Ultrathin-specification ultrahigh-strength weathering resistant steel and plate shape control method

Abstract

The invention discloses ultra-thin specification ultra-high strength weathering resistant steel and a plate shape control method. The ultra-thin specification ultra-high strength weathering resistant steel comprises the following components in percentage by weight: 0.06%-0.12% of C, 0.25%-0.5% of Si, 1.40%-2.1% of Mn, 0.18%-0.55% of Cu, 0.28%-1.25% of Cr, 0.05%-0.1% of Ni, less than or equal to 0.025% of P, less than or equal to 0.01% of S and the balance of Fe and other inevitable residual elements. The unevenness of the ultra-thin specification ultra-high strength weathering resistant steel is controlled within 5 mm / m. The method can ensure that the appearance plate shape of a product is flat and straight, and meets the special requirements of the fields of container steel and the like on high plate shape quality.

Description

Technical Field

[0001] This invention relates to the field of hot-rolled strip steel technology, and more specifically, to an ultra-thin, ultra-high-strength weather-resistant steel and a method for controlling its shape. Background Technology

[0002] Plate shape is an important indicator for measuring the quality of hot-rolled products. Currently, hot-rolled products are developing towards wider and thinner specifications and higher strength. At the same time, downstream users have increasingly higher requirements for plate shape, which leads to greater difficulty in production control.

[0003] Ultra-thin, high-strength weathering steel is used in industries such as containers. It has high resistance to atmospheric corrosion and excellent low-temperature impact toughness. Compared with ordinary structural steel materials, it can reduce the overall weight of containers by 10-15%, which is beneficial to reducing carbon emissions.

[0004] A systematic study was conducted on the shape problem of hot-rolled ultra-high strength steel plates. Chinese patent application number CN202011164375 discloses a method for controlling the shape of thin-gauge hot-rolled structural steel plates. The production process includes heating of continuously cast slabs, 3+3 pass roughing, 7-stand four-high mill finishing, laminar flow cooling after rolling, and finished product coiling and warehousing. By controlling the temperature distribution of the strip during the production process, the plate shape problem caused by internal stress is reduced. However, the yield strength of the steel plates produced by this method is ≤600MPa and lacks Cu element, which cannot meet the performance requirements of ultra-high strength and weather resistance.

[0005] Chinese Patent Publication No. CN113770174A discloses a method for controlling the shape of high-strength and tough engineering machinery steel. The finishing rolling process adopts micro-wave rolling, with a front-end intermittent cooling mode and optimized layer cooling water discharge sequence, so that the produced engineering machinery steel has good microstructure and good shape. However, the process route of this invention lacks straightening and leveling, making it difficult to ensure the high shape requirements of users.

[0006] Chinese patent publication number CN112077152A discloses a method for controlling the shape of ultra-high strength steel for longitudinal beams of commercial vehicles. The method adopts a hot-feeding and hot-charging method for continuously cast billets, control of large crown value in precision rolling, and ultra-fast cooling in the front stage of layer cooling + air cooling in the rear stage. This method ensures the uniformity of the structural stress, strain stress and thermal stress of the strip steel and achieves good control of the strip shape. However, this invention involves specifications of 6 to 10 mm, which is not applicable to extremely thin specifications below 2 mm. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide an ultra-thin, high-strength weather-resistant steel and a method for controlling the shape of the sheet, which can ensure that the product has a straight and flat appearance, meeting the special requirements for high sheet quality in fields such as container steel.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] The first aspect of the present invention provides an ultra-thin ultra-high strength weathering steel and a method for controlling the shape of the plate, comprising the following components by weight percentage: C: 0.06-0.12%, Si: 0.25-0.5%, Mn: 1.40-2.1%, Cu: 0.18-0.55%, Cr: 0.28-1.25%, Ni: 0.05-0.1%, P≤0.025%, S≤0.01%, with the remainder being Fe and other unavoidable residual elements;

[0010] The unevenness of the ultra-thin, high-strength, weather-resistant steel is controlled within 5 mm / m.

[0011] Preferably, the ultra-thin ultra-high strength weathering steel comprises the following components by weight percentage: C: 0.06-0.11%, Si: 0.28-0.46%, Mn: 1.40-2.03%, Cu: 0.18-0.51%, Cr: 0.28-0.62%, Ni: 0.05-0.093%, P≤0.011%, S≤0.009%, with the remainder being Fe and other unavoidable residual elements.

