A production method of low-roughness cold-rolled steel strip for electrotin plating

Abstract

The present invention discloses a method for producing low-roughness cold-rolled steel strip for electrotin plating, comprising the following chemical components: C: 0.03-0.055wt%, Si: ≤0.050wt%, Mn: 0.15-0.25wt%, Al: 0.030-0.055%, P≤0.020%, S≤0.015%, N≤0.006wt%, and the balance being Fe and other inevitable impurities. Based on the above chemical components, the production process of the present invention is as follows: smelting → continuous casting → hot rolling → pickling and cold rolling → cleaning → continuous annealing → leveling → finished product. The technical problem to be solved by the present invention is to focus on the development and use of low-roughness leveler working rolls on the basis of producing electrotin plating substrates that meet customer performance requirements through the adjustment of the whole process process, and to control the roughness of the substrate at a lower level by adjusting the tension of the leveler, the rolling force, etc., thereby ensuring the surface quality of the product after electrotin plating.

Description

Technical Field

[0001] The invention relates to the technical field of electrotin plating sheet base material processing, in particular to a production method of low-roughness cold-rolled strip steel for electrotin plating. Background Art

[0002] The electroplating tin market has experienced steady growth in recent years. Tinplate has a wide range of applications, including food, beverages, pharmaceuticals, paints, cosmetics, and other industries. It exhibits advantages such as long-term freshness preservation, low pollution resistance, ease of circulation, low cost, and easy recycling. Tinplate electroplating requires high surface flatness of the substrate; substrates with poor flatness are prone to welding problems. Therefore, the flatness of the substrate must be strictly controlled during the manufacturing process. Among the mechanical properties of tinplate substrates, hardness and elongation are particularly important. During production, composition control, rolling processes, annealing processes, and flattening process adjustments are used to ensure that the mechanical properties meet the requirements. The surface roughness of the tinplate substrate is particularly important for the post-electroplating surface quality. Therefore, to achieve good post-electroplating surface quality, the substrate roughness must be kept at a low level.

[0003] After searching, a tinplate and its manufacturing method disclosed in Chinese patent number CN202211264096.3 are designed with low-carbon aluminum-killed steel composition. Without increasing the alloy content and the difficulty of production control, by designing the content of elements such as C, Mn, Al, N in the tinplate, and matching the corresponding hot rolling, cold rolling, annealing, and leveling processes, the strengthening effect of conventional elements carbon and manganese is fully utilized, combined with the control of hot-rolled aluminum nitride precipitation, the appropriate cold rolling reduction rate is selected, and the ferrite grain size and cementite precipitation in the steel are controlled through continuous annealing and over-aging treatment. Matching a specific leveling process, tinplate with small fluctuations in strength and hardness, high elongation, and short yield platform is produced. At the same time, the amount of alloy tin is reasonably controlled to meet the requirements of aerosol can top cover for stamping formability, pressure resistance and surface gloss. The tinplate has a simple composition, a simple and easy process, and a low production cost. Patent No. CN200610026315.9 discloses a cold-rolled tinplate for easy-open ends and a production method thereof, which mainly solves the technical problems of cracking and low yield strength of existing cold-rolled tinplate for easy-open ends during the stamping process of manufacturing easy-open ends. The production method adopts, in order of smelting according to the composition, molten iron desulfurization, converter top and bottom combined blowing, ladle bottom argon blowing or LF furnace refining, full-process Ar blowing protection casting, plate bad heating furnace heating, descaling, rough rolling, finish rolling, and coiling to obtain hot-rolled steel coils, which are then re-uncoiled, pickled, cold rolled, annealed in a vertical continuous annealing furnace, electrotinned, and coiled to obtain finished products. The finishing rolling temperature is 820-850°C, the hot rolling coiling temperature is 630-660°C, the cold rolling reduction rate is 85%-90%, the temperature range of the hardened strip after cold rolling in the soaking section of the vertical continuous annealing furnace is 570-590°C, and the soaking time of the strip in the vertical continuous annealing furnace is 30-45s. The strip is mainly used for making easy-open covers. Patent No. CN201410125206.7 discloses a cold-rolled tinplate for beverage can bottom covers and its production method, which mainly solves the technical problems of existing cold-rolled tinplate for beverage can bottom covers cracking and poor performance stability during the stamping process of manufacturing beverage can bottom covers. The production method is to smelt according to the composition, and sequentially adopt molten iron desulfurization, converter top and bottom combined blowing, ladle bottom argon blowing or LF furnace refining, full-process Ar blowing protection casting, slab heating in a heating furnace, rough rolling, finish rolling, and coiling to obtain hot-rolled steel coils, which are then re-uncoiled, pickled, cold rolled, annealed in a vertical continuous annealing furnace, electrotinned, and coiled to obtain finished products with a thickness of 0.17-0.20 mm. The finishing rolling temperature is 851-879°C, the hot rolling coiling temperature is 640-660°C, the cold rolling reduction ratio is 70%-79%, the temperature range of the hardened strip after cold rolling in the soaking section of the vertical continuous annealing furnace is 560-580°C, and the soaking time of the strip in the vertical continuous annealing furnace is 95-105 seconds. The product is mainly used for making beverage can bottom covers.

