Tinplate and method for manufacturing the same

Abstract

The present application belongs to the technical field of alloy materials, and specifically relates to tinplate and its manufacturing method. The manufacturing method of tinplate according to the present application adopts the composition design of low carbon aluminum killed steel, designs the contents of elements such as C, Mn, Al and N in tinplate without increasing the alloy content and the difficulty of controlling production, and combines with the corresponding processes of hot rolling, cold rolling, annealing and flattening, fully utilizes the strengthening effect of traditional elements carbon and manganese, combines with the control of aluminum nitride precipitation in hot rolling, selects a suitable cold rolling reduction, controls the ferrite grain size and cementite precipitation in steel by continuous annealing and overaging treatment, and combines with a specific flattening process to produce tinplate with small change in strength and hardness, high elongation and short yield platform, and the tin content of the alloy is reasonably controlled, and the requirements for press formability, pressure resistance and surface gloss of the top cover of an aerosol can are met, and the composition of the tinplate is simple, the process is simple and easy to implement, and the production cost is low.

Description

Technical Field

[0001] This application belongs to the technical field of alloy materials, and specifically relates to tinplate and its manufacturing method.

[0002] This application claims the priority of a Chinese patent application with an application number of 202211264096.3 and an invention title of "Tinplate and Its Manufacturing Method", which was filed with the Chinese Patent Office on October 17, 2022, and all of its contents are incorporated herein by reference.

Background Art

[0003] An aerosol can is a metal packaging container for containing various reagent products such as air fresheners and insecticides, and is composed of three parts: a top cover, a can body, and a bottom cover. Among them, the top cover has the most complex deformation and is generally obtained by performing multiple press deformation processes using tinplate with a thickness of 0.30 - 0.45 mm. The requirements for the press formability of tinplate are high. If the strength (or hardness) of the tinplate is too high, wrinkling is likely to occur during pressing. Also, after the top cover is connected to the can body and the bottom cover, it is subjected to the pressure of the reagent filled in the can, so the tinplate must have a certain strength (or hardness). Especially in the case of high-pressure aerosol cans, the requirements for pressure resistance are even higher, and correspondingly, the desired strength of the tinplate is higher. In addition, since the top cover is an exterior part, a transparent paint is applied to the surface to maintain the metallic luster, and it is also necessary to keep the color and luster of the appearance constant. During the processing of the top cover, the tinplate is likely to stretch and deform, and the surface is likely to turn black. Therefore, it is necessary to develop a tinplate that meets the requirements for the press formability, pressure resistance, and surface luster of the top cover of the aerosol can.

[0004] Depending on the requirements for press formability and pressure resistance of the top cover of an aerosol can, conventional tinplate for aerosol can top covers mainly employs the following two types of composition designs: (1) Low-carbon aluminum-killed steel is used, employing a batch annealing process. The annealing time is long, carbon and nitrogen atoms are sufficiently precipitated, resulting in excellent aging resistance and thus good press formability. (2) Interstitial-free steel (i.e., IF steel) is used, forming an interstitial-free ferrite structure. It has excellent aging resistance, and alloying elements such as Mn, Ti, and B are added to improve the hardness of the steel sheet through solid solution strengthening and precipitation strengthening to meet the pressure resistance requirements. Depending on the requirements for the surface gloss of the aerosol can top cover, conventional technology increases the amount of tin plating to maintain the surface gloss of the cover after pressing.

[0005] For example, prior art discloses age-resistant tinplate, which employs a low-carbon aluminum-killed steel composition design with C 0.02-0.06% and Al 0.005-0.040% and is produced using a batch annealing process. While it can meet the formability requirements for top cover processing, the product's hardness range is 55±4, which is too low for use in ordinary low-pressure cans. It cannot meet the high-pressure resistance requirements for top covers of medium-pressure and high-pressure cans. Furthermore, the uneven temperature inside the batch-annealed steel coil causes significant variations in hardness between the head, middle, and tail sections of the steel coil, which is unfavorable for production lines that manufacture covers at high speeds.

