A method for optimizing the shape of non-oriented silicon steel sheet by CSP hot rolling and acid continuous rolling in cooperation

Abstract

The application discloses a method for optimizing the shape of non-oriented silicon steel plates through CSP hot rolling and acid continuous rolling cooperation, and belongs to the technical field of non-oriented silicon steel production. The method is characterized in that: through the cooperation of multiple processes such as the CSP hot rolling process parameters, the acid continuous rolling process parameters and the cooperation matching between the two processes, the rationality of each process parameter is evaluated through indexes such as the same plate difference, the flatness of the plate shape, the plate shape deviation and the like, and finally the method for optimizing the shape of non-oriented silicon steel plates is obtained. The method is suitable for the shape control process of various non-oriented silicon steels (including medium and low grade, high grade and new energy non-oriented silicon steels), can effectively improve defects such as uneven plate shape, too large same plate difference and edge wave, and improves the plate shape precision and the use performance in subsequent processing.

Description

Technical Field

[0001] This invention belongs to the field of non-oriented silicon steel production technology, and particularly relates to a method for optimizing the shape of non-oriented silicon steel sheets by coordinating CSP hot rolling and acid continuous rolling. Background Technology

[0002] Non-oriented silicon steel is a core raw material for electromagnetic equipment such as motors and transformers. Its sheet shape quality directly determines the efficiency of subsequent lamination and stacking, as well as the stability of equipment operation. Among them, the thickness difference of the same strip (the deviation of thickness at different points on the same cross-section of the strip) is the core indicator for measuring the sheet shape accuracy. With the rapid development of new energy, high-end home appliances and other fields, the market's requirements for the thickness difference of non-oriented silicon steel are becoming increasingly stringent, and conventional production processes can no longer meet the demands.

[0003] CSP production lines have become one of the mainstream production routes for non-oriented silicon steel due to their short process, low energy consumption, and high production efficiency. However, the generation of sheet shape defects in this production line is affected by the coupling of multiple processes and factors. Among them, the crown control and wedge control of the hot rolling process, the state of the work rolls, and the coordination between the hot rolling and pickling continuous rolling processes are the key factors affecting the sheet shape of non-oriented silicon steel (especially the difference between sheets of the same type).

[0004] Currently, existing technologies for controlling the shape of non-oriented silicon steel sheets produced by CSP (Chemical Sequencing Process) mainly focus on optimizing a single process: such as optimizing only the crown control parameters of the hot rolling process, or only adjusting the work roll profile of the pickling continuous rolling process. There is a lack of coordinated control of the hot rolling and pickling continuous rolling processes, which leads to the mutual transmission and superposition of sheet shape defects between the two processes, making it difficult to achieve precise control of the same sheet difference.

[0005] Application No. 201710006936.9 discloses a method for controlling the longitudinal thickness accuracy of cold-rolled non-oriented silicon steel. It focuses on the location of thickness fluctuations in cold-rolled non-oriented silicon steel and analyzes the correspondence between these fluctuations and the rolling process. The final rolling process involves increasing the speed by 150-250 m / min, then rolling at a constant speed for 200-400 meters. After reaching the required rolling speed, constant speed rolling begins, with a uniform decrease in speed for the last 600-1000 meters of the coil, until the speed reaches zero at the end of the coil. This method overcomes the localized thickness fluctuations and layer characteristics, resulting in cold-rolled non-oriented silicon steel products with high interlayer resistance.

[0006] Application No. 201610105105.2 discloses a method for improving the shape of non-oriented silicon steel sheets. The production process includes smelting, hot rolling, normalizing, cold rolling and annealing coating. The control of the normalizing process is described in detail. Through steps such as preheating, non-oxidizing heating, radiant tube heating, radiant tube cooling, homogenization, rapid water cooling, slow water cooling and air cooling, the wave height of the non-oriented silicon steel sheet is ≤1.7 mm, which effectively improves the yield of the sheet.

