A scratch-resistant tin-plated steel sheet product and a manufacturing method thereof

Abstract

The invention relates to the technical field of steel, and in particular to a scratch-resistant tin-plated steel sheet and a manufacturing method thereof. The chemical composition weight percentage of the steel sheet is C: 0.058-0.082%, Si≤0.02%, Mn: 0.08-0.22%, P≤0.013%, S≤0.012%, Al: 0.025-0.050%, N≤0.0033%, and the rest is Fe and other inevitable impurity elements; the tin-plated steel sheet with a thickness of 0.18-0.28 mm has a yield strength of 360-470 MPa, a surface roughness Ra value of 0.6-0.8 μm, an Rpc value of 70-140 / cm, and an amount of a tin-iron alloy layer of 0.8-1.0 g / m 2 The method comprises the steps of performing alkali washing, continuous annealing, leveling, trimming, oiling and coiling on a low-carbon cold-rolled hard steel plate with a thickness of 0.18 to 0.28 mm to obtain a continuously annealed substrate, and performing alkali washing, pickling, electroplating, fluxing, soft melting, quenching, passivation, oiling and coiling on the continuously annealed substrate to obtain a scratch-resistant tin-plated steel plate.

Description

Technical Field

[0001] This invention relates to the field of steel technology, specifically to a scratch-resistant tin-plated steel sheet and its manufacturing method. Background Technology

[0002] Tin-plated steel sheet, also known as tinplate, possesses excellent processing performance, superior welding properties, and a surface finish suitable for printing. Furthermore, the tin layer is non-toxic and harmless, making it a common material in the metal packaging industry, frequently used for the bodies and lids of food cans, beverage cans, and aerosol cans. Tinplate is transported to tinplate can factories in the form of coils or sheets. During transportation, shearing, coating, printing, and can manufacturing, the steel surface is prone to scratches and abrasions, especially in milk powder cans where the inner surface is not coated and comes into direct contact with production equipment. Scratches and abrasions are a challenging problem to address during long-distance transportation and multi-process manufacturing. Factors affecting the scratch resistance of tinplate mainly include surface morphology and roughness, the tin layer, and the tin-iron alloy layer.

[0003] Patent CN115418685A discloses a method for producing tinplate. This method involves roughening the surface of tension rollers to increase their roughness; constructing a tinplate production line and installing multiple tension rollers within it. These tension rollers provide tension to the tinplate, ensuring stable operation within the production line; and processing the tinplate to obtain the finished tinplate. This method can effectively reduce the number of scratches in the produced tinplate, thereby reducing economic losses caused by these defects. While the patent's technical solution primarily avoids scratches during tinplate production by optimizing the tension roller surface, the arrangement of tension rollers on the production line, and adjusting the tension, it does not improve the scratch resistance of the tinplate itself and cannot prevent surface scratches during transportation and downstream customer use.

[0004] Patent CN104711474B discloses a method for manufacturing cold-rolled tin-plated steel sheets for multiple coating processes. This invention involves feeding, uncoiling, dust removal, straightening, shearing, conveying, and stacking cold-rolled tin-plated steel sheet coils to obtain finished cold-rolled tin-plated steel sheets. In the shearing step, the shear gap is 10±1% of the thickness of the cold-rolled tin-plated steel sheet, and the blade flatness is ≤0.005mm. In the conveying step, the sheared cold-rolled tin-plated steel sheets are conveyed via belt conveyor. The distance between the sheared forward and backward cold-rolled tin-plated steel sheets on the main conveyor belt and the overlapping belt is 30±20mm. By adjusting the shearing speed and the speeds of the main and overlapping belts, this invention achieves zero overlap between the forward and backward strips on the belt conveyor, eliminating the problem of scratches easily occurring on the tin-plated sheet in the overlapping belt area, and ensuring that no directly visible scratches are found on the surface of the cold-rolled tin-plated steel sheet. The patented technical solution mainly eliminates the problem of scratches easily generated in the overlapping belt area during the shearing process of electroplated tin sheets, but it does not improve the surface morphology and plating structure from a process perspective. It only avoids the relevant defects of the shearing process from a production perspective. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a scratch-resistant tin-plated steel sheet and its manufacturing method. By controlling key processes in the continuous annealing and electroplating processes, the scratch resistance of the tin-plated sheet surface is improved, reducing surface scratch defects during transportation, printing, and can making, and increasing the yield of unpainted tin-plated steel sheets for milk powder can manufacturing.

[0006] The technical solution of this invention is as follows: A scratch-resistant tin-plated steel sheet is provided, wherein the chemical composition of the steel sheet by weight percentage is C: 0.058-0.082%, Si≤0.02%, Mn: 0.08-0.22%, P≤0.013%, S≤0.012%, Al: 0.025-0.050%, N≤0.0033%, with the remainder being Fe and other unavoidable impurity elements; the tin-plated steel sheet with a thickness of 0.18~0.28mm has a yield strength of 360~470MPa, a surface roughness Ra value of 0.6~0.8μm, an Rpc value of 70~140 / cm, and a tin-iron alloy layer content of 0.8~1.0g / m². 2 .

[0007] This invention also provides another technical solution: a method for manufacturing a scratch-resistant tin-plated steel sheet, comprising the following steps:

[0008] A continuously annealed substrate is obtained by performing alkaline washing, continuous annealing, leveling, edge trimming, oiling, and coiling processes on a low-carbon cold-rolled hard steel sheet with a thickness of 0.18~0.28mm. The continuously annealed substrate is then subjected to alkaline washing, pickling, electroplating, fluxing, softening, quenching, passivation, oiling, and coiling processes to obtain a scratch-resistant tin-plated steel sheet.

[0009] The low-carbon cold-rolled hard steel sheet is leveled using a double-stand dry leveling process, with the leveling elongation controlled at 1.3±0.5%. The double-stand process includes a first stand and a second stand. The rolling force of the first stand ranges from 5000 to 6000 kN, and the rolling force of the second stand ranges from 3000 to 4000 kN. After the leveling process, the yield strength of the low-carbon cold-rolled hard steel sheet is 360 to 470 MPa, the surface of the steel sheet is grooved, and the surface roughness ranges from Ra value of 0.6 to 0.8 μm and Rpc value of 70 to 140 / cm.

[0010] Furthermore, the dual-frame assembly includes a first frame and a second frame. The working roller of the first frame is an electrical discharge texturing roller with a surface roughness Ra value of 2.0~2.2μm and an Rpc value of 200~300 / cm. The working roller of the second frame is a grinding smoothing roller with a surface roughness Ra value of 0.7~0.8μm and an Rpc value of 100~160 / cm.

[0011] Furthermore, after undergoing the alkaline washing, acid washing, and electroplating processes, the continuously annealed substrate forms a 2.8 g / m² coating on both its upper and lower surfaces. 2 The tin-plated sheet then enters the fluxing process.

[0012] Furthermore, the flux concentration used in the fluxing process is 2.6~3.6 ml / L.

[0013] Furthermore, the flux is sulfosalicylic acid.

[0014] Furthermore, the softening process adopts a high-frequency induction softening method, and the softening temperature is adjusted according to the production speed of the tin-plated steel sheet. When the speed of the tin-plated steel sheet strip is 301~350m / min, the softening temperature is 291~300℃, and when the speed of the tin-plated steel sheet strip is 250~300m / min, the softening temperature is 280~290℃.

[0015] Furthermore, in the softening process, the height of the softening coil from the quenching tank is 4-6m.

[0016] Furthermore, in the quenching process, the quenching tank contains secondary deionized water, and the temperature of the secondary deionized water is 60~70℃.

[0017] Furthermore, after the aforementioned fluxing, softening, and quenching processes, the steel plate surface obtains a tin-iron alloy layer and a pure tin plating layer, wherein the amount of the tin-iron alloy layer is 0.8~1.0 g / m². 2 .