[0006] The prior art further discloses tinplate for aerosol can top covers and methods for manufacturing the same. This tinplate employs an interstitial-free steel (i.e., IF steel) composition design with C 0.0015~0.0030%, Mn 0.50~0.60%, Ti 0.045~0.065%, and B 0.0002~0.0006%. While it exhibits excellent aging resistance and a low press crack rate, it requires controlling the C content to 15~30 ppm, making steelmaking production difficult. Furthermore, the addition of large amounts of alloying elements such as Mn, Ti, and B increases smelting costs. In addition, the high temperatures of the hot rolling and annealing processes result in high power consumption. The thick oxide scale formed during the hot rolling process is difficult to remove, easily causing surface quality problems in subsequent processes, and production control becomes difficult. [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, the technical problem that this application aims to solve is to provide tinplate and a method for manufacturing the same by solving the above-mentioned defects present in tinplate in the prior art. [Means for solving the problem]

[0008] Therefore, this application provides the following technical solutions.

[0009] This application includes the steps of steelmaking and continuous casting, hot rolling, pickling and cold rolling, continuous annealing and planarization, and tin plating. In the steelmaking and continuous casting processes, the mass percentage of the chemical composition of the slab is controlled to be C 0.020~0.040%, Mn 0.15~0.25%, Si≦0.03%, P≦0.015%, S≦0.010%, Al 0.03~0.06%, N≦0.0030%, with the remainder being Fe and other unavoidable impurities, and the mass content of elements Al and N satisfies the relationship Al≧0.02%+11.57N. During the hot rolling process, the slab heating temperature is controlled to 1180-1220°C, the intermediate slab thickness to 40-42 mm, the final rolling temperature to 860-890°C, and the winding temperature to 640-670°C. The present invention provides a method for manufacturing tinplate, in which, during the continuous annealing and planarization process, the strip temperature in the rapid cooling section is controlled to 360-380°C and the cooling rate to 100-130°C / s, the cooled strip enters the aging section, in the aging section 1 region the strip temperature is 400-420°C and the aging time is 60-80 s, and in the aging section 2 region the strip temperature range is 320-420°C and the aging time is 120-140 s, and planarization is performed using a double-frame planarizer, with a planarization rolling force of 4000-4500 kN for frame 1 and a planarization rolling force of 3000-3500 kN for frame 2, the strip tension is 40-60 kN, and the planarization elongation is 1.4-1.6%.

[0010] Selectively, in the tin plating process, the amount of tin plating on one side is 2.7~2.9 g / m 2 The stripping speed is controlled to 320-380 m / min, the reflow temperature to 260-263°C, and the height from the reflow machine to the water quenching tank to 4.2-4.6 m.

[0011] Selectively, the steelmaking and continuous casting process includes smelting molten steel in a converter, performing RH refining, and then continuously casting slabs.

[0012] Selectively, the hot rolling process includes rough rolling, finish rolling, laminar cooling, and winding to obtain a hot-rolled steel coil.

[0013] Selectively, the thickness of the hot-rolled steel coil is 2.5 to 3.0 mm.

[0014] Selectively, the pickling and cold rolling process includes unwinding, pickling, trimming, cold rolling, and winding of a hot-rolled steel coil to obtain a cold coil. During the pickling and cold rolling processes, the thickness of the cold coil is controlled to 0.30-0.45 mm, and the cold rolling reduction ratio is controlled to 85-88%.

[0015] Selectively, the continuous annealing and planarization process includes unwinding, degreasing, continuous annealing, planarization, trimming, and winding of a cold coil to obtain an annealed steel coil.

[0016] Selectively, during the continuous annealing process, the strip speed is controlled to 400-450 m / min, and the strip temperature in the soaking section is controlled to 740-760°C. The aforementioned planarization is dry planarization.

[0017] Selectively, the tin plating process involves unwinding, degreasing, pickling, electroplating, reflowing, passivation, oiling, and winding onto an annealed steel coil to obtain a tin-plated steel coil. The aforementioned reflow is induction reflow. Induction reflow has advantages such as rapid heating and low energy consumption of the alloy layer.

[0018] This application provides tinplate manufactured by the above manufacturing method.

[0019] Selectively, the tinplate has a thickness of 0.30-0.45 mm, a hardness (HR30T) of 58±2, a yield strength of 300-350 MPa, a tensile strength of 360-400 MPa, an elongation after break of 33-38%, and a yield elongation of ≤3%. The microstructure of the tinplate consists of equiaxed ferrite + cementite particles, with a ferrite grain size of 10-11 grade and uniformly dispersed cementite. The amount of tin plating on one side of the tinplate is 2.7-2.9 g / m². 2 Here, the tin content of the alloy is 0.4~0.6 g / m 2 That is the case.

