A method of producing non-oriented electrical steel

Abstract

The application provides a production method of non-oriented electrical steel. It relates to the field of metal processing, and the steps are as follows: selecting a non-oriented electrical steel plate with a single-phase ferrite structure as a base material; the mass fraction of Si in the base material is 2%-4%, and the thickness is 0.3mm-0.5mm; the base material is subjected to cold rolling at a set rolling speed for at least one pass to obtain semi-finished non-oriented electrical steel with a thickness of 0.02mm-0.10mm; during the cold rolling process, the inlet tension of each pass is greater than the outlet tension; annealing is carried out in a reducing atmosphere to obtain finished non-oriented electrical steel; and during the annealing process, the semi-finished non-oriented electrical steel is heated to 850 DEG C-1050 DEG C at a set heating rate and is kept for 30s-90s.

Description

Technical Field

[0001] This invention relates to the field of metal processing, and more particularly to a method for producing non-oriented electrical steel. Background Technology

[0002] The current trend in new energy vehicle drive motors is towards higher frequencies (≥400Hz) and higher power densities, leading to a surge in demand for ultra-thin non-oriented electrical steel ranging from 0.02mm to 0.10mm. Stricter regulations also require further reductions in losses in motors and transformers. Since eddy current losses are proportional to the square of the material thickness, ultra-thinning is the core approach to reducing high-frequency eddy current losses. Currently, the industry primarily relies on short-process technologies (such as twin-roll thin strip casting) and micro-alloying techniques for ultra-thin steel production.

[0003] However, existing non-oriented electrical steels with a Si mass fraction of 2.5~3.5% have the following disadvantages in the production of ultra-thin non-oriented electrical steels:

[0004] (1) Poor compatibility between composition and process: Although the existing high Si (Si+Al≥4.5%) composition system can improve resistivity, it exacerbates the brittleness of the material, making it easy to break the strip during cold rolling, and it cannot take into account both ultra-thinness and processability.

[0005] (2) Insufficient stability of ultra-thin rolling: Production of specifications below 0.10mm requires a large reduction rate (≥85%). Traditional rolling mills have difficulty controlling the plate shape, which easily leads to wavy edges, warping, high strip breakage rate, and a yield of less than 80%.

[0006] (3) Unreasonable annealing process: The existing annealing temperature and holding time have a low matching degree, which leads to the material recrystallization texture biased towards {111}, magnetic induction intensity (B8) is lower than 1.66T, and hysteresis loss is too high;

[0007] (4) Redundant process or rough control: Some processes require multiple cold rolling and intermediate annealing, resulting in long processes and high energy consumption; some short process processes have problems such as component segregation and surface defects, resulting in large fluctuations in product performance. Summary of the Invention

[0008] To address the technical problems existing in the prior art, the present invention aims to provide a method for producing non-oriented electrical steel, which has a simple process, precise control, and can stably produce ultra-thin non-oriented electrical steel with a diameter of 0.02mm to 0.10mm.

[0009] To achieve the above-mentioned objective, this invention provides a method for producing non-oriented electrical steel, comprising the following steps:

[0010] Non-oriented electrical steel sheet with a single-phase ferrite microstructure is selected as the substrate; the mass fraction of Si in the substrate is 2%~4% and the thickness is 0.3mm~0.5mm;

[0011] The substrate is cold-rolled at a rolling speed of 30 m / min to 100 m / min for at least one pass to obtain a semi-finished non-oriented electrical steel with a thickness of 0.02 mm to 0.10 mm; during the cold rolling process, the inlet tension of each pass is greater than the outlet tension; wherein, the inlet tension of each pass is 100 MPa to 150 MPa and the outlet tension is 80 MPa to 120 MPa.

[0012] Annealing is performed in a reducing atmosphere to obtain finished non-oriented electrical steel; during the annealing process, the semi-finished non-oriented electrical steel is heated to 850℃~1050℃ at a set heating rate and held for 30s~90s.

[0013] According to one technical solution of the present invention, the mass fraction of Si in the substrate is 2.5%~3.5%, C≤20ppm, S≤10ppm, and N≤15ppm.

[0014] According to one embodiment of the present invention, the total reduction rate of the cold rolling is 66.7% to 96%.

[0015] The cold rolling process includes 5 to 7 passes, and the reduction rate of each pass is distributed as follows:

[0016] The first pass is 40%~45%;

[0017] The second pass rate was 38%~42%;

[0018] Subsequent passes were set within the range of 28% to 36%.

[0019] According to one technical solution of the present invention, the substrate undergoes six passes of cold rolling;

[0020] The reduction rates for the first pass were 43.3%, the second pass 41.2%, the third pass 35%, the fourth pass 35.4%, the fifth pass 33.3%, and the sixth pass 28.6%.

[0021] According to one technical solution of the present invention, rolling oil is used in the cold rolling process, and the oil temperature of the rolling oil is 40℃~60℃.

[0022] According to one technical solution of the present invention, during the annealing process:

[0023] When the thickness of the semi-finished non-oriented electrical steel is 0.02mm~0.05mm, the semi-finished non-oriented electrical steel is heated to 850℃~950℃ at a set heating rate.

[0024] When the thickness of the semi-finished non-oriented electrical steel is 0.05mm to 0.10mm, the semi-finished non-oriented electrical steel is heated to 850℃ to 1050℃ at a set heating rate.

