A cold-rolled sheet for the casing of an alkaline energy storage battery and its manufacturing method

Abstract

This invention discloses a cold-rolled sheet for an alkaline battery casing and its production method, belonging to the field of metallurgical technology. The cold-rolled sheet for the alkaline battery casing of this invention has the following chemical composition by weight percentage: C: 0.002%–0.006%, Si ≤ 0.030%, Mn: 0.10%–0.30%, 0.008% ≤ P ≤ 0.025%, S ≤ 0.012%, Ti: 0.035%–0.055%, Cu: 0.035%–0.050%, Cr: 0.02%–0.05%, Ca: 0.015%–0.05%. With 0.35% as the remainder being Fe and unavoidable impurities, the cold-rolled sheet produced by precisely controlling the proportions of various elements in the steel, especially Mn, Cu, Ti, and Ca, improves the adhesion of the electroplated nickel layer while also ensuring the corrosion resistance and high stamping performance of the steel sheet. This meets the stringent performance requirements of battery casing steel for energy storage, improves battery life and energy density, and solves the technical problems of poor stamping performance and adhesion of cold-rolled sheets used for alkaline battery casings in existing technologies.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and more specifically, relates to a cold-rolled sheet for the casing of an energy storage alkaline battery and its production method. Background Technology

[0002] In recent years, with the rapid development of the energy storage market, the demand for steel for cylindrical batteries has also increased year by year. At the same time, users have put forward higher requirements for the lifespan of cylindrical batteries. In addition, as the public pays more and more attention to the safety performance of batteries, more stringent requirements have been put forward for the voltage resistance performance of steel batteries.

[0003] When the nickel plating layer of a cylindrical battery does not adhere well to the steel plate, the nickel powder can easily detach and react with the battery fluid, severely affecting battery life and energy density. Furthermore, when a short circuit or impact occurs, the battery experiences significant internal thermal expansion, which can easily cause it to explode.

[0004] Based on the above technical issues, a search revealed that battery casing steel currently on the market has two composition systems: aluminum-killed steel and IF steel, mainly:

[0005] The domestic patent document CN1174109C, entitled "Ultra-thin Steel Strip for Battery Casing and its Manufacturing Method," discloses an ultra-thin steel strip for battery casing and its production method. The chemical composition by weight percentage is: C≤0.0050%, Si≤0.020%, Mn: 0.15~0.30%, P: 0.010%~0.030%, S: ≤0.015%, N≤0.0040%, Al: 0.020%~0.07%, Ti: 0.010%~0.030%, Nb: 0.010%~0.025%, with the balance being Fe. This patent mainly achieves good stamping performance by adding Ti and Nb elements, but the cost is high. At the same time, single-stand rolling results in large differences in thickness at the beginning and end, requiring trimming and resulting in low yield.

[0006] Domestic patent document CN100560770C, entitled "Steel for Battery Casing with Excellent Planar Isotropic Properties and its Manufacturing Method," discloses a steel for battery casings and its manufacturing method. The chemical composition of this battery casing steel by weight percentage is as follows: C: 0.01%–0.05%, Si≤0.03%, Mn: 0.10%–0.50%, P≤0.020%, S≤0.015%, Als: 0.010%–0.10%, N: 0.0020%–0.0070%, Ti: 0.0050%–0.020%, with the remainder being Fe and unavoidable impurities. The production steps include molten iron pretreatment, converter smelting, furnace refining, hot rolling, pickling, cold rolling, bell-type annealing, leveling, and finishing into finished coils. This patent primarily addresses aluminum-killed steel systems, which have relatively poor ductility and toughness.

[0007] The domestic patent document CN102286699B, entitled "Steel for Corrosion-Resistant Battery Casings with a Stamping Speed ​​of ≥150 Pieces per Min and its Preparation Method," discloses a rapidly stamped battery casing steel and its preparation method. The chemical composition of the battery casing steel by weight percentage is as follows: C: 0.0001%~0.005%, Mn: 0.10%~0.20%, Al: 0.010%~0.050%, N: 0.00010%~0.0040%, Nb: 0.010%~0.030%, and P≤0.020%, S≤0.0150%, Cu≤0.050%, Ni≤0.050%, Cr≤0.080%, Mo≤0.050%, Si≤0.02%, with the remainder being Fe and unavoidable impurities. Production steps: Smelting and continuously casting billets according to pure steel processes; heating the continuously cast billets; rough rolling; finish rolling in the single-phase austenite region; coiling; pickling; cold rolling; degreasing; annealing in a full-hydrogen bell-type furnace; leveling and ready for use. This patent belongs to the Nb-IF steel system, which has a higher cost. It uses conventional bell-type annealing, resulting in large fluctuations in coil performance. It adopts an ultra-low C and low Mn composition system design, resulting in low final yield strength and lack of compressive strength.