[0004] It can be seen that the existing patents are all about the whole process production process of electrogalvanized sheets and the improvement of individual defects, and the control details of the surface roughness of electrotinned substrates are not involved. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for producing low-roughness cold-rolled strip steel for electrotin plating. By designing a reasonable strip composition and appropriate hot rolling, pickling and continuous annealing processes, an electrotin-plated substrate that meets the mechanical property requirements is obtained. At the same time, by using rollers with special roughness surfaces, a lower surface roughness is obtained after flattening, so that the surface quality after electrotin plating is better, thereby overcoming the shortcomings of the existing technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for producing low-roughness cold-rolled steel strip for electroplating tin comprises the following chemical components in mass percentage: C: 0.03-0.055wt%, Si: ≤0.050wt%, Mn: 0.15-0.25wt%, Al: 0.030-0.055%, P ≤0.020%, S ≤0.015%, N ≤0.006wt%, with the balance being Fe and other inevitable impurities. The specific production process is as follows:

[0008] Step 1: Smelting and continuous casting: LF furnace is used for slag deoxidation and desulfurization, while molten steel that meets the temperature, composition and cleanliness requirements for continuous casting is provided within a certain period of time. Continuous casting is used to produce ingots. Under the action of the crystallizer, the molten steel is formed and rapidly solidified and crystallized to form slabs.

[0009] Step 2: Hot rolling of cast slabs: austenitic rolling of the continuously cast slabs to obtain hot rolled coils;

[0010] Step 3: Pickling and cold rolling: Use conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold roll it to the required thickness specification of the finished product;

[0011] Step 4: Strip cleaning: remove impurities adhering to the surface of the strip after cold rolling, including rolling oil and iron powder;

[0012] Step 5: Continuous annealing: The cleaned steel plate is continuously annealed, and the steel plate is heated to the recrystallization temperature. After the recovery, recrystallization, and grain growth processes, the annealing temperature is controlled at 730-750°C.

[0013] Step 6: Overaging treatment: Cool the steel plate after high temperature continuous annealing to about 380±20℃ and keep it warm for 200-300 seconds;

[0014] Step 7: Leveling: Use a 6-roller leveler for wet leveling to improve the plate shape and eliminate the slip bands caused by the pinning and deformation of dislocations by the solid solution C and N atoms.

[0015] Furthermore, during the hot rolling process in step 2, the heating temperature is controlled at 1180-1220° C., the final rolling temperature is controlled at 860-900° C., the coiling temperature is controlled at 660-690° C., and the hot rolling crown is controlled at 0.015-0.035 mm.

