A tinplate for easy-open end and a method of manufacturing the same

Abstract

This invention relates to the field of alloy materials technology, and discloses a tinplate for easy-open lids and its manufacturing method. The method includes the following steps: steelmaking, continuous casting, hot rolling, pickling, cold rolling, annealing, leveling, and electroplating with tin. The manufacturing method of the tinplate provided by this invention adopts a low-carbon, low-manganese, and high-nitrogen composition design, eliminating the need for additional Mn, B, Ti, and other alloys, resulting in low smelting costs. Furthermore, by employing an annealing process related to N content, the precipitation strengthening and solid solution strengthening effects of N atoms are fully utilized, enabling the tinplate to achieve a hardness of 65±2 (HR30T). Simultaneously, due to the small fluctuation in N content and the adjustment of the annealing temperature for tinplates with different N contents, the final result is a high hardness with minimal fluctuation. The manufacturing method of this invention features low production costs, simple process control, high manufacturing efficiency, and excellent product quality.

Description

Technical Field

[0001] This invention relates to the field of metal materials technology, specifically to a tin-plated sheet for easy-open covers and its manufacturing method. Background Technology

[0002] Easy-open lids are lids with pre-cut grooves of a certain depth and riveted pull rings, which can be safely torn open along the grooves when opening. They are used for sealing and opening metal cans and are widely used in metal packaging products such as food cans, beverage cans, and dry powder cans. For easy-open lids, the thickness of tinplate is generally no more than 0.25 mm, and for thinner lids, it is no more than 0.20 mm. Tinplate with a temper of T5 (hardness range 65±4) is typically used. During riveting deformation, the tinplate thickness is reduced by more than 50%, and the thickness of the steel plate in the thinned area and at the scoring lines is less than 0.10 mm. Therefore, to ensure the pressure resistance of the easy-open lid, the tinplate must have high hardness. Furthermore, the paint film on the easy-open lid surface needs to withstand multiple deformations and frictions during processing, so the tinplate must also have good paint film adhesion. According to the GB / T1720-2020 "Paint Film Cross-Strike Test" grading standard, an adhesion level of 1 ensures that the paint film remains intact and does not peel off during the easy-open lid processing. Therefore, tinplate for easy-open lids must meet the requirements of high hardness and high adhesion.

[0003] To address the high hardness requirement of tin-plated sheets for easy-open lids, existing technologies mainly employ two approaches to improve hardness:

[0004] (1) Designed with high carbon content components

[0005] Chinese patent document CN104419865A discloses a cold-rolled tinplate for easy-open lids and its manufacturing method. The cold-rolled tinplate for easy-open lids is smelted according to the following composition by mass percentage: C: 0.11%-0.15%, Si: 0.005%-0.03%, Mn: 0.15%-0.25%, P≤0.02%, S≤0.02%, Alt: 0.065%-0.085%, N≤0.0045%, with the balance being Fe. And unavoidable impurity elements; the process involves desulfurization of molten iron, combined blowing from the top and bottom of the converter, argon blowing from the bottom of the ladle or refining in an LF furnace, full-process Ar-protected casting, heating in a slab heating furnace, descaling, rough rolling, finish rolling, and coiling to obtain hot-rolled steel coils, which are then re-coiled, pickled, cold-rolled, annealed in a vertical continuous annealing furnace, tin-plated, and coiled to obtain the finished product; the resulting tin-plated sheet has a lower yield strength of 435MPa-460MPa and a tensile strength of 485MPa-505MPa. This method uses a high-carbon composition to design high-hardness tinplate, with a carbon content of 0.11%-0.15%, which falls within the peritectic steel composition range. However, due to the significant volume shrinkage of molten steel during solidification within this composition range, continuous casting slab cracks are prone to occur. Strict control of process parameters such as casting speed and cooling rate is required, resulting in a narrow process window, significant difficulty in controlling continuous casting production, and unstable slab quality. Furthermore, the high carbon content in the slab leads to high strength in the rolled hot-rolled steel coils, requiring high rolling force from the mill. Especially when rolling 2.0mm thick hot-rolled steel coils into thin 0.18mm-0.20mm tinplate substrates, the cold rolling reduction rate reaches over 90%, placing a heavy load on the cold rolling mill. This necessitates reducing the rolling speed to ensure product quality, resulting in low production efficiency.

[0006] (2) Add alloying elements such as Mn, Ti, and Cr

[0007] Chinese patent document CN106086643A discloses a high-strength, high-elongation tin-plated base plate and its secondary cold rolling method. The tin-plated base plate has the following composition by mass percentage: C: 0.065%-0.12%, Mn: 0.2%-0.8%, Al: 0.01%-0.08%, N: 0.003%-0.015%, with the remainder being Fe and unavoidable impurities. The tin-plated base plate also contains one or more of the following: B: 0.001%-0.005%, Cr: 0.01%-0.05%, Ti: 0.001%-0.1%, Nb: 0.001%-0.2%, Cu: 0.01%-0.03%, and Mo: 0.002%-0.008%. The base plate needs to undergo secondary cold rolling, with the reduction rate controlled at 5%-13% and the rolling tension at 50MPa-100MPa. This method ensures that the tin-plated base plate retains high yield strength and elongation in the RD, 45°, and TD directions after baking, and its yield strength R after baking hardening is [missing information]. P0.2≥520MPa, with elongation A in the rolling direction RD, 45° direction, and vertical direction TD all greater than or equal to 10%. Increasing the hardness of tinplate by adding alloying elements such as Mn, Ti, and Cr obviously increases alloy consumption and production costs. Furthermore, the addition of alloys inevitably leads to an increase in the strength of the hot-rolled raw material, which also increases the difficulty of cold-rolling production.