[0012] Preferably, the ultra-thin ultra-high strength weathering steel has a thickness of 1.1 to 1.6 mm, a tensile strength ≥ 800 MPa, and an elongation after fracture ≥ 12%.

[0013] A second aspect of the present invention provides a method for controlling the shape of ultra-thin, high-strength weathering steel as described in the first aspect of the present invention, comprising the following steps:

[0014] S1, slab heating, placing ultra-thin ultra-high strength weather-resistant steel slabs in a heating furnace for heating;

[0015] S2, rough rolling, the rolling mode adopts 3+3 passes, the rough rolling end temperature is controlled at 1030~1070℃, the first set of descaling water is turned on, and the hot coil box is put into use after rough rolling.

[0016] S3, finishing mill, the vertical roll at the entry of the finishing mill is put into use, the cooling water between the stands is turned off, the finishing mill end temperature is controlled at 840~880℃, and the crown is controlled at 50~70m;

[0017] S4, laminar cooling;

[0018] S5, slow cooling;

[0019] S6, flat, rolling force controlled at 450-550 tons, bending roll force adjusted according to the shape of the incoming material.

[0020] Preferably, in step S1, the heating furnace used for heating the slab is divided into four zones, including a preheating zone, a first heating zone, a second heating zone, and a soaking zone; the final temperature of the preheating zone is ≥850℃, the final temperature of the first heating zone is ≥1100℃, the final temperature of the second heating zone is ≥1230℃, the temperature of the soaking zone is ≥1260℃, the furnace exit temperature is controlled at 1240~1280℃, the total furnace time is ≥170min, and the excess air coefficient of each zone is 0.8~1.0.

[0021] Preferably, in step S2, the thickness of the intermediate billet is controlled at 25-30 mm during the rough rolling process.

[0022] Preferably, in step S3, during the finishing rolling process, the finishing rolling exit side spray and air spray are turned on, the rolling speed is controlled at 10 to 10.6 mm / s, and the finishing rolling exit straightness is controlled in the range of -15 to 15 IU.

[0023] Preferably, in step S4, the layer cooling adopts a forward cooling mode with a cooling rate of 20-40℃ / s, the cooling water of the layer cooling roller table is turned off during the rolling process, and the coiling temperature is controlled at 550-600℃.

[0024] Preferably, in step S5, during the slow cooling process, the steel coils that have been cooled and coiled are promptly placed into the slow cooling wall or piled up in the hot zone of the steel coil warehouse, surrounded by other hot coils.

[0025] Preferably, in step S6, during the leveling process:

[0026] When the incoming material exhibits a double-sided wave shape, the bending roll force adjustment range is 0–80 tons; when the incoming material exhibits a medium wave shape, the bending roll force adjustment range is 0–-50 tons; when the incoming material exhibits a single-sided wave shape, the roll tilt is adjusted according to the location of the single-sided wave, with a tilt adjustment range of -300–300 μm; and / or

[0027] The leveling speed is controlled at 20-150 m / min, and the winding tension is controlled at 7-12 tons.

[0028] The present invention provides an ultra-thin, ultra-high-strength weather-resistant steel and a method for controlling its shape, which has the following beneficial effects:

[0029] 1. This invention employs slab heating, rough rolling, finish rolling, laminar flow cooling, post-rolling slow cooling and leveling processes, and controls the process parameters of each step to ensure that the product has a straight and flat appearance, meeting the special requirements for high plate shape quality in fields such as container steel.

[0030] 2. The slab heating process of the present invention, through a high homogenization temperature and sufficient furnace time, can ensure the uniformity of slab temperature, thereby ensuring the uniformity of microstructure and stress.

[0031] 3. This invention uses a hot coil box to coil the intermediate billet without a mandrel between the roughing and finishing mills, eliminating the temperature difference between the head and tail of the intermediate billet and the temperature difference between the upper and lower surfaces, ensuring product quality, improving the stability of rolling ultra-thin ultra-high strength steel, and reducing the actual power consumption of the finishing mill by slowing down the temperature drop rate of the intermediate billet, thus achieving energy saving and consumption reduction.