[0025] According to one technical solution of the present invention, the reducing atmosphere is a mixture of N2 and H2, and the volume ratio of N2 to H2 is 90:10 to 10:90.

[0026] According to one technical solution of the present invention, it further includes:

[0027] An insulating coating is applied to the surface of the finished non-oriented electrical steel and then dried and cured.

[0028] The present invention provides a method for producing non-oriented electrical steel, which has the following beneficial effects:

[0029] (1) The finished product thickness covers 0.02mm~0.10mm, the magnetic induction intensity B50≥1.70T, and the high frequency (400Hz) iron loss P1.0 / 400≤13W / kg, meeting the needs of high-end scenarios such as new energy vehicle drive motors and high frequency transformers;

[0030] (2) By combining substrate selection with 20-roll cold rolling process, the strip breakage rate is reduced to below 5%, the yield rate is increased to above 88%, and the sheet shape qualification rate is ≥95%;

[0031] (3) The short process of one cold rolling + one annealing is adopted, which shortens the production cycle by more than 30% and reduces energy consumption by about 25% compared with the existing multi-pass process;

[0032] (4) No intermediate annealing equipment is required, reducing process losses and energy costs. The unit production cost of the product is reduced by 15% to 20% compared with the existing process. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0034] Figure 1 The flowchart schematically illustrates a method for producing non-oriented electrical steel according to one embodiment of the present invention. Detailed Implementation

[0035] The description of the embodiments in this specification should be taken in conjunction with the accompanying drawings, which should form part of the complete specification. In the drawings, the shape or thickness of the embodiments may be exaggerated and may be indicated in a simplified or convenient manner. Furthermore, parts of the various structures in the drawings will be described separately; it is worth noting that elements not shown in the figures or not described in words are in a form known to those skilled in the art.

[0036] The descriptions of the embodiments herein, including any references to directions and orientations, are for ease of description only and should not be construed as limiting the scope of the invention. The following description of preferred embodiments involves combinations of features, which may exist independently or in combination; the invention is not particularly limited to the preferred embodiments. The scope of the invention is defined by the claims. Figure 1 As shown;

[0037] Example 1

[0038] This embodiment of a method for producing non-oriented electrical steel includes the following steps:

[0039] Non-oriented electrical steel sheet with a single-phase ferrite microstructure was selected as the substrate; the mass fraction of Si in the substrate was 2%~4% and the thickness was 0.3mm~0.5mm;

[0040] The base material is cold rolled at a rolling speed of 30m / min to 100m / min for at least one pass to obtain a semi-finished non-oriented electrical steel with a thickness of 0.02mm. During the cold rolling process, the inlet tension of each pass is greater than the outlet tension. Specifically, the inlet tension of each pass is 100MPa to 150MPa and the outlet tension is 80MPa to 120MPa.

[0041] Annealing was carried out in a reducing atmosphere to obtain the finished non-oriented electrical steel. During the annealing process, the semi-finished non-oriented electrical steel was heated to 940°C and held at that temperature for 30 seconds at a set heating rate.

[0042] This embodiment relates to the specific process of producing non-oriented electrical steel:

[0043] Step S1: Under alternating magnetic field conditions, increasing the resistivity of the material can effectively increase the resistance of the eddy current loop, suppress the magnitude of eddy currents, and thus significantly reduce eddy current losses. Appropriately increasing the silicon content can improve resistivity and enhance the high-frequency operating efficiency of the core. However, excessively high Si content will significantly increase the brittleness of the material, reduce toughness and rolling performance, and easily lead to strip breakage during cold rolling. Limiting the Si content to the range of 2%~4% (preferably 2.5%~3.5%) allows for the improvement of resistivity and suppression of eddy current losses through appropriate amounts of Si, while avoiding brittle deterioration caused by excessive Si, thus achieving a balance between magnetic properties and rolling performance. Simultaneously, using a finished substrate with a thickness of 0.3mm~0.5mm and no insulating coating reduces surface defects caused by coating peeling during cold rolling and improves rolling stability.

[0044] Among them, non-oriented electrical steel sheets with a single-phase ferrite substrate are used. The single-phase ferrite structure has an extremely low work hardening rate. The low work hardening rate and slow hardening increase after large reduction rate deformation allow the substrate to maintain excellent plasticity even when it is thinned to ultra-thin (e.g., 0.02 mm).

[0045] S2. Leveraging the advantages of a 20-roll mill—multi-roll support, high-precision pressure control, and high-precision shape control—it employs a 20-roll cold rolling process, rolling the base material to its final state in a single pass (i.e., requiring only one continuous cold rolling process). No intermediate annealing process is needed, shortening the process and reducing energy consumption. It is suitable for the high reduction rate rolling requirements of ultra-thin non-oriented electrical steel, reducing defects such as waviness and warping.

[0046] The total reduction rate for cold rolling is specifically 66.7% to 96%.

[0047] Cold rolling involves 5 to 7 passes, and the reduction rate distribution for each pass is as follows:

[0048] The first pass is 40%~45%;

[0049] The second pass rate was 38%~42%;

[0050] Subsequent passes were set within the range of 28% to 36%.

[0051] When the base material thickness is a maximum of 0.5 mm and the thickness of the finished non-oriented electrical steel is a minimum of 0.02 mm, the total reduction rate is (0.5-0.02) / 0.5=96%.