[0008] The domestic patent document CN106148803A, entitled "A Production Method of Steel for Deep-Drawing Battery Casings," discloses a production method for steel used in deep-drawing battery casings. The chemical composition by weight percentage is: C: 0.0150%–0.0350%, Si ≤ 0.020%, Mn: 0.15%–0.25%, P: ≤ 0.018%, S: ≤ 0.015%, N ≤ 0.0030%, Alt: 0.030%–0.060%, Ti: 0.008%–0.015%, with the balance being Fe. This patent uses an aluminum-killed steel system, which has relatively poor stamping performance and is difficult to meet the requirements for rapid stamping of battery casing steel. Summary of the Invention

[0009] 1. The problem to be solved

[0010] To address the issues of poor stamping performance and adhesion of cold-rolled sheets used in existing energy storage alkaline battery casings, this invention provides a cold-rolled sheet for energy storage alkaline battery casings and its production method. By precisely controlling the chemical composition of the steel and optimizing the process parameters, the cold-rolled sheet produced exhibits good nickel adhesion after being stamped into a battery casing, and also possesses excellent stamping performance and corrosion resistance.

[0011] 2. Technical Solution

[0012] To solve the above problems, the present invention adopts the following technical solution:

[0013] A cold-rolled sheet for energy storage alkaline battery casing has the following chemical composition by weight percentage: C: 0.002%–0.006%, Si ≤ 0.030%, Mn: 0.10%–0.30%, 0.008% ≤ P ≤ 0.025%, S ≤ 0.012%, Ti: 0.035%–0.055%, Cu: 0.035%–0.050%, Cr: 0.02%–0.05%, Ca: 0.015%–0.035%, with the balance being Fe and unavoidable impurities. By precisely controlling the elements such as Mn, Cu, Ti, and Ca in the steel, the adhesion of the electroplated nickel layer is improved while also taking into account the corrosion resistance and high stamping performance of the steel sheet, thus meeting the stringent performance requirements of energy storage battery casing steel and improving battery life and energy density.

[0014] Further technical solutions, after testing, show a yield strength of 220MPa~270MPa, a tensile strength of 340MPa~390MPa, an elongation of ≥35%, and 125≤HV. 0.3 Cold-rolled sheets with a thickness of ≤155, r value ≥1.2, 0.5μm≤Ra≤1.0μm, and RPc≥120 exhibit good adhesion for nickel plating after being stamped into battery casings, and also possess good corrosion resistance and pressure resistance.

[0015] A method for producing cold-rolled sheet for alkaline battery casings of one or more types of energy storage, wherein the reduction rate is ≥85% in the pickling and rolling steps. A large reduction rate can increase the grain distortion energy in the steel, reduce the recrystallization temperature, which is beneficial for refining the grains and improving the deep drawing performance of the steel sheet. Furthermore, the final stand uses smooth roll rolling, and the roughness is controlled with Ra≤0.5μm and RPc≥220. This technical means can effectively improve the surface quality of the finished sheet and enhance the adhesion of the steel sheet.

[0016] Further production methods, in the continuous annealing step, the soaking temperature is controlled at 730℃~760℃ and the soaking time is 30s~300s, which is beneficial to the steel plate structure, steel adhesion performance and production stability, and lays the foundation for improving the steel adhesion performance in the subsequent leveling step.

[0017] Further production methods include using laser texturing rollers for leveling in the leveling step, controlling the leveling elongation rate at 0.6-1.2%, and using leveling rollers with Ra of 1.6μm. The surface roughness is controlled at 0.5μm≤Ra (surface roughness)≤1.0μm, and the surface roughness parameter RPc≥120, which is beneficial to the smoothness of the battery casing surface after electroplating.

[0018] 3. Beneficial effects

[0019] The present invention relates to a cold-rolled sheet for energy storage alkaline battery casings and its production method. By precisely controlling the composition of the steel and producing a low-carbon deep-drawing cold-rolled sheet for battery casings through hot rolling, pickling, continuous annealing, and leveling processes, the sheet exhibits a yield strength of 220MPa~270MPa, a tensile strength of 340MPa~390MPa, an elongation ≥35%, and 125≤HV. 0.3 Cold-rolled sheet for battery casing with a surface roughness of ≤155, r value ≥1.2, 0.5μm≤Ra (surface roughness)≤1.0μm, and RPc (surface roughness parameter) ≥120. This cold-rolled sheet exhibits good adhesion for nickel plating after being stamped into battery casings, and also has good corrosion resistance and pressure resistance. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments.

