Stainless steel material, method for manufacturing the same, and use thereof

Abstract

The application provides a stainless steel material, a preparation method and application thereof. The stainless steel material comprises 10%<=Cr<=19%, 0<=Si<=0.5%, 0<=Ti<=1%, 0<=Cu<1%, 0<=Ni<=0.5%, 0<=Nb<=0.5%, 0<Mo<=1%, 0<Y<=0.5%, 0<Sn<=0.5%, 0<=Mn<=1%, C<=0.03%, P<=0.04%, S<=0.03%, the balance of Fe and inevitable impurities; and 0<Cu+Ni+Nb+Mo+Y+Sn<=3%, 0<=Si+Mn<=1%, 0<=Ti+Nb<=1%. The application develops a high-performance stainless steel material with low resistivity, excellent corrosion resistance, sufficient mechanical strength and low cost through component design and further process optimization, so as to meet the performance requirements of the shell material of a large cylindrical lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of stainless steel technology, and more specifically, to a stainless steel material, its preparation method, and its application. Background Technology

[0002] Currently, with the rapid development of the electric vehicle and large-scale energy storage markets, 46-series large cylindrical lithium-ion batteries (cylindrical batteries with a diameter of 46mm and a height of 80mm or more) are highly valued by the industry due to their high energy density, fast charging capability, safety, and long lifespan. Large cylindrical batteries employ a full-tab process, which transforms the battery casing from a simple container into a key multi-functional component integrating structural support, current conduction, and thermal management. The casing material needs to possess high strength, excellent conductivity, and corrosion resistance.

[0003] Currently, nickel-plated low-carbon steel is the dominant and preferred material for large cylindrical shells in the industry. Low-carbon steel offers excellent mechanical strength and cost-effectiveness. Nickel plating significantly improves corrosion resistance and weldability while ensuring good electrical conductivity. Nickel plating on low-carbon steel is intended to balance conductivity and corrosion resistance; however, during deep drawing and long-term use, the nickel layer on nickel-plated low-carbon steel is at high risk of cracking, easily exposing the low-carbon steel and leading to localized corrosion, affecting electrical properties and corrosion resistance.

[0004] Secondly, a small number of batteries also use aluminum alloy casings and 304 austenitic stainless steel casings. Aluminum alloys are lightweight and generally have better electrical and thermal conductivity than steel, making them worth exploring in specific applications where weight is extremely sensitive (such as high-end passenger vehicles). However, aluminum alloy casings lack sufficient mechanical strength, requiring increased thickness or auxiliary structures to meet strength requirements, which limits the improvement of battery energy density. Furthermore, their poor corrosion resistance often necessitates additional surface treatment. Austenitic stainless steel offers excellent corrosion resistance and higher mechanical strength, making it suitable for applications in extremely corrosive environments, where ultimate safety is prioritized, or where cost is not a primary concern. However, austenitic stainless steel casings generally have high resistivity, leading to increased internal resistance in the battery and generating significant Joule heat, severely reducing battery energy efficiency and fast-charging performance. Moreover, the use of nickel as the main alloying element results in high costs. Summary of the Invention

[0005] The main objective of this invention is to provide a stainless steel material, its preparation method, and its application, so as to solve the problem that existing battery casing materials are difficult to balance low resistivity, excellent corrosion resistance, sufficient mechanical strength, and low cost.

[0006] To achieve the above objectives, according to one aspect of the present invention, a stainless steel material is provided, comprising, by weight percentage: 10%≤Cr≤19%, 0≤Si≤0.5%, 0≤Ti≤1%, 0≤Cu<1%, 0≤Ni≤0.5%, 0≤Nb≤0.5%, 0<Mo≤1%, 0<Y≤0.5%, 0<Sn≤0.5%, 0≤Mn≤1%, C≤0.03%, P≤0.04%, S≤0.03%, with the balance being Fe and unavoidable impurities; and 0<Cu+Ni+Nb+Mo+Y+Sn≤3%, 0≤Si+Mn≤1%, 0≤Ti+Nb≤1%.

[0007] Furthermore, based on weight percentage, stainless steel materials include the following components: 11%≤Cr≤17%, 0≤Si≤0.3%, 0%≤Ti≤0.8%, 0%≤Cu≤0.8%, 0≤Ni≤0.2%, 0%≤Nb≤0.2%, 0%<Mo≤0.5%, 0<Y≤0.2%, 0<Sn≤0.2%, 0≤Mn≤0.8%, C≤0.03%, P≤0.04%, S≤0.03%, with the balance being Fe and unavoidable impurities.

[0008] Furthermore, 0.1%≤Cu+Ni+Nb+Mo+Y+Sn≤2.1%; and / or 0<Mo+Y+Sn≤0.9%.

[0009] Furthermore, 0.2% ≤ Ti + Nb ≤ 1%; and / or 0 ≤ Ni + Mn ≤ 1%.

[0010] Further, the resistivity of the stainless steel material is ≤0.77 μΩ·m; preferably, the resistivity of the stainless steel material is ≤0.598 μΩ·m; more preferably, the resistivity of the stainless steel material is ≤0.55 μΩ·m; and / or the tensile strength of the stainless steel material is 275~480MPa; preferably, the tensile strength of the stainless steel material is 275~450MPa; more preferably, the tensile strength of the stainless steel material is 300~450MPa; and / or the time for rust to appear in the salt spray corrosion of the stainless steel material is ≥8h; preferably, the time for rust to appear in the salt spray corrosion of the stainless steel material is ≥16h.