[0018] Beneficial effects:

[0019] 1. In the leveling process of low-carbon cold-rolled hard steel sheet, the roll configuration scheme of this invention is as follows: the working roll of the first stand is an electrical discharge machining (EDM) texturing roll with a surface roughness Ra value of 2.0~2.2μm and an Rpc value of 200~300 / cm; the working roll of the second stand is a grinding and polishing roll with a surface roughness Ra value of 0.7~0.8μm and an Rpc value of 100~160 / cm; when the strip passes through the first and second stands, it is mainly pressed down by the texturing EDM roll of the first stand, and the grinding and polishing roll of the second stand corrects the shape of the strip and gives the substrate a suitable roughness and morphology. In the leveling process of this invention, the leveling elongation of the cold-rolled steel sheet in the leveling step is controlled at 1.3±0.5%. In the leveling process of this invention, the low-carbon cold-rolled hard steel plate after the annealing process is dry leveled by a double stand, and the yield strength is 360~470MPa. It is given a grooved surface with a surface roughness in the following range: Ra value 0.7~0.8μm, Rpc value 70~140 / cm.

[0020] The main reason for needing to control the surface roughness value is that Ra and Rpc can jointly provide surface properties. The morphological characteristics of the alloy layer in the coating are directly related to the morphology of the substrate. When the continuously annealed substrate forms a groove-like surface with a high roughness value, the coating can better bond with the steel substrate surface, which is conducive to forming a dense and uniform tin-iron alloy layer and a complex coating of tin layer. The continuously annealed substrate with the groove-like surface with the above-mentioned roughness value generated by the present invention is more conducive to forming a high-performance scratch-resistant tin-plated steel sheet.

[0021] 2. The flux concentration in the fluxing process of this invention is 2.6~3.6 ml / L. A suitable flux concentration can remove oxides from the surface of the plating layer and improve the leveling effect of the tin layer after softening; in addition, the flux helps to melt the tin layer surface and refine the grains. A reasonable flux concentration helps to form a good plating layer through softening.

[0022] The flux used in this invention is sulfosalicylic acid. While sulfosalicylic acid is not as effective as inorganic salt fluxes in improving the corrosion resistance of tinplate, it can form a thin sulfonate layer on the substrate surface, which helps to enhance the adhesion between the tin layer and the iron substrate. Simultaneously, it can effectively reduce the surface tension of the plating solution before softening, which is beneficial for the uniform distribution of the plating solution on the iron substrate surface, improving the uniformity and smoothness of the tin plating. For tinplate with scratch resistance requirements, the inner surface is usually not painted when manufacturing food cans, and the tinplate is in direct contact with dry powder substances, such as milk powder cans. The corrosion resistance requirements for these types of packaging cans do not need to meet the requirements for tinplate cans used to hold acidic or alkaline solutions or meat. However, the surface quality requirements, such as smoothness, are higher for these cans than for ordinary tinplate. Sulfosalicylic acid fluxes can effectively improve the brightness of the tin layer and the adhesion between the substrate and the plating layer.

[0023] 3. The tin-iron alloy layer can increase the bonding force between the coating and the steel plate. At the same time, the dense tin-iron alloy layer has higher hardness and scratch resistance than the tin layer. Therefore, forming a dense, uniform tin-iron alloy layer with appropriate thickness is one of the keys to improving the scratch resistance of the steel plate surface.

[0024] The morphology of the alloy layer of tinplate is related not only to the heating temperature of the remelting process, but also to the surface morphology of the substrate, the heating time of the remelting process, and the heating rate.

[0025] The remelting process of this invention adopts high-frequency induction remelting method with a strip speed of 250~350m / min. The remelting temperature is adjusted according to the change of the tinplate production speed. When the tinplate strip speed is 301~350m / min, the remelting temperature is 291~300℃, and when the tinplate strip speed is 250~300m / min, the remelting temperature is 280~290℃.

[0026] The remelting temperature is adjusted according to the strip speed suitable for industrial production. When the strip speed is high, the remelting heating time is shortened, and the remelting temperature should be increased to maintain a constant alloy layer thickness and continuity. Conversely, when the strip speed is low, the remelting heating time is longer, and the remelting temperature should be decreased to maintain a constant alloy layer thickness and continuity. Experiments through multiple embodiments have demonstrated that the remelting process of this invention can form a dense, uniform, and appropriately thick tin-iron alloy layer on the steel plate surface, further improving the surface scratch resistance of the steel plate.

[0027] 4. Changes in heating time will cause changes in the thickness of the alloy layer, resulting in tin-plated steel sheets with different scratch resistance. Therefore, the height of the soft-fusing coil from the quenching water surface has a direct impact on the thickness of the tin-iron alloy layer on the surface of the tin-plated steel sheet. In this invention, the height of the soft-fusing coil from the quenching water tank is 4~6m, which is a reasonable setting and can meet the needs of producing tin-plated steel sheets with high scratch resistance.

[0028] 5. In the quenching process of this invention, the quenching tank contains secondary deionized water, and the temperature of the secondary deionized water is kept constant at 60~70℃. In addition to temperature regulation by circulation, deionized water at 20℃ can be added to regulate the water temperature when the temperature rises. After induction heating and softening, the strip steel undergoes quenching treatment. Too high or too low a quenching temperature will cause defects on the strip steel surface during cooling. Therefore, setting a reasonable quenching temperature plays an important role in preventing strip steel oxidation and enabling rapid cooling to solidify and form a bright surface. The tinplate after softening needs to be quickly placed in the quenching tank for cooling; otherwise, its bright surface will be damaged. After water quenching, the strip steel's temperature drops from 280~300℃ to below 100℃. Maintaining a constant temperature and circulation capacity in the quenching tank is required. By setting temperature parameters on the unit equipment, the quenching temperature is controlled within a specified range to prevent quenching spots. If the quenching temperature is too high, dull circular watermarks are easily formed on the tin layer surface; if the temperature is too low, uneven defects are easily formed in the tin layer. Therefore, the temperature of the secondary deionized water in this invention is controlled within a suitable range of 60~70℃.

[0029] 6. After the fluxing, softening, and water quenching processes, a tin-iron alloy layer with strong adhesion to the base iron and a pure tin plating surface layer are obtained, wherein the amount of the tin-iron alloy layer is 0.8~1.0 g / m³. 2 Because the tin-iron alloy layer is relatively brittle, when the total amount of plating is constant, the thicker the alloy layer, the thinner the pure tin layer. Therefore, the amount of tin-iron alloy layer should not be too much, otherwise it will affect the solderability and processing performance of the tin-plated plate.

[0030] It should be understood that all combinations of the foregoing concepts and the additional concepts described in more detail below can be considered part of the inventive subject matter of this disclosure, provided that such concepts do not contradict each other.

[0031] Other additional aspects of the invention, such as features and / or beneficial effects of exemplary embodiments, will become apparent in the following description or may be learned through practice of specific embodiments taught in the invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0033] The terms "first," "second," and similar words used in the specification and claims of this patent application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular forms of "an," "a," or "the," etc., do not indicate a quantity limitation, but rather indicate the presence of at least one. Terms such as "comprising" or "including" mean that the element or object preceding "comprising" encompasses the features, integrals, steps, operations, elements, and / or components listed following "comprising" or "including," and do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or collections thereof.

[0034] The technical solution of this invention is as follows: A scratch-resistant tin-plated steel sheet is provided, wherein the chemical composition of the steel sheet by weight percentage is C: 0.058-0.082%, Si≤0.02%, Mn: 0.08-0.22%, P≤0.013%, S≤0.012%, Al: 0.025-0.050%, N≤0.0033%, with the remainder being Fe and other unavoidable impurity elements; the tin-plated steel sheet with a thickness of 0.18~0.28mm has a yield strength of 360~470MPa, a surface roughness Ra value of 0.6~0.8μm, an Rpc value of 70~140 / cm, and a tin-iron alloy layer content of 0.8~1.0g / m². 2 .