[0021] Basic Implementation

[0022] The cold-rolled sheet used for the energy storage alkaline battery casing in this embodiment has the following main chemical composition by weight percentage: C: 0.002%~0.006%, Si≤0.030%, Mn: 0.10%~0.30%, 0.008%≤P≤0.025%, S≤0.012%, Ti: 0.035%~0.055%, Cu: 0.035%~0.050%, Cr: 0.02%~0.05%, Ca: 0.015%~0.035%, with the balance being Fe and unavoidable impurities.

[0023] The proportions of each ingredient are based on:

[0024] 1) Carbon (C): As the carbon content decreases, the strength of the steel sheet decreases, while the elongation, n-value, and r-value increase, gradually improving the deep-drawing performance of the steel sheet. Therefore, ultra-low carbon is a prerequisite for producing battery casing steel. Simultaneously, trace amounts of carbon help improve the strength and hardness of the steel, ensuring the battery casing is not easily deformed. Therefore, this embodiment adopts an ultra-low carbon composition design, controlling C to 0.002%–0.006%.

[0025] 2) Silicon (Si): Excessive Si content makes it difficult to remove the iron oxide scale from the steel plate surface, and microcracks easily form due to oxide indentation. During high-speed deep drawing of the steel strip, these microcracks can act as crack initiators, leading to steel plate cracking. Furthermore, excessive Si content affects the electroplating performance of the steel plate; therefore, in this embodiment, Si ≤ 0.030%.

[0026] 3) Manganese (Mn): Mn can lower the austenite-ferrite phase transformation temperature (which can compensate for the increase in the austenite-ferrite phase transformation temperature caused by the decrease in C content), expand the hot working temperature range, and is beneficial to refine the ferrite grain size; however, if the Mn content is too high, it will be detrimental to plasticity, stamping performance, and fatigue performance. Taking all factors into consideration, the Mn percentage content in this embodiment is controlled within the range of 0.10% to 0.30%.

[0027] 4) Phosphorus (P): A certain amount of P in steel has a certain corrosion resistance effect, but excessive P in steel is prone to segregation, which is detrimental to the forming performance of steel plates. Therefore, in this embodiment, the content of P element is controlled within the range of 0.008% to 0.025%.

[0028] 5) Sulfur (S): Sulfur is a harmful element in battery casing steel, causing hot brittleness, reducing ductility and toughness, and making it prone to cracking during rolling. Furthermore, S is detrimental to weldability and reduces corrosion resistance. Therefore, in this embodiment, the S content in the steel is controlled to be ≤0.012%.

[0029] 6) Copper (Cu): Cu can effectively improve the corrosion resistance of steel. In addition, Cu can effectively improve the adhesion between the nickel layer and the steel substrate, thereby improving the corrosion resistance of the battery casing. However, excessive Cu will deteriorate the processing performance of the material. Therefore, the Cu content in this invention is controlled within the range of 0.035% to 0.050%.

[0030] 7) Chromium (Cr): Small amounts of Cr improve the corrosion resistance of steel, and also help improve the adhesion of the nickel layer. When Cu and Cr are added to steel simultaneously, the electrochemical reaction in the steel is inhibited, which helps improve the corrosion resistance of the battery casing. However, Cr can significantly increase the strength and hardness of steel, deteriorating the stamping performance of the steel sheet. Therefore, the Cr content should be controlled within the range of 0.02% to 0.05%.

[0031] 8) Calcium (Ca): A small amount of Ca can improve the surface quality of steel plates and effectively enhance the adhesion of the nickel layer, thereby improving the corrosion resistance of the steel plate. Therefore, the Ca content should be controlled within the range of 0.015% to 0.035%.

[0032] 9) Titanium (Ti): Ti is a strong carbide, sulfide, and nitride forming element. These compounds are not easily soluble in austenite at high temperatures, thus hindering austenite grain growth, refining grains, and improving the deep-drawing performance of steel plates. However, excessive second-phase precipitates can also affect the deep-drawing performance of steel plates. Therefore, in this embodiment, the Ti content of the steel is controlled within the range of 0.035% to 0.055%.

[0033] By precisely controlling the elements in the steel, especially Mn, Cu, Ti and Ca, the adhesion of the electroplated nickel layer can be improved while also taking into account the corrosion resistance and high stamping performance of the steel plate, so as to meet the stringent performance requirements of battery shell steel for energy storage and improve battery life and energy density.