[0052] In cold rolling, a pass refers to the stroke of the substrate through the mill rolls in a single pass. It can be achieved using unidirectional multiple rolling or reciprocating multiple rolling. However, in reciprocating multiple rolling, the inlet and outlet should be switched according to the rolling direction (manual switching or automatic switching via a control mechanism). The total reduction rate mentioned above can be gradually achieved through 5-7 passes of cold rolling, with the reduction rate of each subsequent pass typically lower than that of the previous pass.

[0053] Taking a base material thickness of 0.3 mm and a finished non-oriented electrical steel thickness of 0.02 mm as an example: it undergoes a total of 6 cold rolling passes, of which:

[0054] The reduction rate of the first pass was 43.3%, and 0.3mm × (1 - 43.3%) ≈ 0.17mm;

[0055] The reduction rate of the second pass was 41.2%, and 0.17mm × (1-41.2%) ≈ 0.10mm;

[0056] The reduction rate of the third pass is 35%, 0.10mm×(1-35%)≈0.065mm;

[0057] The reduction rate of the fourth pass was 35.4%, and 0.065mm × (1-35.4%) ≈ 0.042mm;

[0058] The reduction rate of the fifth pass was 33.3%, and 0.042mm × (1 - 33.3%) ≈ 0.028mm;

[0059] The reduction rate of the sixth pass was 28.6%, and 0.028mm×(1-28.6%)≈0.02mm.

[0060] Based on actual production experience, as the heat of deformation accumulates more rapidly during the rolling process, coupled with the temperature of the rolling oil, the material is temporarily softened after the third pass, allowing the fourth pass to withstand a slightly larger reduction. Therefore, the reduction rate of the fourth pass is slightly greater than that of the third pass, thus improving rolling efficiency to a certain extent.

[0061] The thickness of the semi-finished non-oriented electrical steel is controlled at 0.02mm, with a thickness tolerance of ≤±1.5μm. The rolling speed is well controlled, and the inlet tension of each pass is set to be greater than the outlet tension to avoid strip breakage caused by tension fluctuations.

[0062] The requirement that the inlet tension be greater than the outlet tension is due to the significant forward slippage of the metal within the deformation zone during rolling, resulting in a higher metal flow velocity at the mill exit than at the inlet. By setting the inlet tension slightly higher than the outlet tension, the velocity difference caused by the forward and backward slippage can be balanced, creating a stable tension gradient. This stabilizes the tension distribution within the deformation zone, reduces the elastic flattening of the rolls, allows the non-oriented electrical steel to adhere tightly to the work rolls, resulting in a flatter strip shape, reduced lateral flow, suppression of strip arching, deviation, and edge waviness, lower rolling pressure, and improved strip shape, thus achieving stable continuous rolling under high reduction rates.

[0063] Maintaining the inlet tension greater than the outlet tension can be achieved by employing independent torque closed-loop control at both the inlet and outlet stations, and configuring an online tension detection device, as detailed below:

[0064] The inlet tension device and the outlet tension device control torque independently and do not interfere with each other.

[0065] The system is preset with a fixed tension difference value, ensuring that the inlet tension is always greater than the outlet tension;

[0066] Speed ​​synchronization compensation is performed by combining rolling speed, forward slip model and thickness deformation;

[0067] Real-time acquisition of actual tension using a tension sensor enables high-precision closed-loop correction.

[0068] Dynamic torque feedforward compensation is introduced during acceleration and deceleration to ensure that the tension difference remains stable under all operating conditions.

[0069] The aforementioned cold rolling method, where the inlet tension is greater than the outlet tension, combined with a substrate that retains excellent plasticity, can effectively offset the accumulation of residual stress during the deformation process. This allows for the one-time completion of cold rolling with an ultra-high reduction rate without the need for intermediate annealing to restore plasticity. This not only significantly reduces production energy consumption but also ensures that the magnetic induction intensity B50 of the ultra-thin non-oriented silicon steel is ≥1.7T.

[0070] In the aforementioned cold rolling process, a high-lubricating rolling oil is selected, and the oil temperature is controlled between 40℃ and 60℃ during rolling. This temperature range balances lubrication, cooling, strip shape control, and surface quality. It ensures the rolling oil is at its optimal working viscosity, forming a stable and continuous rolling oil film, reducing rolling force, minimizing friction between the rolls and the strip, improving surface finish, preventing slippage and roll sticking, and stabilizing the rolling process. It also maintains the stability of the emulsion system, ensuring uniform oil-water mixing, preventing demulsification or stratification, and ensuring consistent lubrication. During rolling, it efficiently removes rolling deformation heat, stabilizes the temperature of the rolls and strip, and reduces strip shape fluctuations and dimensional deviations caused by thermal expansion and contraction. Furthermore, it delays oil oxidation and aging, reduces oil fumes and impurities, ensures strip surface cleanliness, and extends the service life of the rolling oil.

[0071] After rolling, an alkaline degreasing agent (concentration 3%~10%) is used for room temperature cleaning to remove residual rolling oil and impurities from the cold rolling process. After cleaning, it is rinsed with deionized water. After rinsing, the water film on the surface of the finished non-oriented electrical steel is continuous, uniform, and without cracks.

[0072] S3. By clearly defining the annealing temperature and holding time, and combining it with a reducing mixed atmosphere, the semi-finished non-oriented electrical steel can be fully recrystallized, the texture orientation can be optimized, and the magnetic strength and magnetic property stability can be improved.