[0016] Furthermore, in step 3, the cold rolling reduction rate is controlled at 80%-88%, the rolling tonnage is 500-1000 tons, the roughness target of the working roll of the S5 stand is 2.5 μm, the S5 stand reduction rate is ≤3%, and the working roll of the S5 stand is chrome-plated.

[0017] Furthermore, in step 6, the strip processing speed is 100-200 m / min, the temperature in the rapid cooling section is 390-410° C., the strip temperature in the aging section is 360-400° C., and the aging time is 200-300 s.

[0018] Furthermore, in step 7, the rolling force of the skin-pass mill is controlled at 4500-5500 kN, and the skin-pass elongation does not exceed 1.4%.

[0019] Furthermore, the roller diameter of the leveling mill is 460-480 mm, the surface roughness of the roller is 0.8-1.0 μm, the rolling tonnage of the leveling mill is 200-800 tons, the roller diameter difference between the upper and lower rollers of the leveling mill is controlled within 50 μm, and the roller shifting amount of the middle roller of the leveling mill is set to +20 mm.

[0020] Furthermore, the leveling elongation control parameters of the leveling mill include: Leveling mill inlet / outlet tension requirements: Leveling mill inlet tension target value (kN) = strip thickness (mm) × strip width (mm) × 0.08 (kN / mm 2 ), the target value of the tension at the exit of the leveler (kN) = strip thickness (mm) × strip width (mm) × 0.09 (kN / mm 2 ); The height difference between the anti-wrinkle roller at the entrance of the leveling machine and the anti-vibration roller at the exit is kept at 50mm, the anti-vibration roller at the exit is higher than the anti-wrinkle roller at the entrance, and the surface roughness Ra of the anti-wrinkle roller at the entrance and exit is controlled at 0.8-1.6μm.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The method for producing low-roughness cold-rolled strip steel for electrotin plating of the present invention obtains an electrotin plating substrate that meets mechanical property requirements by designing reasonable strip composition and appropriate hot rolling, pickling and continuous annealing processes. At the same time, by using rollers with special roughness surfaces, a lower surface roughness is obtained after leveling, so that the surface quality after electrotin plating is better, the plate shape is good, and the performance meets T2.5 / T3 material requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a production process flow chart of the present invention. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] In an embodiment of the present invention, a method for producing low-roughness cold-rolled steel strip for electroplating tin is provided, comprising the following chemical composition in mass percentage: C: 0.03-0.055wt%, Si: ≤0.050wt%, Mn: 0.15-0.25wt%, Al: 0.030-0.055%, P ≤0.020%, S ≤0.015%, N ≤0.006wt%, and the balance being Fe and other unavoidable impurities; wherein the specific principle for determining the chemical composition is as follows:

[0026] C: is the most effective strengthening element and also the most economical strengthening element. When the C content is low, its formability and weldability are better. However, a low C content will lead to low mechanical properties and hardness of the product, while an excessively high C content will lead to a significant decrease in its formability and elongation. Therefore, in the present invention, the C content is controlled at 0.03-0.055wt%.

[0027] Si: has a strong strengthening effect in steel, but Si is easily enriched and oxidized on the surface, which is not conducive to the surface quality of the product after pickling and annealing, and also reduces the coating property of the steel plate. Therefore, the present invention adds a small amount of Si or no Si is added, which is controlled below 0.05wt%.

[0028] Mn: It plays a role in solid solution strengthening in steel, which can increase the strength and hardness of the material. At the same time, it reacts with the S in the steel to reduce the hot brittleness of the steel. However, too high a Mn content will increase the cost of raw materials. Therefore, in the present invention, Mn mainly improves the strength and hardness of the material and reduces hot brittleness. Its content is controlled in the range of 0.15-0.25%.

