Tinplate for milk powder cans and its preparation method

Abstract

This application relates to the technical field of steel preparation, and particularly to a tinplate for milk powder cans and a preparation method thereof. The method includes: coiling a hot-rolled sheet with a set chemical composition under the condition of a first set temperature to obtain a hot-rolled coil; pickling the hot-rolled coil and then cold rolling it to obtain a cold-rolled coil; subjecting the cold-rolled coil to bell annealing under the condition of a second set temperature and then leveling it; tin plating the leveled cold-rolled coil to obtain a tinplate. The tinplate for milk powder cans prepared by this application has a stable surface quality, the finished product performance meets the requirements for can making, and the cost is lower compared with the tinplate for milk powder cans prepared by the existing continuous annealing process.

Description

Technical Field

[0001] This application relates to the technical field of steel preparation, and particularly to a tinplate for milk powder cans and a preparation method thereof. Background Art

[0002] Tinplate is the earliest and most common packaging for milk powder. It has high sealing and barrier properties, can well prevent milk powder from getting damp, is convenient to use, and has the best sales packaging effect in visual printing. In order to obtain higher surface quality and ideal mechanical properties, all domestic tinplates for milk powder cans are produced by continuous annealing process.

[0003] However, the high cost of continuous annealing equipment, the difficulty in maintenance, the inflexibility of production, and the high price of the finished tinplate produced by the continuous annealing process restrict the production of tinplates for milk powder cans. Summary of the Invention

[0004] This application provides a tinplate for milk powder cans and a preparation method thereof to solve the technical problem of the relatively high cost of preparing tinplates for milk powder cans by the existing continuous annealing.

[0005] In the first aspect, this application provides a preparation method of a tinplate for milk powder cans, and the method includes:

[0006] Under the condition of the first set temperature, coiling a hot-rolled sheet with a set chemical composition to obtain a hot-rolled coil;

[0007] Pickling the hot-rolled coil and then cold rolling it to obtain a cold-rolled coil;

[0008] Under the condition of the second set temperature, subjecting the cold-rolled coil to box annealing and then leveling;

[0009] Tinning the leveled cold-rolled coil to obtain a tinplate.

[0010] Optionally, the second set temperature is 550°C - 580°C.

[0011] Optionally, the first set temperature is 600°C - 640°C.

[0012] Optionally, the elongation of the leveling is 1.8% - 2.2%.

[0013] Optionally, the set chemical composition includes:

[0014] C, Si, Mn, P, S, Als, N, Fe; wherein,

[0015] The content of C is 0.09 wt% - 0.12 wt%, the content of Mn is 0.35 wt% - 0.5 wt%, the content of S is ≤0.01 wt%, and the content of N is 0.004 wt% - 0.008 wt%.

[0016] Optionally, in the set chemical composition, the content of Si is ≤0.03 wt%, the content of P is ≤0.015 wt%, and the content of Als is 0.025 wt% - 0.065 wt%.

[0017] Optionally, tin plating the cold-rolled coil after tempering to obtain a tinplate includes:

[0018] Tin plating the cold-rolled coil after tempering and controlling the tin plating amount and the passivation film amount to obtain a tinplate;

[0019] The tin plating amount is 2.45 g / ㎡ - 2.65 g / ㎡, and the passivation film amount is 3.5 g / ㎡ - 7.5 mg / ㎡.

[0020] Optionally, the reduction rate of cold rolling is 87.4% - 90.6%.

[0021] Optionally, before coiling the hot-rolled sheet with the chemical composition at the first set temperature to obtain a hot-rolled coil, it further includes:

[0022] Heating the slab with the set chemical composition so that the slab has a third temperature;

[0023] Rolling the heated slab at the set finishing rolling temperature to obtain a hot-rolled sheet;

[0024] The third temperature is 1170°C - 1240°C, and the finishing rolling temperature is 860°C - 900°C.

