%, with the balance being Fe and unavoidable impurities; It is prepared by the following steps: molten iron smelting, continuous casting, hot rolling, coiling, pickling, cold rolling, annealing, leveling and passivation; In the process of molten iron smelting and continuous casting, blast furnace molten iron is first desulfurized using the KR method, and then smelted in a converter, degassed, refined in an LF furnace, and cast into billets. The final temperature of the converter is 1640℃. In hot rolling, the heating temperature is 1200℃, and the final hot rolling temperature is 860℃; The winding temperature during winding is 580℃; During pickling, the pickling solution is 10% hydrochloric acid, and the pickling time is 5 minutes. During the cold rolling process, the reduction rate is 78%, and the surface roughness of the steel plate is controlled to be ≤0.6μm; During the annealing process, a full hydrogen protective atmosphere is used, the annealing temperature range is 700℃, and the holding time is 200s; During leveling, the leveling elongation rate is controlled at 0.5%; The passivation process is as follows: After degreasing the steel plate, it is treated in a passivation solution at 50°C for 150 seconds, then rinsed with water and dried.

[0025] The passivation solution is prepared by adding the following ingredients by weight percentage: 2% sodium bisulfite, 3% titanium oxynitrate, 4% citric acid, 3.5% potassium phosphate, 1.5% organically modified zinc oxide nanospheres, 3% self-healing regulator and 0.5% tetraethyl orthosilicate to the remaining water, heating to 50°C and stirring for 10 minutes to obtain the passivation solution. The preparation process of the self-healing regulator includes the following steps: A1. Mix secondary alcohol polyoxyethylene ether, polyethylene glycol, sodium dodecyl sulfonate and water in a mass ratio of 6:4:2:100 and stir for 8 minutes to obtain a premixed solution; A2. Tetramethyldisiloxane was added dropwise to the premixed solution at a rate of 8% of the mass of the premixed solution over a period of 3 minutes. After the addition was complete, the pH was adjusted to 6.0-7.0, the mixture was heated to 40°C, and the reaction was carried out for 2.5 hours. The mixture was then cooled to room temperature to obtain the self-healing regulator. The preparation method of organically modified zinc oxide nanospheres includes the following steps: B1. Disperse zinc oxide nanoparticles with a particle size range of 5~25nm in water, surface activate them with a tertiary aminosilane coupling agent, and then quaternize them with tetramethylammonium bromide. Remove the dispersant to obtain quaternized zinc oxide particles, wherein the mass ratio of zinc oxide nanoparticles, N,N-diethylaminopropyltrimethoxysilane and tetramethylammonium bromide is 100:1:4. B2. Quaternized zinc oxide particles were added to an aqueous solution of methacrylate, with a mass ratio of quaternized zinc oxide particles to methacrylate of 100:8. An initiator was added, and the mixture was heated to 50°C and stirred to react. After the reaction was completed, the mixture was centrifuged, dried, and sieved to obtain organically modified zinc oxide nanospheres.