[0035] This invention also provides another technical solution: a method for manufacturing a scratch-resistant tin-plated steel sheet, comprising the following steps:

[0036] A continuously annealed substrate is obtained by performing alkaline washing, continuous annealing, leveling, edge trimming, oiling, and coiling processes on a low-carbon cold-rolled hard steel sheet with a thickness of 0.18~0.28mm. The continuously annealed substrate is then subjected to alkaline washing, pickling, electroplating, fluxing, softening, quenching, passivation, oiling, and coiling processes to obtain a scratch-resistant tin-plated steel sheet.

[0037] The low-carbon cold-rolled hard steel sheet is leveled using a double-stand dry leveling process, with the leveling elongation controlled at 1.3±0.5%. The double-stand process includes a first stand and a second stand. The rolling force of the first stand ranges from 5000 to 6000 kN, and the rolling force of the second stand ranges from 3000 to 4000 kN. After the leveling process, the yield strength of the low-carbon cold-rolled hard steel sheet is 360 to 470 MPa, the surface of the steel sheet is grooved, and the surface roughness ranges from Ra value of 0.6 to 0.8 μm and Rpc value of 70 to 140 / cm.

[0038] In some embodiments of the present invention, the dual frame includes a first frame and a second frame. The working roller of the first frame is an electrical discharge texturing roller with a surface roughness Ra value of 2.0~2.2μm and an Rpc value of 200~300 / cm. The working roller of the second frame is a grinding smoothing roller with a surface roughness Ra value of 0.7~0.8μm and an Rpc value of 100~160 / cm.

[0039] The first stand's work rolls are electrical discharge machining (EDM) texturing rolls with a surface roughness Ra of 2.0~2.2μm and an Rpc value of 200~300 / cm; the second stand's work rolls are grinding and finishing rolls with a surface roughness Ra of 0.7~0.8μm and an Rpc value of 100~160 / cm. When the strip passes through the first and second stands, it is mainly pressed down by the texturing EDM rolls of the first stand, and the grinding and finishing rolls of the second stand correct the strip shape and impart suitable roughness and morphology to the substrate. In the leveling process of this invention, the leveling elongation of the cold-rolled steel sheet in the leveling step is controlled at 1.3±0.5%. In the leveling process of this invention, the low-carbon cold-rolled hard steel sheet after the annealing process, after being dry-leveled by two stands, has a yield strength of 360~470MPa and is given a grooved surface with a surface roughness in the following range: Ra value 0.7~0.8μm, Rpc value 70~140 / cm.

[0040] The main reason for needing to control the surface roughness value is that Ra and Rpc can jointly provide surface properties. The morphology of the alloy layer in the plating is directly related to the morphology of the substrate. When the continuously annealed substrate forms a grooved surface with a high roughness value, the plating can better bond with the steel substrate surface, which is conducive to forming a dense and uniform tin-iron alloy layer and a complex tin plating. However, to achieve a higher roughness value, a larger rolling force is required, which will have an adverse effect on the shape of the plate, the surface quality of the tinplate, and the service life of the work rolls. Therefore, setting a reasonable rolling force process can avoid the above-mentioned disadvantages and obtain a continuously annealed substrate with a suitable surface. The rolling force range for the first stand during production is set at 5000~6000kN, and the rolling force range for the second stand is set at 3000~4000kN. This range is chosen because a suitable rolling force not only imparts a reasonable surface roughness value to the sheet but is also a crucial factor in achieving a suitable flatness elongation. Tin-plated sheets for milk powder cans typically require a surface roughness range of 0.5~0.8μm. When the rolling force of the first stand is below 5000kN or the rolling force of the second stand is below 3000kN, the surface roughness of the continuously annealed substrate risks falling below the standard value, and it cannot meet the 0.7~0.8μm requirement set in this invention. The μm requirement and lower surface roughness increase the probability of irreversible defects such as burn marks during tinplate printing. Furthermore, lower rolling forces cannot achieve adequate flattening elongation, thus failing to eliminate the yield plateau and causing defects such as ridges or slip lines during subsequent can making. Larger rolling forces beyond these limits negatively impact the sheet shape, surface quality of the tinplate, and the lifespan of the work rolls. In actual production, high rolling forces lead to increased surface-pressed iron oxide powder defects and persistently high temperatures in the leveling machine bearing rolls, causing the lubricating grease inside the bearing housing to melt and irregularly splash onto the steel plate surface, resulting in batches of continuously annealed substrates being damaged. If a product is deemed defective, frequent roll changes will occur due to the significantly shortened lifespan of the work rolls, delaying production efficiency. Based on several years of production statistics, the roll change cycle of work rolls with excessive rolling force is usually 1 / 5 to 1 / 3 of that of work rolls with appropriate rolling force. Therefore, setting a reasonable rolling force process can avoid the above-mentioned drawbacks and obtain a continuously annealed substrate with a suitable surface. Through long-term testing in actual production, this invention has set a reasonable leveling process, which can stably obtain the morphology and roughness value of the target board surface. The continuously annealed substrate with the grooved surface of the above-mentioned roughness value generated by this invention is more conducive to forming high-performance scratch-resistant tin-plated steel sheets.

[0041] In some embodiments of the present invention, after the continuous annealing substrate undergoes the alkaline washing, acid washing, and electroplating processes, a 2.8 g / m² coating is formed on the upper and lower surfaces. 2 The tin-plated sheet then enters the fluxing process.

[0042] In some embodiments of the present invention, the flux concentration used in the fluxing process is 2.6~3.6 ml / L.

[0043] In some embodiments of the present invention, the flux is sulfosalicylic acid.

[0044] The flux used in this invention is sulfosalicylic acid. Although sulfosalicylic acid is not as effective as inorganic salt fluxes in improving the corrosion resistance of tin-plated sheets, it can form a thin sulfonate layer on the substrate surface, which helps to enhance the adhesion between the tin layer and the iron substrate. At the same time, it can effectively reduce the surface tension of the electroplating solution before softening, which is conducive to the uniform distribution of the electroplating solution on the iron substrate surface, improving the uniformity and smoothness of the tin plating.

[0045] For tinplate with scratch-resistant properties, the inner surface is usually unpainted when manufacturing food cans, as the tinplate comes into direct contact with dry powder substances, such as milk powder cans. The corrosion resistance requirements for these types of cans do not need to meet the requirements for tinplate cans used to hold acidic or alkaline solutions or meat. However, the surface finish and other surface quality requirements for these cans are higher than for ordinary tinplate. Sulfosalicylic acid fluxes can effectively improve the brightness of the tin layer and the adhesion between the substrate and the plating.

[0046] In some embodiments of the present invention, the remelting process adopts a high-frequency induction remelting method, and the remelting temperature is adjusted according to the production speed of the tin-plated steel sheet. When the strip speed of the tin-plated steel sheet is 301~350m / min, the remelting temperature is 291~300℃, and when the strip speed of the tin-plated steel sheet is 250~300m / min, the remelting temperature is 280~290℃.

[0047] The remelting temperature is adjusted according to the strip speed suitable for industrial production. When the strip speed is high, the remelting heating time is shortened, and the remelting temperature should be increased to maintain a constant alloy layer thickness and continuity. Conversely, when the strip speed is low, the remelting heating time is longer, and the remelting temperature should be decreased to maintain a constant alloy layer thickness and continuity. Experiments through multiple embodiments have demonstrated that the remelting process of this invention can form a dense, uniform, and appropriately thick tin-iron alloy layer on the steel plate surface, further improving the surface scratch resistance of the steel plate.