[0025] In a second aspect, the present application provides a tinplate for milk powder cans. The tinplate includes a steel substrate and a tin coating attached to at least a part of the surface of the steel substrate. The tinplate is prepared by the method according to any one of the embodiments of the first aspect.

[0026] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0027] The preparation method of the tinplate for milk powder cans provided by the embodiments of the present application prepares a tinplate for milk powder cans with stable surface quality and finished product performance meeting the can-making requirements through chemical composition design and batch annealing process, and has a lower cost compared with the tinplate for milk powder cans prepared by the existing continuous annealing process. Description of the Drawings

[0028] The accompanying drawings here are incorporated into and form a part of this specification, showing embodiments consistent with this application and, together with the specification, are used to explain the principles of this application.

[0029] In order to more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following will briefly introduce the accompanying drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0030] Figure 1 It is a schematic flow chart of a preparation method of a tinplate for milk powder cans provided by an embodiment of this application. Detailed embodiments

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the following will clearly and completely describe the technical solutions in the embodiments of this application with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are some but not all of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this application without creative efforts fall within the scope of protection of this application.

[0032] The various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0033] In this application, unless otherwise stated, the orientation terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Additionally, in the description of this application's specification, the terms "include", "comprise", etc. mean "include but not limited to".

[0034] In this text, relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this text, "and / or" describes the associated relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural. In this text, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one of the following items" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (that is, a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0035] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in this application can be obtained through market purchases or can be prepared by existing methods.

[0036] In a first aspect, the present application provides a method for preparing a tinplate for milk powder cans. Please refer to Figure 1 , the method includes:

[0037] S1. Under the condition of a first set temperature, coiling a hot-rolled sheet with a set chemical composition to obtain a hot-rolled coil;

[0038] S2. Pickling the hot-rolled coil and then cold rolling it to obtain a cold-rolled coil;

[0039] S3. Under the condition of a second set temperature, subjecting the cold-rolled coil to batch annealing and then leveling;

[0040] S4. Tin plating the leveled cold-rolled coil to obtain a tinplate.

[0041] In some embodiments, the second set temperature is 550°C - 580°C.

[0042] "The second set temperature" refers to the batch annealing temperature of the above-mentioned cold-rolled coil. The positive effect of controlling the second set temperature to be 550°C - 580°C: mainly controlling the final product performance of the tinplate. When the annealing temperature is too low, it will cause the steel to have too high hardness and poor plasticity; when the annealing temperature is too high, it will cause the steel to have too low hardness. Specifically, the second set temperature can be 550°C, 555°C, 560°C, 565°C, 570°C, 575°C, 580°C, etc.

[0043] In some embodiments, the first set temperature is 600°C - 640°C.

[0044] The "first set temperature" refers to the coiling temperature of the above hot-rolled sheet. The positive effects of controlling the first set temperature to be 600°C - 640°C are as follows: obtaining a suitable hot-rolled grain size and reducing earing. When the coiling temperature is too low, it is difficult to achieve in industrial production; when the coiling temperature is too high, the surface quality of the hot-rolled coil is affected due to the precipitation of coarse-grained carbides at the grain boundaries. Specifically, the first set temperature can be 600°C, 610°C, 620°C, 630°C, 640°C, etc.

[0045] In some embodiments, the elongation of the skin pass is 1.8% - 2.2%.

[0046] The positive effects of controlling the elongation of the skin pass to be 1.8% - 2.2% are as follows: ensuring the surface quality of the steel. When the elongation is too low, it will result in too low yield strength of the steel, a small replication of the strip surface topography, and greater production difficulty. When the elongation is too high, it may lead to an increase in the anisotropy of the steel. Specifically, the elongation can be 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, etc.

[0047] In some embodiments, the set chemical composition includes:

[0048] C, Si, Mn, P, S, Als, N, Fe; where

[0049] the content of C is 0.09 wt% - 0.12 wt%, the content of Mn is 0.35 wt% - 0.5 wt%, the content of S is ≤0.01 wt%, and the content of N is 0.004 wt% - 0.008 wt%.