[0011] According to another aspect of the present invention, a method for preparing the stainless steel material described above is provided, comprising the following steps: Step S1, batching and smelting according to the composition of the stainless steel material, and then casting into steel ingots; Step S2, subjecting the steel ingots to hot rough rolling, intermediate rolling and hot finish rolling in sequence to obtain hot-rolled plates; Step S3, subjecting the hot-rolled plates to cold rolling to obtain cold-rolled plates; Step S4, subjecting the cold-rolled plates to non-oxidizing bright annealing and cooling to obtain stainless steel material.

[0012] Further, in step S1, the melting temperature is 1500~1700℃, preferably 1550~1650℃; and / or in step S2, the intermediate rolling temperature is the same as the final rolling temperature of the hot roughing; and / or the initial rolling temperature of the hot finishing is the same as the intermediate rolling temperature; and / or the initial rolling temperature of the hot roughing is 1100~1250℃, and the final rolling temperature is 900~1100℃; preferably, the initial rolling temperature of the hot roughing is 1100~1200℃, and the final rolling temperature is 900~1000℃; and / or the intermediate rolling time is 10~100s, preferably 30~70s; and / or the final rolling temperature of the hot finishing is 800~950℃, preferably 820~920℃; and / or in step S3, the cold rolling reduction rate is 50~80%, preferably 55~70%.

[0013] Further, in step S4, the temperature of the non-oxidizing bright annealing is 800~1000℃, and the holding time is 30s~10min; preferably, the temperature of the non-oxidizing bright annealing is 850~950℃, and the holding time is 1~5min, and / or the oxygen content in the atmosphere of the non-oxidizing bright annealing is <10 ppm; and / or the atmosphere of the non-oxidizing bright annealing is a hydrogen atmosphere, or a nitrogen-hydrogen mixed atmosphere; preferably, the atmosphere of the non-oxidizing bright annealing is a nitrogen-hydrogen mixed atmosphere, and the volume ratio of nitrogen to hydrogen is (92~98):(2~8).

[0014] According to another aspect of the present invention, a battery casing is provided, the material of which includes the stainless steel material described above.

[0015] According to another aspect of the present invention, a secondary battery is provided, comprising the battery casing described above, wherein optionally, the secondary battery comprises a cylindrical battery.

[0016] By applying the technical solution of this invention, the resistivity and cost of stainless steel materials are significantly reduced through composition design (further process optimization), while ensuring corrosion resistance and mechanical strength. Specifically, the Cr content is controlled at a low level to minimize the solid solution strengthening effect of Cr while ensuring corrosion resistance, thereby avoiding increased resistance; the Si content is controlled at an extremely low level to reduce the impact of Si on lattice distortion, thus improving the free flow of electrons; the types and contents of alloying elements are controlled to reduce obstacles to electron migration; and the use of corrosion-resistant alloying elements is low in content and cost, reducing material costs. This invention resolves the contradiction between conductivity, corrosion resistance, mechanical strength, and cost-effectiveness in existing stainless steel materials, particularly in the application of large cylindrical lithium-ion batteries. Through composition design and further process optimization, a high-performance stainless steel material with low resistivity, excellent corrosion resistance, sufficient mechanical strength, and low cost is developed to meet the performance requirements of large cylindrical lithium-ion batteries for casing materials. Detailed Implementation

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0018] As described in the background section of this invention, existing technologies suffer from the problem of difficulty in simultaneously achieving low resistivity, excellent corrosion resistance, sufficient mechanical strength, and low cost in battery casing materials. To address these issues, in a typical embodiment of this invention, a stainless steel material is provided, comprising the following components by weight percentage: 10%≤Cr≤19%, 0≤Si≤0.5%, 0≤Ti≤1%, 0≤Cu<1%, 0≤Ni≤0.5%, 0≤Nb≤0.5%, 0<Mo≤1%, 0<Y≤0.5%, 0<Sn≤0.5%, 0≤Mn≤1%, C≤0.03%, P≤0.04%, S≤0.03%, with the balance being Fe and unavoidable impurities; and 0<Cu+Ni+Nb+Mo+Y+Sn≤3%, 0≤Si+Mn≤1%, 0≤Ti+Nb≤1%.

[0019] The roles and content requirements of each element in the high-performance stainless steel material of this invention are described below:

[0020] Cr: Cr is the most important alloying element in stainless steel. Cr reacts with oxygen on the surface of stainless steel to form a very thin but dense and stable Cr₂O₃ passivation film, which prevents further corrosion of the internal iron matrix. The solid solution strengthening effect of Cr can improve the strength of the steel, but it significantly increases the resistivity. Further considering the balance between cost, resistivity, and corrosion resistance, the Cr content in this invention is limited to the range described above.

[0021] Si: When Si dissolves in stainless steel, it increases lattice distortion and hinders the free movement of electrons, thus significantly increasing the resistivity of the material. However, Si can form a more stable oxide film at high temperatures, improving oxidation resistance. To balance resistivity and corrosion resistance, the Si content is controlled at an extremely low level in this invention.

[0022] Ti and Nb are both stabilizing elements. They have a stronger affinity for C than Cr and preferentially combine with C to form stable carbides (NbC, TiC), thereby preventing the precipitation of Cr carbides at grain boundaries and preventing intergranular corrosion. Further considering the balance between cost and corrosion resistance, the amounts of Ti, Nb, and Ti+Nb in this invention are controlled within the aforementioned ranges.

[0023] Cu: Cu can promote the enrichment of Cr in the passivation film on the surface of stainless steel, thereby improving the corrosion resistance of stainless steel. An appropriate amount of Cu can increase the stacking fault energy and anisotropy ratio of stainless steel, thereby reducing the strength and cold work hardening tendency of stainless steel, and improving the plasticity and deep drawing properties of steel.