[0048] Variations in heating time result in variations in the thickness of the alloy layer, leading to tin-plated steel sheets with different scratch resistance properties. Therefore, the height of the soft-fusing coil from the quenching water surface directly affects the thickness of the tin-iron alloy layer on the surface of the tin-plated steel sheet. In this invention, the soft-fusing coil is 4-6m above the quenching water tank, which is a reasonable setting that meets the needs of producing tin-plated steel sheets with high scratch resistance.

[0049] In some embodiments of the present invention, in the softening process, the height of the softening coil from the quenching tank is 4-6m.

[0050] In some embodiments of the present invention, in the quenching process, the quenching tank contains secondary deionized water, and the temperature of the secondary deionized water is 60~70℃.

[0051] In the quenching process of this invention, the quenching tank contains secondary deionized water, the temperature of which is kept constant at 60-70°C. Besides temperature regulation via circulation, deionized water at 20°C can be added to adjust the water temperature when it rises. After induction heating and softening, the strip steel undergoes quenching. Quenching temperatures that are too high or too low can cause defects on the strip surface during cooling. Therefore, setting a reasonable quenching temperature plays a crucial role in preventing strip oxidation and ensuring rapid cooling to solidify and form a bright surface. The tinplate after softening needs to be quickly placed in the quenching tank for cooling; otherwise, its bright surface will be damaged. After water quenching, the strip steel's temperature drops from 280-300°C to below 100°C. Maintaining a constant temperature and circulation capacity in the quenching tank is essential. By setting temperature parameters on the equipment, the quenching temperature is controlled within a specified range to prevent quenching spots. If the quenching temperature is too high, dull circular watermarks are easily formed on the tin layer surface; if the temperature is too low, uneven defects are easily formed in the tin layer. Therefore, the temperature of the secondary deionized water in this invention is controlled within a suitable range of 60~70℃.

[0052] In some embodiments of the present invention, after the fluxing, softening, and quenching processes, a tin-iron alloy layer and a pure tin plating layer are obtained on the surface of the steel plate, wherein the amount of the tin-iron alloy layer is 0.8~1.0 g / m. 2 Because the tin-iron alloy layer is relatively brittle, when the total amount of plating is constant, the thicker the alloy layer, the thinner the pure tin layer. Therefore, the amount of tin-iron alloy layer should not be too much, otherwise it will affect the solderability and processing performance of the tin-plated plate.

[0053] The present invention will be further described below with reference to the embodiments.

[0054] Example 1

[0055] The composition of the scratch-resistant tin-plated steel sheet product provided in Example 1 is shown in Table 1. The remainder consists of Fe and other unavoidable impurity elements. The manufacturing method used for the product in Example 1 includes the following steps: the low-carbon cold-rolled hard steel sheet is sequentially subjected to alkaline washing, continuous annealing, leveling, edge trimming, oiling, and winding to obtain a continuously annealed substrate. Then, the continuously annealed substrate is subjected to alkaline washing, pickling, electroplating, fluxing, softening, quenching, passivation, oiling, and winding to obtain the tin-plated steel sheet.

[0056] Specifically, a low-carbon cold-rolled hard steel sheet with a thickness of 0.18 mm is used as the substrate, and continuous annealing is carried out after alkaline washing;

[0057] The subsequent leveling step involves dry leveling of the low-carbon cold-rolled hard steel sheet using a dual-stand dry leveling process, with a leveling elongation of 1.65%. The first stand's work rolls have a surface roughness Ra of 2.0 μm, a wave crest number Rpc of 207 / cm, and a first stand rolling force of 6000 kN. The second stand's work rolls have a surface roughness Ra of 0.72 μm, a wave crest number Rpc of 100 cm, and a second stand rolling force of 4000 kN. After leveling, the substrate's surface roughness Ra is measured to be 0.8 μm, and the wave crest number Rpc is 128 / cm.

[0058] In this embodiment 1, the continuously annealed substrate, after alkaline washing, acid washing, and electroplating, forms a 2.8 g / m² coating on both the upper and lower surfaces. 2 The tin-plated sheet then enters the fluxing process.

[0059] The flux concentration in the fluxing process is 2.98 ml / L;

[0060] In the softening process, high-frequency induction softening is used, the softening temperature is 280℃, the speed of the strip passing through the softening device is 250m / min, and the height of the softening coil from the quenching tank is 4m.

[0061] In the quenching process, the quenching tank contains secondary deionized water, and the temperature of the secondary deionized water is 65℃.

[0062] In this embodiment, the final tin-iron alloy layer thickness of the tin-plated sheet is 0.8 g / m. 2 The final tin-plated steel sheet has a yield strength of 398 MPa.

[0063] Example 2

[0064] The composition of the scratch-resistant tin-plated steel sheet product provided in Example 2 is shown in Table 1. The remainder is Fe and other unavoidable impurity elements. The manufacturing method used for the product in Example 2 includes the following steps: the low-carbon cold-rolled hard steel sheet is subjected to alkaline washing, continuous annealing, leveling, edge trimming, oiling, and winding in sequence to obtain a continuously annealed substrate. Then, the continuously annealed substrate is subjected to alkaline washing, pickling, electroplating, fluxing, softening, quenching, passivation, oiling, and winding to obtain the tin-plated steel sheet.

[0065] Specifically, a low-carbon cold-rolled hard steel sheet with a thickness of 0.23 mm is used as the substrate, and continuous annealing is carried out after alkaline washing;

[0066] The subsequent leveling step involves dry leveling of the low-carbon cold-rolled hard steel sheet using a dual-stand dry leveling process, with a leveling elongation of 0.93%. The first stand's work rolls have a surface roughness Ra of 2.1 μm, a wave crest number Rpc of 246 / cm, and a first stand rolling force of 5500 kN. The second stand's work rolls have a surface roughness Ra of 0.75 μm, a wave crest number Rpc of 120 / cm, and a second stand rolling force of 3450 kN. After leveling, the substrate's surface roughness Ra is measured to be 0.72 μm, and the wave crest number Rpc is 105 / cm.

[0067] In Example 2, the continuously annealed substrate, after alkaline washing, acid washing, and electroplating, forms a 2.8 g / m² coating on both the upper and lower surfaces. 2 The tin-plated sheet then enters the fluxing process.

[0068] The flux concentration in the fluxing process is 3.10 ml / L;

[0069] In the softening process, high-frequency induction softening is used, the softening temperature is 290℃, the speed of the strip passing through the softening device is 300m / min, and the height of the softening coil from the quenching tank is 4.2m.

[0070] In the quenching process, the quenching tank contains secondary deionized water, and the temperature of the secondary deionized water is 60℃.

[0071] In this embodiment, the final tin-iron alloy layer thickness of the tin-plated sheet is 0.83 g / m. 2 The final tin-plated steel sheet has a yield strength of 470 MPa.

[0072] Example 3

[0073] The composition of the scratch-resistant tin-plated steel sheet product provided in Example 3 is shown in Table 1. The remainder is Fe and other unavoidable impurity elements. The manufacturing method used for the product in Example 3 includes the following steps: the low-carbon cold-rolled hard steel sheet is subjected to alkaline washing, continuous annealing, leveling, edge trimming, oiling, and winding in sequence to obtain a continuously annealed substrate. Then, the continuously annealed substrate is subjected to alkaline washing, pickling, electroplating, fluxing, softening, quenching, passivation, oiling, and winding to obtain the tin-plated steel sheet.

[0074] Specifically, a low-carbon cold-rolled hard steel sheet with a thickness of 0.28 mm is used as the substrate, and continuous annealing is carried out after alkaline washing;

[0075] The subsequent leveling step involves dry leveling of the low-carbon cold-rolled hard steel sheet using a dual-stand dry leveling process with a leveling elongation of 0.80%. The first stand's work rolls have a surface roughness Ra of 2.2 μm, a wave crest number Rpc of 294 / cm, and a first stand rolling force of 5000 kN. The second stand's work rolls have a surface roughness Ra of 0.79 μm, a wave crest number Rpc of 160 / cm, and a second stand rolling force of 3000 kN. After leveling, the substrate's surface roughness Ra is measured to be 0.70 μm, and the wave crest number Rpc is 112 / cm.