[0073] The annealing temperature should be adjusted according to the thickness of the semi-finished non-oriented electrical steel. Thinner semi-finished non-oriented electrical steel should use a lower annealing temperature range, while thicker semi-finished non-oriented electrical steel should use a higher annealing temperature range. Similarly, the thinner the semi-finished non-oriented electrical steel, the shorter the holding time.

[0074] When the thickness of the semi-finished non-oriented electrical steel is 0.02 mm, the semi-finished non-oriented electrical steel is heated to 940°C at a set heating rate.

[0075] Furthermore, after annealing, the furnace is cooled to room temperature.

[0076] The 0.02mm thick semi-finished non-oriented electrical steel obtained in this embodiment has a magnetic induction intensity B50=1.7T, a high-frequency (400Hz) iron loss P1.0 / 400=11W / kg, and the strip has uniform tension during the annealing process, with no obvious defects such as waviness, warping, or edge wrinkles. The flatness of the strip meets the high-precision requirements for ultra-thin strip.

[0077] Example 2

[0078] This embodiment of a method for producing non-oriented electrical steel includes the following steps:

[0079] Non-oriented electrical steel sheet with a single-phase ferrite microstructure was selected as the substrate; the mass fraction of Si in the substrate was 2%~4% and the thickness was 0.3mm~0.5mm;

[0080] The base material is cold rolled at a rolling speed of 30m / min to 100m / min for at least one pass to obtain a semi-finished non-oriented electrical steel with a thickness of 0.05mm. During the cold rolling process, the inlet tension of each pass is greater than the outlet tension. Specifically, the inlet tension of each pass is 100MPa to 150MPa and the outlet tension is 80MPa to 120MPa.

[0081] Annealing was carried out in a reducing atmosphere to obtain the finished non-oriented electrical steel. During the annealing process, the semi-finished non-oriented electrical steel was heated to 940°C and held at that temperature for 45 seconds at a set heating rate.

[0082] This embodiment relates to the specific process of producing non-oriented electrical steel:

[0083] Step S1: Under alternating magnetic field conditions, increasing the resistivity of the material can effectively increase the resistance of the eddy current loop, suppress the magnitude of eddy currents, and thus significantly reduce eddy current losses. Appropriately increasing the silicon content can improve resistivity and enhance the high-frequency operating efficiency of the core. However, excessively high Si content will significantly increase the brittleness of the material, reduce toughness and rolling performance, and easily lead to strip breakage during cold rolling. Limiting the Si content to the range of 2%~4% (preferably 2.5%~3.5%) allows for the improvement of resistivity and suppression of eddy current losses through appropriate amounts of Si, while avoiding brittle deterioration caused by excessive Si, thus achieving a balance between magnetic properties and rolling performance. Simultaneously, using a finished substrate with a thickness of 0.3mm~0.5mm and no insulating coating reduces surface defects caused by coating peeling during cold rolling and improves rolling stability.

[0084] Among them, non-oriented electrical steel sheets with a single-phase ferrite substrate are used. The single-phase ferrite structure has an extremely low work hardening rate. The low work hardening rate and slow hardening increase after large reduction rate deformation allow the substrate to maintain excellent plasticity even when it is thinned to ultra-thin.

[0085] S2. Leveraging the advantages of a 20-roll mill—multi-roll support, high-precision pressure control, and high-precision shape control—it employs a 20-roll cold rolling process, rolling the base material to its final state in a single pass (i.e., requiring only one continuous cold rolling process). No intermediate annealing process is needed, shortening the process and reducing energy consumption. It is suitable for the high reduction rate rolling requirements of ultra-thin non-oriented electrical steel, reducing defects such as waviness and warping.

[0086] The total reduction rate for cold rolling is specifically 66.7% to 96%.

[0087] Cold rolling involves 5 to 7 passes, and the reduction rate distribution for each pass is as follows:

[0088] The first pass is 40%~45%;

[0089] The second pass rate was 38%~42%;

[0090] Subsequent passes were set within the range of 28% to 36%.

[0091] In cold rolling, a pass refers to the stroke of the substrate through the mill rolls in a single pass. It can be achieved using unidirectional multiple rolling or reciprocating multiple rolling. However, in reciprocating multiple rolling, the inlet and outlet should be switched according to the rolling direction (manual switching or automatic switching via a control mechanism). The total reduction rate mentioned above can be gradually achieved through 5-7 passes of cold rolling, with the reduction rate of each subsequent pass typically lower than that of the previous pass.

[0092] Based on actual production experience, as the heat of deformation accumulates more rapidly during the rolling process, coupled with the temperature of the rolling oil, the material is temporarily softened after the third pass, allowing the fourth pass to withstand a slightly larger reduction. Therefore, the reduction rate of the fourth pass is slightly greater than that of the third pass, thus improving rolling efficiency to a certain extent.

[0093] The thickness of the semi-finished non-oriented electrical steel is controlled at 0.05 mm, with a thickness tolerance of ≤ ±1.5 μm. The rolling speed is well controlled, and the inlet tension of each pass is set to be greater than the outlet tension to avoid strip breakage caused by tension fluctuations.