[0024] Ni and Mn: Ni is a strong austenite-forming element that can improve the strength and low-temperature toughness of steel, and enhance its corrosion resistance in reducing media. Mn has a similar effect to Ni, but its ability is weaker. It is often used to partially replace Ni to reduce costs. However, excessive Mn can lead to the formation of more and larger MnS inclusions, reducing corrosion resistance. Further considering the balance between cost, corrosion resistance, and mechanical strength, the Ni and Mn contents in this invention are controlled within the aforementioned ranges.

[0025] Mo, Y, Sn: Mo dissolves in the ferrite lattice, which can improve the strength and high-temperature strength of steel. It can also promote the formation of a more stable passivation film and inhibit the anodic dissolution process in the early stage of corrosion, significantly improving the resistance to pitting and crevice corrosion in chloride environments. Y can promote the formation of a denser and more adhesive protective oxide film and inhibit the volatilization loss of chromium in the film, thereby improving high-temperature oxidation resistance. It can also reduce the number of inclusions in steel and lower the starting point of electrochemical corrosion, thereby improving corrosion resistance. In acidic and chloride-containing environments, the dense single-atom Sn layer formed on the surface of stainless steel can effectively inhibit the active dissolution of elements such as Fe and Cr in stainless steel, thereby significantly improving the resistance to uniform corrosion. In this invention, the content of Mo, Y, and Sn is controlled within the above ranges so as to improve the corrosion resistance and mechanical strength of stainless steel materials through the synergistic effect of the three, while keeping the cost under control.

[0026] C, P, and S: C has extremely low solubility in stainless steel. C combines with Cr to form Cr carbides (such as Cr2). 23 Chromium (C6) precipitates at grain boundaries, leading to chromium depletion in the vicinity of grain boundaries and thus inducing intergranular corrosion. Therefore, the C content needs to be strictly controlled. In this invention, the C content is C≤0.03%. P and S are impurity elements that are detrimental to the properties of stainless steel. P segregates at grain boundaries, leading to temper brittleness, which is detrimental to toughness and weldability. S combines with Fe to form low-melting-point FeS, leading to hot brittleness and making it prone to cracking during hot working. In this invention, the P and S contents are P≤0.04% and S≤0.03%, respectively.

[0027] In particular, this invention controls the content of Cu+Ni+Nb+Mo+Y+Sn within the aforementioned range, thereby ensuring the corrosion resistance and low cost of stainless steel through the synergistic effect of different elements, and keeping the resistivity at a low level. The introduction of Si and Mn elements will cause significant lattice distortion. Controlling the total content of Si and Mn within the aforementioned range can further reduce the adverse effects on the lattice, improve the free movement of electrons, and thus further reduce the resistivity of stainless steel.

[0028] This invention achieves good corrosion resistance and low resistivity by adding necessary but low amounts of Cr; significantly reduces the resistivity of stainless steel by controlling the content of Si and Mn to extremely low levels or even omitting them; improves corrosion resistance by adding trace amounts of Ti, Cu, Ni, Nb, Mo, Y, Sn, and Mn; controls the amount of Ti and Nb added to achieve optimal corrosion resistance; controls the amount of precious metal elements such as Cu, Ni, Nb, Mo, Y, and Sn added to reduce material costs to some extent; strictly controls the C content to reduce carbide precipitation and avoid intergranular corrosion; and strictly controls the content of P and S impurities to reduce their impact on overall performance. Ultimately, this invention yields a high-performance stainless steel material with low resistivity, excellent corrosion resistance, high mechanical strength, and low cost.

[0029] The stainless steel material of this invention exhibits significantly reduced resistivity, which can reduce the internal resistance of the battery to a certain extent, thereby improving the battery's thermal management and power performance, and greatly enhancing its application value in cylindrical lithium-ion batteries. It possesses excellent corrosion resistance, superior to nickel-plated low-carbon steel, and eliminates the risk of corrosion caused by surface coating breakage, making it more suitable as a casing material for cylindrical lithium-ion batteries. It also boasts high mechanical strength, with tensile strength slightly higher than nickel-plated low-carbon steel, effectively suppressing battery expansion and deformation, thus improving safety. Furthermore, it offers significant cost advantages, with a low Cr content, limited content of expensive alloying elements, and no surface modification process. The production process is highly compatible with traditional processes, facilitating large-scale production. The stainless steel material prepared by this invention has good economic viability and industrialization prospects. It is a high-performance stainless steel material that combines low resistivity, excellent corrosion resistance, sufficient mechanical strength, and low cost, meeting the performance requirements of large cylindrical lithium-ion batteries for casing materials.

[0030] For similar reasons, in a preferred embodiment, the stainless steel material comprises, by weight percentage: 11%≤Cr≤17%, 0≤Si≤0.3%, 0%≤Ti≤0.8%, 0%≤Cu≤0.8%, 0≤Ni≤0.2%, 0%≤Nb≤0.2%, 0%<Mo≤0.5%, 0<Y≤0.2%, 0<Sn≤0.2%, 0≤Mn≤0.8%, C≤0.03%, P≤0.04%, S≤0.03%, with the balance being Fe and unavoidable impurities.

[0031] In a preferred embodiment, 0.1% ≤ Cu + Ni + Nb + Mo + Y + Sn ≤ 2.1%. These conditions further optimize the corrosion resistance and mechanical strength of the material while maximizing cost-effectiveness. The added Cu and Ni effectively promote the formation of a passivation film on the stainless steel surface, enhancing its stability in corrosive environments, while the synergistic effect of Nb and Ti significantly inhibits intergranular corrosion, improving the material's service life. Even in low concentrations, the addition of Mo, Y, and Sn enhances the material's corrosion resistance, particularly significantly improving protection against pitting and crevice corrosion in chloride environments. Through precise control of these precious metal elements, superior corrosion resistance, higher mechanical strength, and controllable material costs can be achieved while maintaining a low resistivity in the stainless steel material.