[0050] The positive effects of controlling the content of C to be 0.09 wt% - 0.12 wt% are as follows: C plays a strengthening role in the steel. An appropriate amount of C element can provide sufficient strength for the tinplate prepared from the steel matrix to meet the strength requirements during the circular can-making process of the tinplate prepared in this application. When the content of C is too high, it is easy to cause slab cracking, an increase in the strength and hardness of the steel, and a risk of cracking during the can-making forming process; when the content is too low, it may lead to insufficient slab strength and poor circular forming of the steel during the circular forming process. Specifically, the content of C can be 0.09 wt%, 0.10 wt%, 0.11 wt%, 0.12 wt%, etc.

[0051] Positive effects of controlling the Mn content to be 0.35 wt% - 0.5 wt%: Mn, C, and N, as solid-solution strengthening elements, form various solid solutions, improving the strength and elongation of the tinplate prepared from the steel matrix. When the Mn content is too low, the yield limit and strength limit can be significantly increased while maintaining (or only slightly decreasing) the original plasticity and impact toughness. However, when the Mn content is too high, it may increase the supercooling ability of austenite. In this case, manganese mainly plays a role in increasing the formation of cold cracks, deteriorating the welding performance of the steel. Specifically, the content of Mn can be 0.35 wt%, 0.37 wt%, 0.39 wt%, 0.41 wt%, 0.43 wt%, 0.45 wt%, 0.47 wt%, 0.49 wt%, etc.

[0052] Positive effects of controlling the S content to be ≤ 0.01 wt%: To avoid reducing the plasticity of the steel matrix and reducing the formation of MnS inclusions. Specifically, the content of S can be 0.01 wt%, 0.005 wt%, etc.

[0053] Positive effects of controlling the N content to be 0.004 wt% - 0.008 wt%: N has a strengthening effect in the tinplate prepared from the steel matrix and can be used as a solid-solution strengthening element. An appropriate amount of N will form sufficient solid solutions, reducing the anisotropy of the tinplate prepared from the steel matrix and increasing the strength of the tinplate prepared from the steel matrix. When the N content is too low, it may degrade the strength of the steel and increase its plasticity, resulting in problems such as corrugation and wrinkling during the can-making process of the steel. However, too high an N content may increase the aging tendency, cold brittleness, and hot brittleness, damaging the welding performance and cold bending performance of the steel. Specifically, the content of N can be 0.004 wt%, 0.005 wt%, 0.006 wt%, 0.007 wt%, 0.008 wt%, etc.

[0054] In some embodiments, in the set chemical composition, the Si content is ≤ 0.03 wt%, the P content is ≤ 0.015 wt%, and the Als content is 0.025 wt% - 0.065 wt%.

[0055] Positive effects of controlling the Si content to be ≤ 0.03 wt%: Improving the surface quality of the steel matrix and the actual cost and difficulty of removing Si. Specifically, the content of Si can be 0.03 wt%, 0.02 wt%, 0.015 wt%, etc.

[0056] Positive effects of controlling the P content to be ≤ 0.015 wt%: Avoiding a reduction in plasticity and reducing cold working brittleness. Specifically, the content of P can be 0.001 wt%, 0.015 wt%, etc.

[0057] Positive effects of controlling the Als content to be 0.025 wt% - 0.065 wt%: Al can form fine-grained carbides, which can reduce the anisotropy of the tinplate prepared from the steel matrix and improve the strength of the tinplate obtained from the steel matrix. When the content is too high or too low, it may cause surface defects or affect the strength of the tinplate. Specifically, the content of Als can be 0.025 wt%, 0.030 wt%, 0.035 wt%, 0.045 wt%, 0.050 wt%, 0.055 wt%, 0.060 wt%, 0.065 wt%, etc.