[0076] In this embodiment 3, the continuously annealed substrate, after alkaline washing, acid washing, and electroplating, forms a 2.8 g / m² coating on both the upper and lower surfaces. 2 The tin-plated sheet then enters the fluxing process.

[0077] The flux concentration in the fluxing process is 2.60 ml / L;

[0078] In the remelting process, high-frequency induction remelting is used, the remelting temperature is 275℃, the speed of the strip passing through the remelting device is 288m / min, and the height of the remelting coil from the quenching tank is 5.0m.

[0079] In the quenching process, the quenching tank contains secondary deionized water, and the temperature of the secondary deionized water is 62℃.

[0080] In this embodiment, the final tin-iron alloy layer thickness of the tin-plated sheet is 0.88 g / m. 2 The final tin-plated steel sheet has a yield strength of 453 MPa.

[0081] Example 4

[0082] The composition of the scratch-resistant tin-plated steel sheet product provided in Example 4 is shown in Table 1. The remainder is Fe and other unavoidable impurity elements. The manufacturing method used for the product in Example 4 includes the following steps: the low-carbon cold-rolled hard steel sheet is subjected to alkaline washing, continuous annealing, leveling, edge trimming, oiling, and winding in sequence to obtain a continuously annealed substrate. Then, the continuously annealed substrate is subjected to alkaline washing, pickling, electroplating, fluxing, softening, quenching, passivation, oiling, and winding to obtain the tin-plated steel sheet.

[0083] Specifically, a low-carbon cold-rolled hard steel sheet with a thickness of 0.20 mm is used as the substrate, and after alkaline washing, it is continuously annealed.

[0084] The subsequent leveling step involves dry leveling of the low-carbon cold-rolled hard steel sheet using a two-stand dry leveling process, with a leveling elongation of 1.15%. The surface roughness Ra of the first stand's work rolls is 2.08 μm, the number of peaks Rpc is 200 / cm, and the first stand's rolling force is 5900 kN. The surface roughness Ra of the second stand's work rolls is 0.8 μm, the number of peaks Rpc is 146 / cm, and the second stand's rolling force is 3500 kN. After leveling, the surface roughness Ra of the substrate is measured to be 0.66 μm, and the number of peaks Rpc is 70 / cm.

[0085] In Example 4, the continuously annealed substrate, after alkaline washing, acid washing, and electroplating, forms a 2.8 g / m² coating on both the upper and lower surfaces. 2 The tin-plated sheet then enters the fluxing process.

[0086] The flux concentration in the fluxing process is 3.43 ml / L;

[0087] In the remelting process, high-frequency induction remelting is used, the remelting temperature is 285℃, the speed of the strip passing through the remelting device is 268m / min, and the height of the remelting coil from the quenching tank is 5.1m.

[0088] In the quenching process, the quenching tank contains secondary deionized water, and the temperature of the secondary deionized water is 63℃.

[0089] In this embodiment, the final tin-iron alloy layer thickness of the tin-plated sheet is 0.91 g / m. 2 The final tin-plated steel sheet has a yield strength of 405 MPa.

[0090] Example 5

[0091] The composition of the scratch-resistant tin-plated steel sheet product provided in Example 5 is shown in Table 1. The remainder is Fe and other unavoidable impurity elements. The manufacturing method used for the product in Example 5 includes the following steps: the low-carbon cold-rolled hard steel sheet is subjected to alkaline washing, continuous annealing, leveling, edge trimming, oiling, and winding in sequence to obtain a continuously annealed substrate. Then, the continuously annealed substrate is subjected to alkaline washing, pickling, electroplating, fluxing, softening, quenching, passivation, oiling, and winding to obtain the tin-plated steel sheet.

[0092] Specifically, a low-carbon cold-rolled hard steel sheet with a thickness of 0.21 mm is used as the substrate, and continuous annealing is carried out after alkaline washing;

[0093] The subsequent leveling step involves dry leveling of the low-carbon cold-rolled hard steel sheet using a dual-stand dry leveling process with a leveling elongation of 1.3%. The surface roughness Ra of the first stand's work rolls is 2.13 μm, the number of peaks Rpc is 250 / cm, and the first stand's rolling force is 5400 kN. The surface roughness Ra of the second stand's work rolls is 0.76 μm, the number of peaks Rpc is 130 / cm, and the second stand's rolling force is 3300 kN. After leveling, the surface roughness Ra of the substrate is measured to be 0.6 μm, and the number of peaks Rpc is 88 / cm.

[0094] In Example 5, the continuously annealed substrate, after alkaline washing, acid washing, and electroplating, forms a 2.8 g / m² coating on both the upper and lower surfaces. 2 The tin-plated sheet then enters the fluxing process.

[0095] The flux concentration in the fluxing process is 3.6 ml / L;

[0096] In the remelting process, high-frequency induction remelting is used, the remelting temperature is 295℃, the speed of the strip passing through the remelting device is 325m / min, and the height of the remelting coil from the quenching tank is 5.6m.

[0097] In the quenching process, the quenching tank contains secondary deionized water, and the temperature of the secondary deionized water is 65℃.

[0098] In this embodiment, the final tin-iron alloy layer thickness of the tin-plated sheet is 0.96 g / m. 2 The final tin-plated steel sheet has a yield strength of 360 MPa.

[0099] Example 6

[0100] The composition of the scratch-resistant tin-plated steel sheet product provided in Example 6 is shown in Table 1. The remainder is Fe and other unavoidable impurity elements. The manufacturing method used for the product in Example 6 includes the following steps: the low-carbon cold-rolled hard steel sheet is subjected to alkaline washing, continuous annealing, leveling, edge trimming, oiling, and winding in sequence to obtain a continuously annealed substrate. Then, the continuously annealed substrate is subjected to alkaline washing, pickling, electroplating, fluxing, softening, quenching, passivation, oiling, and winding to obtain the tin-plated steel sheet.

[0101] Specifically, a low-carbon cold-rolled hard steel sheet with a thickness of 0.19 mm is used as the substrate, and continuous annealing is carried out after alkaline washing;

[0102] The subsequent leveling step involves dry leveling of the low-carbon cold-rolled hard steel sheet using a dual-stand dry leveling process with a leveling elongation of 1.8%. The surface roughness Ra of the first stand's work rolls is 2.18 μm, the number of peaks Rpc is 300 / cm, and the first stand's rolling force is 5100 kN. The surface roughness Ra of the second stand's work rolls is 0.7 μm, the number of peaks Rpc is 102 / cm, and the second stand's rolling force is 3800 kN. After leveling, the surface roughness Ra of the substrate is measured to be 0.76 μm, and the number of peaks Rpc is 140 / cm.

[0103] In Example 6, the continuously annealed substrate, after alkaline washing, acid washing, and electroplating, forms a 2.8 g / m² coating on both the upper and lower surfaces. 2 The tin-plated sheet then enters the fluxing process.

[0104] The flux concentration in the fluxing process is 2.79 ml / L;

[0105] In the remelting process, high-frequency induction remelting is used, the remelting temperature is 291℃, the speed of the strip passing through the remelting device is 301m / min, and the height of the remelting coil from the quenching tank is 4.9m.

[0106] In the quenching process, the quenching tank contains secondary deionized water, and the temperature of the secondary deionized water is 70℃.

[0107] In this embodiment, the final tin-iron alloy layer thickness of the tin-plated sheet is 0.89 g / m. 2 The final tin-plated steel sheet has a yield strength of 385 MPa.