[0007] Application No. 202310052891.4 discloses a method for controlling the shape of high-grade non-oriented silicon steel rolled using a 20-roll oil mill, which solves the technical problems of poor shape control and high defect rate in high-grade non-oriented silicon steel. By controlling the pass reduction, exit unit tension, roll system configuration, target shape curve, and roll roughness, full-width rolling of 1000mm-1300mm wide steel strips is achieved, resulting in good shape, no rib stripes, and meeting the requirements for subsequent lamination processing. Summary of the Invention

[0008] To address the problems in existing CSP production of non-oriented silicon steel, such as the disconnect between hot rolling and pickling continuous rolling processes, unreasonable work roll profile design, and inaccurate control of crown and wedge shape, which lead to the superposition of sheet shape defects and excessive differences between sheets, the purpose of this invention is to provide a method for optimizing the sheet shape of non-oriented silicon steel through the coordinated operation of CSP hot rolling and pickling continuous rolling. By coordinating the management and control of the two processes, optimizing the work roll profile, and dynamically adjusting the crown and wedge shape, precise control of the sheet shape (especially the differences between sheets) of non-oriented silicon steel can be achieved, thereby improving product quality and production efficiency.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0010] This invention discloses a method for optimizing the shape of non-oriented silicon steel sheets through synergistic combination of CSP hot rolling and pickling continuous rolling, comprising:

[0011] Hot rolling process parameters:

[0012] The thickness of the continuously cast billet is controlled at 42~72 mm, the casting speed is 3~4.5 m / min, and the water flow rate of each section of the continuous casting sector is adjusted according to preset parameters to avoid corrugated defects on the billet surface. When the target plate difference is ≤5μm, the crown is controlled within the range of 0~8μm and the wedge shape is ≤3μm.

[0013] The actual hot-rolled strip crown test data is compared with the target crown. When the crown deviation is >2μm, it is corrected by adjusting the bending roll force and roll shifting amount of the finishing mill stand. The bending roll force adjustment range is 500~2000kN, and the roll shifting amount adjustment range is 0~150mm.

[0014] By adjusting the difference in roll gap between the left and right sides of the hot rolling mill stand, the wedge shape deviation of the strip is controlled. When the wedge shape deviation is >1μm, the roll gap on one side is adjusted by 0.01~0.05mm to ensure that the wedge shape of the strip is controlled within the target range. At the same time, the finishing rolling temperature is optimized to 830~920℃ and the coiling temperature is optimized to 580~720℃ to reduce wedge defects caused by temperature deviation.

[0015] Pickling and rolling process parameters:

[0016] A high-precision strip shape detection device is installed at the exit of the acid continuous rolling mill to collect the strip's same-strip difference data in real time and compare it with the target same-strip difference. When the same-strip difference deviation is >1μm, fine adjustment is made by adjusting the bending roll force, rolling pressure and roll shifting amount of the acid continuous rolling mill stand. The bending roll force adjustment range is 300~1500kN, the rolling pressure adjustment range is 1000~5000kN, and the roll shifting amount adjustment range is 0~120 mm.

[0017] The wear of the work rolls in the acid continuous rolling mill is monitored in real time. When the wear is greater than 0.1 mm, the impact of the wear on the plate shape is compensated by adjusting the roll shifting amount and the roll bending force. At the same time, a work roll replacement cycle model is established to determine the optimal replacement cycle based on the wear rate of the rolls and the product specifications and batch size, so as to avoid the aggravation of plate shape defects due to excessive wear of the rolls.

[0018] Connection between hot rolling and pickling processes:

[0019] Establish a collaborative feedback mechanism to transmit the hot-rolled strip crown and wedge data, as well as the work roll surface wear data collected in the hot rolling process, to the control unit of the pickling and rolling process in real time, so as to ensure that the pickling and rolling process can accurately grasp the strip shape status of the hot-rolled material.

[0020] Based on the shape data of the hot-rolled material, the pickling and rolling process adjusts the inlet tension and speed matching parameters. The inlet tension is controlled at 10~30kN, and the difference between the pickling and rolling speed and the hot-rolling exit speed is controlled at ±0.5m / s to avoid shape deformation caused by speed mismatch and tension fluctuation.

[0021] Based on the crown and wedge deviation of hot-rolled strip, the bending roll force and rolling pressure of the pickling continuous rolling mill stand are adjusted in advance to pre-compensate for the strip shape defects transmitted by hot rolling.