[0008] To address the need for high adhesion, existing technologies primarily rely on the combined control of tin-plated substrates and passivation processes, specifically including:

[0009] (1) Optimize the substrate surface structure

[0010] By limiting process parameters such as surface roughness, service life, and rolling force of the working rollers in the leveling process, the roughness and peak density of the substrate can be increased to improve the adhesion between the tinplate surface and the paint film. However, this method is not suitable for high-hardness tinplates. High tinplate hardness leads to high leveling rolling force and rapid attenuation of roller surface roughness, which affects product quality stability and increases the cost of roller use.

[0011] (2) Optimize passivation process

[0012] By adjusting parameters such as passivation solution concentration, pH, and passivation current density in combination with the strip running speed, the thickness and composition of the passivation film can be controlled. At the same time, the content and relative ratio of Cr2O3 and Cr(OH)3 in the passivation film can be changed to improve adhesion. The production speed can be reduced to improve the uniformity of the passivation film, and finally the adhesion can meet the requirements of easy-to-open cap. However, this method has a narrow process window, is difficult to control, and has low production efficiency.

[0013] In summary, the analysis shows that, to meet the requirements of high hardness and high adhesion for easy-open tinplate, the existing manufacturing methods for easy-open tinplate suffer from high production costs, narrow process windows, difficult production control, and unstable product quality. Therefore, optimizing and improving the manufacturing methods for easy-open tinplate to obtain tinplate with low production costs, wide process windows, simple process control, stable product quality, and good adhesion and hardness is a pressing technical challenge that needs to be addressed in this field. Summary of the Invention

[0014] In view of this, the present invention provides a method for manufacturing tinplate with simple process control, wide process window, low production cost, high hardness and small hardness fluctuation. The method adopts a low carbon, low manganese and high nitrogen composition design, combined with a specific annealing process, to make full use of the solid solution strengthening and precipitation strengthening effects of nitrogen in steel, so that the hardness of the tinplate reaches 65±2HR30T.

[0015] Furthermore, the present invention also provides a method for manufacturing tin-plated sheets. This method employs a two-stage drying process based on the above-mentioned process, enabling the tin-plated sheet to achieve an adhesion level of Grade 1, thereby meeting the requirements for high hardness and high adhesion of thin-gauge, easy-open tin-plated sheets. Moreover, this method has low production costs, a wide process window, simple process control, stable product quality, and wide applicability, resulting in products with good quality stability.

[0016] To achieve the above objectives, the present invention adopts the following technical solution:

[0017] In a first aspect, the present invention provides a method for manufacturing a tin-plated sheet, comprising the following steps in sequence:

[0018] Steelmaking, continuous casting, hot rolling, pickling, cold rolling, annealing, leveling, and tin plating; among which,

[0019] Controlling the chemical composition of slabs during steelmaking and continuous casting includes, by mass percentage: C: 0.060%-0.080%, Mn: 0.15%-0.25%, Si: ≤0.03%, P: ≤0.015%, S: ≤0.010%, Al: 0.04%-0.06%, N: 0.0060%-0.0090%, with the balance being Fe and other unavoidable impurities. The mass percentages of C, Mn, and N elements must satisfy the following relationship: 3 ≤ 1.0 × (100 × C content - 0.06) / 0.01 + 0.2 × (100 × Mn content - 0.15) / 0.10 + 0.5 × (100 × N content - 0.0030) / 0.001 ≤ 5.

[0020] During the annealing process, the strip speed is controlled at 450m / min-500m / min, and the annealing temperature T (°C) is set according to the N content in the strip: T = 660 + 5 × (100 × N content - 0.0060) / 0.0010.

[0021] In one optional implementation, the speed fluctuation of the same steel coil is controlled to be no more than ±10 m / min and the annealing temperature fluctuation is controlled to be no more than ±3℃ during the annealing process.

[0022] In one alternative embodiment, a nitrogen enrichment process is performed using a wire feeding method to obtain the N content in the slab, and the nitrogen enrichment material used is manganese nitride cored wire.

[0023] In one alternative embodiment, during the hot rolling process, the slab heating temperature is controlled at 1180℃-1220℃, the final rolling temperature at 850℃-880℃, and the coiling temperature at 650℃-680℃.

[0024] In one alternative implementation, the molten steel is first subjected to RH vacuum treatment during the steelmaking process, followed by nitrogen enrichment treatment.

[0025] In one optional embodiment, the tin plating process includes sequentially uncoiling, degreasing and cleaning, pickling, electroplating, remelting, passivation, rinsing, drying, cooling, oiling, and winding up the annealed steel coil to obtain a tin-plated steel coil.

[0026] In one optional embodiment, a two-stage drying process is used to dry the passivation film after rinsing, and the mass of the passivation film per square meter is 4mg-6mg based on the Cr content; wherein,

[0027] The first stage is hot air drying.

[0028] The second stage is high-frequency induction heating treatment, with a heating temperature of 190℃-200℃ and a heating time of 0.5s-0.7s;

[0029] Furthermore, during the passivation step, the pH of the passivation solution is 4.1-4.4.

[0030] In one optional embodiment, the drying temperature in the first stage is 110℃-120℃, and the drying time is 1s-3s.

[0031] In one alternative implementation, the second stage employs inert gas protection during the heating process;

[0032] And / or, the frequency of the high-frequency sensing is 150kHz-160kHz.