[0032] 4. The present invention puts the vertical roll at the entry of the finishing mill into use, shuts off the cooling water between the stands, improves the stability of the rolling process and the accuracy of the final rolling temperature, turns on the side spray and air spray at the exit of the finishing mill, improves the temperature uniformity of the strip in the width direction, and the small crown control is conducive to obtaining a good finished strip shape.

[0033] 5. The present invention adopts a forward cooling mode for layer cooling, and the cooling water of the layer cooling roller table is turned off during the rolling process, which helps to ensure the accuracy of coiling temperature control and reduce the adverse effects of cooling water on strip shape.

[0034] 6. After the steel coils are produced, they are placed in a slow cooling wall or piled up in the hot zone of the steel coil warehouse, surrounded by other hot coils, which can improve the temperature uniformity of the steel coil cooling process and improve the plate shape quality.

[0035] 7. The flattening process of this invention adopts a reasonable flattening shape control scheme according to the product characteristics, and gives full play to the role of flattening force, bending roller force, winding tension and flattening speed to improve the shape of the incoming material, which can ensure that the flatness of the finished product is controlled within 5mm / m.

[0036] 8. The ultra-thin, high-strength weathering steel prepared according to the method of the present invention has a thickness of 1.1 to 1.6 mm, a tensile strength ≥ 800 MPa, an elongation after fracture ≥ 12%, and a flat and straight appearance. After leveling, it can meet the user's requirements. Detailed Implementation

[0037] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with embodiments.

[0038] The present invention provides an ultra-thin, ultra-high-strength weathering steel comprising the following components by weight percentage: C: 0.06–0.12%, Si: 0.25–0.5%, Mn: 1.40–2.1%, Cu: 0.18–0.55%, Cr: 0.28–1.25%, Ni: 0.05–0.1%, P≤0.025%, S≤0.01%, with the remainder being Fe and other unavoidable residual elements;

[0039] The unevenness of the aforementioned ultra-thin, high-strength weather-resistant steel is controlled within 5 mm / m.

[0040] In a specific embodiment, the ultra-thin ultra-high strength weathering steel comprises the following components by weight percentage: C: 0.06–0.11%, Si: 0.28–0.46%, Mn: 1.40–2.03%, Cu: 0.18–0.51%, Cr: 0.28–0.62%, Ni: 0.05–0.093%, P≤0.011%, S≤0.009%, with the remainder being Fe and other unavoidable residual elements.

[0041] The aforementioned ultra-thin, high-strength weather-resistant steel has a thickness of 1.1–1.6 mm, a width of 1000–1400 mm, a tensile strength ≥800 MPa, and an elongation after fracture ≥12%. The product has a flat and straight appearance, and after leveling, it can meet the high-quality requirements for container steel and other fields.

[0042] This invention also provides a method for controlling the shape of the aforementioned ultra-thin ultra-high strength weathering steel, including slab heating, rough rolling, finish rolling, laminar flow cooling, post-rolling slow cooling and leveling processes, specifically including the following steps:

[0043] S1, slab heating, placing ultra-thin ultra-high strength weather-resistant steel slabs in a heating furnace for heating;

[0044] The heating furnace used for slab heating is divided into four zones: a preheating zone, a first heating zone, a second heating zone, and a soaking zone. The final temperature of the preheating zone is ≥850℃, the final temperature of the first heating zone is ≥1100℃, the final temperature of the second heating zone is ≥1230℃, and the temperature of the soaking zone is ≥1260℃. The furnace exit temperature is controlled between 1240℃ and 1280℃. The total furnace time is ≥170 min (preferably 170 to 250 min), which can effectively improve the temperature uniformity of the slab. To avoid the risk of copper embrittlement, the excess air coefficient for each zone is set between 0.8 and 1.0. The excess air coefficient is the ratio of the actual air consumption to the theoretical air consumption, usually represented by α. This coefficient reflects the degree of excess air during fuel combustion and is an important parameter to ensure complete fuel combustion.

[0045] S2, rough rolling, the rolling mode adopts 3+3 passes, the rough rolling end temperature is controlled at 1030~1070℃, the first set of descaling water is turned on, and the hot coil box is put into use after rough rolling.

