Method for reducing rolling strip breakage of high-grade non-oriented electrical steel

Abstract

The invention discloses a method for reducing high-grade non-oriented electrical steel rolling strip breakage, and relates to the technical field of non-oriented electrical steel production. Comprising the following steps of smelting, continuous casting, hot rolling, finishing, normalizing and pickling, rolling, annealing and coating, rewinding and slitting and packaging. The temperature of normalizing treatment is 820-850 DEG C, and cooling is conducted at the cooling speed of 30-50 DEG C / s after normalizing treatment; after acid pickling, the edge of the strip steel is heated to 150-200 DEG C, and then edge cutting is conducted; in the rolling step, the reduction rate of the first pass is controlled to be 32-33%; when the diameter phi of the steel coil is 508-800mm, the coiling tension adopts a taper tension control mode; when the coiling diameter of the strip steel reaches phi 800mm, the coiling tension adopts a constant tension control mode; the rolling strip breakage rate of the high-grade non-oriented electrical steel can be reduced to 40% or below, the production stability and the yield are remarkably improved, and the method is suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of non-oriented electrical steel technology, specifically relating to a method for reducing strip breakage during the rolling of high-grade non-oriented electrical steel. Background Technology

[0002] High-grade non-oriented electrical steel is a key soft magnetic material for core equipment such as drive motors for new energy vehicles, high-end industrial motors, and large transformers. Its magnetic properties directly determine the energy efficiency and operational stability of the equipment. With the rapid development of the global new energy industry and high-end equipment manufacturing industry, the market demand for high-grade non-oriented electrical steel continues to grow, and the requirements for its magnetic performance indicators are constantly increasing to meet the development trend of equipment miniaturization and high efficiency.

[0003] To achieve the aforementioned superior magnetic properties, high-grade non-oriented electrical steel needs to optimize permeability and eddy current loss by increasing the content of silicon and aluminum. Si and Al are key elements for improving magnetic properties, but excessive content of both will significantly increase the difficulty of rolling. When the sum of Si and Al exceeds 4.0%, the plasticity of the strip decreases, and cracks are prone to occur during rolling. When the Si content exceeds 3.5% or the sum of Si and Al is greater than 4.4%, the strip breakage rate during rolling can even reach over 80%, seriously affecting the yield and production efficiency.

[0004] Therefore, how to solve the problem of strip breakage during the rolling of high-grade non-oriented electrical steel has become a core technological bottleneck restricting its large-scale, high-quality production. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for reducing strip breakage during the rolling of high-grade non-oriented electrical steel. By optimizing the normalization process, rolling parameters, and edge pretreatment, the breakage rate is significantly reduced, thereby improving production stability and yield.

[0006] The technical solution adopted in this invention is as follows:

[0007] This invention provides a method for reducing strip breakage during the rolling of high-grade non-oriented electrical steel, comprising the following steps: smelting → continuous casting → hot rolling → finishing → normalizing and pickling → rolling → annealing and coating → rewinding and slitting → packaging.

[0008] In the smelting process, the phosphorus (P) content must be strictly controlled to be P≤0.010%. If the P content is too high, embrittlement is likely to occur during the rolling process.

[0009] In the hot rolling step, the hot rolling heating temperature is 1080-1150℃, the heating time is 2-3 hours, and the soaking time is ≥25 minutes to ensure uniform internal structure of the steel billet and reduce component segregation; the final rolling temperature is 830-860℃, and the coiling temperature is 550-580℃ to avoid abnormal grain growth after hot rolling of the strip and to lay a good plasticity foundation for subsequent rolling.

[0010] In the normalizing and pickling step, the normalizing temperature is 820-850℃ to avoid excessively large grain size, as excessively large grains will reduce the plasticity of the strip and increase the risk of strip breakage during rolling. After normalizing, the strip is cooled at a cooling rate of 30-50℃ / s to fully release the internal stress of the strip and avoid the superposition of internal stress generated during cooling and rolling stress, which would lead to strip breakage. Before trimming after pickling, the edge temperature of the strip is heated to 150-200℃ before trimming to reduce shear stress and reduce the occurrence of edge cracks during rolling.