[0033] In one optional embodiment, the passivation film is prepared using a two-stage passivation process, wherein the first stage of passivation is chemical passivation and the second stage of passivation is electrochemical passivation.

[0034] In one optional embodiment, the chemical passivation and the electrochemical passivation use the same passivation solution and passivation temperature, wherein the passivation solution is an aqueous solution of sodium dichromate at a concentration of 18 g / L to 24 g / L, and the passivation temperature is 40°C to 45°C.

[0035] In one optional embodiment, the passivation time of the chemical passivation is 0.5s-0.7s.

[0036] In one optional embodiment, the passivation time of the electrochemical passivation is 0.5s-0.7s.

[0037] In one alternative embodiment, the passivation charge density during the electrochemical passivation is 0.9 C / dm³. 2 -1.2C / dm 2 .

[0038] Secondly, the present invention provides a tin-plated plate prepared as described above.

[0039] In one alternative embodiment, the passivation film in the tin-plated plate has a mass of 4 mg-6 mg per square meter, calculated based on Cr content, and the weight percentage of Cr(OH)3 in the passivation film is 10%-20%.

[0040] In one alternative embodiment, the tin-plated plate has a thickness of 0.18 mm to 0.20 mm.

[0041] In one alternative embodiment, the tinplate has a hardness (HR30T) of 65±1.5 and an elongation after fracture of 16%-21%.

[0042] Thirdly, the present invention provides an application of the above-mentioned tin-plated sheet as an easy-open lid in packaging products.

[0043] The following is a detailed analysis and explanation of the main functions of each chemical component in this invention and the selection of their dosage:

[0044] Carbon (C) is the most economical strengthening element in steel. Retaining a certain C content during steelmaking is beneficial for achieving material strength and hardness at low cost. However, as the C content increases to 0.09% or higher, it enters the peritectic steel composition range, making it prone to casting cracks. Simultaneously, excessively high C content results in high strength in hot-rolled raw materials, making cold rolling difficult. Therefore, this invention selects a C content of 0.06%-0.08%.

[0045] Mn: As a solid solution strengthening element, Mn can improve the strength of steel plates without significantly reducing plasticity. Simultaneously, Mn combines with S to form MnS, reducing the hot brittleness of steel. However, excessively high Mn content will increase alloy costs. Therefore, this invention selects an Mn content of 0.15%-0.25%.

[0046] Si: Si tends to accumulate and oxidize on the steel surface, which is detrimental to the surface quality and coating performance of the steel plate. Therefore, the lower the Si content, the better. In this invention, Si ≤ 0.03% is selected.

[0047] P: P has a strong solid solution strengthening effect, but it is prone to segregation, forming banded structures, which reduces the plasticity and toughness of the steel plate and is detrimental to its formability. In this invention, P ≤ 0.015% is selected.

[0048] S: For tinplate, S is a harmful impurity element that easily forms sulfide inclusions, which is detrimental to the forming of steel plates. In this invention, S ≤ 0.010% is selected.

[0049] Nitrogen (N): In steel, nitrogen is an interstitial solid solution atom and can combine with al to form AlN precipitates, playing a role in solid solution strengthening and precipitation strengthening. For tinplate, increasing the nitrogen content can effectively improve the strength and hardness of the tinplate. However, if the nitrogen content is too high, the tinplate will have excessive hardness and poor plasticity, which is not conducive to the processing and forming of the tinplate. At the same time, the recrystallization temperature of the steel sheet will increase, requiring a higher annealing temperature and increasing production costs. In addition, a larger range of nitrogen content control can easily lead to large fluctuations in the hardness of different batches of tinplate. This invention selects an nitrogen content range of 0.0060%-0.0090%. Meanwhile, this invention found that the hardness of tinplate is most strongly correlated with the content of C, Mn, and N. Based on the composition content of C: 0.06%, Mn: 0.15%, and N: 0.0030%, an increase of 0.01% in C content increases the hardness by 1.0 (HR30T), an increase of 0.1% in Mn content increases the hardness by approximately 0.2 (HR30T), and an increase of 0.0010% in N content increases the hardness by 0.5 (HR30T). To ensure that the hardness value of the tinplate reaches 65 (HR30T) and reduce hardness fluctuations, a reasonable N content is matched according to the C and Mn contents. The N content range satisfies the relationship 3≤1.0×(100×C content-0.06) / 0.01+0.2×(100×Mn content-0.15) / 0.10+0.5×(100×N content-0.0030) / 0.001≤5.

[0050] Al: Al is added during steelmaking as a deoxidizer. Al can also combine with nitrogen to form AlN, which strengthens the steel through precipitation. However, excessively high Al content can lead to increased inclusions, poorer continuous casting properties, and higher alloy costs. Therefore, this invention selects an Al content range of 0.04%-0.06%.

[0051] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0052] 1. The manufacturing method of tin-plated sheet provided by the present invention includes the following steps: steelmaking, continuous casting, hot rolling, pickling, cold rolling, annealing, leveling, and electroplating with tin; wherein, during the steelmaking and continuous casting processes, the chemical composition of the slab is controlled as follows (by mass percentage): C: 0.060%-0.080%, Mn: 0.15%-0.25%, Si: ≤0.03%, P: ≤0.015%, S: ≤0.010%, Al: 0.04%-0.06%, N: 0.0060%-0.0090%, with the balance being Fe and other unavoidable impurities. Impurities, and the mass percentage content of C, Mn, and N elements satisfies the following relationship: 3≤1.0×(100×C content-0.06) / 0.01+0.2×(100×Mn content-0.15) / 0.10+0.5×(100×N content-0.0030) / 0.001≤5; During the annealing process, the strip speed is controlled at 450m / min-500m / min, and the annealing temperature T (°C) is set according to the N content in the strip, T=660+5×(100×N content-0.0060) / 0.0010. The manufacturing method of tinplate provided by this invention adopts a low-carbon, low-manganese, and high-nitrogen composition design, eliminating the need for additional additions of alloys such as Mn, B, and Ti, resulting in low smelting costs. Furthermore, by employing an annealing process related to N content, the precipitation strengthening and solid solution strengthening effects of N atoms are fully utilized, enabling the hardness of the tinplate to reach the range of 65±2. Preferably, the hardness can be controlled to the range of 65±1.5. Simultaneously, due to the small fluctuation of N content and the adjustment of annealing temperature for tinplates with different N contents, the final result is a tinplate with high hardness and small fluctuation.