[0058] In some embodiments, tinning the cold-rolled coil after temper rolling to obtain a tinplate includes:

[0059] Tinning the cold-rolled coil after temper rolling and controlling the tin coating weight and the passivation film weight to obtain a tinplate;

[0060] The tin coating weight is 2.45 g / ㎡ - 2.65 g / ㎡, and the passivation film weight is 3.5 g / ㎡ - 7.5 mg / ㎡.

[0061] Positive effects of controlling the tin coating weight to be 2.45 g / ㎡ - 2.65 g / ㎡: Ensure the corrosion resistance of the tinplate. When the tin coating weight is too low, it will affect the corrosion resistance of the finished product. When the tin coating weight is too high, it will increase the cost. Positive effects of controlling the passivation film weight to be 3.5 g / ㎡ - 7.5 mg / ㎡: Ensure the corrosion resistance and painting performance of the tinplate. When the passivation film weight is too low, the wettability of the steel is poor, affecting the printing quality; when the passivation film weight is too high, the adhesion between the steel and the paint film becomes poor. Specifically, the tin coating weight can be 2.45 mg / ㎡, 2.47 mg / ㎡, 2.49 mg / ㎡, 2.51 mg / ㎡, 2.53 mg / ㎡, 2.55 mg / ㎡, 2.57 mg / ㎡, 2.59 mg / ㎡, etc.; the passivation film weight can be 3.5 mg / ㎡, 4.0 mg / ㎡, 4.5 mg / ㎡, 5.0 mg / ㎡, 5.5 mg / ㎡, 6.0 mg / ㎡, 6.5 mg / ㎡, 7.0 mg / ㎡, 7.5 mg / ㎡, etc. During the tinning process, an electroplating method is used, and the current density is set to 15 A / dm 2 - 28 A / dm 2 and the passivation current density is 0.5 As / dm 2 .

[0062] In some embodiments, the reduction ratio of the cold rolling is 87.4% - 90.6%.

[0063] Positive effects of controlling the reduction ratio of cold rolling to 87.4%-90.6%: Crushing and refining grains, and controlling the thickness range of the cold-rolled finished product to be 0.246 mm - 0.262 mm. When the reduction ratio is too small, the grains cannot be completely crushed, thus preventing the precipitation of carbides during annealing and affecting the strength. When the reduction ratio is too large, the target thickness and strength cannot be obtained. Specifically, the reduction ratio can be 87.4%, 88.0%, 89.0%, 90.0%, 90.6%, etc.

[0064] In some embodiments, before coiling the hot-rolled sheet having the chemical composition under the condition of the first set temperature to obtain a hot-rolled coil, it further includes:

[0065] Heating the slab having a set chemical composition to make the slab have a third temperature;

[0066] Rolling the heated slab under the condition of a set finishing temperature to obtain a hot-rolled sheet;

[0067] The third temperature is 1170°C - 1240°C, and the finishing temperature is 860°C - 900°C.

[0068] "The third temperature" refers to the temperature of the slab after heating. Positive effects of controlling the third temperature to 1170°C - 1240°C: Completing austenitization of the slab, reducing the re-dissolution of nitrides, and controlling the heating cost. When the temperature is too low, the slab cannot be completely austenitized, affecting the strength of the steel matrix and the edge structure; when the temperature is too high, the hot-rolling heating cost will increase. Specifically, the third temperature can be 1170°C, 1180°C, 1190°C, 1200°C, 1210°C, 1220°C, 1230°C, 1240°C, etc.

[0069] Positive effects of controlling the finishing temperature to 860°C - 900°C: Enabling finish rolling in the austenite region and avoiding mixed grains. When the finishing temperature is too low, the slab cannot be completely rolled in the austenite region, resulting in mixed grains at the edges, uneven properties, and poor sheet shape; when the finishing temperature is too high, more scale will form on the surface of the slab, affecting the surface quality of the hot-rolled coil. Specifically, the finishing temperature can be 860°C, 870°C, 880°C, 890°C, 900°C, etc.