[0026] Example 3 This embodiment provides a hot-pressed ultra-high strength steel for battery casings, the chemical composition and mass percentage of which are as follows: C: 0.003%, Si: 0.02%, Mn: 0.52%, Als: 0.04%, V: 0.13%, Nb: 0.025%, Ti: 0.015%, B: 0.002%, P: 0.011%, S: 0.06%, N: 0.008%, with the balance being Fe and unavoidable impurities; It is prepared by the following steps: molten iron smelting, continuous casting, hot rolling, coiling, pickling, cold rolling, annealing, leveling and passivation; In the process of molten iron smelting and continuous casting, blast furnace molten iron is first desulfurized using the KR method, and then smelted in a converter, degassed, refined in an LF furnace, and cast into billets. The final temperature of the converter is 1660℃. In hot rolling, the heating temperature is 1250℃, and the final hot rolling temperature is 900℃; The winding temperature during winding is 620℃; In the pickling process, the pickling solution is 10% hydrochloric acid by mass, and the pickling time is 10 minutes. During the cold rolling process, the reduction rate is 82%, and the surface roughness of the steel plate is controlled to be ≤0.6μm; During the annealing process, a full hydrogen protective atmosphere is used, the annealing temperature range is 740℃, and the holding time is 100s; During leveling, the leveling elongation rate is controlled at 1.2%; The passivation process is as follows: After degreasing the steel plate, it is treated in a passivation solution at 60℃ for 90 seconds, then rinsed with water and dried. The passivation solution is prepared by adding the following ingredients by weight percentage: 3% sodium bisulfite, 5% titanium nitrate, 6% citric acid, 4.5% potassium phosphate, 2.5% organically modified zinc oxide nanospheres, 5% self-healing regulator and 2% tetraethyl orthosilicate to the remaining water, heating to 60°C and stirring for 5 minutes to obtain the passivation solution. The preparation process of the self-healing regulator includes the following steps: A1. Mix secondary alcohol polyoxyethylene ether, polyethylene glycol, sodium dodecyl sulfonate and water in a mass ratio of 10:6:3:100 and stir for 12 min to obtain a premixed solution; A2. Tetramethyldisiloxane was added dropwise to the premixed solution at a concentration of 12% of the premixed solution mass over a period of 10 minutes. After the addition was complete, the pH was adjusted to 6.0-7.0, the mixture was heated to 50°C, reacted for 1.5 hours, and then cooled to room temperature to obtain the self-healing regulator. The preparation method of organically modified zinc oxide nanospheres includes the following steps: B1. Disperse zinc oxide nanoparticles with a particle size range of 5~25nm in water, surface activate them with a tertiary aminosilane coupling agent, and then quaternize them with tetramethylammonium bromide. Remove the dispersant to obtain quaternized zinc oxide particles, wherein the mass ratio of zinc oxide nanoparticles, N,N-diethylaminopropyltrimethoxysilane and tetramethylammonium bromide is 100:2:6. B2. Quaternized zinc oxide particles were added to an aqueous solution of methacrylate at a mass ratio of 100:12. The mixture was heated to 70°C, an initiator was added, and the mixture was stirred to react. After the reaction was completed, the mixture was centrifuged, dried, and sieved to obtain organically modified zinc oxide nanospheres.

[0027] Example 4 This embodiment provides a hot-pressed ultra-high strength steel for battery casings, the chemical composition and mass percentage of which are as follows: C: 0.002%, Si: 0.02%, Mn: 0.51%, Als: 0.03%, V: 0.10%, Nb: 0.03%, Ti: 0.005%, B: 0.0018%, P: 0.013%, S: 0.07%, N: 0.006%, with the balance being Fe and unavoidable impurities; It is prepared by the following steps: molten iron smelting, continuous casting, hot rolling, coiling, pickling, cold rolling, annealing, leveling and passivation; In the process of molten iron smelting and continuous casting, blast furnace molten iron is first desulfurized using the KR method, and then smelted in a converter, degassed, refined in an LF furnace, and cast into billets. The final temperature of the converter is 1645℃. In hot rolling, the heating temperature is 1220℃, and the final hot rolling temperature is 880℃; The winding temperature during winding is 590℃; In the pickling process, the pickling solution is 10% hydrochloric acid, and the pickling time is 7 minutes. During the cold rolling process, the reduction rate is 79%, and the surface roughness of the steel plate is controlled to be ≤0.6μm; During the annealing process, a full hydrogen protective atmosphere is used, the annealing temperature range is 725℃, and the holding time is 180s; During leveling, the leveling elongation rate is controlled at 0.8%; The passivation process is as follows: After degreasing the steel plate, it is treated in a passivation solution at 55℃ for 100 seconds, then rinsed with water and dried. The passivation solution is prepared by adding the following ingredients by weight percentage: 2% sodium bisulfite, 5% titanium oxynitrate, 6% citric acid, 3.5% potassium phosphate, 2% organic modified zinc oxide nanospheres, 3% self-healing regulator and 1% tetraethyl orthosilicate to the remaining water, heating to 55°C and stirring for 10 min to obtain the passivation solution. The preparation process of the self-healing regulator includes the following steps: A1. Mix secondary alcohol polyoxyethylene ether, polyethylene glycol, sodium dodecyl sulfonate and water in a mass ratio of 8:5:2:100 and stir for 10 min to obtain a premixed solution; A2. Tetramethyldisiloxane was added dropwise to the premixed solution at a concentration of 8% of the premixed solution mass over a period of 3 minutes. After the addition was complete, the pH was adjusted to 6.0-7.0, the mixture was heated to 45°C, reacted for 2 hours, and then cooled to room temperature to obtain the self-healing regulator. The preparation method of organically modified zinc oxide nanospheres includes the following steps: B1. Disperse zinc oxide nanoparticles with a particle size range of 5~25nm in water, surface activate them with a tertiary aminosilane coupling agent, and then quaternize them with tetramethylammonium bromide. Remove the dispersant to obtain quaternized zinc oxide particles, wherein the mass ratio of zinc oxide nanoparticles, N,N-diethylaminopropyltrimethoxysilane and tetramethylammonium bromide is 100:1:5. B2. Quaternized zinc oxide particles were added to an aqueous solution of methacrylate, with a mass ratio of quaternized zinc oxide particles to methacrylate of 100:10. An initiator was added, and the mixture was heated to 60°C and stirred to react. After the reaction was completed, the mixture was centrifuged, dried, and sieved to obtain organically modified zinc oxide nanospheres.