[0011] Tracking the strip breakage during rolling on-site, it was found that the breakage of high-grade non-oriented electrical steel strips always started from the shear plane of the strip cross-section, with no cracks on the torn surface. Figure 1 , 2 As shown, the reason for cracks appearing on the sheared surface is that conventional normalized edge cutting is done when the strip is cold-state, resulting in a large accumulation of shear stress on the sheared surface. Therefore, the sheared surface is very prone to cracking during rolling. This invention addresses this by adding a set of flame heating devices on each side of the strip before disc shearing, raising the strip edge temperature to 150-200°C before disc shearing, which significantly reduces the shear stress on the strip's sheared surface.

[0012] In the rolling process, the first pass starting rolling force is 350-450t to reduce the instantaneous impact force during start-up and prevent the strip from breaking due to excessive stress; the first pass reduction rate is controlled at 32-33% to reduce the amount of strip edge deformation and reduce the risk of cracking; when the coil diameter is φ508-800mm, the coiling tension adopts a tapered tension control mode; when the strip coil diameter reaches φ800mm, the coiling tension adopts a constant tension control mode.

[0013] In the rolling process, when the coiling tension adopts the taper tension control mode, the initial coiling tension for the first pass is controlled at 180-200 kN; the initial coiling tension for the second pass is controlled at 150-170 kN; the initial coiling tension for the third pass is controlled at 120-140 kN; the initial coiling tension for the fourth pass is controlled at 100-120 kN; the initial coiling tension for the fifth pass is controlled at 70-90 kN; and the initial coiling tension for the sixth pass is controlled at 50-60 kN; the taper coefficient is set to 120-130%.

[0014] In the rolling step, when the coiling tension adopts the constant tension control mode, the tension control is as follows: first pass 216-260kN, second pass 180-221kN, third pass 144-182kN, fourth pass 120-156kN, fifth pass 84-117kN, and sixth pass 60-78kN.

[0015] In the rolling process, the rolling speed of the first pass is controlled at 200-300 m / min; the rolling speed of the second pass is controlled at 300-400 m / min; the rolling speed of the third and fourth passes is controlled at 400-550 m / min; and the rolling speed of the fifth and sixth passes is controlled at 550-650 m / min.

[0016] In the rolling step, a 6-pass rolling process is adopted, and the reduction rates of the 1st to 6th passes are 30-33%, 32-36%, 33-36%, 30-33%, 24-27%, and 22-26%, respectively; preferably 32.17%, 35.9%, 34.00%, 31.82%, 26.67%, and 24.55%, respectively.

[0017] In the rolling process, edge rolling is used from the second to the sixth pass to control the strip shape I value within the range of 15-20, so that the tension at the edge of the strip is close to zero, thereby reducing the risk of the strip breaking during the rolling process.

[0018] The high-grade non-oriented electrical steel comprises the following chemical composition by weight percentage: C≤0.003%, Si:3.0-3.5%, Al:0.6-1.2%, Mn:0.2-0.5%, S≤0.002%, P≤0.010%, N≤0.0025%, Cu≤0.0030%, Ti≤0.0020%, V≤0.0025%, Sn:0.03-0.08%, with the remainder being Fe and unavoidable impurities.

[0019] The method for reducing strip breakage during rolling of high-grade non-oriented electrical steel provided by this invention significantly reduces shear stress on the shearing surface by heating the strip edge before trimming, thereby reducing the occurrence of edge cracks during rolling. Using taper tension control during rolling start-up significantly reduces the risk of strip breakage due to excessive tension at the start-up moment. Reducing the pass reduction rate and starting rolling force reduces edge cracking in the first pass. Subsequent passes employ appropriate edge waviness rolling, controlling the strip profile I value within the range of 15-20, bringing the tension at the edge waviness position of the strip close to zero, thus reducing the risk of strip breakage during rolling.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention addresses the entire process from composition control, hot rolling homogenization, normalization stress release, and rolling parameter optimization. Through multi-stage collaborative control, it solves the strip breakage problem caused by insufficient strip plasticity and internal stress concentration. After adopting this method, the strip breakage rate of high-grade non-oriented electrical steel rolling is reduced to below 40%. The reduced breakage rate decreases downtime for coil change, and the process parameters are easy to control industrially, making it suitable for large-scale continuous production. Attached Figure Description

[0022] Figure 1 The location of the primary breakage and crack in high-grade non-oriented electrical steel;

[0023] Figure 2 A cross-sectional view of a high-grade non-oriented electrical steel cut-off coil after normalization and cold trimming.