[0046] The roughing process adopts a 3+3 pass rolling pattern (i.e., three passes on the R1 mill and three passes on the R2 mill). During the roughing process, the thickness of the intermediate slab is controlled at 25-30 mm. The finishing temperature of the roughing is controlled at 1030-1070℃. The first set of descaling water is turned on to remove surface iron oxide scale and other substances. After roughing, the strip is put into a hot coil box to improve the temperature uniformity along the entire length of the strip.

[0047] S3, finishing mill, the vertical roll at the entry of the finishing mill is put into use, the cooling water between the stands is turned off, the finishing mill end temperature is controlled at 840~880℃, and the crown is controlled at 50~70m;

[0048] In the finishing rolling process, the vertical roll at the finishing mill entrance is put into use, the cooling water between the stands is turned off, and the side spray and air spray at the finishing mill exit are turned on to improve the stability of the rolling process and the accuracy of the final rolling temperature. The finishing mill end temperature is controlled at 840-880℃, the rolling speed is controlled at 10-10.6mm / s, and the finishing mill exit straightness is controlled in the range of -15 to 15IU.

[0049] S4, laminar cooling;

[0050] The layer cooling process adopts a forward cooling mode with a cooling rate of 20-40℃ / s. During the rolling process, the cooling water of the layer cooling roller table is turned off to ensure the accuracy of coiling temperature control and reduce the adverse effects of cooling water on the strip shape. The coiling temperature is controlled at 550-600℃.

[0051] S5, slow cooling;

[0052] The slow cooling process involves placing the steel coils that have been cooled and coiled into the slow cooling wall in a timely manner, or stacking them in the hot zone of the steel coil warehouse, surrounded by other hot coils.

[0053] S6, flat, rolling force controlled at 450-550 tons, adjusting bending roll force and roll inclination according to the shape of the incoming material.

[0054] During the leveling process, the rolling force is controlled between 450 and 550 tons. The bending roll force and roll inclination are adjusted according to the shape of the incoming strip. When the incoming strip exhibits double-sided waviness, the bending roll force is adjusted from 0 to 80 tons; when the incoming strip exhibits medium waviness, the bending roll force is adjusted from 0 to -50 tons; when the incoming strip exhibits single-sided waviness, the roll inclination is adjusted accordingly based on the location of the waviness, with an adjustment range of -300 to 300 μm. The greater the waviness of the incoming strip, the greater the bending roll force. The leveling speed is controlled between 20 and 150 m / min, and the coiling tension is controlled between 7 and 12 tons to facilitate observation of the strip shape and ensure sufficient extension, thus guaranteeing the shape improvement effect.

[0055] Example

[0056] The chemical composition by weight percentage of the ultra-thin ultra-high strength weathering steel in this embodiment is as follows: C: 0.06–0.12%, Si: 0.25–0.5%, Mn: 1.40–2.1%, Cu: 0.18–0.55%, Cr: 0.28–1.25%, Ni: 0.05–0.1%, P≤0.025%, S≤0.01%, with the remainder being Fe and other unavoidable residual elements; the chemical composition of the ultra-thin ultra-high strength weathering steel in Examples 1–6 is shown in Table 1.

[0057] Table 1. Chemical composition (wt%) of ultra-thin ultra-high strength weathering steels of specifications 1-6 in Examples 1-6

[0058] element C Si Mn Cu Cr Ni P S Example 1 0.07 0.3 1.84 0.233 0.28 0.081 0.008 0.005 Example 2 0.1 0.35 1.65 0.32 0.33 0.06 0.005 0.006 Example 3 0.08 0.42 1.58 0.184 0.62 0.075 0.011 0.009 Example 4 0.6 0.28 1.43 0.424 0.52 0.088 0.009 0.006 Example 5 0.9 0.33 1.55 0.264 0.44 0.056 0.004 0.005 Example 6 0.8 0.39 1.72 0.285 0.59 0.064 0.007 0.006 Example 7 0.11 0.46 1.67 0.373 1.18 0.093 0.004 0.007 Example 8 0.07 0.32 2.03 0.51 0.75 0.075 0.007 0.004

[0059] The sheet shape control methods for ultra-thin ultra-high strength weathering steel in Examples 1-6 include slab heating, rough rolling, finish rolling, laminar flow cooling, post-rolling slow cooling, and leveling processes. The following description uses a 1780 hot strip mill production line as an example:

[0060] (1) Slab heating: a reducing atmosphere is used. The slab exit temperature is 1240-1280℃, the soaking time is 25-50min, the total time in the furnace is ≥170min, and the excess air coefficient is 0.8-1.0. For specific process parameters, please refer to Table 2.