[0070] In a second aspect, the present application provides a tinplate for milk powder cans. The tinplate includes a steel matrix and a tin coating attached to at least a part of the surface of the steel matrix. The tinplate is prepared by the method according to any one of the embodiments of the first aspect.

[0071] The tinplate for milk powder cans is realized based on the above-mentioned preparation method of tinplate for milk powder cans. The specific steps of the preparation method of tinplate for milk powder cans can refer to the above-mentioned embodiments. Since the tinplate for milk powder cans adopts some or all of the technical solutions of the above-mentioned embodiments, it has at least all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be elaborated one by one here.

[0072] The following further elaborates the present application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods without specific conditions noted in the following embodiments are usually determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0073] Table 1 Main components of the tinplate in each group (wt%, the rest is Fe and inevitable impurities).

[0074] Table 1

[0075]

[0076]

[0077] The slab billets with different components shown in Table 1 are subjected to hot rolling, pickling, cold rolling, batch annealing and tin plating. The main process parameters are shown in Table 2.

[0078] Table 2

[0079]

[0080] The performance of the tinplate obtained by the above process is tested and statistically shown in Table 3.

[0081] Table 3

[0082]

[0083]

[0084] From the results of Tables 1-3, it can be seen that by adopting the chemical composition and process of the tinplate of the present application, the yield strength of the batch-annealed tinplate for milk powder cans is lower than that of the continuously annealed tinplate for milk powder cans, and the tensile strength, hardness and surface quality are all equivalent to those of the continuously annealed tinplate for milk powder cans. The can-making qualification rate is >90%, meeting the can-making requirements of downstream customers.

[0085] In summary, the present application provides a tinplate for milk powder cans, which can realize the preparation of high-end tinplate for milk powder cans that can be produced by an expensive continuous annealing furnace with a lower-cost batch annealing furnace.

[0086] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather will be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A preparation method of tinplate for milk powder cans, characterized in that, The method includes: heating a continuous casting billet with a set chemical composition to a temperature of 1170°C - 1240°C; rolling the heated continuous casting billet to obtain a hot-rolled sheet, with a finishing rolling temperature of 860°C - 900°C; coiling the hot-rolled sheet to obtain a hot-rolled coil, with a coiling temperature of 550°C - 580°C; pickling the hot-rolled coil and then cold rolling it to obtain a cold-rolled coil, with a cold rolling reduction rate of 87.4% - 90.6%; at a temperature of 550°C - 580°C, batch annealing the cold-rolled coil and then skin-passing it, with a skin-pass elongation of 1.8% - 2.2%; Tinplate is obtained by tinning the flattened cold-rolled coil. During the tinning process, electroplating is used, and the current density is set to 15 A / dm 2 -28 A / dm 2 , and the passivation current density is 0.5 As / dm 2 ; The set chemical composition includes: C, Si, Mn, P, S, Als, N, Fe; wherein, the content of C is 0.09 wt% - 0.12 wt%, the content of Mn is 0.35 wt% - 0.5 wt%, the content of S is ≤0.01 wt%, the content of N is 0.004 wt% - 0.008 wt%, the content of Si is ≤0.03 wt%, the content of P is ≤0.015 wt%, and the content of Als is 0.025 wt% - 0.065 wt%.

2. The method according to claim 1, wherein The process of tin-plating the skin-passed cold-rolled coil to obtain a tinplate includes: tin-plating the skin-passed cold-rolled coil and controlling the tin coating weight and the passivation film weight to obtain a tinplate; the tin coating weight is 2.45 g / ㎡ - 2.65 g / ㎡, and the passivation film weight is 3.5 g / ㎡ - 7.5 mg / ㎡.

3. A tinplate for milk powder cans, characterized in that, The tinplate includes a steel substrate and a tin coating attached to at least a part of the surface of the steel substrate, and the tinplate is prepared by the method according to any one of claims 1 - 2.

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