[0028] Example 5 This embodiment provides a hot-pressed ultra-high strength steel for battery casings, the chemical composition and mass percentage of which are as follows: C: 0.004%, Si: 0.012%, Mn: 0.48%, Als: 0.02%, V: 0.20%, Nb: 0.02%, Ti: 0.015%, B: 0.0015%, P: 0.015%, S: 0.08%, N: 0.006%, with the balance being Fe and unavoidable impurities; It is prepared by the following steps: molten iron smelting, continuous casting, hot rolling, coiling, pickling, cold rolling, annealing, leveling and passivation; In the process of molten iron smelting and continuous casting, blast furnace molten iron is first desulfurized using the KR method, and then smelted in a converter, degassed, refined in an LF furnace, and cast into billets. The final temperature of the converter is 1660℃. In hot rolling, the heating temperature is 1250℃, and the final hot rolling temperature is 900℃; The winding temperature during winding is 620℃; During pickling, the pickling solution is 10% hydrochloric acid, and the pickling time is 5 minutes. During the cold rolling process, the reduction rate is 82%, and the surface roughness of the steel plate is controlled to be ≤0.6μm; During the annealing process, a full hydrogen protective atmosphere is used, the annealing temperature range is 740℃, and the holding time is 100s; During leveling, the leveling elongation rate is controlled at 1.0%; The passivation process is as follows: After degreasing the steel plate, it is treated in a passivation solution at 55℃ for 90 seconds, then rinsed with water and dried. The passivation solution is prepared by adding the following ingredients by weight percentage: 2% sodium bisulfite, 5% titanium oxynitrate, 4% citric acid, 4.5% potassium phosphate, 2% organically modified zinc oxide nanospheres, 3% self-healing regulator and 0.5% tetraethyl orthosilicate to the remaining water, heating to 60°C and stirring for 5 minutes to obtain the passivation solution. The preparation process of the self-healing regulator includes the following steps: A1. Mix secondary alcohol polyoxyethylene ether, polyethylene glycol, sodium dodecyl sulfonate and water in a mass ratio of 6:4:2:100 and stir for 10 min to obtain a premixed solution; A2. Tetramethyldisiloxane was added dropwise to the premixed solution at a rate of 10% of the mass of the premixed solution over a period of 5 minutes. After the addition was complete, the pH was adjusted to 6.0-7.0, the solution was heated to 45°C, and the reaction was carried out for 2 hours. The solution was then cooled to room temperature to obtain the self-healing regulator. The preparation method of organically modified zinc oxide nanospheres includes the following steps: B1. Disperse zinc oxide nanoparticles with a particle size range of 5~25nm in water, surface activate them with a tertiary aminosilane coupling agent, and then quaternize them with tetramethylammonium bromide. Remove the dispersant to obtain quaternized zinc oxide particles, wherein the mass ratio of zinc oxide nanoparticles, N,N-diethylaminopropyltrimethoxysilane and tetramethylammonium bromide is 100:1.5:5. B2. Quaternized zinc oxide particles were added to an aqueous solution of methacrylate, with a mass ratio of quaternized zinc oxide particles to methacrylate of 100:10. An initiator was added, and the mixture was heated to 70°C and stirred to react. After the reaction was completed, the mixture was centrifuged, dried, and sieved to obtain organically modified zinc oxide nanospheres.