[0053] The manufacturing method of this invention has low production cost, simple process control, high manufacturing efficiency, and excellent product quality.

[0054] 2. The method for manufacturing tinplate provided by the present invention controls the slab heating temperature to 1180℃~1220℃, the final rolling temperature to 850℃~880℃, and the coiling temperature to 650℃~680℃ during the hot rolling process. This controls the precipitation of AlN and appropriate coarsening of grains in the hot-rolled steel coil, reduces the strength of the hot-rolled raw material, effectively reduces the rolling force of the cold rolling, and improves production efficiency.

[0055] 3. The manufacturing method of tin-plated sheet provided by the present invention uses a wire feeding method to perform quantitative nitrogen addition treatment, so as to achieve a stable N content in the tin-plated sheet within the range of 0.0060%-0.0090%, with high precision in nitrogen content control.

[0056] 4. The method for manufacturing tin-plated plates provided by the present invention uses a drying method combining hot air drying and high-frequency induction heating to dry a passivation film of a specific thickness. This method can promote the full conversion of Cr(OH)3 on the surface of the passivation film into Cr2O3, remove the water of crystallization from the surface of the passivation film, and achieve a stable control of the Cr(OH)3 content in the passivation film at 10%-20%. This solves the problem of poor adhesion caused by high Cr(OH)3 content in the prior art.

[0057] Specifically, the drying process includes two stages. The first stage is hot air drying, which allows the moisture on the surface of the passivation film to evaporate quickly and be carried away by the dry hot air, thereby removing residual moisture from the steel plate surface and achieving thorough drying. The second stage is high-frequency induction heating treatment, which rapidly heats the strip steel, completely removes the moisture from the strip steel surface, and promotes the conversion of Cr(OH)3 in the passivation film surface layer to Cr2O3. The crystal water in the passivation film surface layer is released and carried away by the dry gas, so that the weight percentage of Cr(OH)3 in the passivation film is stably maintained at 10%-20%, thereby avoiding changes in the passivation film structure during the painting and baking process that would cause a decrease in adhesion.

[0058] In the passivation step, the pH of the passivation solution is 4.1-4.4. If it is too high or too low, the Cr(OH)3 content will be too high during the film formation process, making it difficult to fully convert through drying treatment. In the end, the Cr(OH)3 ratio on the tin-plated plate surface will be high, and the adhesion will not reach level 1.

[0059] 5. The tin-plated plate manufacturing method provided by the present invention uses the same passivation solution parameters for both chemical passivation and electrochemical passivation processes: sodium dichromate concentration of 18 g / L-24 g / L, pH value of 4.1-4.4, and passivation temperature of 40℃-45℃. This method can obtain a passivation film with Cr(OH)3 and Cr2O3 as the main components, ensuring the quality of the film formation.

[0060] 6. The tin-plated sheet provided by this invention has high hardness and small hardness fluctuation, while the paint adhesion is stable at level 1, effectively solving the problems of insufficient pressure resistance and paint film peeling when thin-gauge tin-plated sheets are used in easy-open covers. Detailed Implementation

[0061] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0062] Where specific experimental steps or conditions are not specified in the examples, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0063] Tinplate refers to steel sheets with a thin layer of tin plating on their surface. It is produced by rolling low-carbon steel into sheets approximately 2mm thick, followed by pickling, cold rolling, electrolytic cleaning and annealing, leveling, edge trimming, cleaning, electroplating, remelting, passivation, rinsing, drying, cooling, oiling, and finally cutting into finished tinplate sheets. Tinplate is widely used in the food canning industry, electronic components, chemical paints, and many other fields due to its advantages such as being odorless, non-toxic, lightweight, easy to process and shape, and easy to print patterns on.

[0064] Paint film adhesion is a key indicator for tinplate. According to the national standard GB / T1720-2020 "Paint Film Cross-Cut Test", adhesion is divided into 7 levels, with level 1 being the best. Many factors affect paint film adhesion, including the surface structure of the tinplate, the printing process, the quality of the coating, the coating thickness, and the passivation film. Regarding the passivation film, research has found that its thickness and structure significantly affect paint film adhesion. If the passivation film is too thin, the corrosion resistance, sulfur resistance, and acid resistance of the tinplate will decrease. Conversely, if the passivation film is too thick, it is prone to cracking and has a loose structure, thus reducing paint film adhesion. The chemical structure of the passivation film mainly consists of Cr(III) hydroxyl-bridged compound Cr(OH)3 and oxygen-bridged compound Cr2O3. Due to hydrogen bonding, Cr(OH)3 has a denser spatial configuration than Cr2O3, which is beneficial for the formation of... To form a dense film, Cr(OH)3 is an essential component for the passivation film to possess good corrosion resistance. However, Cr(OH)3 is unstable. If the weight percentage of Cr(OH)3 in the passivation film is too high, Cr(OH)3 easily loses its water of crystallization and transforms into Cr2O3 during the tin-plating process, damaging the bonding force between the passivation film and the paint film on the tin-plated surface, which is detrimental to adhesion. If the weight percentage of Cr(OH)3 in the passivation film is less than 10%, the barrier effect against external corrosive media decreases, resulting in insufficient corrosion resistance and negatively impacting the overall performance of the tin-plated board. Therefore, preparing a passivation film with appropriate thickness and Cr(OH)3 content is crucial for improving the adhesion of tin-plated boards.