[0022] The chemical composition of the non-oriented silicon steel by mass percentage is as follows: C≤0.0025%, 0.35%~1.40% Si, 0.35~0.85% Mn, 0.030%~0.095% P, S≤0.0030%, 0.25~0.35% Als, N≤0.0030%, O≤0.0020%, Ti≤0.0030%, with the remainder being Fe and unavoidable impurities.

[0023] Furthermore, the pickling and rolling process involves dividing the width into multiple width ranges based on the width specifications of the hot-rolled material, designing multiple sets of adaptable roll shapes to ensure that the roll shape matches the width of the material; and incorporating the roll shape parameters into the control software to achieve efficient and automated solution of the roll shape curve, allowing for flexible adjustment of parameters based on the on-site roll shape usage and edge reduction requirements.

[0024] Furthermore, when there is a positive convexity deviation in hot-rolled strip, the positive bending roll force of the pickling stand is increased to compensate for the convexity defect; when there is a wedge-shaped deviation, the difference in the left and right roll gaps of the pickling stand is adjusted to offset the wedge-shaped defect, thus achieving cross-process offsetting of the defect.

[0025] Furthermore, the thickness of the finished steel plate is 0.50 mm.

[0026] Furthermore, the chemical composition of the non-oriented silicon steel by mass percentage is: C 0.0025%, Si 0.85%, Mn 0.35%, P 0.060%, S 0.0030%, Al 0.25%, N 0.0030%, O 0.0020%, Ti 0.0030%, with the remainder being Fe and unavoidable impurities.

[0027] Furthermore, the chemical composition of the non-oriented silicon steel by mass percentage is: C 0.0025%, Si 1.25%, Mn 0.75%, P 0.090%, S 0.0030%, Als 0.29%, N 0.0030%, O 0.0020%, Ti 0.0030%, with the remainder being Fe and unavoidable impurities.

[0028] Furthermore, the compliance rate of the prepared non-oriented silicon steel with a plate difference of ≤5μm is greater than 95%.

[0029] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0030] This invention achieves coordinated control of the CSP hot rolling and pickling continuous rolling processes, establishes a real-time feedback mechanism, and transmits the sheet shape data of the hot-rolled incoming material to the pickling continuous rolling process in real time. This enables cross-process compensation for sheet shape defects, avoids defect superposition, and improves the sheet shape control accuracy from the entire process level. It solves the problem of excessive sheet shape difference caused by the disconnect between the two processes in the prior art. It effectively solves problems such as corrugated defects, edge thinning, and strip breakage in the production of non-oriented silicon steel by CSP, and takes into account both sheet shape accuracy and product magnetic properties, meeting the stringent requirements of the high-end market for non-oriented silicon steel. Detailed Implementation

[0031] To better explain the present invention, the main contents of the present invention are further illustrated below with reference to specific embodiments.

[0032] Example 1 (The chemical composition of the non-oriented silicon steel by mass percentage is: C 0.0025%, Si 0.85%, Mn 0.35%, P 0.060%, S 0.0030%, Al 0.25%, N 0.0030%, O 0.0020%, Ti 0.0030%, with the remainder being Fe and unavoidable impurities)

[0033] This embodiment focuses on non-oriented silicon steel with a thickness of 0.5 mm and a width of 1200 mm. The method of this invention is used to optimize the plate shape. The specific steps are as follows:

[0034] Step 1: Pre-treatment and parameter initialization for hot rolling process

[0035] 1.1 The CSP continuous casting billet (thickness 57 mm, casting speed 3.5 m / min) was heated at a temperature of 1150℃.

[0036] 1.2 Determine the target plate shape parameters: same plate difference ≤ 5μm, crown control range 0~8μm, wedge ≤ 3μm, initialize the rolling force of hot rolling finishing mill stand (F1~F4) to 1800kN, bending roll force 1200kN, and rolling speed 8m / s;

[0037] 1.3 A strip shape detection device is installed at the hot-rolled finishing mill exit to collect data on the crown, wedge shape, and same-plate difference of hot-rolled strip in real time, and transmit it to the collaborative control unit to establish a hot-rolled strip shape database.