[0020] The effects of the main components designed in this application and their selective descriptions. Carbon (C): Carbon (C) is the most economical strengthening element in steel, and maintaining a constant C content during the steelmaking process is advantageous for achieving material strength and hardness at low cost. As the C content increases, the material hardness increases, but if the C content is too high, the tinplate becomes too hard, which tends to cause a low elongation rate, reducing the press formability and aging resistance of the tinplate. Furthermore, while the control range of the C content affects the change in material hardness, if the control range is too narrow, the steelmaking cost increases significantly. Therefore, in this application, the C content is set to 0.02-0.04%. Mn: As a solid solution strengthening element, manganese (Mn) can improve the strength of steel sheets without significantly reducing plasticity. Furthermore, when Mn combines with sulfur (S) to form MnS, it reduces the thermal brittleness of steel. However, if the Mn content is too high, the cost of the alloy increases. Therefore, in this application, the Mn content is set to 0.15-0.25%. Si: Si is prone to enriching and oxidizing the surface of steel, which is detrimental to the surface quality and coatability of steel sheets. Therefore, a lower Si content is preferable, and in this application, Si ≤ 0.03%. While P:P exhibits a strong solid solution strengthening effect, it is prone to segregation and formation of a band-like structure, reducing the plasticity and toughness of the steel sheet and making it unfavorable for formability. Therefore, in this application, P ≤ 0.015% is specified. S: Regarding tinplate, S is a harmful impurity element that readily forms sulfide inclusions, which is unfavorable for forming steel sheets. Therefore, in this application, S ≤ 0.010%. N: Regarding tinplate, N is a harmful impurity element. When N atoms are dissolved in the gaps, the strength and hardness of the steel plate improve, but the plasticity decreases, and stretcher strain marks are more likely to occur when the steel plate is pressed. Therefore, it is necessary to reduce the N content in the steel, and in this application, N ≤ 0.0030%. Al: Al is added in the process of steelmaking as a deoxidizer. Also, Al can combine with N to form AlN. Since N in steel cannot be completely removed, a certain amount of Al is added to immobilize N in steel and improve the aging resistance. When Al that plays the role of immobilizing nitrogen is maintained at a certain excess ratio, it is beneficial for N in low-carbon steel to be sufficiently immobilized, that is, (Al - 0.02%) / 27 ≥ 6 × (N / 14). However, if the Al content is too high, the inclusions in steelmaking increase, the pouring property of continuous casting deteriorates, and the cost of the alloy increases. Therefore, in this application, the range of the Al content is set to 0.03 - 0.06%, and the relational expression Al ≥ 0.02% + 11.57N is satisfied.