[0029] Al: It plays a major role in deoxidation in steel. Al can also form AlN precipitation, fix the nitrogen element, improve the aging properties of the material, and play a certain role in refining the grains. A small amount of Al can improve material properties. However, if the Al content is too high, the crystallizer is prone to clogging, the castability deteriorates, and the cost is increased. Therefore, the Al weight percentage content of the present invention is controlled within a range of 0.030% to 0.055%.

[0030] P: It is easy to segregate, reduce the formability and plasticity of the material, and have adverse effects on the stamping performance, cold brittleness, secondary processing brittleness, etc. of the steel. In the present invention, the P content is controlled to be below 0.020wt%.

[0031] N: It is a harmful impurity that mainly causes yield effect and strain aging. Therefore, the upper limit of N content is strictly controlled. In the present invention, N is controlled below 0.006 wt%.

[0032] S: is an unavoidable harmful impurity in steel, which has an adverse effect on the isotropy, hot brittleness, stamping performance, cold bending performance, and flanging forming performance of the steel. Strictly controlling the S content in steel will increase the smelting cost of the steel. Therefore, in the present invention, the upper limit of the S content is controlled at 0.015%.

[0033] The balance is Fe and unavoidable impurity elements. The less impurity elements there are, the better without increasing additional costs.

[0034] like Figure 1 As shown, based on the ratio of the above chemical components, the production process of the present invention includes: smelting → continuous casting → hot rolling → pickling and cold rolling → cleaning → continuous annealing → flattening → finished product, which is specifically as follows:

[0035] Step 1: Smelting and continuous casting: LF furnace is used for slag deoxidation and desulfurization, while molten steel that meets the temperature, composition and cleanliness requirements for continuous casting is provided within a certain period of time. Continuous casting is used to produce ingots. Under the action of the crystallizer, the molten steel is formed and rapidly solidified and crystallized to form slabs.

[0036] Step 2: Hot rolling of slabs: Austenite rolling is performed on the continuously cast slabs to obtain hot-rolled coils. During the hot rolling process, a relatively low rolling temperature is used. A higher heating temperature will cause an increase in scale, coarsening of grains, and dissolution of AlN, which increases the solid-solution nitrogen. Therefore, the heating temperature is controlled at 1180-1220°C. To avoid two-phase rolling, the final rolling temperature is controlled at 860-900°C. To ensure that the steel plate performance meets the requirements, low-temperature coiling is adopted. However, too low a temperature is not conducive to the precipitation of solid-solution nitrogen. The coiling temperature is controlled at 660-690°C. A smaller crown can achieve a smaller difference between the same plate, but an excessively small crown is difficult to control during hot rolling and can easily lead to an excessively large wedge. Therefore, the hot-rolled crown is controlled at 0.015-0.035mm.

[0037] Step 3: Pickling and cold rolling: A conventional pickling process is used to fully remove the iron oxide scale on the surface of the strip, and then cold rolling is carried out to the required thickness specification of the finished product. In order to obtain finer grains and ensure certain mechanical properties, a higher reduction rate is required. However, too high a reduction rate will cause instability in the production process. The yield platform will be extended after recovery and recrystallization, which is not conducive to stamping. The cold rolling reduction rate is controlled at 80%-88%. To ensure the surface roughness range of the finished product, the production of electroplated tin substrates has special requirements for the pickling rolling tonnage, the roughness of the working rolls of the S5 stand, and the reduction rate. The rolling tonnage is required to be 500-1000 tons, the roughness target of the working rolls of the S5 stand is 2.5μm, and the reduction rate of the S5 stand is required to be ≤3%. To ensure a low decay rate of the plate surface roughness, the working rolls of the S5 stand must be chrome-plated.