[0024] Figure 3 Image of high-grade non-oriented electrical steel hard-rolled coil produced in Example 1;

[0025] Figure 4 The image shows the high-grade non-oriented electrical steel hard-rolled coil produced in Example 2;

[0026] Figure 5 The image shows the steel coils removed after the high-grade non-oriented electrical steel produced in Comparative Example 1 broke.

[0027] Figure 6 The image shows a high-grade non-oriented electrical steel hard-rolled coil produced in Comparative Example 1. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the embodiments.

[0029] In all embodiments and comparative examples, the annealing conditions in the annealing coating step are: process speed 140 m / min and process temperature 950 °C.

[0030] Example 1

[0031] A method for reducing strip breakage during the rolling of high-grade non-oriented electrical steel includes the following steps: smelting → continuous casting → hot rolling → finishing → normalizing and pickling → rolling → annealing and coating → rewinding and slitting → packaging.

[0032] In the continuous casting step, the composition and mass percentage of the billet obtained after continuous casting are as follows: C 0.0025%, Si 3.5%, Al 1.05%, Mn 0.35%, S 0.0018%, P 0.008%, N 0.0020%, Cu 0.0022%, Ti 0.0011%, V 0.0012%, Sn 0.055%, with the remainder being Fe.

[0033] In the hot rolling process, the heating temperature is 1050-1120℃, the heating time is 3 hours, the soaking time is 60 minutes, the final rolling temperature is 850℃, the coiling temperature is 580℃, and the thickness of the hot-rolled coil is 2.3 mm.

[0034] In the normalizing and pickling process, the normalizing temperature is 840℃. After normalizing, the water jacket provides indirect cooling with a flow rate of 280 m³ / h. 3 / h, cooling rate 40℃ / s, heating the edge before normalizing and trimming, heating to 160℃ before trimming.

[0035] In the rolling process, the finished product thickness is 0.25 mm, and six passes are used for rolling. The reduction rates for each pass are 32.61%, 35.48%, 34.50%, 31.30%, 26.67%, and 24.55%, respectively. When the coil diameter is between φ508-800 mm, the coiling tension is controlled according to the taper tension. The initial coiling tension for the first pass is controlled at 190 kN; the second pass at 160 kN; the third pass at 130 kN; the fourth pass at 110 kN; the fifth pass at 80 kN; and the sixth pass at 60 kN, with a taper coefficient of 130%.

[0036] Once the diameter of the steel coil reaches φ800mm, the coiling tension adopts a constant tension control mode, with the tension control values ​​as follows: 247kN for the first pass, 208kN for the second pass, 169kN for the third pass, 143kN for the fourth pass, 104kN for the fifth pass, and 78kN for the sixth pass.

[0037] In the rolling process, the starting rolling force for the first pass is set to 400 tons, and the rolling speed is controlled at 250 m / min; the rolling speed for the second pass is controlled at 300 m / min; the rolling speed for the third and fourth passes is controlled at 550 m / min; and the edge waviness is controlled for the fifth and sixth passes, with an edge shape value of 15I and a rolling speed of 600 m / min.

[0038] In this embodiment, no strip breakage occurred during the rolling process, the number of cracks on both sides was less than 20, and the crack depth was 1-2 mm.

[0039] The hardened coil obtained in this embodiment is as follows: Figure 3 As shown in the figure, the surface of the finished roll is flat, with few edges and cracks, and the cracks are shallow.

[0040] Example 2

[0041] A method for reducing strip breakage during the rolling of high-grade non-oriented electrical steel includes the following steps: smelting → continuous casting → hot rolling → finishing → normalizing and pickling → rolling → annealing and coating → rewinding and slitting → packaging.

[0042] In the continuous casting step, the composition and mass percentage of the billet obtained after continuous casting are as follows: C 0.0021%, Si 3.2%, Al 1.10%, Mn 0.42%, S 0.0016%, P 0.007%, N 0.0022%, Cu 0.0025%, Ti 0.0010%, V 0.0015%, Sn 0.061%, with the remainder being Fe.

[0043] In the hot rolling process, the heating temperature is 1150℃, the heating time is 2.5 h, the soaking time is 55 min, the final rolling temperature is 840℃, the coiling temperature is 560℃, and the thickness of the hot-rolled coil is 2.3 mm.