[0065] To address the demand for high hardness, existing technologies employ two approaches. One is to use a high-carbon composition design, but this can easily lead to cracks in continuously cast slabs. It requires strict control of process parameters such as casting speed and cooling rate, resulting in a narrow process window, making steelmaking continuous casting production control difficult and causing unstable slab quality. On the other hand, adding alloying elements such as Mn, Ti, and Cr to increase the hardness of tinplate obviously increases alloy consumption and production costs. At the same time, the addition of alloys inevitably leads to an increase in the strength of hot-rolled raw materials, which also increases the difficulty of cold-rolling production.

[0066] To address the problems existing in the aforementioned related technologies, according to a first aspect of the present invention, the present invention provides a method for manufacturing tin-plated sheets, comprising sequentially performing steelmaking and continuous casting, hot rolling, pickling and cold rolling, continuous annealing and leveling, and electroplating with tin.

[0067] (1) Steelmaking and continuous casting: The molten steel is smelted in a converter and treated with RH vacuum, which can effectively improve the cleanliness of the molten steel, reduce the number and size of inclusions in the steel, avoid cracking caused by inclusions during the processing of tinplate, and ensure the processability of tinplate; the molten steel is treated with nitrogen by wire feeding method, which greatly improves the accuracy of nitrogen content control compared with the bottom blowing nitrogen method in the existing technology; the nitrogen-enhancing material is selected as manganese nitride cored wire, which can simultaneously control the Mn and N content in the steel, reduce the amount of expensive metal Mn added, save alloy costs, and avoid the introduction of elements such as Si that are detrimental to the surface quality of tinplate by adding silicon nitride alloy;

[0068] The chemical composition of the slab is controlled as follows during steelmaking and continuous casting: by mass percentage, C: 0.060%-0.080%, Mn: 0.15%-0.25%, Si: ≤0.03%, P: ≤0.015%, S: ≤0.010%, Al: 0.04%-0.06%, N: 0.0060%-0.0090%, with the balance being Fe and other unavoidable impurities. The mass percentages of C, Mn, and N elements satisfy the following relationship: 3≤1.0×(100×C content-0.06) / 0.01+0.2×(100×Mn content-0.15) / 0.10+0.5×(100×N content-0.0030) / 0.001≤5.

[0069] (2) Hot rolling: An austenitic rolling process is used. If the slab heating temperature is too high, a large amount of AlN dissolves during heating, leading to an increase in dissolved nitrogen content. This requires a higher aluminum content and a longer, higher-temperature coiling time to fully precipitate AlN. If the slab heating temperature is too low, the hot rolling force increases, which can easily lead to a low final rolling temperature. Therefore, the slab heating temperature is controlled between 1180℃ and 1220℃. This ensures the rolling temperature is above the phase transformation point A. r3 Under these conditions, a lower final rolling temperature is used to avoid uneven grain size and coarseness caused by rolling in the two-phase region. Therefore, a final rolling temperature of 850℃-880℃ is selected. If the coiling temperature is too low, the cooling rate needs to be increased, resulting in fine grains and difficulty in AlN precipitation. The strong solid solution strengthening effect of N atoms leads to high steel plate strength, but also increases the difficulty of cold rolling. If the coiling temperature is too high, the surface iron oxide is not easy to remove, which can easily cause surface defects in tinplate. Therefore, a coiling temperature of 650℃-680℃ is selected.

[0070] (3) The pickling and cold rolling steps include sequentially uncoiling, pickling, trimming, cold rolling and coiling the hot-rolled steel coil to obtain a cold-hardened coil with a thickness of 0.18mm-0.20mm;

[0071] (4) Continuous annealing and leveling: If the strip speed is too low, it will affect the output and easily cause coarse grains and low hardness; while if the strip speed is too high, the annealing time will be short, which is not conducive to grain homogenization and nitride precipitation during the annealing process, and is prone to large hardness fluctuations. Therefore, a strip speed of 450m / min-500m / min is selected. Since AlN precipitates in steel inhibit recrystallization, the N content increases and the recrystallization temperature of tinplate rises. If the annealing temperature is too low, insufficient recrystallization will easily occur, resulting in banded structure, which is not conducive to processing and forming; while if the annealing temperature is too high, the hardness will be too low and cannot meet the high hardness requirement for easy opening. Meanwhile, tinplates with different nitrogen contents exhibit significant differences in hardness when annealed at the same temperature. Therefore, the annealing temperature is controlled based on the nitrogen content. Within the nitrogen content range of 0.0060%-0.0090%, the strip speed is 450m / min-500m / min, and the annealing temperature range is 660℃-675℃. The annealing temperature T (℃) is set according to the nitrogen content of the tinplate, satisfying the relationship T=660+5×(100N-0.0060) / 0.0010. The strip speed fluctuation of the same steel coil is controlled to not exceed ±10m / min, and the annealing temperature fluctuation is controlled to not exceed ±3℃, thereby further reducing the hardness fluctuation of the tinplate.