[0029] Comparative Example 1 This comparative example does not contain V and Nb elements. Its chemical composition and mass percentage are as follows: C: 0.003%, Si: 0.016%, Mn: 0.50%, Als: 0.03%, Ti: 0.011%, B: 0.0013%, P: 0.011%, S: 0.06%, N: 0.006%, with the balance being Fe and unavoidable impurities. Meanwhile, no self-healing modifier was added during the preparation of the passivation solution, as detailed below: By weight percentage, 2.5% sodium bisulfite, 4% titanium nitrate, 5% citric acid, 4% potassium phosphate, 2% organic modified zinc oxide nanospheres and 1% tetraethyl orthosilicate were added to the remaining water, heated to 55°C and stirred for 8 minutes to obtain a passivation solution. The other preparation process is the same as in Example 1.

[0030] Comparative Example 2 This comparative example does not contain V and Nb elements. Its chemical composition and mass percentage are as follows: C: 0.003%, Si: 0.016%, Mn: 0.50%, Als: 0.03%, Ti: 0.011%, B: 0.0013%, P: 0.011%, S: 0.06%, N: 0.006%, with the balance being Fe and unavoidable impurities. The preparation process is the same as in Example 1.

[0031] Comparative Example 3 The only difference between this comparative example and Example 1 is that no self-healing modifier was added in the preparation of the passivation solution, as detailed below: By weight percentage, 2.5% sodium bisulfite, 4% titanium nitrate, 5% citric acid, 4% potassium phosphate, 2% organic modified zinc oxide nanospheres and 1% tetraethyl orthosilicate were added to the remaining water, heated to 55°C and stirred for 8 minutes to obtain a passivation solution. The other preparation process is the same as in Example 1.

[0032] Comparative Example 4 The only difference between this comparative example and Example 1 is that, in the preparation of the passivation solution, the nano-zinc oxide was not organically modified; that is, the organically modified zinc oxide nanospheres were replaced with nano-zinc oxide with a particle size range of 5~25 nm, as detailed below: By weight percentage, 2.5% sodium bisulfite, 4% titanium oxynitrate, 5% citric acid, 4% potassium phosphate, 2% nano zinc oxide with a particle size range of 5~25nm, 4% self-healing regulator and 1% tetraethyl orthosilicate were added to the remaining water, heated to 55℃ and stirred for 8min to obtain a passivation solution. The other preparation process is the same as in Example 1.

[0033] Comparative Example 5 The only difference between this comparative example and Example 1 is that no self-healing regulator was added in the preparation of the passivation solution, and the nano zinc oxide was not organically modified, as detailed below: By weight percentage, 2.5% sodium bisulfite, 4% titanium nitrate, 5% citric acid, 4% potassium phosphate, 2% nano zinc oxide with a particle size range of 5~25nm and 1% tetraethyl orthosilicate were added to the remaining water, heated to 55℃ and stirred for 8min to obtain a passivation solution. The other preparation process is the same as in Example 1.