[0021] The manufacturing method of the tin described in this application achieves a balance between the press formability, pressure resistance, and production economy required for the top cover of the aerosol can. The important steps of each process in the manufacturing method described in this application will be explained. Steelmaking: By RH vacuum degassing treatment, the C content can be accurately controlled within the range of 0.02 - 0.04%, and the desired hardness of the tin can be achieved by fully utilizing the solid solution strengthening effect of C. Also, the RH process can effectively remove N and reduce the N content in steel, which is beneficial for press formability and also reduces the Al content required to immobilize N. Hot Rolling: The austenitic rolling process controls the heating and rolling temperatures of the slab to a low level and appropriately controls the thickness of the intermediate slab, thereby avoiding problems such as high energy consumption, poor surface quality, and coarse grains that occur with high-temperature rolling. If the heating temperature of the slab is too high, a large amount of AlN dissolves during the heating process, increasing the solid solution nitrogen content. To sufficiently precipitate AlN, a higher aluminum content and longer high-temperature winding are required. On the other hand, if the temperature is too low, rolling becomes difficult, and the final rolling temperature tends to be low. Therefore, the heating temperature of the slab is controlled to 1180-1220°C. If the thickness of the intermediate slab is too small, the temperature drops significantly during the rolling process, making it impossible to guarantee the final rolling temperature and resulting in poor temperature uniformity of the steel coil. If the thickness of the intermediate slab is too large, rolling becomes more difficult. Therefore, the thickness of the intermediate slab is set to 40-42 mm. By ensuring that the temperature is higher than the Ar3 transformation point and employing a low final rolling temperature, two-phase rolling is avoided, and the final rolling temperature is set to 860-890°C. If the winding temperature is too high, coarse grains are likely to form, reducing strength, and if the temperature is too low, it is unfavorable for the precipitation of solid-solution nitrogen, so the winding temperature is set to 640-670°C. Cold rolling: If the cold rolling reduction ratio is too high, the recrystallization temperature will be high, requiring a higher annealing temperature. Also, after annealing, the crystal grain size of the steel sheet will be smaller, the hardness will be higher, the yield platform will be extended, and uniform deformation during the pressing process will be unfavorable. If the cold rolling reduction ratio is too low, the crystal grain of the steel sheet will be coarse, the hardness will be lower, requiring thinner hot-rolled raw materials and increasing production costs. Therefore, the cold rolling reduction ratio is set at 85-88%. Continuous Annealing: Continuous annealing is a crucial process for controlling the structure and properties of steel sheets. It involves heating the steel sheet above the recrystallization temperature to perform the processes of recovery, recrystallization, grain growth, and cementite precipitation. First, a ferrite structure with a constant grain size is obtained by combining the strip speed and the temperature of the soaking section. Rapid cooling (100-130°C / s) is used to supersaturate the solid-solution carbon atoms in the ferrite, obtaining sufficient precipitation storage energy. In the first aging stage, an overaging process is employed. After rapid cooling, the strip is reheated to the aging temperature (400-420°C) and held for a certain period of time to promote the rapid and large-scale precipitation of cementite. In the second aging stage, a gradient aging process is used, making full use of the strip temperature (320-420°C) and extending the holding time to further precipitate cementite, reducing the adverse effect on press deformation caused by solid-solution carbon atoms in the gaps. Therefore, a reasonable annealing process is used depending on the composition of the steel sheet of the present invention and the hot rolling and cold rolling processes. Specifically, the stripping speed is 400-450 m / min, the temperature in the soaking section is 740-760°C, the temperature in the rapid cooling section is 360-380°C and the cooling rate is 100-130°C / s, the strip temperature in aging section 1 is 400-420°C and the aging time is 60-80 s, and the strip temperature range in aging section 2 is 320-420°C and the aging time is 120-140 s. Flattening: The flattening effect includes adjusting the mechanical properties of the steel plate after annealing, imparting various surface structures and roughness to the strip, and improving the shape and quality. Adopting the mode of large rolling force and small tension is beneficial for obtaining more movable dislocations and reducing the yield elongation rate. However, if the rolling force is too large and the tension is too small, it is disadvantageous for controlling the shape and surface structure of the strip. Therefore, the rolling forces of the two flattening frames are 4000 - 4500 kN and 3000 - 3500 kN respectively, and the strip tension is 40 - 60 kN. For low-carbon aluminum-killed steel, as the flattening elongation rate increases, the yield strength of the steel plate decreases first and then increases. When the flattening elongation rate reaches 1.2% or more, the yield platform of the annealed steel plate with a thickness of 0.30 - 0.45 mm can be eliminated. When the yield strength reaches the lowest point, if the flattening elongation rate is continuously improved to 1.4% or more, more movable dislocations can be achieved, and the yield strength and hardness of the steel plate can be appropriately improved. However, if the flattening elongation rate is too high, the hardness will be significantly improved, the plasticity will be reduced, and the load on the flattening machine will increase. Therefore, the flattening elongation rate should not exceed 1.6%. Reflow: The blister is rapidly heated by the reflow device to a temperature above the melting point of tin (232 °C) to melt the tin plating layer to smooth the surface and form a tin-iron alloy layer, thereby improving the adhesion and corrosion resistance of the tin layer. If the reflow temperature is too low, the reflow of the tin layer will be insufficient. If the reflow temperature is too high, the alloy layer will become thick and the oxidation of the tin layer will be serious. Therefore, the reflow temperature is set at 260 - 263 °C, and the reflow device is adjusted so that the height of the water quenching tank is 4.2 - 4.6 m, and the time of the reflow reaction is controlled. Thereby, the thickness of the tin-iron alloy layer is reduced, the amount of tin plating is kept constant, and more shiny pure tin layers are retained to improve the surface gloss of the cover manufactured by pressing the blister and avoid the problem of darkening.