[0072] (5) Tin plating: The tin plating process includes uncoiling, degreasing and cleaning, pickling, electroplating, softening, passivation, rinsing, drying, cooling, oiling and winding of the annealed steel coil in sequence to obtain tin-plated steel coil.

[0073] The passivation film is prepared using a two-stage passivation process, wherein the first stage is chemical passivation and the second stage is electrochemical passivation. Both the chemical and electrochemical passivations use the same passivation solution and temperature. The passivation solution is an aqueous solution of sodium dichromate at a concentration of 18 g / L-24 g / L with a pH of 4.1-4.4. The passivation temperature is 40℃-45℃. The passivation time for both chemical and electrochemical passivation is 0.5 s-0.7 s. In the electrochemical passivation, the passivation charge density is 0.9 C / dm³. 2 -1.2C / dm 2 .

[0074] Based on Cr content, the mass of the passivation film per square meter is 4mg-6mg. If the passivation film is too thin, the corrosion resistance will be insufficient; if the passivation film is too thick, the adhesion will decrease. At the same time, the drying process adopts a two-stage drying process. The first drying stage is hot air drying. This stage can make the moisture on the surface of the passivation film evaporate quickly and be carried away by the dry hot air, thereby removing the residual moisture on the steel plate surface and achieving thorough drying of the steel plate surface. If the drying temperature is too low, it will not be conducive to removing moisture; if the drying temperature is too high, it will easily lead to oxidation of the plate surface, which is detrimental to the surface performance. Therefore, the drying temperature is selected as 110℃-120℃ and the drying time is 1s-3s. The second drying stage is high-frequency induction heating treatment. Inert gas protection is used during the heating process. The frequency of high-frequency induction is 150kHz-160kHz, the heating temperature is 190℃-200℃, and the drying time is 0.5s-0.7s. This can quickly heat the strip steel, completely remove the moisture on the strip steel surface, and promote the conversion of Cr(OH)3 in the passivation film surface layer to Cr2O3. The crystal water in the passivation film surface layer is released and carried away by the dry gas, so that the weight percentage of Cr(OH)3 in the passivation film is stably maintained at 10%-20%. This avoids the change in the passivation film structure during the painting and baking process, which would cause a decrease in adhesion.

[0075] The present invention will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention.

[0076] Examples and Comparative Examples

[0077] The manufacturing method of tin-plated steel sheet of the present invention includes sequentially performing steelmaking and continuous casting, hot rolling, pickling and cold rolling, continuous annealing and leveling and electroplating with tin to obtain steel coils, and then sequentially performing uncoiling, degreasing and cleaning, pickling, electroplating, softening, passivation, rinsing, drying, cooling, oiling and winding to obtain tin-plated steel coils.

[0078] (1) Steelmaking and Continuous Casting: After smelting in a converter and refining with RH, the molten steel undergoes nitrogen-enhancing treatment before being continuously cast into slabs. The nitrogen-enhancing treatment in steelmaking employs a wire-feeding method to increase the nitrogen content in the slabs. The nitrogen-enhancing material used is manganese nitride cored wire. The chemical composition of the slabs is controlled as follows (mass percentage): C 0.060%-0.080%, Mn 0.15%-0.25%, Si≤0.03%, P≤0.015%, S≤0.010%, Al 0.04%-0.06%, N The content of C, Mn, and N elements is 0.0060%-0.0090%, with the balance being Fe and other unavoidable impurities. The mass percentage content of C, Mn, and N elements satisfies the relationship I: 3≤1.0×(100×C content-0.06) / 0.01+0.2×(100×Mn content-0.15) / 0.10+0.5×(100×N content-0.0030) / 0.001≤5. The chemical composition of the slabs of each embodiment and comparative example is shown in Table 1.

[0079] Table 1 Chemical composition of slabs from various embodiments and comparative examples

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[0081] (2) Hot rolling: The continuously cast slab is successively heated, rough rolled, finish rolled and coiled to obtain a hot rolled steel coil with a thickness of 2.0 mm. The slab heating temperature is 1180℃-1220℃, the final rolling temperature is 850℃-880℃, and the coiling temperature is 650℃-680℃. The hot rolling process parameters of each embodiment and comparative example are shown in Table 2.

[0082] Table 2 Hot rolling process parameters for each embodiment and comparative example

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[0085] (3) Pickling and cold rolling: The hot-rolled steel coil is sequentially uncoiled, pickled, trimmed, cold rolled and coiled to obtain a cold-hardened coil with a thickness of 0.18mm-0.20mm. The thickness of the cold-hardened coil in each embodiment and comparative example is shown in Table 3.

[0086] Table 3 Cold-rolled coil thickness of each embodiment and comparative example

[0087] Serial Number Cold-rolled coil thickness (mm) Example 1 0.18 Example 2 0.19 Example 3 0.20 Example 4 0.18 Example 5 0.18 Comparative Example 1 0.18 Comparative Example 2 0.19 Comparative Example 3 0.20 Comparative Example 4 0.18 Comparative Example 5 0.18 Comparative Example 6 0.18 Comparative Example 7 0.18

[0088] (4) Continuous annealing and leveling: The cold-hardened coil is sequentially uncoiled, degreased and cleaned, annealed, leveled, trimmed and rolled to obtain an annealed steel coil. The strip speed is 450m / min-500m / min. During the annealing process, the strip speed fluctuation of the same steel coil is controlled to not exceed ±10m / min. The annealing temperature is 660℃-675℃, and the annealing temperature fluctuation does not exceed ±3℃. The annealing temperature T (℃) is set according to the N content of the tinplate, satisfying the relationship II: T=660+5×(100×N content-0.0060) / 0.0010. The continuous annealing and leveling parameters of each embodiment and comparative example are shown in Table 4.