[0038] Step 2: Optimization of work roll profile and control of crown and wedge shape in hot rolling process

[0039] 2.1 Frames F1 to F4 employ a four-stage CVC roll profile;

[0040] 2.2 When the crown of the hot-rolled strip is detected to be 10μm (deviation 2μm), adjust the bending roll force of the F3~F4 stand to 1400kN and the roll shifting amount to 100mm;

[0041] 2.3 Wedge control: The thickness difference between the left and right sides of the strip was detected to be 4μm (wedge deviation 1μm). The right roll gap was adjusted by 0.03mm, the final rolling temperature was controlled at 880℃, the coiling temperature was controlled at 650℃, and the wedge was corrected to 2.5μm.

[0042] Step 3: Coordination and connection of hot rolling and pickling continuous rolling processes

[0043] 3.1 The data on the crown of the hot-rolled strip (7μm), wedge shape (2.5μm), and difference between strip sizes (6μm), as well as the wear data of the work roll surface, are transmitted in real time to the pickling and rolling control unit.

[0044] 3.2 Adjust the inlet tension of the acid rolling mill to 20kN and the speed of the acid rolling mill to 8.2m / s, and control the difference between the speed of the acid rolling mill and the exit speed of the hot rolling mill to 0.2m / s;

[0045] 3.3 For hot-rolled strip with a crown of 7μm, increase the positive bending roll force of the pickling continuous rolling mill stand to 800kN to pre-compensate for the crown defect; for a wedge shape of 2.5μm, adjust the difference between the left and right roll gaps of the pickling continuous rolling mill to 0.02mm to offset the wedge defect.

[0046] Step 4: Optimization of work roll profile and fine-tuning of strip shape in pickling and rolling process

[0047] 4.1 When the difference between the same plate size and the rolling mill exit is detected to be 5.5μm (deviation 0.5μm), adjust the bending roll force to 900kN, the rolling pressure to 3000kN, and the roll shifting amount to 80mm; at the same time, adjust the automatic crown control gain coefficient according to the rolling force deviation to ensure that the bending roll force adjustment is within the preset threshold, and correct the difference between the same plate size and the rolling mill to 4.8μm.

[0048] 4.2 Real-time detection of the wear amount of the work roll surface in acid continuous rolling. When the wear amount reaches 0.08mm, adjust the roll shifting amount to 90mm and the roll bending force to 950kN to compensate for the impact of roll surface wear.

[0049] In this embodiment, the optimized non-oriented silicon steel has a plate-to-plate difference of 4.8 μm, a convexity of 6.5 μm, and a wedge shape of 2.2 μm, all of which meet the target requirements; the compliance rate of plate-to-plate difference ≤ 5 μm is 96.2%, which significantly improves the plate shape accuracy compared with the prior art.

[0050] Example 2 (The chemical composition of the non-oriented silicon steel by mass percentage is: C 0.0025%, Si 1.25%, Mn 0.75%, P 0.090%, S 0.0030%, Als 0.29%, N 0.0030%, O 0.0020%, Ti 0.0030%, with the remainder being Fe and unavoidable impurities)

[0051] This embodiment focuses on non-oriented silicon steel with a thickness of 0.35 mm and a width of 1000 mm. The method of this invention is used to optimize the plate shape. The specific steps are as follows:

[0052] Step 1: Pre-treatment and parameter initialization for hot rolling process

[0053] 1.1 The CSP continuous casting billet (thickness 42mm, casting speed 3.0m / min) is heated at a temperature of 1080℃;

[0054] 1.2 The plate difference is ≤5μm, the crown control range is 0~8μm, the wedge shape is ≤3μm, and the initial hot rolling finishing mill stand (F1~F4) has a rolling force of 1500kN, a bending roll force of 1000kN, and a rolling speed of 7m / s;

[0055] 1.3 A strip shape detection device is installed at the hot-rolled finishing mill exit to collect data on the crown, wedge shape, and same-plate difference of hot-rolled strip in real time, and transmit it to the collaborative control unit to establish a hot-rolled strip shape database.

[0056] Step 2: Optimization of work roll profile and control of crown and wedge shape in hot rolling process

[0057] 2.1 Optimization of work roll profile: Frames F1 to F4 adopt a four-stage CVC roll profile;

[0058] 2.2 Dynamic control of crown: When the crown of the hot-rolled strip is detected to be 9μm (deviation 1μm), adjust the bending roll force of the F3~F4 stand to 1100kN and adjust the roll shifting amount to 90mm;

[0059] 2.3 Wedge control: The thickness difference between the left and right sides of the strip was detected to be 3.5μm (wedge deviation 0.5μm). The left roll gap was adjusted by 0.02mm, the final rolling temperature was controlled at 850℃, the coiling temperature was controlled at 600℃, and the wedge was corrected to 2.8μm.