[0038] Step 4: Strip cleaning: remove impurities adhering to the surface of the strip after cold rolling, such as rolling oil and iron powder, to improve the cleanliness of the strip surface and obtain better surface quality;

[0039] Step 5: Continuous annealing: Continuous annealing of the cleaned steel plate is a key process for controlling the structure and performance of the steel plate. The steel plate is heated to the recrystallization temperature and undergoes recovery, recrystallization, grain growth and other processes to obtain a structure with a certain grain size and appropriate performance. Too high an annealing temperature will result in a coarse material structure and an obvious orange peel on the surface after stamping. Therefore, the annealing temperature is controlled at 730-750℃.

[0040] Step 6: Overaging treatment: After the continuous annealing, the steel plate undergoes rapid cooling, and a large amount of supersaturated carbon remains, which is not conducive to stamping. After rapid cooling, an overaging process is used to promote the precipitation of a large number of C atoms. The overaging treatment is to cool the steel plate that has undergone high-temperature continuous annealing to about 380±20℃ and then keep it warm for 200-300 seconds. Since rapid cooling increases the precipitation power of carbon, maintaining heating can promote the precipitation of carbon, thereby ensuring that the product has good stamping and anti-aging properties. Therefore, the strip speed of the present invention is 100-200m / min, the temperature of the rapid cooling section is 390-410℃, the strip temperature of the aging section is 360-400℃, and the aging time is 200-300s.

[0041] Step 7: Leveling: The leveling process uses 6-roll wet leveling, which mainly improves the plate shape, eliminates the slip band (yield platform) caused by the pinning and deformation of dislocations by solid solution C and N atoms, avoids tensile strain marks caused by subsequent processing, and adjusts the mechanical properties of the material after annealing, and transfers different surface structures and roughness of the strip. Using a larger rolling force is beneficial to eliminating the yield platform and reducing the yield elongation, but excessive rolling force is not conducive to the control of strip shape and roughness. Therefore, the rolling force of the leveling mill is controlled at 4500-5500kN; for low-carbon aluminum-killed steel, as the leveling elongation increases, the yield strength of the steel plate first decreases and then increases. The leveling elongation reaches about 1.0%-1.2%, which can eliminate the yield platform of 0.25-0.35mm thick annealed steel plate. At the same time, the yield strength reaches the lowest point. Continuing to increase the leveling elongation can lead to dislocation strengthening in the structure, increase the yield strength and hardness of the steel plate, reduce processing performance, and increase the load of the leveling mill. The operating stability is reduced. Therefore, the leveling elongation of thin-gauge products should not exceed 1.4%.

[0042] In the above embodiment, in order to ensure that the surface quality of the plate meets the requirements after electrotin plating, the roughness of the base material must be low enough, so the leveling process adopts smooth roller rolling, and the resulting plate and strip exhibits a roughness of less than 0.6μm. In order to reduce the rolling force of the leveling mill and achieve smooth rolling, a 6-roller leveling mill is used to further reduce the diameter of the working roller. The roller diameter is required to be 460-480mm during production. The working roller adopts a ground surface and is not roughened. The surface roughness of the roller is controlled to be in the range of 0.8-1.0μm. In order to control the roughness range of the plate surface, the rolling tonnage of the leveling mill is required to be 200-800 tons. The plate shape of the electrotinned substrate is required to be relatively high. To ensure that no warping occurs, the difference in roller diameter between the upper and lower rollers of the leveling mill must be controlled within 50μm. In order to improve the plate shape control ability of the leveling mill and reduce harmful contact, the middle roller of the leveling mill must be shifted, and the shifting amount is set to +20mm.