[0094] The requirement that the inlet tension be greater than the outlet tension is due to the significant forward slippage of the metal within the deformation zone during rolling, resulting in a higher metal flow velocity at the mill exit than at the inlet. By setting the inlet tension slightly higher than the outlet tension, the velocity difference caused by the forward and backward slippage can be balanced, creating a stable tension gradient. This stabilizes the tension distribution within the deformation zone, reduces the elastic flattening of the rolls, allows the non-oriented electrical steel to adhere tightly to the work rolls, resulting in a flatter strip shape, reduced lateral flow, suppression of strip arching, deviation, and edge waviness, lower rolling pressure, and improved strip shape, thus achieving stable continuous rolling under high reduction rates.

[0095] Maintaining the inlet tension greater than the outlet tension can be achieved by employing independent torque closed-loop control at both the inlet and outlet stations, and configuring an online tension detection device, as detailed below:

[0096] The inlet tension device and the outlet tension device control torque independently and do not interfere with each other.

[0097] The system is preset with a fixed tension difference value, ensuring that the inlet tension is always greater than the outlet tension;

[0098] Speed ​​synchronization compensation is performed by combining rolling speed, forward slip model and thickness deformation;

[0099] Real-time acquisition of actual tension using a tension sensor enables high-precision closed-loop correction.

[0100] Dynamic torque feedforward compensation is introduced during acceleration and deceleration to ensure that the tension difference remains stable under all operating conditions.

[0101] The aforementioned cold rolling method, where the inlet tension is greater than the outlet tension, combined with a substrate that retains excellent plasticity, can effectively offset the accumulation of residual stress during the deformation process. This allows for the one-time completion of cold rolling with an ultra-high reduction rate without the need for intermediate annealing to restore plasticity. This not only significantly reduces production energy consumption but also ensures that the magnetic induction intensity B50 of the ultra-thin non-oriented silicon steel is ≥1.7T.

[0102] In the aforementioned cold rolling process, a high-lubricating rolling oil is selected, and the oil temperature is controlled between 40℃ and 60℃ during rolling. This temperature range balances lubrication, cooling, strip shape control, and surface quality. It ensures the rolling oil is at its optimal working viscosity, forming a stable and continuous rolling oil film, reducing rolling force, minimizing friction between the rolls and the strip, improving surface finish, preventing slippage and roll sticking, and stabilizing the rolling process. It also maintains the stability of the emulsion system, ensuring uniform oil-water mixing, preventing demulsification or stratification, and ensuring consistent lubrication. During rolling, it efficiently removes rolling deformation heat, stabilizes the temperature of the rolls and strip, and reduces strip shape fluctuations and dimensional deviations caused by thermal expansion and contraction. Furthermore, it delays oil oxidation and aging, reduces oil fumes and impurities, ensures strip surface cleanliness, and extends the service life of the rolling oil.

[0103] After rolling, an alkaline degreasing agent (concentration 3%~10%) is used for room temperature cleaning to remove residual rolling oil and impurities from the cold rolling process. After cleaning, it is rinsed with deionized water. After rinsing, the water film on the surface of the finished non-oriented electrical steel is continuous, uniform, and without cracks.

[0104] S3. By clearly defining the annealing temperature and holding time, and combining it with a reducing mixed atmosphere, the semi-finished non-oriented electrical steel can be fully recrystallized, the texture orientation can be optimized, and the magnetic strength and magnetic property stability can be improved.

[0105] The annealing temperature should be adjusted according to the thickness of the semi-finished non-oriented electrical steel. Thinner semi-finished non-oriented electrical steel should use a lower annealing temperature range, while thicker semi-finished non-oriented electrical steel should use a higher annealing temperature range. Similarly, the thinner the semi-finished non-oriented electrical steel, the shorter the holding time.

[0106] When the thickness of the semi-finished non-oriented electrical steel is 0.05mm, the semi-finished non-oriented electrical steel is heated to 940℃ at a set heating rate.

[0107] Furthermore, after annealing, the furnace is cooled to room temperature.

[0108] The 0.05mm thick semi-finished non-oriented electrical steel obtained in this embodiment has a magnetic induction intensity B50=1.71T, a high-frequency (400Hz) iron loss P1.0 / 400=12.9W / kg, and the overall flatness of the strip meets the standard. There is no serious waviness or warping, and only very slight unevenness of edge stress exists, which does not affect subsequent processing and use.

[0109] Example 3

[0110] This embodiment of a method for producing non-oriented electrical steel includes the following steps:

[0111] Non-oriented electrical steel sheet with a single-phase ferrite microstructure was selected as the substrate; the mass fraction of Si in the substrate was 2%~4% and the thickness was 0.3mm~0.5mm;

[0112] The base material is cold rolled at a rolling speed of 30m / min to 100m / min for at least one pass to obtain a semi-finished non-oriented electrical steel with a thickness of 0.10mm. During the cold rolling process, the inlet tension of each pass is greater than the outlet tension. Specifically, the inlet tension of each pass is 100MPa to 150MPa and the outlet tension is 80MPa to 120MPa.

[0113] Annealing was carried out in a reducing atmosphere to obtain the finished non-oriented electrical steel. During the annealing process, the semi-finished non-oriented electrical steel was heated to 1000℃ at a set heating rate and held for 70s.