[0034] The manufacturing method for cold-rolled steel sheets used in ultra-low carbon energy storage alkaline battery casings requires the following steps: molten iron smelting, continuous casting of slabs, flame cleaning, homogenization in a soaking furnace, hot continuous rolling with controlled cooling, coiling, pickling, cold rolling, and continuous annealing. The process requirements are as follows:

[0035] (1) In smelting and continuous casting, pre-slag removal and post-slag removal measures are adopted during the hot metal pretreatment process to adjust the [S] element, so as to reduce the harmful elements in the molten steel. Self-circulating scrap steel is added in the early and middle stages of decarburization to modify the ladle top slag, which helps to reduce the impurity elements in the molten steel.

[0036] (2) Hot rolling and coiling: The heating temperature is controlled at 1200℃~1250℃. At high temperatures, the second-phase particles dissolve in the steel, which is beneficial for rolling. During the coiling process, fine particles are re-precipitated, which is beneficial for improving the stamping performance and corrosion resistance of the material. The final rolling temperature is controlled at 850℃~920℃. This temperature ensures that the final rolling temperature is controlled above the austenite temperature, avoiding the mixed crystal phenomenon caused by rolling in the two-phase region. The coiling temperature is set at 650℃~710℃ to achieve fine and uniform grains and precipitates.

[0037] (3) Pickling and rolling: Pickling and rolling are carried out using five-stand continuous rolling with a pickling reduction rate of ≥85%. A large reduction rate can increase the grain distortion energy in the steel, reduce the recrystallization temperature, and is conducive to grain refinement and improving the deep drawing performance of the steel plate. The last stand uses smooth roll rolling with a roughness control of ≤0.5μm and RPc≥220. This measure can effectively improve the surface quality of the finished plate and increase the adhesion of the steel plate.

[0038] (8) Continuous annealing: the soaking temperature is controlled at 730℃~760℃ and the soaking time is 30s~300s.

[0039] (9) Smoothing: Laser texturing rollers are used for smoothing, and the smoothing elongation is controlled at 0.6-1.2%. A smoothing roller with Ra of 1.6μm is used to ensure that the surface roughness of the plate is 0.5μm≤Ra≤1.0μm and RPc≥120. This roughness is beneficial to the smoothness of the battery shell surface after electroplating.

[0040] The cold-rolled sheet obtained was tested and found to have a yield strength of 220MPa~270MPa, a tensile strength of 340MPa~390MPa, an elongation of ≥35%, and 125≤HV. 0.3Cold-rolled sheets with a thickness of ≤155, r value ≥1.2, 0.5μm≤Ra≤1.0μm, and RPc≥120 exhibit good adhesion for nickel plating after being stamped into battery casings, and also possess good corrosion resistance and pressure resistance.

[0041] Specific Examples 1 to 6 and Comparative Examples 1 to 7

[0042] The basic steps of Examples 1 to 6 below are the same as those of the basic examples above. The chemical composition ratios, step parameters of the method for improving steel adhesion performance, and the performance of steel products for battery casings are shown in Tables 1, 2, and 3. Comparative Examples 1 to 7 are smelted using existing smelting methods:

[0043] Table 1 Chemical composition, wt%

[0044] category C Si Mn P S Cu Cr Ca Ti Example 1 0.0021 0.023 0.10 0.008 0.006 0.036 0.026 0.018 0.035 Example 2 0.0057 0.015 0.28 0.024 0.011 0.048 0.043 0.032 0.053 Example 3 0.0035 0.021 0.19 0.015 0.008 0.042 0.035 0.025 0.046 Example 4 0.0048 0.018 0.29 0.018 0.010 0.040 0.036 0.022 0.041 Example 5 0.0058 0.005 0.18 0.022 0.007 0.038 0.026 0.020 0.038 Example 6 0.0026 0.008 0.15 0.013 0.009 0.045 0.025 0.017 0.043 Comparative Example 1 0.0030 0.013 0.22 0.010 0.008 0.025 - - 0.045 Comparative Example 2 0.0021 0.014 0.20 0.006 0.004 - - - 0.050 Comparative Example 3 0.0023 0.022 0.23 0.012 0.005 0.036 0.055 0.016 0.055 Comparative Example 4 0.0045 0.009 0.32 0.015 0.005 - - 0.023 0.047 Comparative Example 5 0.025 0.018 0.18 0.012 0.007 0.043 0.027 - - Comparative Example 6 0.032 0.006 0.21 0.011 0.005 0.014 0.028 - 0.012 Comparative Example 7 0.031 0.012 0.30 0.012 0.007 0.041 0.049 0.024 0.046

[0045] All production processes were trial-produced according to Table 2, and the thickness of the finished product was 0.25mm.