[0089] Table 4 Annealing and leveling parameters for each embodiment and comparative example.

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[0092] (5) Tin plating: Annealed steel coils undergo uncoiling, degreasing and cleaning, pickling, electroplating, remelting, passivation, rinsing, drying, cooling, oiling, and winding to obtain tin-plated steel coils. The tin plating parameters for each embodiment and comparative example are shown in Tables 5 and 6; among which,

[0093] The passivation process comprises two stages: the first stage uses chemical passivation ("300 passivation"), and the second stage uses electrochemical passivation ("311 passivation"). Both stages use the same passivation solution, which is sodium dichromate with a concentration of 18 g / L-24 g / L, a pH of 4.1-4.4, a passivation temperature of 40℃-45℃, and a passivation charge density of 0.9 C / dm³ for the electrochemical passivation. 2 -1.2C / dm 2 The chemical passivation time is 0.5s-0.7s, and the electrochemical passivation time is 0.5s-0.7s.

[0094] The drying process includes two stages: the first stage is hot air drying at a temperature of 110℃-120℃ for 1-3 seconds; the second stage is high-frequency induction heating at a temperature of 190℃-200℃ for 0.5-0.7 seconds. The frequency of the high-frequency induction is 150kHz-160kHz. During the high-frequency induction heating process, the strip is protected by inertia.

[0095] Table 5. Main process parameters for passivation steps in each embodiment and comparative example.

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[0098] Table 6. Drying step parameters for each embodiment and comparative example.

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[0100] The tin-plated steel coils provided in the embodiments and comparative examples of the present invention are applied to the production of tin-plated sheets for easy-open lids. The tin-plated sheet comprises a steel substrate, a tin layer, a passivation film, and an oil film in sequence. Calculated based on Cr content, the mass of the passivation film per square meter is 4mg-6mg, and the weight percentage of Cr(OH)3 in the passivation film is 10%-20%. The thickness of the tin-plated sheet is 0.18mm-0.20mm, as shown in Table 7.

[0101] Table 7. Features of the tin-plated sheet for easy-open lids in each embodiment and comparative example.

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[0104] Experimental Example 1

[0105] The tin-plated steel coils obtained in the above embodiments and comparative examples were tested for hardness, tensile strength and paint adhesion. The specific test methods were performed in accordance with GB / T 2520-2017 "Cold-rolled tin-plated steel sheet and strip" and GB / T1720-2020 "Paint film cross-cut test". The test results are shown in Table 8.

[0106] Table 8. Test results of the electroplated tin steel coils prepared in each embodiment and comparative example.

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[0108] As can be seen from the table above, the tin-plated steel coils prepared in Examples 1-5 of this invention have a hardness in the range of 65±1.5, an elongation after fracture of 16%-21%, and stable paint adhesion reaching Grade 1. However, the tin-plated plates provided by Comparative Examples 1-6 have a hardness range exceeding 65±2, indicating either too high or too low hardness. This is because the contents of C, Mn, and N in the chemical composition of Comparative Examples 1-4 are either too high or too low, and the element contents do not satisfy Equation I. This results in the incoordination of the effects of each element on hardness, yield strength, tensile strength, and elongation after fracture. When the contents are too high, the solid solution strengthening and precipitation strengthening effects of the elements are too great, leading to high hardness, yield strength, and tensile strength, while the elongation after fracture is low, which is detrimental to formability. Conversely, when the contents are too low, the hardness, yield strength, and tensile strength are low, making it impossible to achieve a hardness in the range of 65±2, which is detrimental to compressive strength. In Comparative Example 5, the hot rolling temperature was too high. During the rolling process, ferrite grains coarsened and AlN precipitates grew, reducing the strengthening effect and resulting in lower hardness, yield strength, and tensile strength. In Comparative Example 6, the annealing temperature was too high, exceeding the range of Relationship II. The decrease in hardness caused by ferrite grain growth exceeded the increase in hardness caused by the corresponding N element, resulting in lower hardness. Similarly, the yield strength and tensile strength were also lower. Comparative Examples 1-3 and 7 also had cases where the paint film adhesion did not reach level 1. This was because Comparative Examples 1-3 did not undergo high-frequency induction heating after passivation, and the high-frequency induction heating temperature in Comparative Example 7 was too low. Both resulted in a high Cr(OH)3 content in the passivation film, which easily led to a transformation of the film structure during the painting and baking process, reducing the paint film adhesion.

[0109] Experiment Example 2

[0110] The results of the easy-open tinplate obtained in the above embodiments and comparative examples for lid forming performance, paint film appearance, and pressure resistance are shown in Table 9. The pressure resistance test method was performed in accordance with GB / T 17590-2008 "Aluminum Easy-Open Three-Piece Cans".