Advantages of the Invention

[0022] The technical solution of the present application has the following advantages.

[0023] The tinplate manufacturing method described in this application adopts a low-carbon aluminum-killed steel composition design, and without increasing the alloy content or the difficulty of production control, designs the elemental content of C, Mn, Al, N, etc. in the tinplate, combines corresponding hot rolling, cold rolling, annealing, and planarization processes, fully utilizes the strengthening effect of conventional elements such as carbon and manganese, combines control of aluminum nitride precipitation during hot rolling and annealing, selects an appropriate cold rolling reduction ratio, controls ferrite grain size and cementite precipitation in the steel through continuous annealing and overaging treatment, and combines this with a specific planarization process, thereby producing tinplate with small changes in strength and hardness, high elongation, and a short yield platform. Furthermore, it satisfies the requirements for press formability and pressure resistance of aerosol can top covers, the tinplate composition is simple, the process is easy to implement, and the production cost is low. Specifically, this invention employs a design that combines steelmaking components with the processes of hot rolling, annealing, and planarization. This design controls the precipitation of aluminum nitride and cementite, minimizes the amount of C and N atoms dissolved in the gaps within the steel, effectively shortens the yield platform, and is advantageous for press formability. In the hot rolling process of this invention, by controlling the rolling temperature to a low level and appropriately controlling the thickness of the intermediate slab, problems such as high energy consumption, poor surface quality, and coarse grain size associated with high-temperature rolling are avoided. This improves the surface quality and structural uniformity of the product, and further reduces production costs.

[0024] The present invention's method for manufacturing tinplate employs induction reflow to control the reflow temperature and reaction time, and rationally controls the tin content of the alloy, thereby achieving precise control of the tin layer of the alloy, resulting in a tin content of 0.4~0.6 g / m². 2 This is advantageous for maintaining the gloss of the tinplate surface after press deformation.

[0025] The tinplate according to this application has a hardness (HR30T) of 58±2, a yield strength of 300-350 MPa, a tensile strength of 360-400 MPa, an elongation after fracture of 33-38%, and a yield elongation of 3% or less. Of these, the hardness and strength of the steel plate can meet the pressure resistance requirements for the top cover of an aerosol can. Furthermore, the range of change in hardness and strength is small, the elongation is high, and the yield platform is short, so rigging does not occur when pressing the top cover of an aerosol can. In addition, the microstructure of the steel plate consists of equiaxed ferrite + cementite particles, and the cementite is uniformly dispersed and distributed without band-like cementite. As a result, cracks due to inconsistent local deformation are avoided and the uniformity of processing deformation is improved. By controlling the mechanical properties and microstructure of tinplate, such as hardness, strength, elongation, and yield elongation, the difficult problem of achieving both press formability and pressure resistance in conventional low-carbon aluminum-killed steel is effectively solved, meeting the requirements for use as a top cover for aerosol cans.

[0026] To more clearly describe specific embodiments of the present application or technical solutions in the prior art, the following briefly introduces the drawings that may be used to describe specific embodiments or the prior art. Clearly, the drawings in the following description are some embodiments of the present application, and those skilled in the art can obtain further drawings based on these without any creative work. [Brief explanation of the drawing]

[0027] [Figure 1] This is a photograph of the microstructure of tinplate obtained in Example 1 of the present invention. [Figure 2] This is a photograph of the microstructure of tinplate obtained in Comparative Example 1 of the present invention. [Figure 3] This is the curve of the annealing process in the embodiment of the present application. [Modes for carrying out the invention]

[0028] The following embodiments are provided for the better understanding of the Application and are not limited to the above-described best embodiments, nor do they limit the content or scope of the Application. Any product identical or similar to the Application, obtained by someone combining the teachings of the Application or the features of the Application with other prior art features, is also within the scope of the Application.

[0029] In the examples, unless specific experimental steps or conditions are specified, the procedures or conditions should be followed according to conventional experimental steps described in the literature of the relevant field. Unless the manufacturer is specified, all reagents and equipment used are standard commercially available reagent products.

[0030] The tinplate manufacturing method according to the examples and comparative examples of this application includes the steps of steelmaking and continuous casting, hot rolling, pickling, cold rolling, continuous annealing and planarization, and tin plating, and specifically the steps are as follows.