[0034] The mass percentages of chemical components other than iron in the steels of Examples 1-5 and Comparative Examples 1-5 are shown in Table 1: Table 1. Chemical composition of steels prepared by different processes, excluding iron. C / % 0.003 0.004 0.003 0.002 0.004 0.003 0.003 Si / % 0.015 0.01 0.02 0.02 0.012 0.016 0.014 Mn / % 0.50 0.48 0.52 0.51 0.48 0.50 0.50 Als / % 0.03 0.04 0.04 0.03 0.02 0.03 0.03 V / % 0.14 0.14 0.13 0.10 0.20 - 0.14 Nb / % 0.02 0.025 0.025 0.03 0.02 - 0.02 Ti / % 0.009 0.015 0.015 0.005 0.015 0.011 0.009 B / % 0.0016 0.0012 0.002 0.0018 0.0015 0.0013 0.0016 P / % 0.011 0.01 0.011 0.013 0.015 0.011 0.011 S / % 0.06 0.06 0.06 0.07 0.08 0.06 0.06 N / % 0.006 0.008 0.008 0.006 0.006 0.006 0.006 Proof of effectiveness The steel samples obtained in Examples 1-5 and Comparative Examples 1-5 were used to prepare specimens for testing tensile strength and corrosion resistance. Tensile strength was tested according to GB / T 228.1-2021 "Metallic materials, tensile testing—Part 1: Tests at room temperature." Corrosion resistance was tested by subjecting the steel specimens to an accelerated corrosion test using 5% NaCl salt spray. The tensile strength retention rate of the steel specimens after 7 × 24 h was calculated as: tensile strength retention rate = (tensile strength after corrosion / initial tensile strength) × 100%. Specific test results are shown in Table 2. Table 2. Performance test data of steels prepared by different processes. Example 1 376 92.4 Example 2 371 92.1 Example 3 374 92.0 Example 4 372 91.9 Example 5 373 92.3 Comparative Example 1 322 86.4 Comparative Example 2 326 90.1 Comparative Example 3 373 88.6 Comparative Example 4 374 87.9 Comparative Example 5 370 86.1 Results Analysis Analyze Examples 1-5 and Comparative Examples 1-5, and combine with the data in Table 2 and Figure 1 As can be seen, the tensile strength of the steel produced by the present invention (Examples 1-5) reaches over 371 MPa, and the tensile strength retention rate is over 91.9% after salt spray corrosion. This indicates that the hot-pressed ultra-high strength steel for battery casings provided by the present invention has high mechanical strength and excellent corrosion resistance. The specific analysis is as follows: Comparing Comparative Example 1 and Comparative Example 2, compared with Comparative Example 1, Comparative Example 2 added a self-healing modifier in the preparation of the passivation solution, and the tensile strength retention rate increased from 86.4% to 90.1%, indicating that the addition of the self-healing modifier in the passivation solution can improve the corrosion resistance of steel. Comparing Comparative Example 1 and Comparative Example 3, compared with Comparative Example 1, Comparative Example 3 added V and Nb elements to the chemical composition, and the tensile strength increased from 322 MPa to 373 MPa, and the tensile strength retention rate increased from 86.4% to 88.6%. This shows that in this preparation system, adding V and Nb elements to the chemical composition of steel can improve the mechanical strength of steel and improve its corrosion resistance. Comparing Comparative Example 3 and Comparative Example 5, compared with Comparative Example 5, Comparative Example 3 underwent organic modification of nano zinc oxide in the preparation of passivation solution, and the tensile strength retention rate increased from 86.1% to 88.6%, indicating that organic modification of nano zinc oxide can improve the corrosion resistance of steel. Comparing Comparative Example 4 and Comparative Example 5, compared with Comparative Example 5, Comparative Example 4 added a self-healing modifier in the preparation of the passivation solution, and the tensile strength retention rate increased from 86.1% to 87.9%, indicating that the addition of the self-healing modifier in the passivation solution can improve the corrosion resistance of steel. A comprehensive analysis of Examples 1 and Comparative Examples 3-5 shows that the addition of a self-healing modifier to the passivation solution and the organic modification treatment with nano-zinc oxide can both improve the tensile strength retention rate of steel, i.e., improve the corrosion resistance of steel. Furthermore, when these two treatments are used in combination (simultaneously), the increase in tensile strength retention rate (the difference between Example 1 and Comparative Example 5) is significantly greater than the sum of the increases when the two treatments are used alone (the sum of the differences between Comparative Examples 3 and 5 and the differences between Comparative Examples 4 and 5). This indicates that the two treatments have a significant synergistic effect, and their combined use can greatly improve the corrosion resistance of steel.