[0043] In order to avoid the surface twill defect of the 6-roller leveler under large elongation, special control of the leveler entrance / exit tension and the leveler entrance anti-wrinkle roller / exit anti-vibration roller is required. The leveler entrance / exit tension requirements are as follows: Leveler entrance tension target value (kN) = strip thickness (mm) × strip width (mm) × 0.08 (kN / mm 2 ), the target value of the tension at the exit of the leveler (kN) = strip thickness (mm) × strip width (mm) × 0.09 (kN / mm 2 ); For example: when producing 0.3mm thickness and 1000mm width strip steel, the target value of the tension at the level pass mill entrance is set to 0.3mm×1000mm×0.08kN / mm 2 That is 24kN, the target value of the tension at the leveling machine outlet is set to 0.3mm×1000mm×0.09kN / mm 2That is 27kN, the height difference between the inlet anti-wrinkle roller and the outlet anti-vibration roller of the leveling machine is kept at 50mm, the outlet anti-vibration roller is higher than the inlet anti-wrinkle roller, and the surface roughness Ra of the inlet anti-wrinkle roller and the outlet anti-vibration roller needs to be controlled in the range of 0.8-1.6μm.

[0044] In order to further better explain the embodiments of the present invention, based on the above method, the following specific case parameters are provided for illustration:

[0045] Steelmaking and continuous casting: Molten steel is smelted in a converter, refined by HR or LF, and then continuously cast into slabs. The chemical composition of the slabs is shown in Table 1:

[0046] Table 1 Chemical composition / %

[0047] Serial number C Si Mn P S Als N Example 1 0.043 0.005 0.180 0.014 0.012 0.031 0.0017 Example 2 0.044 0.020 0.190 0.014 0.006 0.051 0.0018 Example 3 0.048 0.019 0.174 0.015 0.008 0.045 0.0018 Example 4 0.044 0.021 0.185 0.010 0.004 0.043 0.0024 Comparative Example 1 0.040 0.016 0.222 0.014 0.006 0.050 0.0022 Comparative Example 2 0.043 0.007 0.202 0.012 0.009 0.051 0.0022 Comparative Example 3 0.054 0.004 0.199 0.017 0.017 0.034 0.0024 Comparative Example 4 0.056 0.017 0.183 0.009 0.006 0.044 0.0018

[0048] Hot rolling of slab: The continuous casting slab goes through heating, rough rolling, finishing rolling, laminar cooling and coiling to obtain hot rolled steel coil with a thickness of 2mm. The specific hot rolling process parameters are shown in Table 2:

[0049] Table 2 Hot rolling process

[0050]

[0051] Pickling and cold rolling: The hot rolled steel coil is sequentially uncoiling, pickling, trimming, cold rolling, and coiling to obtain a chilled coil with a thickness of 0.25-0.35mm. The specific hot rolling process parameters are shown in Table 3.

[0052] Table 3 Pickling reduction control

[0053] Serial number Hot coil thickness / mm Thickness of hard rolled coil / mm Reduction rate / % Example 1 2 0.25 0.875 Example 2 2 0.35 0.825 Example 3 2 0.35 0.825 Example 4 2 0.25 0.875 Comparative Example 1 2.8 0.5 0.821 Comparative Example 2 3.2 0.7 0.781 Comparative Example 3 5 1.5 0.700 Comparative Example 4 5 1.8 0.640

[0054] Continuous annealing and leveling: The chilled coil undergoes uncoiling, degreasing and cleaning, annealing, leveling, edge trimming, and coiling to obtain the cold-rolled annealed steel coil. The specific process parameters are shown in Tables 4 and 5.

[0055] Table 4 Continuous Annealing Process

[0056]

[0057] Table 5 Leveling process

[0058]

[0059] The actual performance is shown in Table 6:

[0060] Table 6 Performance

[0061]

[0062] As demonstrated by the use of appropriate hot rolling and annealing processes, cold-rolled strip with excellent performance can be obtained, meeting T2.5 / T3 requirements. The use of low-roughness work rolls, along with appropriate tension, rolling force, and roll shifting, can produce cold-rolled strip with low surface roughness and good flatness. Customer trials have shown that these requirements are met.