[0114] This embodiment relates to the specific process of producing non-oriented electrical steel:

[0115] Step S1: Under alternating magnetic field conditions, increasing the resistivity of the material can effectively increase the resistance of the eddy current loop, suppress the magnitude of eddy currents, and thus significantly reduce eddy current losses. Appropriately increasing the silicon content can improve resistivity and enhance the high-frequency operating efficiency of the core. However, excessively high Si content will significantly increase the brittleness of the material, reduce toughness and rolling performance, and easily lead to strip breakage during cold rolling. Limiting the Si content to the range of 2%~4% (preferably 2.5%~3.5%) allows for the improvement of resistivity and suppression of eddy current losses through appropriate amounts of Si, while avoiding brittle deterioration caused by excessive Si, thus achieving a balance between magnetic properties and rolling performance. Simultaneously, using a finished substrate with a thickness of 0.3mm~0.5mm and no insulating coating reduces surface defects caused by coating peeling during cold rolling and improves rolling stability.

[0116] Among them, non-oriented electrical steel sheets with a single-phase ferrite substrate are used. The single-phase ferrite structure has an extremely low work hardening rate. The low work hardening rate and slow hardening increase after large reduction rate deformation allow the substrate to maintain excellent plasticity even when it is thinned to ultra-thin.

[0117] S2. Leveraging the advantages of a 20-roll mill—multi-roll support, high-precision pressure control, and high-precision shape control—it employs a 20-roll cold rolling process, rolling the base material to its final state in a single pass (i.e., requiring only one continuous cold rolling process). No intermediate annealing process is needed, shortening the process and reducing energy consumption. It is suitable for the high reduction rate rolling requirements of ultra-thin non-oriented electrical steel, reducing defects such as waviness and warping.

[0118] The total reduction rate for cold rolling is specifically 66.7% to 96%.

[0119] Cold rolling involves 5 to 7 passes, and the reduction rate distribution for each pass is as follows:

[0120] The first pass is 40%~45%;

[0121] The second pass rate was 38%~42%;

[0122] Subsequent passes were set within the range of 28% to 36%.

[0123] Specifically, when the base material thickness is a maximum of 0.5 mm and the thickness of the finished non-oriented electrical steel is a minimum of 0.02 mm, the total reduction rate is (0.5-0.02) / 0.5=96%; similarly, when the base material thickness is a minimum of 0.3 mm and the thickness of the finished non-oriented electrical steel is a maximum of 0.10 mm, the total reduction rate is (0.3-0.1) / 0.3≈66.7%.

[0124] In cold rolling, a pass refers to the stroke of the substrate through the mill rolls in a single pass. It can be achieved using unidirectional multiple rolling or reciprocating multiple rolling. However, in reciprocating multiple rolling, the inlet and outlet should be switched according to the rolling direction (manual switching or automatic switching via a control mechanism). The total reduction rate mentioned above can be gradually achieved through 5-7 passes of cold rolling, with the reduction rate of each subsequent pass typically lower than that of the previous pass.

[0125] Based on actual production experience, as the heat of deformation accumulates more rapidly during the rolling process, coupled with the temperature of the rolling oil, the material is temporarily softened after the third pass, allowing the fourth pass to withstand a slightly larger reduction. Therefore, the reduction rate of the fourth pass is slightly greater than that of the third pass, thus improving rolling efficiency to a certain extent.

[0126] The thickness of the semi-finished non-oriented electrical steel is controlled at 0.10 mm, with a thickness tolerance of ≤ ±1.5 μm. The rolling speed is well controlled, and the inlet tension of each pass is set to be greater than the outlet tension to avoid strip breakage caused by tension fluctuations.

[0127] The requirement that the inlet tension be greater than the outlet tension is due to the significant forward slippage of the metal within the deformation zone during rolling, resulting in a higher metal flow velocity at the mill exit than at the inlet. By setting the inlet tension slightly higher than the outlet tension, the velocity difference caused by the forward and backward slippage can be balanced, creating a stable tension gradient. This stabilizes the tension distribution within the deformation zone, reduces the elastic flattening of the rolls, allows the non-oriented electrical steel to adhere tightly to the work rolls, resulting in a flatter strip shape, reduced lateral flow, suppression of strip arching, deviation, and edge waviness, lower rolling pressure, and improved strip shape, thus achieving stable continuous rolling under high reduction rates.

[0128] Maintaining the inlet tension greater than the outlet tension can be achieved by employing independent torque closed-loop control at both the inlet and outlet stations, and configuring an online tension detection device, as detailed below:

[0129] The inlet tension device and the outlet tension device control torque independently and do not interfere with each other.

[0130] The system is preset with a fixed tension difference value, ensuring that the inlet tension is always greater than the outlet tension;

[0131] Speed ​​synchronization compensation is performed by combining rolling speed, forward slip model and thickness deformation;

[0132] Real-time acquisition of actual tension using a tension sensor enables high-precision closed-loop correction.

[0133] Dynamic torque feedforward compensation is introduced during acceleration and deceleration to ensure that the tension difference remains stable under all operating conditions.

[0134] The aforementioned cold rolling method, where the inlet tension is greater than the outlet tension, combined with a substrate that retains excellent plasticity, can effectively offset the accumulation of residual stress during the deformation process. This allows for the one-time completion of cold rolling with an ultra-high reduction rate without the need for intermediate annealing to restore plasticity. This not only significantly reduces production energy consumption but also ensures that the magnetic induction intensity B50 of the ultra-thin non-oriented silicon steel is ≥1.7T.