[0108] Example 7

[0109] The composition of the scratch-resistant tin-plated steel sheet product provided in Example 7 is shown in Table 1. The remainder is Fe and other unavoidable impurity elements. The manufacturing method used for the product in Example 7 includes the following steps: the low-carbon cold-rolled hard steel sheet is subjected to alkaline washing, continuous annealing, leveling, edge trimming, oiling, and winding in sequence to obtain a continuously annealed substrate. Then, the continuously annealed substrate is subjected to alkaline washing, pickling, electroplating, fluxing, softening, quenching, passivation, oiling, and winding to obtain the tin-plated steel sheet.

[0110] Specifically, a low-carbon cold-rolled hard steel sheet with a thickness of 0.25 mm is used as the substrate, and continuous annealing is carried out after alkaline washing;

[0111] The subsequent leveling step involves dry leveling of the low-carbon cold-rolled hard steel sheet using a dual-stand dry leveling process, with a leveling elongation of 0.95%. The surface roughness Ra of the first stand's work rolls is 2.02 μm, the number of peaks Rpc is 228 / cm, and the first stand's rolling force is 5200 kN. The surface roughness Ra of the second stand's work rolls is 0.73 μm, the number of peaks Rpc is 118 / cm, and the second stand's rolling force is 3160 kN. After leveling, the surface roughness Ra of the substrate is measured to be 0.62 μm, and the number of peaks Rpc is 97 / cm.

[0112] In Example 7, the continuously annealed substrate, after alkaline washing, acid washing, and electroplating, forms a 2.8 g / m² coating on both the upper and lower surfaces. 2 The tin-plated sheet then enters the fluxing process.

[0113] The flux concentration in the fluxing process is 2.68 ml / L;

[0114] In the remelting process, high-frequency induction remelting is used, the remelting temperature is 300℃, the speed of the strip passing through the remelting device is 346m / min, and the height of the remelting coil from the quenching tank is 6m.

[0115] In the quenching process, the quenching tank contains secondary deionized water, and the temperature of the secondary deionized water is 68℃.

[0116] In this embodiment, the final tin-iron alloy layer thickness of the tin-plated sheet is 1g / m. 2 The final tin-plated steel sheet has a yield strength of 382 MPa.

[0117] Example 8

[0118] The composition of the scratch-resistant tin-plated steel sheet product provided in Example 8 is shown in Table 1. The remainder consists of Fe and other unavoidable impurity elements. The manufacturing method used for the product in Example 8 includes the following steps: the low-carbon cold-rolled hard steel sheet is sequentially subjected to alkaline washing, continuous annealing, leveling, edge trimming, oiling, and winding to obtain a continuously annealed substrate. Then, the continuously annealed substrate is subjected to alkaline washing, pickling, electroplating, fluxing, softening, quenching, passivation, oiling, and winding to obtain the tin-plated steel sheet.

[0119] Specifically, a low-carbon cold-rolled hard steel sheet with a thickness of 0.27 mm is used as the substrate, and continuous annealing is carried out after alkaline washing;

[0120] The subsequent leveling step involves dry leveling of the low-carbon cold-rolled hard steel sheet using a dual-stand dry leveling process, with a leveling elongation of 1.48%. The surface roughness Ra of the first stand's work rolls is 2.15 μm, the number of peaks Rpc is 228 / cm, and the first stand's rolling force is 5600 kN. The surface roughness Ra of the second stand's work rolls is 0.77 μm, the number of peaks Rpc is 262 / cm, and the second stand's rolling force is 3920 kN. After leveling, the surface roughness Ra of the substrate is measured to be 0.73 μm, and the number of peaks Rpc is 118 / cm.

[0121] In Example 8, the continuously annealed substrate, after alkaline washing, acid washing, and electroplating, forms a 2.8 g / m² coating on both the upper and lower surfaces. 2 The tin-plated sheet then enters the fluxing process.

[0122] The flux concentration in the fluxing process is 3.35 ml / L;

[0123] In the remelting process, high-frequency induction remelting is used, the remelting temperature is 298℃, the speed of the strip passing through the remelting device is 350m / min, and the height of the remelting coil from the quenching tank is 5.2m.

[0124] In the quenching process, the quenching tank contains secondary deionized water, and the temperature of the secondary deionized water is 69℃.

[0125] In this embodiment, the final tin-iron alloy layer thickness of the tin-plated sheet is 0.9 g / m. 2 The final tin-plated steel sheet has a yield strength of 432 MPa.

[0126] The composition of the scratch-resistant tin-plated steel sheet in each embodiment of the present invention is shown in Table 1.

[0127] Table 1 shows the composition of the scratch-resistant tin-plated steel sheet for each embodiment.

[0128]

[0129] Comparative Example 1

[0130] Comparative Example 1 provides a scratch-resistant tin-plated steel sheet and its manufacturing method. The only difference from Example 1 is that, in the leveling step, the surface roughness Ra of the first frame work roller is 1.85 μm and the number of peaks Rpc is 180 / cm; the surface roughness Ra of the second frame work roller is 0.56 μm and the number of peaks Rpc is 95 / cm.

[0131] Comparative Example 2

[0132] Comparative Example 2 provides a scratch-resistant tin-plated steel sheet and its manufacturing method. The only difference from Example 1 is that, in the leveling step, the surface roughness Ra of the first frame work roller is 2.35 μm and the number of peaks Rpc is 330 / cm; the surface roughness Ra of the second frame work roller is 0.86 μm and the number of peaks Rpc is 172 / cm.

[0133] Comparative Example 3

[0134] Comparative Example 3 provides a scratch-resistant tin-plated steel sheet and its manufacturing method. The only difference from Example 1 is that in the leveling step, the rolling force of the first stand is 3000kN and the rolling force of the second stand is 1500kN.

[0135] Comparative Example 4

[0136] Comparative Example 4 provides a scratch-resistant tin-plated steel sheet and its manufacturing method. The only difference from Example 1 is that in the leveling step, the rolling force of the first stand is 7000kN and the rolling force of the second stand is 4500kN.

[0137] Comparative Example 5

[0138] Comparative Example 5 provides a scratch-resistant tin-plated steel sheet and its manufacturing method, which differs from Example 1 only in that the flux concentration in the fluxing step is 2.1 ml / L.

[0139] Comparative Example 6

[0140] Comparative Example 6 provides a scratch-resistant tin-plated steel sheet product and its manufacturing method. The only difference from Example 1 is that the flux concentration in the fluxing step is 4.2 ml / L.

[0141] When the flux concentration is in the low range of 0~2.6 ml / L, as shown in Comparative Example 5, the aforementioned beneficial effects are significantly weakened, directly affecting the reflow effect. Since the effect of flux concentration on the reflow process is not linearly increasing, when the concentration is high, as shown in Comparative Example 6, it can actually affect the stability of the aforementioned beneficial effects and also cause flux waste, increasing unnecessary processing costs. The scratch resistance of the aforementioned comparative examples is inferior to that of the tin-plated sheets produced within the process range set by this invention.

[0142] Comparative Example 7

[0143] Comparative Example 7 provides a scratch-resistant tin-plated steel sheet and its manufacturing method. The only difference from Example 1 is that in the remelting step, the remelting temperature is 265°C, the speed of the strip passing through the remelting device is 250 m / min, and the height of the remelting coil from the quenching tank is 3.5 m.

[0144] Comparative Example 8

[0145] Comparative Example 8 provides a scratch-resistant tin-plated steel sheet and its manufacturing method. The only difference from Example 1 is that in the remelting step, the remelting temperature is 305°C, the speed of the strip passing through the remelting device is 380 m / min, and the height of the remelting coil from the quenching tank is 6.5 m.

[0146] Comparative Example 9

[0147] Comparative Example 9 provides a scratch-resistant tin-plated steel sheet and its manufacturing method. The only difference from Example 1 is that the quenching step uses recirculating deionized water for cooling, and the deionized water temperature is 50°C.