[0032] In a preferred embodiment, 0 < Mo + Y + Sn ≤ 0.9%. Controlling the total content of Mo, Y, and Sn within the above range can further enhance the material's protective ability under specific corrosion conditions, especially its resistance to uniform corrosion in acidic and chloride-containing environments.

[0033] In a preferred embodiment, 0.2% ≤ Ti + Nb ≤ 1%; and / or 0 ≤ Ni + Mn ≤ 1%. When the total content of Ti and Nb is controlled within the above range, the precipitation of carbides at grain boundaries can be effectively suppressed, further reducing intergranular corrosion. As elements that preferentially combine with carbon to form stable carbides, Ti and Nb, by adjusting their content, can improve the corrosion resistance of the material while maintaining good mechanical strength. In addition, when the total content of Ni and Mn is controlled within the above range, it is beneficial to improve the toughness of the material in low-temperature environments and enhance its corrosion resistance in reducing media, while significantly reducing the cost burden caused by the use of expensive alloying elements.

[0034] As described above, by controlling the elemental composition, the present invention enables stainless steel materials to simultaneously achieve low resistivity, excellent corrosion resistance, sufficient mechanical strength, and low cost. In a preferred embodiment, the resistivity of the stainless steel material is ≤0.77 μΩ·m; preferably, the resistivity of the stainless steel material is ≤0.598 μΩ·m; more preferably, the resistivity of the stainless steel material is ≤0.55 μΩ·m; and / or the tensile strength of the stainless steel material is 275~480MPa; preferably, the tensile strength of the stainless steel material is 275~450MPa; more preferably, the tensile strength of the stainless steel material is 300~450MPa; and / or the time for rust to appear in salt spray corrosion of the stainless steel material is ≥8h, such as 8~96h; preferably, the time for rust to appear in salt spray corrosion of the stainless steel material is ≥16h, such as 16~72h.

[0035] In another typical embodiment of the present invention, a method for preparing the stainless steel material described above is also provided, comprising the following steps: Step S1, preparing and smelting according to the composition of the stainless steel material, and then casting it into a steel ingot; Step S2, subjecting the steel ingot to hot rough rolling, intermediate rolling and hot finish rolling in sequence to obtain a hot-rolled plate; Step S3, subjecting the hot-rolled plate to cold rolling to obtain a cold-rolled plate; Step S4, subjecting the cold-rolled plate to non-oxidizing bright annealing and cooling to obtain the stainless steel material.

[0036] First, raw materials are prepared according to the composition ratio and smelted in a melting furnace to precisely control the chemical composition, ensuring the material's corrosion resistance and formability while also considering production costs. The resulting ingots are then cast. A "rough rolling + finish rolling" process is used to heat and hold the ingots, transforming the coarse, uneven as-cast structure into a fine, uniform rolled structure. This lays a solid foundation for the microstructure and performance of subsequent cold rolling and the final product. Intermediate billets are placed between the rough and finish rolling processes to provide conditions and time for recrystallization, resulting in hot-rolled plates of the required specifications. The hot-rolled plates are then cold-rolled to prepare the internal microstructure for subsequent annealing, obtaining cold-rolled plates of the desired specifications. Finally, a non-oxidizing bright annealing process is used to anneal the cold-rolled plates, eliminating work hardening caused by cold rolling, restoring the material's plasticity and toughness, promoting recrystallization and grain growth, reducing the number of grain boundaries, and ultimately improving corrosion resistance and electrical conductivity. After holding at the heat, the plates are rapidly cooled to room temperature, resulting in annealed plates, i.e., stainless steel.

[0037] This invention employs a non-oxidizing bright annealing process, which eliminates the need for pickling while ensuring a bright surface and achieving ideal performance. Furthermore, by combining this with a suitable annealing process, the grain size is moderate, and the number of grain boundaries is reduced, which is beneficial for achieving lower resistivity; the good surface quality of the steel also contributes to improved corrosion resistance.

[0038] To achieve more precise control over chemical composition, improve material corrosion resistance and formability, and simultaneously reduce production costs, in a preferred embodiment, the melting temperature in step S1 is 1500~1700℃, preferably 1550~1650℃; and / or in step S2, the temperature of the intermediate rolling mill is the same as the final rolling temperature of the hot roughing mill; and / or the starting rolling temperature of the hot finishing mill is the same as the temperature of the intermediate rolling mill; and / or the starting rolling temperature of the hot roughing mill is 1100~1500℃. The rolling temperature is 250℃, and the final rolling temperature is 900~1100℃; preferably, the initial rolling temperature of hot roughing is 1100~1200℃, and the final rolling temperature is 900~1000℃; and / or the intermediate steel-laying time is 10~100s, preferably 30~70s; and / or the final rolling temperature of hot finishing is 800~950℃, preferably 820~920℃; and / or in step S3, the reduction rate of cold rolling is 50~80%, preferably 55~70%.