[0031] 1) Steelmaking and continuous casting: Molten steel is smelted in a converter, then RH refining is performed, and finally the slabs are continuously cast. The chemical composition of the slabs is shown in Table 1.

[0032] [Table 1]

[0033] 2) Hot rolling: The continuous cast slab is sequentially heated, roughly rolled, finish rolled, laminar cooled, and wound to obtain hot-rolled steel coils with a thickness of 2.5 to 3.0 mm. Specifically, the parameters of the hot rolling process are shown in Table 2.

[0034] [Table 2]

[0035] 3) Pickling and cold rolling: The hot-rolled steel coil is sequentially unwound, pickled, trimmed, continuously cold-rolled, and rewound to obtain a cold coil with a thickness of 0.30 to 0.45 mm. Specifically, the parameters of the hot-rolling process are shown in Table 3.

[0036] [Table 3]

[0037] 4) Continuous annealing and planarization: The cold coil is unwound, degreased and cleaned, annealed, planarized, trimmed, and wound up to obtain an annealed steel coil. The curve of the annealing process in the embodiment of this application is shown in Figure 3, and the specific process parameters are shown in Tables 4 and 5.

[0038] [Table 4]

[0039] [Table 5]

[0040] 5) Tin Plating: The annealed steel coil is unwound, degreased and cleaned, pickled, electroplated, reflowed, passivated, oiled, and wound up to obtain a tin-plated steel coil (tinplate). Specifically, the process parameters are shown in Table 6.

[0041] [Table 6]

[0042] In this comparative example, the operating steps and parameters of the other processes are the same as in Example 1, except that the chemical composition of the slab is different. The specific composition of the slab is shown in the table below.

[0043] [Table 7]

[0044] Comparative Example 5 In this comparative example, only the continuous annealing operation parameters differ from those in Example 1, and these are specifically shown in the table below.

[0045] [Table 8]

[0046] In this comparative example, only the operating parameters for continuous hot rolling differ from those in Example 1, which are specifically shown in the table below.

[0047] [Table 9]

[0048] In this comparative example, only the flattening operation parameters differ from those in Example 1, and these are specifically shown in the table below.

[0049] [Table 10]

[0050] The mechanical properties, microstructure, and tin plating content of tin-plated steel coils manufactured based on the above examples and comparative examples were detected. The specific test methods were performed referring to GB / T2520-2017 "Cold-rolled tin-plated steel sheets and strips" and GB / T4335-2013 "Method for measuring ferrite grain size of cold-rolled low-carbon steel sheets." The test results are shown in Table 11.

[0051] [Table 11]

[0052] Table 12 shows the results of moldability, pressure resistance tests, and visual inspections of covers manufactured by applying the tin-plated steel coils according to the examples and comparative examples of this application to a production line for aerosol can top covers. The pressure resistance test method was performed in reference to GB / T13042-2008 "Packaging Containers: Iron Aerosol Cans".

[0053] In the embodiments of this application, the manufactured covers are well-formed, free from cracks and riddleds, and all achieve a pressure resistance of 1.8 MPa or higher, meeting the requirements for high-pressure aerosol can products, and the surface gloss of the covers is good. On the other hand, while Comparative Examples 1 and 3 meet the pressure resistance requirements, the manufactured covers have problems with cracks and riddleds during molding. Comparative Example 2 is well-formed, but its pressure resistance is insufficient and it cannot be used for high-pressure aerosol cans. Furthermore, Comparative Examples 1 to 3 have the problem of the manufactured covers appearing dark. Comparative Examples 4 to 7 meet the pressure resistance requirements, but the manufactured covers have problems with cracks and riddleds during molding.

[0054] [Table 12]

[0055] Figure 1 is a photograph of the microstructure of tinplate according to Example 1 of the present application. As can be seen from the figure, the microstructure consists of equiaxed ferrite + cementite particles. Here, the ferrite grains are equiaxed and uniform in size, with a grain size of 11. The cementite is uniformly dispersed and distributed in small numbers, resulting in a uniform overall structure. Figure 2 is a photograph of the microstructure of tinplate according to Comparative Example 1 of the present application. As can be seen from the figure, the microstructure consists of equiaxed ferrite + cementite particles, but the ferrite grains are fine, with a grain size of 11.5. The cementite is large in size, numerous, and in a band- or cluster-like manner, with an uneven distribution. The overall structure is uneven, making it prone to uneven deformation and causing riddled and cracks during the manufacturing of the cover.