[0060] Step 3: Coordination and connection of hot rolling and pickling continuous rolling processes

[0061] 3.1 The data on the crown of the hot-rolled strip (6.8μm), wedge shape (2.8μm), and difference between strip sizes (5.8μm), as well as the wear data of the work roll surface, are transmitted in real time to the pickling and rolling control unit.

[0062] 3.2 Adjust the inlet tension of the pickling continuous rolling mill to 15kN, the pickling continuous rolling speed to 7.3m / s, and control the difference between the speed of the pickling continuous rolling mill and the exit speed of the hot rolling mill to 0.3m / s;

[0063] 3.3 For hot-rolled strip with a crown of 6.8μm, increase the positive bending roll force of the pickling continuous rolling mill stand to 700kN to pre-compensate for the crown defect; for a wedge shape of 2.8μm, adjust the difference between the left and right roll gaps of the pickling continuous rolling mill to 0.015mm to offset the wedge defect.

[0064] Step 4: Optimization of work roll profile and fine-tuning of strip shape in pickling and rolling process

[0065] 4.1 When the difference between the same plate size and the rolling mill exit is detected to be 5.2μm (deviation 0.2μm), the bending roll force is adjusted to 750kN, the rolling pressure to 2500kN, and the roll shifting amount to 70mm; at the same time, according to the rolling force deviation, the automatic crown control gain coefficient is adjusted to ensure that the bending roll force adjustment is within the preset threshold, and the difference between the same plate size and the rolling mill is corrected to 4.9μm.

[0066] 4.2 Real-time detection of the wear of the working roll surface in acid continuous rolling. When the wear reaches 0.07mm, adjust the roll shifting amount to 75mm and the roll bending force to 800kN to compensate for the impact of roll surface wear.

[0067] In this embodiment, the optimized non-oriented silicon steel has a plate-to-plate difference of 4.9 μm, a convexity of 6.2 μm, and a wedge shape of 2.5 μm, all of which meet the target requirements; the compliance rate of plate-to-plate difference ≤ 5 μm is 95.8%, the scrap rate caused by plate shape defects is reduced by 40.7% per month, and the plate shape accuracy and production efficiency are significantly improved.