[0039] In step S2, the temperature setting of the intermediate billet is consistent with the final rolling temperature of the hot roughing roll, and the starting rolling temperature of the hot finishing roll is also the same as that of the intermediate billet. This helps maintain the continuity of the material's thermodynamic state and reduces the negative impact of temperature fluctuations on material properties. Controlling the starting and final rolling temperatures of the hot roughing roll within the aforementioned range promotes the repair of internal defects in the material and effectively controls grain growth, resulting in good processing performance and mechanical strength. The time window for the intermediate billet provides the necessary recrystallization time and conditions, promoting the refinement of the material's microstructure and enhancing mechanical properties and corrosion resistance. Setting the final rolling temperature of the hot finishing roll within the aforementioned range helps maintain good plasticity while ensuring material strength, facilitating subsequent forming processes, reducing residual stress after heat treatment, and improving the material's uniformity and durability. Controlling the cold rolling reduction rate within the aforementioned range helps increase the surface finish of the material, optimize thickness and dimensional accuracy, and, by controlling the reduction rate, adjust the material's hardness and ductility, thus meeting the physical properties required for the battery casing. The above rolling parameters not only improve the conductivity and corrosion resistance of the material, but also help it achieve high strength in battery casing applications, significantly improving the overall performance of the material.

[0040] In a preferred embodiment, in step S4, the temperature of the non-oxidizing bright annealing is 800~1000℃, and the holding time is 30s~10min; preferably, the temperature of the non-oxidizing bright annealing is 850~950℃, and the holding time is 1~5min, and / or the oxygen content in the atmosphere of the non-oxidizing bright annealing is <10 ppm; and / or the atmosphere of the non-oxidizing bright annealing is a hydrogen atmosphere, or a nitrogen-hydrogen mixed atmosphere; preferably, the atmosphere of the non-oxidizing bright annealing is a nitrogen-hydrogen mixed atmosphere, and the volume ratio of nitrogen to hydrogen is (92~98):(2~8).

[0041] Controlling the temperature and holding time within the aforementioned ranges during non-oxidizing bright annealing promotes recrystallization and grain growth, reduces the number of grain boundaries, and thus improves the material's microstructure. Suitable grain size and fewer grain boundaries help reduce grain boundary scattering, thereby reducing resistivity and improving conductivity. Simultaneously, the oxygen content in the annealing atmosphere is strictly controlled to reduce oxidation reactions and maintain the material's surface gloss and corrosion resistance. Using a hydrogen atmosphere or a nitrogen-hydrogen mixed atmosphere, especially a nitrogen-hydrogen mixed atmosphere, effectively prevents oxidation of the material at high temperatures, keeps the surface clean, further reduces resistivity and improves corrosion resistance, and simultaneously promotes the optimization of material properties.

[0042] In another typical embodiment of the present invention, a battery casing is also provided, the material of which includes the stainless steel material described above.

[0043] In another typical embodiment of the present invention, a secondary battery is also provided, including the aforementioned battery casing. Optionally, the secondary battery includes a cylindrical battery. Because the battery casing is made of a specific stainless steel material, it not only provides superior corrosion resistance compared to nickel-plated low-carbon steel, but also possesses comparable or even higher mechanical strength. The resistivity of the material is relatively reduced, and costs are effectively controlled, which is beneficial for improving the battery's corrosion resistance and power performance, demonstrating good economic viability and industrialization prospects.

[0044] The high-performance ferritic stainless steel material of this invention, with its extremely low resistivity, intrinsically high corrosion resistance, excellent tensile strength, and coating-free processing characteristics, is not only suitable for cylindrical battery casings but also widely applicable to prismatic battery casings and multi-layer composite battery casings. In prismatic batteries, this material can be directly used as a casing or cover, meeting the requirements of complex bending, laser welding, and expansion resistance, without the risk of coating peeling. In multi-layer composite casings (such as steel / aluminum), its high corrosion resistance eliminates the need for additional surface treatment, significantly improving structural reliability and manufacturing efficiency. The stainless steel material of this invention, through composition and process design that balances formability and cost, can be seamlessly adapted to existing stamping and welding production lines, achieving full-scenario coverage from cylindrical to prismatic batteries, and from single-layer casings to composite casings, demonstrating significant technological versatility and industrial expansion value.

[0045] Typical, but not limiting, stainless steel materials, by weight percentage, contain: Cr ranging from 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or any two of these values; Si ranging from 0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% or any two of these values; and Ti ranging from 0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0... The values ​​are 0.9%, 1%, or any two of these values ​​for Cu, and 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any two of these values ​​for Ni, and 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any two of these values ​​for Nb. Mo is a range of 0.001%, 0.005%, 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any two of these values; Y is a range of 0.001%, 0.005%, 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any two of these values; and Sn is 0. 0.001%, 0.005%, 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% or any two of these values; Mn is 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or any two of these values; C≤0.03%, P≤0.04%, S≤0.03%; the balance is Fe and unavoidable impurities.

[0046] Typical, but not limiting, values ​​for Cu+Ni+Nb+Mo+Y+Sn are 0.01%, 0.05%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.1%, 2.5%, 3%, or any two of these values; values ​​for Si+Mn are 0%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, or any two of these values; values ​​for Ti+Nb are 0%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, or any two of these values. The range of values ​​formed by any two values; Mo+Y+Sn is 0.001%, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or any two of these values; Ni+Mn is 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or any two of these values.

[0047] Typical, but not limiting, resistivity of stainless steel is 0.30 μΩ·m, 0.35 μΩ·m, 0.40 μΩ·m, 0.45 μΩ·m, 0.50 μΩ·m, 0.55 μΩ·m, 0.598 μΩ·m, 0.65 μΩ·m, 0.70 μΩ·m, 0.75 μΩ·m, 0.77 μΩ·m or any two of these values; tensile strength of stainless steel is 275 MPa, 280 MPa, 300 MPa, 320 MPa, 350 MPa, 380 MPa, 400 MPa, 420 MPa, 450 MPa, 480 MPa or any two of these values.