[0148] Comparative Example 10

[0149] Comparative Example 10 provides a scratch-resistant tin-plated steel sheet and its manufacturing method, which differs from Example 1 only in that the quenching step uses recirculating deionized water for cooling, and the deionized water temperature is 90°C.

[0150] Experimental Example 1

[0151] The edges of the tin-plated steel sheets manufactured in each embodiment and comparative example were cut into 125mm × 50mm samples. The surface scratch resistance was tested using a coating scratch tester. The test method is as follows:

[0152] Take a scribing needle (the needle tip is a 1mm diameter hardened steel ball, included with the coating scratch tester), and inspect the needle tip with a 30x magnifying glass. The needle tip should be smooth and hemispherical, without obvious wear or contaminants; otherwise, it should be replaced with a new scribing needle. Fix the scribing needle to the chuck and position it perpendicular to the tinplate plating.

[0153] Cut a 125mm x 50mm flat template from tinplate, with the long side facing the rolling direction. The sampling position is 1 / 4 of the way across the transverse plate (perpendicular to the rolling direction).

[0154] With the coating facing upwards, clamp the test plate onto the sliding plate of the coating scratch tester. The long side of the test plate should be parallel to the direction in which the scratch is to be made.

[0155] Place the weight on the support above the scriber to obtain a given load. The load can be 100g to 2000g depending on the experimental requirements. In this experiment, 500g was used.

[0156] Start the instrument and move the sliding plate horizontally at a constant speed (30~40mm / s), and scratches will be made on the surface of the test plate.

[0157] Methods for evaluating scratch resistance:

[0158] Remove the test plate and check for scratches on the back side. Observe and measure the width of the scratches under a metallographic microscope. Under a certain load, the wider the scratch, the lower the scratch hardness and the worse the scratch resistance. The narrower the scratch, the higher the scratch hardness and the better the scratch resistance.

[0159] Note: Flanges will form on both sides of the scratch. When measuring, the flanges and outer edges of the scratch should not be measured; instead, the width of the actual scratch should be measured. An appropriate magnifying glass or optical microscope can be used for observation, but the magnification should be indicated in the test report. In this application, 100x magnification optical microscope was used for observation. Experimental results are shown in Table 2.

[0160] Table 2. Test Results of Experimental Examples

[0161]

[0162] According to the experimental results of Comparative Examples 1 and 2, the copy rate of the surface roughness of the continuously annealed substrate by the work roll is within a certain range. When the surface roughness and peak number of the work roll are lower than the range set by this invention, the surface roughness of the continuously annealed substrate is easily lower than the target value, which in turn affects the scratch resistance of the final tin-plated plate. In addition, in order to avoid the phenomenon that the surface roughness of the continuously annealed substrate is too low due to the low-roughness work roll, the rolling force is usually increased. Even so, the effect of improving the surface with low roughness is very limited and cannot fundamentally obtain the surface condition required by this invention. Moreover, increasing the rolling force can easily affect the life of the work roll, which can have adverse effects on the surface or plate shape of the continuously annealed substrate. When the roughness or peak number of the work roll is higher than the set value, the surface roughness of the continuously annealed plate is easily too high, exceeding the national standard requirements for tin-plated plates of milk powder can type. At the same time, the high-roughness work roll will cause changes in the morphology of the continuously annealed substrate during actual use, resulting in the formation of a surface that is not conducive to the bonding between the iron substrate and the tin layer, thus reducing the scratch resistance.

[0163] Based on the experimental results of Comparative Examples 3 and 4, it can be seen that the rolling force range for the first stand during production is set to 5000~6000kN, and the rolling force range for the second stand is set to 3000~4000kN. The reason for selecting these rolling force ranges is that a suitable rolling force not only imparts a reasonable surface roughness value to the plate but is also a crucial factor in achieving a suitable flatness elongation. Tinplate for milk powder cans typically requires a surface roughness range of 0.5~0.8μm. When the rolling force of the first stand is lower than 5000kN or the rolling force of the second stand is lower than 3000kN, the surface roughness of the continuously annealed substrate is at risk of falling below the standard value, and it cannot meet the 0.7~0.8μm requirement set by this invention. Tinplate with a lower surface roughness increases the probability of irreversible defects such as burn marks during printing, and the lower rolling force cannot achieve a suitable flatness elongation, thus failing to eliminate the yield plateau, resulting in defects such as ridges or slip lines during subsequent can manufacturing. Furthermore, rolling forces exceeding the above ranges... High rolling force negatively impacts the shape of the sheet, the surface quality of the tinplate, and the service life of the work rolls. In actual production, high rolling force leads to increased iron oxide powder defects pressed into the surface and causes the bearing rolls of the leveling machine to remain at high temperatures. This causes the lubricating grease inside the bearing housing to melt, resulting in irregular oil splashing onto the steel plate surface. Consequently, batches of continuously annealed substrates are judged as defective. Furthermore, the significantly shortened lifespan of the work rolls leads to frequent roll changes, delaying production efficiency. Based on several years of production statistics, the roll change cycle for work rolls with excessive rolling force is typically 1 / 5 to 1 / 3 of that with appropriate rolling force. Therefore, setting a reasonable rolling force process can avoid the above-mentioned drawbacks and obtain continuously annealed substrates with suitable surfaces. Through long-term testing in actual production, this invention has set a reasonable leveling process that can stably obtain the morphology and roughness value of the target plate surface. The continuously annealed substrates with the grooved surface of the aforementioned roughness value generated by this invention are more conducive to forming high-performance scratch-resistant tinplate.

[0164] The experimental results of Comparative Examples 5 and 6 show that when the flux concentration is in the low range of 0~2.6 ml / L, as shown in Comparative Example 5, the aforementioned beneficial effects are significantly weakened, directly affecting the reflow effect. Since the effect of flux concentration on the reflow process is not linearly increasing, when the concentration is high, as shown in Comparative Example 6, it can actually affect the stability of the aforementioned beneficial effects and also cause flux waste, increasing unnecessary processing costs. The scratch resistance of the aforementioned comparative examples is inferior to that of the tin-plated sheets produced within the process range set by this invention.

[0165] Based on the experimental results of Comparative Examples 7 and 8, it can be seen that when the melting temperature is between 232 and 280℃, a coating with a thicker tin layer and a thinner tin-iron alloy layer is usually formed. Using an octetrate method to determine the tin-iron alloy layer at different melting temperatures, the tin plating weight was 2.8 g / m² when the melting temperature was 250℃. 2The tin-iron alloy layer has a density of 0.64 g / m. 2 When the melting temperature is 265℃, as in Comparative Example 7, the tin plating weight is 2.8 g / m. 2 The tin-iron alloy layer has a density of 0.69 g / m. 2 Ultimately, its scratch resistance is inferior to that of the tin-plated sheet produced by this invention, and it can only be used for ordinary tin-plated sheets with no special requirements for scratch resistance. When the maximum heating temperature changes, the grains of the tin-iron alloy layer will change from needle-like to columnar, and its hardness will also increase. It should be noted that although the increase in hardness gives the tin-iron alloy layer better scratch resistance, in the subsequent can-making deformation process, especially involving large deformations such as flanging or necking, an excessively hard alloy layer will hinder deformation, and in severe cases, it will lead to defects in the surface tin layer. Therefore, in the actual production process, the softening temperature should be avoided to be heated above 300°C, as in Comparative Example 8, where the tin plating amount is 2.8 g / m 2 Tin-iron alloy layer 1.18g / m 2 Although it has good scratch resistance, it has poor welding performance and poor can forming properties during can making, which cannot meet the high-speed can making needs of modern can manufacturing plants.