[0056] Clearly, the above embodiments are merely illustrative examples for clarity and do not limit the embodiments. Those skilled in the art can make various other forms of variations or modifications based on the above description. It is not necessary, nor is it possible, to list all embodiments here. Any obvious variations or modifications derived therefrom still fall within the scope of the invention.

Claims

1. A method for manufacturing tinplate, The process includes the steps of steelmaking and continuous casting, hot rolling, pickling and cold rolling, continuous annealing and planarization, and tin plating. In the steelmaking and continuous casting processes, the mass percentage of the chemical composition of the slab is controlled to be C: 0.020–0.040%, Mn: 0.15–0.25%, Si ≤ 0.03%, P ≤ 0.015%, S ≤ 0.010%, Al: 0.03–0.06%, N ≤ 0.0030%, with the remainder being Fe and other unavoidable impurities, and the mass content of elements Al and N satisfies the relationship Al ≥ 0.02% + 11.57N. During the hot rolling process, the slab heating temperature is controlled to 1180-1220°C, the intermediate slab thickness to 40-42 mm, the final rolling temperature to 860-890°C, and the winding temperature to 640-670°C. The method is characterized in that, during the continuous annealing and planarization process, the strip speed is controlled to 400-450 m / min, the strip temperature is controlled to 740-760°C in the soaking section, the strip temperature is controlled to 360-380°C and the cooling rate to 100-130°C / s in the rapid cooling section, the cooled strip enters the aging section, the aging section 1 region has a strip temperature of 400-420°C and an aging time of 60-80 s, the aging section 2 region has a strip temperature range of 320-420°C and an aging time of 120-140 s, planarization is performed using a double-frame planarizer, the planarization rolling force of frame 1 is 4000-4500 kN, the planarization rolling force of frame 2 is 3000-3500 kN, the strip tension is 40-60 kN, and the planarization elongation is 1.4-1.6%.

2. In the tin plating process, the amount of tin plating on one side is 2.7 to 2.9 g / m². 2 The method for manufacturing tinplate according to claim 1, characterized in that the stripping speed is controlled to 320 to 380 m / min, the reflow temperature to 260 to 263°C, and the height from the reflow apparatus to the water quenching tank to 4.2 to 4.6 m.

3. The method for producing tinplate according to claim 1 or 2, characterized in that the steelmaking and continuous casting include smelting molten steel in a converter, RH refining, and then continuously casting slabs.

4. The method for producing tinplate according to claim 1 or 2, characterized in that the hot rolling includes rough rolling, finish rolling, laminar cooling, and winding to obtain a hot-rolled steel coil.

5. The method for manufacturing tinplate according to claim 4, characterized in that the thickness of the hot-rolled steel coil is 2.5 to 3.0 mm.

6. The aforementioned pickling and cold rolling process includes unwinding, pickling, trimming, cold rolling, and winding of a hot-rolled steel coil to obtain a cold coil. The method for producing tinplate according to claim 1 or 2, characterized in that during the pickling and cold rolling process, the thickness of the cold coil is controlled to 0.30 to 0.45 mm and the cold rolling reduction rate is controlled to 85 to 88%.

7. The method for producing tinplate according to claim 1 or 2, characterized in that the continuous annealing and planarization includes unwinding, degreasing and cleaning, continuous annealing, planarization, trimming, and winding of a cold coil to obtain an annealed steel coil.

8. The method for producing tinplate according to claim 7, characterized in that the planarization is dry planarization.

9. The tin plating process involves unwinding, degreasing, pickling, electroplating, reflowing, passivation, oiling, and winding onto an annealed steel coil to obtain a tin-plated steel coil. The method for producing tinplate according to claim 1 or 2, characterized in that the reflow is an inductive reflow.

10. The method for producing tinplate according to claim 1, characterized in that the tinplate has a thickness of 0.30 to 0.45 mm, a hardness of HR30T of 58 ± 2, a yield strength of 300 to 350 MPa, a tensile strength of 360 to 400 MPa, an elongation at break of 33 to 38%, and a yield elongation ratio of ≤ 3%, the microstructure of the tinplate is equiaxed ferrite + cementite particles, the grain size of the ferrite is grade 10 to 11, and the cementite is uniformly dispersed.

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