[0048] Typically, but not limitingly, in step S2, the initial rolling temperature of the hot roughing rolling is 1100℃, 1150℃, 1180℃, 1200℃, 1220℃, 1250℃ or any two of these values; the final rolling temperature is 900℃, 950℃, 1000℃, 1050℃, 1100℃ or any two of these values; the intermediate steel-holding time is 10s, 20s, 30s, 50s, 70s, 80s, 100s or any two of these values; and the final rolling temperature of the hot finishing rolling is 800℃, 820℃, 850℃, 880℃, 900℃, 920℃, 950℃ or any two of these values.

[0049] Typically, but not limitingly, in step S4, the temperature for non-oxidizing bright annealing is 800℃, 820℃, 850℃, 880℃, 900℃, 920℃, 950℃, 980℃, 1000℃ or any two of these values, and the holding time is 30s, 1min, 2min, 5min, 8min, 10min or any two of these values.

[0050] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0051] Example 1

[0052] Step S1: Prepare and smelt the stainless steel materials according to the composition in Tables 1 and 2. Smelt the materials in a smelting furnace at 1580℃, and then cast them into steel ingots, strictly controlling the C, P and S contents.

[0053] Step S2: Using the "hot roughing rolling + hot finishing rolling" process, the above-mentioned ingot is heated and held at 1150℃. The exit temperature of the hot roughing rolling is controlled at 950℃, and the exit temperature of the hot finishing rolling is controlled at 850℃. A 30-second intermediate steel-laying time is set between the hot roughing rolling and the hot finishing rolling to obtain the hot-rolled plate of the required specifications.

[0054] Step S3: The hot-rolled plate is cold-rolled with a reduction rate of 60% to obtain a cold-rolled plate with a thickness of 0.5 mm.

[0055] Step S4 involves a non-oxidizing bright annealing process, where the cold-rolled sheet is annealed at 870℃ for 2 minutes in a nitrogen-hydrogen mixed atmosphere (nitrogen and hydrogen volume contents of 95% and 5%, respectively), with the oxygen content in the furnace controlled below 10 ppm. The sheet is then rapidly cooled to room temperature to obtain stainless steel material.

[0056] Examples 2 to 6

[0057] The difference from Example 1 is that the composition of the stainless steel material is different, as detailed in Tables 1 and 2.

[0058] Example 7

[0059] Step S1: Prepare and smelt the stainless steel materials according to the composition in Tables 1 and 2. Smelt the materials in a smelting furnace at 1600℃, and then cast them into steel ingots, strictly controlling the C, P and S contents.

[0060] Step S2: Using the "hot roughing rolling + hot finishing rolling" process, the above-mentioned ingot is heated and held at 1180℃. The exit temperature of the hot roughing rolling is controlled at 950℃, and the exit temperature of the hot finishing rolling is controlled at 850℃. A 30-second intermediate steel-laying time is set between the hot roughing rolling and the hot finishing rolling to obtain the hot-rolled plate of the required specifications.

[0061] Step S3: The hot-rolled plate is cold-rolled with a reduction rate of 60% to obtain a cold-rolled plate with a thickness of 0.5 mm.

[0062] Step S4 involves a non-oxidizing bright annealing process, where the cold-rolled sheet is annealed at 890℃ for 2 minutes in a nitrogen-hydrogen mixed atmosphere (nitrogen and hydrogen volume contents of 95% and 5%, respectively), with the oxygen content in the furnace controlled below 10 ppm. The sheet is then rapidly cooled to room temperature to obtain stainless steel material.

[0063] Example 8

[0064] The difference from Example 7 is that the composition of the stainless steel material is different, as detailed in Tables 1 and 2.

[0065] Example 9

[0066] The difference from Example 5 is that in step S4, a non-oxidizing bright annealing process is used to anneal the above-mentioned cold-rolled sheet at 840°C.

[0067] Example 10

[0068] The difference from Example 5 is that in step S4, a non-oxidizing bright annealing process is used to anneal the above-mentioned cold-rolled sheet at 930°C.

[0069] Examples 11 to 18

[0070] The difference from Example 1 is that the composition of the stainless steel material is different, as detailed in Tables 1 and 2.

[0071] Example 19

[0072] Step S1: Prepare and smelt the stainless steel material according to the composition of Example 6 in Tables 1 and 2. Smelt the material in a smelting furnace at 1550°C and then cast it into steel ingots, strictly controlling the C, P and S contents.

[0073] Step S2: Using the "hot roughing rolling + hot finishing rolling" process, the above-mentioned ingot is heated and held at 1100℃, the exit temperature of the hot roughing rolling is controlled at 900℃, the exit temperature of the hot finishing rolling is controlled at 820℃, and a 30-second intermediate steel-hanging time is set between the hot roughing rolling and the hot finishing rolling to obtain the hot-rolled plate.

[0074] Step S3: The hot-rolled plate is cold-rolled, and the reduction rate is controlled at 55% to obtain a cold-rolled plate;

[0075] Step S4 involves a non-oxidizing bright annealing process, where the cold-rolled sheet is annealed at 850°C for 5 minutes in a nitrogen-hydrogen mixed atmosphere (nitrogen and hydrogen volume contents of 95% and 5%, respectively), with the oxygen content in the furnace controlled below 10 ppm. The sheet is then rapidly cooled to room temperature to obtain stainless steel material.

[0076] Example 20

[0077] Step S1: Prepare and smelt the stainless steel material according to the composition of Example 6 in Tables 1 and 2. Smelt the material in a smelting furnace at 1650°C and then cast it into steel ingots, strictly controlling the C, P and S contents.