[0035] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0036] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A hot-pressed ultra-high strength steel for battery casings, characterized in that, It contains the following chemical composition by mass percentage: C: 0.002~0.004%, Si: 0.01~0.02%, Mn: 0.48~0.52%, Als: 0.02~0.04%, V: 0.10~0.20%, Nb: 0.02~0.03%, Ti: 0.005~0.015%, B: 0.0012~0.0020%, P: ≤0.015%, S: ≤0.08%, while satisfying 0.60%≤Mn+V≤0.68%, Nb / (C+N)≥2, with the balance being Fe and unavoidable impurities; The preparation method of the ultra-high strength steel includes the following steps: molten iron smelting, continuous casting, hot rolling, coiling, pickling, cold rolling, annealing, leveling and passivation. The passivation solution prepared in the passivation treatment includes the following steps: by weight percentage, 2-3% sodium bisulfite, 3-5% titanium oxynitrate, 4-6% citric acid, 3.5-4.5% potassium phosphate, 1.5-2.5% organically modified zinc oxide nanospheres, 3-5% self-healing regulator, and 0.5-2% tetraethyl orthosilicate are added to the remaining water, and the mixture is heated and stirred to obtain the passivation solution; wherein the organically modified zinc oxide nanospheres are prepared by quaternizing nano zinc oxide and then grafting acrylate. The preparation process of the self-healing regulator includes the following steps: A1. Mix secondary alcohol polyoxyethylene ether, polyethylene glycol, sodium dodecyl sulfonate and water in a mass ratio of 6~10:4~6:2~3:100 and stir to obtain a premixed solution; A2. Add tetramethyldisiloxane dropwise to the premixed solution. The amount of tetramethyldisiloxane added is 8-12% of the mass of the premixed solution. After the addition is complete, adjust the pH to 6.0-7.0, heat to 40-50℃, react for 1.5-2.5 hours, and cool to room temperature to obtain the self-healing regulator.

2. The hot-pressed ultra-high strength steel for battery casing according to claim 1, characterized in that, The preparation method of the organically modified zinc oxide nanospheres includes the following steps: B1. Disperse nano zinc oxide in water, surface activate it with a tertiary aminosilane coupling agent, and then quaternize it with tetramethylammonium bromide. Remove the dispersant to obtain quaternized zinc oxide particles, wherein the mass ratio of nano zinc oxide, N,N-diethylaminopropyltrimethoxysilane and tetramethylammonium bromide is 100:1~2:4~6. B2. Quaternized zinc oxide particles were added to an aqueous solution of acrylate, with a mass ratio of quaternized zinc oxide particles to acrylate of 100:8~12. After heating and stirring, the mixture was centrifuged, dried, and sieved to obtain organically modified zinc oxide nanospheres.

3. The hot-pressed ultra-high-strength steel for battery casing according to claim 1, characterized in that, In the molten iron smelting and continuous casting, the blast furnace molten iron is first stirred and desulfurized by KR, and then it is smelted in a converter, degassed, refined in an LF furnace, and cast into billets. The final temperature of the converter is 1640~1660℃.

4. The hot-pressed ultra-high strength steel for battery casing according to claim 1, characterized in that, The hot rolling heating temperature is 1200~1250℃, and the hot rolling final temperature is controlled at 860~900℃.

5. The hot-pressed ultra-high strength steel for battery casing according to claim 1, characterized in that, The cold rolling reduction rate is 78~82%, and the surface roughness of the steel plate is controlled to be ≤0.6μm.

6. The hot-pressed ultra-high strength steel for battery casing according to claim 1, characterized in that, During the annealing process, the annealing temperature range is 700~740℃, and the holding time is 100~200s.

7. The hot-pressed ultra-high strength steel for battery casing according to claim 1, characterized in that, The passivation process is as follows: After degreasing the steel plate, treat it in a passivation solution at 50~60℃ for 90~150 s, then rinse it with water and dry it.

Images