[0111] Table 9 Performance Test Results of Easy-Opening Tinplate

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[0114] As can be seen from the table above, the easy-open tin-plated plates prepared using Examples 1-5 of this invention showed no cracking during forming, and their compressive strength all reached over 230 kPa. The paint film did not peel off, fully meeting the requirements for easy-open products. While Comparative Examples 1 and 3 had acceptable compressive strength, cracking occurred during cap forming. This was because the C content in Comparative Example 1 was too high, and the N content in Comparative Example 3 was too high, resulting in excessively high hardness and low elongation, leading to insufficient formability. Comparative Examples 1-3 also exhibited paint film peeling in deformed areas. This was because high-frequency induction heating was not performed after passivation, resulting in a high Cr(OH)3 content in the passivation film. This easily caused a structural transformation of the film layer during the painting and baking process, reducing the paint film adhesion and failing to reach Grade 1. Comparative Examples 2 and 4-6 showed good cap forming, but their compressive strength was low. This was because the C, Mn, and N contents of Comparative Example 2 did not satisfy Relationship I, resulting in insufficient improvement in hardness. Comparative Example 4... The low nitrogen content resulted in low hardness and low compressive strength. In Comparative Example 5, the hot rolling temperature was too high, leading to coarsening of ferrite grains and growth of AlN precipitates during rolling, reducing the strengthening effect and resulting in low hardness and low compressive strength. In Comparative Example 6, the annealing temperature was too high, exceeding the range of Relationship II. The decrease in hardness caused by ferrite grain growth exceeded the increase in hardness due to the corresponding nitrogen element, resulting in low hardness and low compressive strength. Comparative Example 7 had acceptable cap forming and compressive strength, but exhibited minor paint film peeling in the deformed area. This was because the high-frequency induction heating temperature in Comparative Example 7 was too low, preventing sufficient conversion of Cr(OH)3 in the passivation film, resulting in a high Cr(OH)3 content and an adhesion level of only 2.

[0115] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for manufacturing a tin-plated sheet, characterized in that, The steps are as follows: Steelmaking, continuous casting, hot rolling, pickling, cold rolling, annealing, leveling, and tin plating; among which, Controlling the chemical composition of slabs during steelmaking and continuous casting includes, by mass percentage, C: 0.060%-0.080%, Mn: 0.15%-0.25%, Si: ≤0.03%, P: ≤0.015%, S: ≤0.010%, Al: 0.04%-0.06%, N: 0.0060%-0.0090%, with the balance being Fe and other unavoidable impurities. The mass percentages of C, Mn, and N elements must satisfy the following relationship: 3 ≤ 1.0 × (100 × C content - 0.06) / 0.01 + 0.2 × (100 × Mn content - 0.15) / 0.10 + 0.5 × (100 × N content - 0.0030) / 0.001 ≤ 5. During hot rolling, the slab heating temperature is controlled at 1180℃-1220℃, the final rolling temperature at 850℃-880℃, and the coiling temperature at 650℃-680℃. During annealing, the strip speed is controlled at 450m / min-500m / min, and the annealing temperature T (℃) is set according to the N content in the strip: T = 660 + 5 × (100 × N content - 0.0060) / 0.0010. The tin-plating process includes sequentially uncoiling, degreasing and cleaning, pickling, electroplating, remelting, passivation, rinsing, drying, cooling, oiling, and winding of annealed steel coils to obtain tin-plated steel coils. The passivation film after rinsing was dried using a two-stage drying process. The mass of the passivation film per square meter, calculated based on Cr content, was 4 mg-6 mg. The first stage is hot air drying. The second stage is high-frequency induction heating, with a heating temperature of 190℃-200℃ and a heating time of 0.5s-0.7s.

2. The method for manufacturing tin-plated steel sheet according to claim 1, characterized in that, During annealing, the speed fluctuation of the same steel coil should not exceed ±10 m / min, and the annealing temperature fluctuation should not exceed ±3℃; and / or, The nitrogen content in the slab is obtained by using a wire feeding method for nitrogen enrichment treatment, and the nitrogen enrichment material used is manganese nitride cored wire.

3. The method for manufacturing tin-plated steel sheet according to claim 2, characterized in that, In the steelmaking process, the molten steel is first subjected to RH vacuum treatment, and then nitrogen enrichment treatment is carried out.

4. The method for manufacturing tin-plated steel sheet according to claim 1, characterized in that, During the passivation step, the pH of the passivation solution is 4.1-4.

4.

5. The method for manufacturing a tin-plated sheet according to claim 1, characterized in that, The drying temperature in the first stage is 110℃-120℃, and the drying time is 1s-3s; and / or, The second stage employs inert gas protection during the heating process; And / or, the frequency of the high-frequency sensing is 150kHz-160kHz.

6. The method for manufacturing a tin-plated sheet according to claim 1, characterized in that, The passivation film is prepared using a two-stage passivation process, wherein the first stage of passivation is chemical passivation and the second stage of passivation is electrochemical passivation; The chemical passivation and the electrochemical passivation use the same passivation solution and passivation temperature. The passivation solution is an aqueous solution of sodium dichromate with a concentration of 18 g / L to 24 g / L, and the passivation temperature is 40°C to 45°C.

7. The method for manufacturing a tin-plated sheet according to claim 6, characterized in that, The passivation time for the chemical passivation is 0.5s-0.7s; And / or, the passivation time of the electrochemical passivation is 0.5s-0.7s; And / or, in the electrochemical passivation, the passivation charge density is 0.9 C / dm³. 2 -1.2C / dm 2 .

8. A tin-plated sheet, characterized in that, It is prepared by the manufacturing method according to any one of claims 1-7.

9. The tin-plated sheet according to claim 8, characterized in that, Based on the Cr content, the mass of the passivation film per square meter of the tin-plated sheet is 4mg-6mg, and the weight percentage of Cr(OH)3 in the passivation film is 10%-20%. And / or, the thickness of the tin-plated plate is 0.18mm-0.20mm; And / or, the hardness HR30T of the tinplate is 65±2, and the elongation after fracture is 16%-21%.

10. The use of the tin-plated sheet as an easy-open lid in packaged products according to claim 8 or 9.

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