[0078] Step S2: Using the "hot roughing rolling + hot finishing rolling" process, the above-mentioned ingot is heated and held at 1200℃, the exit temperature of the hot roughing rolling is controlled at 1000℃, the exit temperature of the hot finishing rolling is controlled at 920℃, and a 70-second intermediate steel-laying time is set between the hot roughing rolling and the hot finishing rolling to obtain the hot-rolled plate.

[0079] Step S3: The hot-rolled sheet is cold-rolled, with the reduction rate controlled at 70%, to obtain a cold-rolled sheet;

[0080] Step S4 involves a non-oxidizing bright annealing process, where the cold-rolled sheet is annealed at 950°C for 1 minute in a nitrogen-hydrogen mixed atmosphere (nitrogen and hydrogen volume contents of 95% and 5%, respectively), with the oxygen content in the furnace controlled below 10 ppm. The sheet is then rapidly cooled to room temperature to obtain stainless steel material.

[0081] Example 21

[0082] Step S1: Prepare and smelt the stainless steel material according to the composition of Example 6 in Tables 1 and 2. Smelt the material in a smelting furnace at 1500°C and then cast it into steel ingots, strictly controlling the C, P and S contents.

[0083] Step S2: Using the "hot roughing rolling + hot finishing rolling" process, the above-mentioned ingot is heated and held at 1100℃, the exit temperature of the hot roughing rolling is controlled at 900℃, the exit temperature of the hot finishing rolling is controlled at 800℃, and a 10-second intermediate steel-placing time is set between the hot roughing rolling and the hot finishing rolling to obtain the hot-rolled plate.

[0084] Step S3: The hot-rolled plate is cold-rolled with a reduction rate of 50% to obtain a cold-rolled plate.

[0085] Step S4 involves a non-oxidizing bright annealing process, where the cold-rolled sheet is annealed at 800℃ for 10 minutes in a nitrogen-hydrogen mixed atmosphere (nitrogen and hydrogen volume contents of 92% and 8%, respectively), with the oxygen content in the furnace controlled below 10 ppm. The sheet is then rapidly cooled to room temperature to obtain stainless steel material.

[0086] Example 22

[0087] Step S1: Prepare and smelt the stainless steel material according to the composition of Example 6 in Tables 1 and 2. Smelt the material in a smelting furnace at 1700°C and then cast it into steel ingots, strictly controlling the C, P and S contents.

[0088] Step S2: Using the "hot roughing rolling + hot finishing rolling" process, the above-mentioned ingot is heated and held at 1250℃, the exit temperature of the hot roughing rolling is controlled at 1100℃, the exit temperature of the hot finishing rolling is controlled at 950℃, and a 100s intermediate steel-hanging time is set between the hot roughing rolling and the hot finishing rolling to obtain the hot-rolled plate.

[0089] Step S3: The hot-rolled plate is cold-rolled, and the reduction rate is controlled at 80% to obtain a cold-rolled plate;

[0090] Step S4 involves a non-oxidizing bright annealing process, where the cold-rolled sheet is annealed at 1000℃ for 0.5 minutes in a nitrogen-hydrogen mixed atmosphere (nitrogen and hydrogen volume contents of 98% and 2%, respectively), with the oxygen content in the furnace controlled below 10 ppm. The sheet is then rapidly cooled to room temperature to obtain stainless steel material.

[0091] Comparative Example 1

[0092] The 409 ferritic stainless steel was purchased from Jiuquan Iron & Steel (Group) Co., Ltd., and its grade is 409L.

[0093] Comparative Example 2

[0094] Purchased nickel-plated low-carbon steel, manufactured by Maanshan Iron & Steel (Group) Holding Co., Ltd., model SPCC.

[0095] Performance testing:

[0096] The stainless steel samples from the above embodiments and comparative examples were subjected to the following tests, and the results are shown in Table 3.

[0097] Resistivity: Tested in accordance with GB / T 351-2019 Metallic Materials Resistivity Test Method.

[0098] Salt spray corrosion performance: Tested in accordance with GB / T 10125-2021 Artificial Atmosphere Corrosion Test Salt Spray Test (-2022 Edition)

[0099] Tensile properties: Tested in accordance with GB / T 228.1-2021 Metallic materials, tensile testing - Part 1: Test method at room temperature.

[0100] Table 1

[0101]

[0102] Table 2

[0103]

[0104] Table 3

[0105]

[0106] Comparative Example 1 is a commercially available 409 ferritic stainless steel. Although its resistivity is slightly lower than that of Examples 12, 14, 16, and 18, its tensile strength is much lower, and its corrosion resistance is also much lower, resulting in poor overall performance. Compared to Comparative Example 1, the resistivity of the stainless steel material of this invention, after compositional design and process optimization, is significantly reduced, and the salt spray corrosion time is effectively improved. Comparative Example 2 is a commercially available nickel-plated low-carbon steel. Compared to Comparative Example 2, the salt spray corrosion time of the stainless steel material in this invention is generally longer, indicating excellent corrosion resistance, which can meet the corrosion resistance requirements of cylindrical lithium-ion battery casings; the tensile strength is high, all above 300 MPa, which can meet the mechanical performance requirements of cylindrical lithium-ion battery casings. Moreover, the stainless steel material of this invention has a low content of the main alloying element Cr, and the content of precious metal elements among the trace alloying elements is relatively limited, resulting in a significant cost advantage.