[0068] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for optimizing the shape of non-oriented silicon steel sheets through synergistic combination of CSP hot rolling and pickling continuous rolling, characterized in that: include: Hot rolling process parameters: The thickness of the continuously cast billet is controlled at 42~72 mm, the casting speed is 3~4.5 m / min, and the water flow rate of each section of the continuous casting sector is adjusted according to the preset parameters to avoid corrugated defects on the surface of the billet; when the target plate difference is ≤5μm, the convexity is controlled within the range of 0~8μm and the wedge shape is ≤3μm. The actual hot-rolled strip crown test data is compared with the target crown. When the crown deviation is >2μm, it is corrected by adjusting the bending roll force and roll shifting amount of the finishing mill stand. The bending roll force adjustment range is 500~2000kN, and the roll shifting amount adjustment range is 0~150mm. By adjusting the difference in roll gap between the left and right sides of the hot rolling mill stand, the wedge shape deviation of the strip is controlled. When the wedge shape deviation is >1μm, the roll gap on one side is adjusted by 0.01~0.05mm to ensure that the wedge shape of the strip is controlled within the target range. At the same time, the finishing rolling temperature is optimized to 830~920℃ and the coiling temperature is optimized to 580~720℃ to reduce wedge defects caused by temperature deviation. Pickling and rolling process parameters: A high-precision strip shape detection device is installed at the exit of the acid continuous rolling mill to collect the strip's same-strip difference data in real time and compare it with the target same-strip difference. When the same-strip difference deviation is >1μm, fine adjustment is made by adjusting the bending roll force, rolling pressure and roll shifting amount of the acid continuous rolling mill stand. The bending roll force adjustment range is 300~1500kN, the rolling pressure adjustment range is 1000~5000kN, and the roll shifting amount adjustment range is 0~120 mm. The wear of the work rolls in the acid continuous rolling mill is monitored in real time. When the wear is greater than 0.1 mm, the impact of the wear on the plate shape is compensated by adjusting the roll shifting amount and the roll bending force. At the same time, a work roll replacement cycle model is established to determine the optimal replacement cycle based on the wear rate of the rolls and the product specifications and batch size, so as to avoid the aggravation of plate shape defects due to excessive wear of the rolls. Connection between hot rolling and pickling processes: Establish a collaborative feedback mechanism to transmit the hot-rolled strip crown and wedge data, as well as the work roll surface wear data collected in the hot rolling process, to the control unit of the pickling and rolling process in real time, so as to ensure that the pickling and rolling process can accurately grasp the strip shape status of the hot-rolled material. Based on the shape data of the hot-rolled material, the pickling and rolling process adjusts the inlet tension and speed matching parameters. The inlet tension is controlled at 10~30kN, and the difference between the pickling and rolling speed and the hot-rolling exit speed is controlled at ±0.5m / s to avoid shape deformation caused by speed mismatch and tension fluctuation. Based on the crown and wedge deviation of hot-rolled strip, the bending roll force and rolling pressure of the pickling continuous rolling mill stand are adjusted in advance to pre-compensate for the strip shape defects transmitted by hot rolling. The chemical composition of the non-oriented silicon steel by mass percentage is as follows: C≤0.0025%, 0.35%~1.40% Si, 0.35~0.85% Mn, 0.030%~0.095% P, S≤0.0030%, 0.25~0.35% Als, N≤0.0030%, O≤0.0020%, Ti≤0.0030%, with the remainder being Fe and unavoidable impurities.

2. The method for optimizing the shape of non-oriented silicon steel sheets by synergistic combination of CSP hot rolling and pickling continuous rolling according to claim 1, characterized in that: The pickling and rolling process involves dividing the width into multiple width ranges based on the width specifications of the hot-rolled material and designing multiple sets of adaptable roll shapes to ensure that the roll shape matches the width of the material. The roll shape parameters are programmed into the control software to achieve efficient and automated solution of the roll shape curve. The parameters can be flexibly adjusted according to the on-site roll shape usage and edge reduction requirements.

3. The method for optimizing the shape of non-oriented silicon steel sheets by synergistic combination of CSP hot rolling and pickling continuous rolling according to claim 1, characterized in that: When there is a positive convexity deviation in hot-rolled strip, the positive bending roll force of the pickling continuous rolling mill is increased to compensate for the convexity defect; when there is a wedge-shaped deviation, the difference between the left and right roll gaps in the pickling continuous rolling mill is adjusted to offset the wedge-shaped defect and achieve cross-process offsetting of the defect.

4. The method for optimizing the shape of non-oriented silicon steel sheets by synergistic combination of CSP hot rolling and pickling continuous rolling according to claim 1, characterized in that: The finished steel plate has a thickness of 0.50 mm.

5. The method for optimizing the shape of non-oriented silicon steel sheets by synergistic combination of CSP hot rolling and pickling continuous rolling according to claim 1, characterized in that: The chemical composition of the non-oriented silicon steel by mass percentage is as follows: C 0.0025%, Si 0.85%, Mn 0.35%, P 0.060%, S 0.0030%, Al 0.25%, N 0.0030%, O 0.0020%, Ti 0.0030%, with the remainder being Fe and unavoidable impurities.

6. The method for optimizing the shape of non-oriented silicon steel sheets by synergistic combination of CSP hot rolling and pickling continuous rolling according to claim 1, characterized in that: The chemical composition of the non-oriented silicon steel by mass percentage is as follows: C 0.0025%, Si 1.25%, Mn 0.75%, P 0.090%, S 0.0030%, Al 0.29%, N 0.0030%, O 0.0020%, Ti 0.0030%, with the remainder being Fe and unavoidable impurities.

7. The method for optimizing the shape of non-oriented silicon steel sheets by synergistic combination of CSP hot rolling and pickling continuous rolling according to claim 1, characterized in that: The compliance rate of the prepared non-oriented silicon steel with a plate difference of ≤5μm is greater than 95%.