[0063] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for producing low-roughness cold-rolled steel strip for electrotinning, characterized in that: The chemical composition includes the following mass percentage ratio: C: 0.03-0.055wt%, Si: ≤0.050wt%, Mn: 0.15-0.25wt%, Al: 0.030-0.055%, P≤0.020%, S≤0.015%, N≤0.006wt%, and the balance is Fe and other inevitable impurities. The specific production process is as follows: Step 1: Smelting and continuous casting: LF furnace is used for slag deoxidation and desulfurization, while molten steel that meets the temperature, composition and cleanliness requirements for the continuous casting process is provided within a certain period of time. Continuous casting is used to produce ingots. The molten steel is formed and rapidly solidified and crystallized in the crystallizer to form slabs. Step 2: Hot rolling of cast slabs: austenitic rolling of the continuously cast slabs to obtain hot rolled coils; Step 3: Pickling and cold rolling: Use conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold roll it to the required thickness specification of the finished product; Step 4: Strip cleaning: remove impurities adhering to the surface of the strip after cold rolling, including rolling oil and iron powder; Step 5: Continuous annealing: The cleaned steel plate is continuously annealed, and the steel plate is heated to the recrystallization temperature. After the recovery, recrystallization, and grain growth processes, the annealing temperature is controlled at 730-750°C. Step 6: Overaging treatment: Cool the steel plate after high temperature continuous annealing to 380±20℃ and keep it warm for 200-300 seconds; Step 7: Leveling: Use a 6-roller leveler for wet leveling to improve the plate shape and eliminate the slip bands caused by the pinning and deformation of dislocations by the solid solution C and N atoms.

2. The method for producing a low-roughness cold-rolled steel strip for electrotinning according to claim 1, wherein: During the hot rolling process in step 2, the heating temperature is controlled at 1180-1220° C., the final rolling temperature is controlled at 860-900° C., the coiling temperature is controlled at 660-690° C., and the hot rolling crown is controlled at 0.015-0.035 mm.

3. The method for producing a low-roughness cold-rolled steel strip for electrotinning according to claim 1, wherein: In step 3, the cold rolling reduction rate is controlled at 80%-88%, the rolling tonnage is 500-1000 tons, the working roll roughness target of the S5 stand is 2.5μm, the S5 stand reduction rate is ≤3%, and the working roll of the S5 stand is chrome-plated.

4. The method for producing a low-roughness cold-rolled steel strip for electrotinning according to claim 1, wherein: In step 6, the strip processing speed is 100-200 m / min, the temperature in the rapid cooling section is 390-410°C, the strip temperature in the aging section is 360-400°C, and the aging time is 200-300s.

5. The method for producing a low-roughness cold-rolled steel strip for electrotinning according to claim 1, wherein: In step 7, the rolling force of the leveler is controlled at 4500-5500 kN, and the leveling elongation does not exceed 1.4%.

6. The method for producing a low-roughness cold-rolled steel strip for electrotinning according to claim 5, characterized in that: The roller diameter of the leveling mill is 460-480 mm, the surface roughness of the roller is 0.8-1.0 μm, the rolling tonnage of the leveling mill is 200-800 tons, the roller diameter difference between the upper and lower rollers of the leveling mill is controlled within 50 μm, and the roller shifting amount of the middle roller of the leveling mill is set to +20 mm.

7. The method for producing a low-roughness cold-rolled steel strip for electrotinning according to any one of claim 5, characterized in that: The leveling elongation control parameters of the leveling mill include: Leveling mill entrance / exit tension requirements: Leveling mill entrance tension target value (kN) = strip thickness (mm) × strip width (mm) × 0.08 (kN / mm 2 ), the target value of the tension at the exit of the leveler (kN) = strip thickness (mm) × strip width (mm) × 0.09 (kN / mm 2 ); The height difference between the inlet anti-wrinkle roller and the outlet anti-trembling roller of the leveling machine is kept at 50mm, the outlet anti-trembling roller is higher than the inlet anti-wrinkle roller, and the surface roughness Ra of the inlet anti-wrinkle roller and the outlet anti-trembling roller is controlled at 0.8-1.6μm.

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