[0044] In the normalizing and pickling process, the normalizing temperature is 820℃. After normalizing, the water jacket provides indirect cooling with a flow rate of 30 m³ / h. 3 / h, cooling rate 50℃ / s, heating the edge before normalizing and trimming, heating to 200℃ before trimming.

[0045] In the rolling process, the finished product thickness is 0.25 mm, and six passes are used for rolling. The reduction rates for each pass are 32.17%, 35.9%, 34.00%, 31.82%, 26.67%, and 24.55%, respectively. When the coil diameter is between φ508-800 mm, the coiling tension is controlled according to the taper tension. The initial coiling tension for the first pass is controlled at 180 kN; the second pass at 150 kN; the third pass at 120 kN; the fourth pass at 100 kN; the fifth pass at 70 kN; and the sixth pass at 50 kN, with a taper coefficient of 120%.

[0046] When the diameter of the steel coil reaches φ800mm, the tension control mode is constant, and the tension control is as follows: 216kN for the first pass, 180kN for the second pass, 144kN for the third pass, 120kN for the fourth pass, 84kN for the fifth pass, and 60kN for the sixth pass.

[0047] In the rolling process, the starting rolling force for the first pass is set to 380 tons, and the rolling speed is controlled at 250 m / min; the rolling speed for the second pass is controlled at 300 m / min; the rolling speed for the third and fourth passes is controlled at 550 m / min; and the edge waviness is controlled for the fifth and sixth passes, with an edge shape value of 15I and a rolling speed of 600 m / min.

[0048] In this embodiment, no strip breakage occurred during the rolling process, and there were no cracks at the edges. The resulting hard-rolled coil was as follows: Figure 4 As shown.

[0049] Comparative Example 1

[0050] A method for producing high-grade non-oriented electrical steel includes the following steps: smelting → continuous casting → hot rolling → finishing → normalizing and pickling → rolling → annealing and coating → rewinding and slitting → packaging.

[0051] In the continuous casting step, the composition and mass percentage of the billet obtained after continuous casting are as follows: C: 0.0020%, Si: 3.45%, Al: 0.98%, Mn: 0.34%, S: 0.0020%, P: 0.012%, N: 0.0022%, Cu: 0.0024%, Ti: 0.0016%, V: 0.0010%, Sn: 0.058%, with the remainder being Fe.

[0052] In the hot rolling process, the heating temperature is 1050-1120℃, the heating time is 3 hours, the soaking time is 60 minutes, the final rolling temperature is 850℃, the coiling temperature is 580℃, and the thickness of the hot-rolled coil is 2.3 mm.

[0053] In the normalizing and pickling process, the normalizing temperature is 840℃. After normalizing, the water jacket provides indirect cooling with a flow rate of 280 m³ / h. 3 / h, cooling rate 40℃ / s, edge heating was not turned on before normalizing and trimming.

[0054] In the rolling process, the finished product thickness is 0.25 mm, and six passes are used for rolling. The pass reduction rates are 35.65%, 36.08%, 31.82%, 30.23%, 26.67%, and 24.55%, respectively. Constant tension control is used during rolling. The tension for the first pass is set at 240 kN. The starting rolling force for the first pass is set at 500 tons, and the rolling speed is controlled at 250 m / min; the tension for the second pass is set at 220 kN, and the rolling speed is controlled at 350 m / min; the tension for the third pass is set at 180 kN, and the rolling speed is controlled at 450 m / min; the tension for the fourth pass is set at 150 kN, and the rolling speed is controlled at 450 m / min; the tension for the fifth pass is set at 110 kN, and the rolling speed is controlled at 550 m / min; the tension for the sixth pass is set at 70 kN, and the rolling speed is controlled at 650 m / min. Edge waviness is controlled in the fifth and sixth passes, and the edge profile value is 5I.

[0055] In this comparative example, the strip broke twice during the first rolling pass and once during the second rolling pass. The broken strip coils showed obvious tears at the edges. Figure 5 As shown, and judging from the edge crack of the first-stage broken strip steel coil, the breakage location originates at the shear plane, as... Figure 1 As shown. The rolled hardened edge is covered with dense cracks, with a depth of 5-10mm, as... Figure 6 As shown.