[0166] The speed of tin-plated strip is influenced and constrained by the electroplating, remelting, and passivation processes, affecting the production quality of these three steps. Strip speed directly impacts heating time; excessively high temperatures or prolonged heating times result in excessive tin oxide formation on the tinplate surface, leading to decreased surface quality and poor strip shape. Conversely, insufficient heating time or low temperatures result in unmelted tin layers and surface defects. In the electroplating process, according to Faraday's law, the tin plating amount is determined by strip speed, strip width, current magnitude, and current efficiency. Currently available scratch-resistant tinplate is primarily used for manufacturing milk powder cans, with a surface tin plating amount of 2.8 g / m². 2The width of this type of tinplate is 800~1000mm, and the current efficiency is 80~95%. Therefore, under production conditions where the above-mentioned influencing factors are relatively fixed, coordinating the current magnitude and the strip speed during production is extremely necessary. When the current is too high, due to the increased concentration polarization, the cathode region will be severely lacking in divalent tin ions, causing hydrogen ions to undergo a reduction reaction on the cathode and precipitate hydrogen gas. This gas will precipitate from the surface of the tin layer, causing defects such as a loose and blackened tin layer, resulting in batch rejection of the tinplate. According to Faraday's law and the above production conditions, the current magnitude is positively correlated with the strip speed. Therefore, limiting the current magnitude limits the strip speed during production. In this invention, a strip speed of 350m / min is preferred. In addition, the lower limit of the strip speed is also constrained by production efficiency and passivation effect. The lower the strip speed, the lower the production efficiency, leading to higher processing costs for enterprises. On the other hand, the lower the strip speed, the longer the passivation time, which will affect the thickness and structure of the passivation film. Exceeding the passivation time within the process range can cause unstable surface quality of the tinplate, resulting in abnormal changes in the thickness and structure of the passivation film. In particular, it can lead to poor surface adhesion. Tinplate with poor adhesion is at risk of paint film peeling and scratches during surface printing or can making, affecting the sales and use of the final milk powder can products. Therefore, setting a lower limit of strip speed of 250m / min ensures that the softening and passivation processes are not too long while maintaining production efficiency.

[0167] The experimental results of Comparative Examples 9 and 10 show that the tinplate after remelting needs to be quickly cooled in a quenching bath; otherwise, its bright surface will be damaged. After water quenching, the strip temperature drops from 280-300℃ to below 100℃, requiring the quenching bath to maintain a constant temperature and have good circulation capacity. By setting temperature parameters on the equipment, the quenching temperature is controlled within a specified range to prevent quenching spots. If the quenching temperature is too high, dull circular watermarks are easily formed on the tin layer surface; if the temperature is too low, uneven defects are easily formed in the tin layer. If Comparative Examples 9 and 10 are quenched at temperatures exceeding the range set by this invention, it will not only lead to related defects but also affect scratch resistance. Therefore, the secondary deionized water temperature in this invention is controlled within a suitable range of 60-70℃.

[0168] The method for measuring roughness in this invention is to use a MarSurf M400C roughness measuring instrument to measure the surface roughness Ra and Rpc values ​​of the continuously annealed substrate. Random samples are taken from the steel coils of the continuously annealed substrate after production. Five points are measured on the upper and lower surfaces of each continuously annealed substrate. The maximum and minimum values ​​are removed from all measured values, and then the average value is taken.

[0169] The method for determining the amount of tin plating is the coulometric method. The principle of this method is that the tin plating layer dissolves in hydrochloric acid under the action of an anodic current. The time required for the free tin and alloy in the plating layer to dissolve is distinguished by the change in the point between the test piece and the reference point, allowing for a direct calculation of the amount of tin-iron alloy layer or tin layer. This method has been applied to commercially available instruments and equipment, using relevant equipment to measure the amount of tin plating on the surface of tin-plated boards produced under different process conditions, with calibration performed before each measurement.

[0170] In summary, this invention employs a combination of multiple technical improvements to significantly enhance the scratch resistance of tin-plated steel sheets. This allows the tin-plated steel sheets to withstand the test in application scenarios prone to scratches, overcoming the problem of easy abrasions and scratches on the steel sheet surface during transportation, shearing, coating, printing, and can manufacturing. It meets the usage requirements of tin-plated steel sheets in the field of milk powder cans. This product has high practical value, increases market penetration, and can improve economic benefits for the metal packaging industry.

[0171] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for manufacturing a scratch-resistant tin-plated steel sheet, characterized in that the steps include: The low-carbon cold-rolled hard steel plate with a thickness of 0.18-0.28 mm is subjected to alkali washing, continuous annealing, leveling, trimming, oiling, and coiling to obtain a continuously annealed substrate, and the continuously annealed substrate is subjected to alkali washing, pickling, electroplating, fluxing, soft melting, quenching, passivation, oiling, and coiling to obtain a scratch-resistant tin-plated steel plate; The flattening of the low-carbon cold-rolled hard steel plate is a double-stand dry flattening, and the flattening elongation is controlled to be 1.3±0.5%; the double stand includes a first stand and a second stand, the rolling force range of the first stand is 5000~6000kN; the rolling force range of the second stand is 3000~4000kN; the yield strength of the low-carbon cold-rolled hard steel plate after the flattening process is 360~470MPa, the surface of the steel plate is gully-shaped, and the surface roughness range is Ra value 0.6~0.8μm, Rpc value 70~140 / cm; The reflow process adopts a high-frequency induction reflow method, and the reflow temperature is adjusted according to the change of the production speed of the tin-plated steel sheet. When the tin-plated steel sheet strip speed is 301-350 m / min, the reflow temperature is 291-300°C, and when the tin-plated steel sheet strip speed is 250-300 m / min, the reflow temperature is 280-290°C. The double frame includes a first frame and a second frame, the working roller of the first frame is an electric spark texturing roller, the surface roughness Ra value of the working roller of the first frame is 2.0-2.2 μm, and the Rpc value is 200-300 / cm; the working roller of the second frame is a ground smooth roller, the surface roughness Ra value of the working roller of the second frame is 0.7-0.8 μm, and the Rpc value is 100-160 / cm; The chemical composition weight percentage of the scratch-resistant tin-plated steel sheet is C: 0.058-0.082%, Si≤0.02%, Mn: 0.08-0.22%, P≤0.013%, S≤0.012%, Al: 0.025-0.050%, N≤0.0033%, and the rest is Fe and other inevitable impurity elements; the yield strength of the tin-plated steel sheet with a thickness of 0.18-0.28 mm is 360-470 MPa, the surface roughness Ra value is 0.6-0.8 μm, the Rpc value is 70-140 / cm, and the amount of the tin-iron alloy layer is 0.8-1.0 g / m 2 .

2. The method for manufacturing a scratch-resistant tin-plated steel sheet according to claim 1, characterized in that: After the alkali washing, acid washing and electroplating process, the continuous annealing substrate forms a 2.8 g / m2 coating on the upper and lower surfaces. 2 The tin-plated sheet then enters the fluxing process.

3. The method for manufacturing a scratch-resistant tin-plated steel sheet according to claim 1, characterized in that: The fluxing liquid concentration used in the fluxing process is 2.6-3.6 ml / L.

4. The method for manufacturing a scratch-resistant tin-plated steel sheet according to claim 3, characterized in that: The fluxing liquid is sulfosalicylic acid.

5. The method for manufacturing a scratch-resistant tin-plated steel sheet according to claim 1, characterized in that: In the reflow process, the reflow coil is 4 to 6 meters away from the quenching tank.

6. The method for manufacturing a scratch-resistant tin-plated steel sheet according to claim 1, characterized in that: In the quenching process, secondary deionized water is stored in the quenching tank, and the temperature of the secondary deionized water is 60-70°C.

7. The method for manufacturing a scratch-resistant tin-plated steel sheet according to claim 1, characterized in that: After the fluxing, reflowing and quenching steps, a tin-iron alloy layer and a pure tin coating surface layer are obtained on the surface of the steel plate, wherein the amount of the tin-iron alloy layer is 0.8-1.0 g / m 2 .

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