[0046] Table 2 Production Process

[0047]

[0048]

[0049] The final mechanical properties and electroplating adhesion test results are shown in Table 3. The electroplating adhesion test method involved bending the electroplated battery casing 180°, securing it with 3M tape, and then peeling it off to check for nickel powder detachment. The casing was then bent 360° in the opposite direction of the previous bending mark, secured with 3M tape again, and peeled off to check for nickel powder detachment. If no nickel powder detached, the test was successful; otherwise, it was unsuccessful.

[0050] Table 3 Mechanical properties and electroplating adhesion

[0051]

[0052] The comparison in Table 3 shows that all performance parameters of Examples 1 to 6 meet the requirements. Among them, although the proportions of each element are in the middle range and many performance indicators are also in the middle range, Example 3 has the highest r value (plastic strain ratio) while meeting the requirements of the electroplating nickel adhesion and strength of the cold-rolled sheet for battery casing of the present invention. It is the most preferred example.

[0053] Comparative Examples 1-7:

[0054] In Comparative Example 1, although the r value was relatively high due to the absence of Cr and Ca elements, the RPc value was lower than 120, the yield strength was lower than 220 MPa, the hardness was low, the electroplating adhesion was poor, and nickel powder fell off during 0T bending, which could not meet the requirements of high-speed stamping and pressure resistance of battery casing steel.

[0055] Comparative Example 2 uses a common IF steel composition system. Although the r value is also relatively high, the yield strength and hardness are relatively low, and the adhesion of nickel powder is poor.

[0056] In comparison, the Cr element in column 3 exceeds the upper limit requirement of this invention, resulting in excessively high performance, high tensile strength, and low r value. This makes it easy for iron filings to fall off during the stamping process, which cannot meet the high-speed stamping requirements of battery casing steel.

[0057] Comparative Example 4 had a yield strength and hardness values ​​that were too low due to an annealing temperature higher than 760℃, which could not meet the requirements of the finished product. At the same time, the electroplating adhesion was poor, and the mixed crystals occurred due to the low final rolling temperature.

[0058] Compared with columns 5 and 6, which both use aluminum-killed steel, the final product has a significantly lower r value. At the same time, due to the low RPc value, the plate surface is rough, the electroplating adhesion is poor, and nickel powder falls off during 0T bending.

[0059] In Comparative Example 7, except for element C which exceeds the upper limit requirement of this invention, all other elements meet the design requirements of this invention. The final product exhibits a high yield strength and a low r-value. Although the electroplating effect meets the requirements, it does not meet the stamping requirements of battery casing steel.

[0060] The examples described herein are merely preferred embodiments of the invention and are not intended to limit the concept and scope of the invention. Any modifications and improvements made by those skilled in the art to the technical solutions of the invention without departing from the design concept of the invention should fall within the protection scope of the invention.

Claims

1. A cold-rolled sheet for an alkaline battery casing, characterized in that: The chemical composition by weight percentage of each element is as follows: C: 0.002%~0.006%, Si≤0.030%, Mn: 0.10%~0.30%, 0.008%≤P≤0.025%, S≤0.012%, Ti: 0.035%~0.055%, Cu: 0.035%~0.050%, Cr: 0.02%~0.05%, Ca: 0.015%~0.035%, with the balance being Fe and unavoidable impurities; In the pickling and rolling steps of cold-rolled sheet, the reduction rate is ≥85%, and the final stand is rolled with smooth rolls, with a roughness control of ≤0.5μm and RPc≥220; In the leveling step, laser texturing rollers are used for leveling, the leveling elongation is controlled at 0.6%~1.2%, and leveling rollers with Ra of 1.6μm are used. The surface roughness is controlled at 0.5μm≤Ra≤1.0μm and RPc≥120.

2. The cold-rolled sheet for the casing of an alkaline energy storage battery according to claim 1, characterized in that: Yield strength 220MPa~270MPa, tensile strength 340 MPa~390MPa, elongation ≥35%, 125≤HV0.3≤155, r value ≥1.2, 0.5μm≤Ra≤1.0μm, RPc≥120.

3. The cold-rolled sheet for the casing of an alkaline energy storage battery according to claim 2, characterized in that: During the continuous annealing process, the soaking temperature is controlled at 730℃~760℃, and the soaking time is 30s~300s.

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