[0107] As can be seen from the above, compared with the comparative examples, the embodiments of the present invention significantly reduce the resistivity and cost of stainless steel materials through composition design and process optimization, while ensuring corrosion resistance and mechanical strength. Specifically, the Cr content is controlled at a low level to minimize the solid solution strengthening effect of Cr while ensuring corrosion resistance, thereby avoiding an increase in resistance; the Si content is controlled at an extremely low level to reduce the influence of Si on lattice distortion, thereby improving the free flow of electrons; the types and contents of alloying elements are controlled to reduce obstacles to electron migration; and the use of corrosion-resistant alloying elements with low content and low cost reduces material costs. The present invention resolves the contradiction between conductivity, corrosion resistance, mechanical strength, and cost-effectiveness in existing stainless steel materials, especially in the application of large cylindrical lithium-ion batteries. Through composition design and further process optimization, a high-performance stainless steel material with low resistivity, excellent corrosion resistance, sufficient mechanical strength, and low cost is developed to meet the performance requirements of large cylindrical lithium-ion batteries for casing materials.

[0108] Furthermore, it can be seen that the overall effect is better when all process parameters are within the preferred range of the present invention.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A stainless steel material, characterized in that, Based on weight percentage, it includes the following components: 10%≤Cr≤19%, 0≤Si≤0.5%, 0≤Ti≤1%, 0≤Cu<1%, 0≤Ni≤0.5%, 0≤Nb≤0.5%, 0<Mo≤1%, 0<Y≤0.5%, 0<Sn≤0.5%, 0≤Mn≤1%, C≤0.03%, P≤0.04%, S≤0.03%, with the balance being Fe and unavoidable impurities; and 0<Cu+Ni+Nb+Mo+Y+Sn≤3%, 0≤Si+Mn≤1%, 0≤Ti+Nb≤1%.

2. The stainless steel material according to claim 1, characterized in that, The stainless steel material comprises the following components by weight percentage: 11%≤Cr≤17%, 0≤Si≤0.3%, 0%≤Ti≤0.8%, 0%≤Cu≤0.8%, 0≤Ni≤0.2%, 0%≤Nb≤0.2%, 0%<Mo≤0.5%, 0<Y≤0.2%, 0<Sn≤0.2%, 0≤Mn≤0.8%, C≤0.03%, P≤0.04%, S≤0.03%, with the balance being Fe and unavoidable impurities.

3. The stainless steel material according to claim 1 or 2, characterized in that, 0.1%≤Cu+Ni+Nb+Mo+Y+Sn≤2.1%; and / or 0 < Mo + Y + Sn ≤ 0.9%.

4. The stainless steel material according to any one of claims 1 to 3, characterized in that, 0.2%≤Ti+Nb≤1%; and / or 0≤Ni+Mn≤1%.

5. The stainless steel material according to any one of claims 1 to 4, characterized in that, The resistivity of the stainless steel material is ≤0.77 μΩ·m; preferably, the resistivity of the stainless steel material is ≤0.598 μΩ·m; more preferably, the resistivity of the stainless steel material is ≤0.55 μΩ·m; and / or The tensile strength of the stainless steel material is 275~480MPa; preferably, the tensile strength of the stainless steel material is 275~450MPa; more preferably, the tensile strength of the stainless steel material is 300~450MPa; and / or The time for rust to appear in the stainless steel material due to salt spray corrosion is ≥8 hours; preferably, the time for rust to appear in the stainless steel material due to salt spray corrosion is ≥16 hours.

6. The method for preparing the stainless steel material according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step S1: Prepare and smelt the stainless steel material according to its composition, and then cast it into steel ingots; Step S2: The steel ingot is subjected to hot rough rolling, intermediate rolling and hot finish rolling in sequence to obtain a hot-rolled plate; Step S3: The hot-rolled plate is cold-rolled to obtain a cold-rolled plate; Step S4: Perform non-oxidizing bright annealing on the cold-rolled sheet and cool it to obtain the stainless steel material.

7. The method for preparing stainless steel material according to claim 6, characterized in that, In step S1, the melting temperature is 1500~1700℃, preferably 1550~1650℃; and / or In step S2, the temperature of the intermediate sway bar is the same as the final rolling temperature of the hot roughing roll; and / or the starting rolling temperature of the hot finishing roll is the same as the temperature of the intermediate sway bar; and / or The initial rolling temperature of the hot roughing roll is 1100~1250℃, and the final rolling temperature is 900~1100℃; preferably, the initial rolling temperature of the hot roughing roll is 1100~1200℃, and the final rolling temperature is 900~1000℃; and / or The intermediate steel-swing time is 10~100s, preferably 30~70s; and / or The final rolling temperature of the hot finishing rolling is 800~950℃, preferably 820~920℃; and / or In step S3, the reduction rate of the cold rolling is 50-80%, preferably 55-70%.

8. The method for preparing stainless steel material according to claim 6 or 7, characterized in that, In step S4 The oxidation-free bright annealing temperature is 800~1000℃, and the holding time is 30s~10min; preferably, the oxidation-free bright annealing temperature is 850~950℃, and the holding time is 1~5min, and / or In the non-oxidizing bright annealing atmosphere, the oxygen content is <10 ppm; and / or The atmosphere for the non-oxidizing bright annealing is a hydrogen atmosphere or a nitrogen-hydrogen mixture atmosphere; preferably, the atmosphere for the non-oxidizing bright annealing is a nitrogen-hydrogen mixture atmosphere, with a nitrogen-hydrogen volume ratio of (92~98):(2~8).

9. A battery casing, characterized in that, The battery casing is made of stainless steel as described in any one of claims 1 to 5.

10. A secondary battery, characterized in that, The battery casing includes the battery casing of claim 9, and optionally, the secondary battery includes a cylindrical battery.

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