[0135] In the aforementioned cold rolling process, a high-lubricating rolling oil is selected, and the oil temperature is controlled between 40℃ and 60℃ during rolling. This temperature range balances lubrication, cooling, strip shape control, and surface quality. It ensures the rolling oil is at its optimal working viscosity, forming a stable and continuous rolling oil film, reducing rolling force, minimizing friction between the rolls and the strip, improving surface finish, preventing slippage and roll sticking, and stabilizing the rolling process. It also maintains the stability of the emulsion system, ensuring uniform oil-water mixing, preventing demulsification or stratification, and ensuring consistent lubrication. During rolling, it efficiently removes rolling deformation heat, stabilizes the temperature of the rolls and strip, and reduces strip shape fluctuations and dimensional deviations caused by thermal expansion and contraction. Furthermore, it delays oil oxidation and aging, reduces oil fumes and impurities, ensures strip surface cleanliness, and extends the service life of the rolling oil.

[0136] After rolling, an alkaline degreasing agent (concentration 3%~10%) is used for room temperature cleaning to remove residual rolling oil and impurities from the cold rolling process. After cleaning, it is rinsed with deionized water. After rinsing, the water film on the surface of the finished non-oriented electrical steel is continuous, uniform, and without cracks.

[0137] S3. By clearly defining the annealing temperature range and holding time, and combining it with a reducing mixed atmosphere, the semi-finished non-oriented electrical steel can be fully recrystallized, the texture orientation can be optimized, and the magnetic strength and magnetic property stability can be improved.

[0138] The annealing temperature should be adjusted according to the thickness of the semi-finished non-oriented electrical steel. Thinner semi-finished non-oriented electrical steel should use a lower annealing temperature range, while thicker semi-finished non-oriented electrical steel should use a higher annealing temperature range. Similarly, the thinner the semi-finished non-oriented electrical steel, the shorter the holding time.

[0139] When the thickness of the semi-finished non-oriented electrical steel is 0.10 mm, the semi-finished non-oriented electrical steel is heated to 1000℃ at a set heating rate.

[0140] Furthermore, after annealing, the furnace is cooled to room temperature.

[0141] The 0.1mm thick semi-finished non-oriented electrical steel obtained in this embodiment has a magnetic induction intensity B50=1.73T, a high-frequency (400Hz) iron loss P1.0 / 400=12.5W / kg, and high tensile strength effectively offsets the thermal stress during the high-temperature annealing process. The strip steel is free from warping and waviness, and the flatness of the plate meets the industrial application standards.

[0142] In Examples 1-3 above, if the cold rolling process encounters a bottleneck in plastic deformation resistance, resulting in insufficient metal fluidity in the deformation zone and making it difficult to reach the process threshold for the reduction rate per pass, the following solutions are provided:

[0143] If the thickness requirement for the semi-finished non-oriented electrical steel is 0.05mm~0.08mm, continue cold rolling until the preset number of cold rolling passes is reached;

[0144] If the thickness requirement of the semi-finished non-oriented electrical steel is 0.02mm~0.05mm, then after reaching a thickness of 0.05mm~0.08mm, an intermediate annealing process is required, with an intermediate annealing temperature of 650℃~800℃.

[0145] However, the above-mentioned method of adding intermediate annealing is only a remedial measure and is not the technical solution to be protected in this application.

[0146] In the above Examples 1 to 3, the substrate components were strictly screened: the Si content was controlled at 2.5-3.5%, and the impurity content of C≤20ppm, S≤10ppm, N≤15ppm (unless otherwise specified, percentage and ppm refer to mass fraction) was strictly controlled to avoid the adverse effects of impurities on magnetic properties;

[0147] Base material specifications: Select non-oriented electrical steel products with a thickness of 0.3mm~0.5mm, no insulating coating on the surface, and flat shape (wavy edge ≤3mm / m) to ensure uniform stress during cold rolling and reduce surface defects.

[0148] In Examples 1-3 above, the reducing atmosphere is a mixture of N2 and H2, and the volume ratio of N2 to H2 is 90:10 to 10:90. This N2:H2 mixture with a volume ratio of 90:10 to 10:90 ensures a reducing atmosphere within the annealing furnace, preventing strip oxidation and promoting recrystallization.

[0149] In the above embodiments 1 to 3, after annealing, the process further includes:

[0150] An insulating coating is applied to the surface of the finished non-oriented electrical steel and then dried and cured.

[0151] For ultra-thin non-oriented electrical steel, high-temperature resistant and highly adhesive organic insulating coatings (alkyd resin coatings, epoxy resin coatings, phenolic resin coatings, C3 self-adhesive coatings) or semi-organic coatings (organic resin + inorganic phosphate, divided into chromium-containing semi-organic and chromium-free environmentally friendly semi-organic) are selected. A roller coating process is adopted, and the coating speed is matched with the speed of the finished non-oriented electrical steel after annealing (10m / min~20m / min). The dry film thickness of the coating is controlled at 0.5μm~1.5μm. The coating thickness is precisely controlled during the coating process to improve the coating adhesion and uniformity, and ensure the stacking coefficient and corrosion resistance.

[0152] After application, the coating is dried and cured at 550℃~700℃ for 30s~90s to ensure a tight bond between the coating and the strip, without cracking or peeling.

[0153] This invention addresses the shortcomings of existing ultra-thin non-oriented electrical steel surfaces, which have a high coating thickness ratio (≥5%), leading to coating cracking, poor adhesion, and affecting the lamination factor and corrosion resistance. The adhesion of semi-organic insulating coatings (such as chromium-free K ultra-thin semi-organic coating liquid and ultra-thin Z-type chromium-free self-adhesive semi-organic coating liquid) meets the standards (no peeling during bending tests), the lamination factor is ≥95%, and the corrosion resistance meets the requirements of a 48-hour neutral salt spray test with no rust.