[0056] The above detailed description of a method for reducing strip breakage in the rolling of high-grade non-oriented electrical steel, with reference to the embodiments, is illustrative rather than limiting. Several embodiments may be listed within the defined scope. Therefore, variations and modifications that do not depart from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A method of reducing rolled strip breakage of high grade non-oriented electrical steel, comprising the steps of: The process is characterized in that the process comprises smelting, continuous casting, hot rolling, finishing, normalizing and pickling, rolling, annealing, coating, recoiling, slitting and packaging, wherein In the normalizing and pickling step, the temperature of the normalizing treatment is 820-850 DEG C, and the cooling rate after the normalizing treatment is 30-50 DEG C / s; the temperature of the edge of the strip is heated to 150-200 DEG C before the edge cutting after the pickling. In the rolling step, the rolling force of the first pass is 350-450 t, and the reduction of the first pass is controlled to be 32-33%; when the coil diameter is φ508-800 mm, the coiling tension is controlled in the taper tension control mode; when the coil diameter reaches φ800 mm, the coiling tension is controlled in the constant tension control mode.

2. The method of reducing high grade non-oriented electrical steel strip breakage during rolling of claim 1, wherein, In the hot rolling step, the hot rolling heating temperature is 1080-1150 DEG C, the heating time is 2-3 h, the soaking time is ≥25 min, the finish rolling temperature is 830-860 DEG C, and the coiling temperature is 550-580 DEG C.

3. The method of reducing high grade non-oriented electrical steel strip breakage during rolling of claim 1, wherein, In the rolling step, when the coiling tension is controlled in the taper tension control mode, the initial coiling tension of the first pass is controlled to be 180-200 kN, the initial coiling tension of the second pass is controlled to be 150-170 kN, the initial coiling tension of the third pass is controlled to be 120-140 kN, the initial coiling tension of the fourth pass is controlled to be 100-120 kN, the initial coiling tension of the fifth pass is controlled to be 70-90 kN, the initial coiling tension of the sixth pass is controlled to be 50-60 kN, and the taper coefficient is set to be 120-130%.

4. The method of reducing high grade non-oriented electrical steel strip breakage during rolling of claim 1, wherein, In the rolling step, when the coiling tension is controlled in the constant tension control mode, the tension control is respectively: 216-260 kN for the first pass, 180-221 kN for the second pass, 144-182 kN for the third pass, 120-156 kN for the fourth pass, 84-117 kN for the fifth pass, and 60-78 kN for the sixth pass.

5. The method of reducing high grade non-oriented electrical steel strip breakage during rolling of claim 1, wherein, In the rolling step, the rolling speed of the first pass is controlled to be 200-300 m / min, the rolling speed of the second pass is controlled to be 300-400 m / min, the rolling speed of the third and fourth passes is controlled to be 400-550 m / min, and the rolling speed of the fifth and sixth passes is controlled to be 550-650 m / min.

6. The method of reducing strip breaks during rolling of high grade non-oriented electrical steel of any of claims 1-5, wherein, In the rolling step, six passes are adopted, and the reduction of the first to sixth passes is respectively 30-33%, 32-36%, 33-36%, 30-33%, 24-27%, and 22-26%.

7. The method of reducing strip breaks during rolling of high grade non-oriented electrical steel of any of claims 1-5, wherein, In the rolling step, the reduction of the first to sixth passes is respectively 32.17%, 35.9%, 34.00%, 31.82%, 26.67%, and 24.55%.

8. The method of reducing strip breaks during rolling of high grade non-oriented electrical steel of any of claims 1-5, wherein, In the rolling step, the edge wave rolling is adopted for the second to sixth passes, and the plate shape I value is controlled to be in the range of 15-20.

9. The method of reducing strip breaks during rolling of high grade non-oriented electrical steel of any of claims 1-5, wherein, The high-grade non-oriented electrical steel comprises the following chemical components by weight percentage: C≤0.003%, Si: 3.0-3.5%, Al: 0.6-1.2%, Mn: 0.2-0.5%, S≤0.002%, P≤0.010%, N≤0.0025%, Cu≤0.0030%, Ti≤0.0020%, V≤0.0025%, Sn: 0.03-0.08%, and the rest is Fe and inevitable impurities.

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