[0061] Table 2 Process parameters for slab heating

[0062] Process parameters excess air coefficient Furnace temperature / min Soaking time / min Total time in the furnace / min Example 1 0.88 1278 31 192 Example 2 0.91 1260 27 185 Example 3 0.85 1266 28 188 Example 4 0.83 1272 34 198 Example 5 0.96 1275 35 205 Example 6 0.92 1262 26 184 Example 7 0.85 1264 29 174 Example 8 0.94 1266 31 182

[0063] (2) Rolling process, including roughing and finishing. The roughing process uses a 3+3 pass rolling method, i.e., three passes of reciprocating rolling on the R1 mill and three passes of reciprocating rolling on the R2 mill. The first set of descaling water is turned on. The finishing temperature is controlled at 1030-1070℃, the intermediate billet thickness is controlled at 25-30mm, and the hot coil box is put into use. The finishing process uses a 7-pass continuous rolling method. The vertical roll at the finishing mill entrance is put into use, the cooling water between the stands is turned off, and the side spray and air spray at the finishing mill exit are turned on. The finishing temperature is controlled at 840-880℃, the crown is controlled at 50-70μm, the rolling speed is 10-10.6m / s, the straightness at the finishing mill exit is controlled in the range of -15 to 15IU, and the coiling temperature is controlled in the range of 550-600℃. See Table 3 for specific process parameters.

[0064] Table 3 Main parameters of rolling process

[0065]

[0066] (3) Laminar cooling and slow cooling: The laminar cooling process adopts a forward cooling mode with a cooling rate of 20-40℃ / s. During the rolling process, the cooling water of the laminar cooling roller table is turned off to ensure the accuracy of coiling temperature control and reduce the adverse effects of cooling water on the strip shape. The coiling temperature is controlled at 550-600℃. In the slow cooling process, the steel coils after laminar cooling are promptly placed into the slow cooling wall or piled up in the hot zone of the steel coil warehouse, surrounded by other hot coils.

[0067] (4) Leveling process: Rolling force is controlled at 450-550t. The bending roll force and roll inclination are adjusted according to the shape of the incoming material. The bending roll force adjustment range is -50-80t, the roll inclination adjustment range is -300-300μm, the coiling tension is controlled at 7-12t, and the leveling speed is controlled at 20-150m / min. For specific process parameters, please refer to Table 4.

[0068] Table 4 Main parameters of leveling process

[0069] Process parameters Rolling force / t Bending roller force / t Winding tension / t Inclination / μm Leveling speed (m / s) Example 1 510 -6 10 -120 50 Example 2 497 15 9 0 45 Example 3 500 20 10 200 64 Example 4 516 8 11 60 77 Example 5 504 -12 9 90 60 Example 6 508 5 11 -240 80 Example 7 465 -25 8 20 90 Example 8 505 55 10 0 58

[0070] The ultra-thin ultra-high strength weathering steel obtained by the plate shape control method in Examples 1-6 has a thickness of 1.1-1.6 mm, a width of 1000-1400 mm, a tensile strength of 809-842 MPa (all ≥800 MPa), an elongation after fracture of 15-26% (all ≥12%), and a flatness of 1.5-4.3 mm / m (all ≤5 mm / m). Specific properties are shown in Table 5.

[0071] Table 5 Performance of Ultra-thin High-strength Weathering Steel

[0072] Process parameters Tensile strength / MPa Elongation / % Strip unevenness (mm / m) Example 1 821 24 3.5 Example 2 830 21 2 Example 3 842 19 4.3 Example 4 815 23 3.2 Example 5 826 21 1.5 Example 6 809 26 2.8 Example 7 840 15 2.9 Example 8 826 22 3.8

[0073] In summary, the ultra-thin, high-strength, weather-resistant steel products produced in Embodiments 1-6 of this invention have a straight appearance, which can meet the processing and usage requirements of users.