[0154] The production method of non-oriented electrical steel of the present invention, and the specific data of embodiments 1 to 3 are shown in Table 1 below. The data mainly include the thickness of the finished non-oriented electrical steel, annealing temperature, holding time, specific magnetic property test data (B50, P1.0 / 400), and plate shape evaluation results; the comparison of different thickness specifications is shown in Table 2.

[0155] Table 1

[0156]

[0157] Table 2

[0158]

[0159] As can be seen from Table 1:

[0160] 1. The thickness of finished non-oriented electrical steel is positively correlated with annealing temperature and holding time;

[0161] 2. As the thickness of the finished non-oriented electrical steel decreases, the iron loss is significantly reduced.

[0162] Therefore, based on the method of this invention, the thickness, annealing temperature and holding time of the finished non-oriented electrical steel are strongly coupled and jointly determine the magnetic properties and flatness of the ultra-thin non-oriented silicon steel; the thinner the ultra-thin strip, the more sensitive it is to the thermal process window, and the process parameters need to be precisely adjusted in sync with the reduction of thickness.

[0163] A comparative analysis of Table 1 and Table 2 shows that:

[0164] Comparative Example 1 was annealed at a lower temperature (800℃), which resulted in insufficient material recrystallization, failure to effectively optimize the texture orientation, a significant reduction in magnetic induction intensity B50, and obvious defects such as waviness and warping in the strip due to mismatched process parameters.

[0165] Comparative Example 2 shows that the entry tension (50MPa~80MPa) of each pass in the cold rolling process is too low, which cannot effectively offset the accumulation of residual stress during the deformation process. In addition, the holding time is too long (120s), which leads to serious deterioration of the strip shape and high iron loss.

[0166] Comparative Example 3 suffered from abnormally coarse grains due to excessively high annealing temperature (1100℃), resulting in a significant deterioration in magnetic induction intensity B50.

[0167] This demonstrates that the present invention, through strong coupling and precise control of the finished product thickness, annealing temperature, and holding time, enables ultra-thin non-oriented silicon steel to achieve both excellent magnetic properties and high-precision flatness.

[0168] Furthermore, it should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0169] Finally, it should be noted that the above description represents a preferred embodiment of the present invention. It should be pointed out that although preferred embodiments have been described, those skilled in the art, once they understand the basic inventive concept of the present invention, can make various improvements and modifications without departing from the principles described herein. These improvements and modifications should also be considered within the scope of protection of the present invention. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the embodiments of the present invention.

Claims

1. A method for producing non-oriented electrical steel, characterized in that, The steps are as follows: Non-oriented electrical steel sheet with a single-phase ferrite microstructure is selected as the substrate; the mass fraction of Si in the substrate is 2%~4% and the thickness is 0.3mm~0.5mm; The substrate is cold-rolled at a rolling speed of 30 m / min to 100 m / min for at least one pass to obtain a semi-finished non-oriented electrical steel with a thickness of 0.02 mm to 0.10 mm; during the cold rolling process, the inlet tension of each pass is greater than the outlet tension; wherein, the inlet tension of each pass is 100 MPa to 150 MPa and the outlet tension is 80 MPa to 120 MPa. The total reduction rate of the cold rolling is 66.7% to 96%; The cold rolling process includes 5 to 7 passes, and the reduction rate of each pass is distributed as follows: The first pass is 40%~45%; The second pass rate was 38%~42%; Subsequent passes were set within the range of 28% to 36%; Annealing is performed in a reducing atmosphere to obtain finished non-oriented electrical steel; during the annealing process, the semi-finished non-oriented electrical steel is heated to 850℃~1050℃ at a set heating rate and held for 30s~90s. During the annealing process: When the thickness of the semi-finished non-oriented electrical steel is greater than or equal to 0.02 mm and less than 0.05 mm, the semi-finished non-oriented electrical steel is heated to 850℃~950℃ at a set heating rate. When the thickness of the semi-finished non-oriented electrical steel is greater than or equal to 0.05 mm and less than or equal to 0.10 mm, the semi-finished non-oriented electrical steel is heated to 850℃~1050℃ at a set heating rate.

2. The method for producing non-oriented electrical steel according to claim 1, characterized in that, The substrate contains 2.5%~3.5% Si by mass, C≤20ppm, S≤10ppm, and N≤15ppm.

3. The method for producing non-oriented electrical steel according to claim 1, characterized in that, The substrate undergoes six cold rolling passes; The reduction rates for the first pass were 43.3%, the second pass 41.2%, the third pass 35%, the fourth pass 35.4%, the fifth pass 33.3%, and the sixth pass 28.6%.

4. The method for producing non-oriented electrical steel according to claim 3, characterized in that, Rolling oil is used in the cold rolling process, and the oil temperature is 40℃~60℃.

5. The method for producing non-oriented electrical steel according to claim 1, characterized in that, The reducing atmosphere is a mixture of N2 and H2, with a volume ratio of N2 to H2 of 90:10 to 10:

90.

6. The method for producing non-oriented electrical steel according to claim 5, characterized in that, After annealing, it also includes: An insulating coating is applied to the surface of the finished non-oriented electrical steel and then dried and cured.

Images