[0074] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. An ultra-thin, high-strength weather-resistant steel, characterized in that, It includes the following components by weight percentage: C: 0.06–0.12%, Si: 0.25–0.5%, Mn: 1.40–2.1%, Cu: 0.18–0.55%, Cr: 0.28–1.25%, Ni: 0.05–0.1%, P≤0.025%, S≤0.01%, with the remainder being Fe and other unavoidable residual elements; The unevenness of the ultra-thin, high-strength, weather-resistant steel is controlled within 5 mm / m.

2. The ultra-thin, ultra-high-strength weather-resistant steel according to claim 1, characterized in that: The ultra-thin, ultra-high-strength weathering steel comprises the following components by weight percentage: C: 0.06–0.11%, Si: 0.28–0.46%, Mn: 1.40–2.03%, Cu: 0.18–0.51%, Cr: 0.28–0.62%, Ni: 0.05–0.093%, P≤0.011%, S≤0.009%, with the remainder being Fe and other unavoidable residual elements.

3. The ultra-thin, ultra-high-strength weather-resistant steel according to claim 1, characterized in that: The ultra-thin ultra-high strength weathering steel has a thickness of 1.1 to 1.6 mm, a tensile strength of ≥800 MPa, and an elongation after fracture of ≥12%.

4. A method for controlling the shape of ultra-thin, ultra-high-strength weathering steel as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1, slab heating, placing ultra-thin ultra-high strength weather-resistant steel slabs in a heating furnace for heating; S2, rough rolling, the rolling mode adopts 3+3 passes, the rough rolling end temperature is controlled at 1030~1070℃, the first set of descaling water is turned on, and the hot coil box is put into use after rough rolling. S3, finishing mill, the vertical roll at the entry of the finishing mill is put into use, the cooling water between the stands is turned off, the finishing mill end temperature is controlled at 840~880℃, and the crown is controlled at 50~70m; S4, laminar cooling; S5, slow cooling; S6, flat, rolling force controlled at 450-550 tons, adjusting bending roll force and roll inclination according to the shape of the incoming material.

5. The method for controlling the shape of ultra-thin, ultra-high-strength weathering steel according to claim 4, characterized in that: In step S1, the heating furnace used for heating the slab is divided into four zones: a preheating zone, a first heating zone, a second heating zone, and a soaking zone. The final temperature of the preheating zone is ≥850℃, the final temperature of the first heating zone is ≥1100℃, the final temperature of the second heating zone is ≥1230℃, the temperature of the soaking zone is ≥1260℃, the furnace exit temperature is controlled between 1240℃ and 1280℃, the total furnace time is ≥170 minutes, and the excess air coefficient for each zone is 0.8 to 1.

0.

6. The method for controlling the plate shape of ultra-thin ultra-high strength weathering steel according to claim 4, characterized in that: In step S2, during the rough rolling process, the thickness of the intermediate billet is controlled at 25-30 mm.

7. The method for controlling the plate shape of ultra-thin ultra-high strength weathering steel according to claim 4, characterized in that: In step S3, during the finishing rolling process, the finishing mill exit side spray and air spray are turned on, the rolling speed is controlled at 10 to 10.6 mm / s, and the finishing mill exit flatness is controlled within the range of -20 to 50 IU.

8. The method for controlling the plate shape of ultra-thin ultra-high strength weathering steel according to claim 4, characterized in that: In step S4, the layer cooling adopts a forward cooling mode with a cooling rate of 20-40℃ / s. During the rolling process, the cooling water of the layer cooling roller table is turned off, and the coiling temperature is controlled at 550-600℃.

9. The method for controlling the shape of ultra-thin ultra-high strength weathering steel according to claim 4, characterized in that: In step S5, during the slow cooling process, the steel coils that have been cooled and coiled are promptly placed into the slow cooling wall or piled up in the hot zone of the steel coil warehouse, surrounded by other hot coils.

10. The method for controlling the plate shape of ultra-thin ultra-high strength weathering steel according to claim 4, characterized in that: In step S6, during the leveling process: When the incoming material exhibits a double-sided wave shape, the bending roll force adjustment range is 0–80 tons; when the incoming material exhibits a medium wave shape, the bending roll force adjustment range is 0–-50 tons; when the incoming material exhibits a single-sided wave shape, the roll tilt is adjusted according to the location of the single-sided wave, with a tilt adjustment range of -300–300 μm; and / or The leveling speed is controlled at 20-150 m / min, and the winding tension is controlled at 7-12 tons.

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