Non-oriented electrical steel sheet with excellent high-temperature fatigue performance and manufacturing method therefor

Abstract

The present disclosure relates to a non-oriented electrical steel sheet with excellent high-temperature fatigue performance. The non-oriented electrical steel sheet comprises, in addition to Fe and unavoidable impurities, the following chemical elements in percentage by mass: 0<C<=0.0028%, Si: 3.05-3.95%, Mn: 0.12-0.65%, Al: 0.14-1.15%, and Sn: 0.0035-0.25%. The number of Al2O3 inclusions having a size of 1.5 μm or more in the non-oriented electrical steel sheet does not exceed 4.5 pieces / mm2. In addition, the present disclosure further relates to a manufacturing method for the non-oriented electrical steel sheet. The manufacturing method comprises steps of: smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, final annealing, and coating of an insulating coating. In the RH refining step: a circulating blown air amount V1 in a decarburization process and a circulating blown air amount V0 at the end of decarburization satisfy the following: V1 / V0≥1.12, and V0≥135 Nm3 / h. After the decarburization ends, the content of free oxygen in molten steel does not exceed 225 ppm.

Description

Non-oriented electrical steel sheet with excellent high-temperature fatigue performance and manufacturing method thereof Technical Field

[0001] The present disclosure relates to a steel plate and a method for manufacturing the same, and in particular to a non-oriented electrical steel plate and a method for manufacturing the same. Background Art

[0002] With the rapid development of the new energy vehicle market, electric vehicle drive motors, as core components, are also constantly developing towards high power density, high speed and lightweight.

[0003] Generally speaking, the rated operating environment temperature of the drive motor is higher than room temperature. In order to adapt to the high speed under such high temperature conditions, the non-oriented silicon steel material used as the rotor needs to have excellent high-temperature fatigue performance and yield strength to ensure sufficient stability and safety of the rotor during repeated operation, and to prevent deformation, fracture, sudden stop and other abnormal operating conditions.

[0004] However, there is no mature technical solution in the prior art that can solve the above technical problems.

[0005] Based on this, it is desired to obtain a non-oriented electrical steel sheet that can be used for driving a motor and can meet the above requirements.

[0006] Summary of the Invention

[0007] One of the objectives of the present disclosure is to provide a non-oriented electrical steel sheet with excellent high-temperature fatigue performance, wherein the non-oriented electrical steel sheet has excellent high-temperature fatigue performance and can meet the requirements of driving a motor to rotate at high speeds in the range of room temperature to 150°C without deformation or fracture.

[0008] In order to achieve the above object, the present disclosure provides a non-oriented electrical steel sheet, which, in addition to Fe and unavoidable impurities, further contains the following chemical elements in the following mass percentages:

[0009] 0 <C≤0.0028%,Si:3.05-3.95%,Mn:0.12-0.65%,Al:0.14-1.15%,Sn:0.0035-0.25%;

[0010] The number of Al2O3 inclusions with a size of 1.5 μm or more in the non-oriented electrical steel sheet does not exceed 4.5 per mm 2 .

[0011] Preferably, the mass percentage of each chemical element in the non-oriented electrical steel sheet disclosed herein is:

[0012] 0 < C ≤ 0.0028%, Si: 3.05 - 3.95%, Mn: 0.12 - 0.65%, Al: 0.14 - 1.15%, Sn: 0.0035 - 0.25%; the balance is Fe and inevitable impurities.

[0013] Preferably, the non-oriented electrical steel sheet of the present disclosure further contains Ca and / or REM, and by mass percentage, Ca: 0.0002 - 0.0065% and / or REM: 0.0002 - 0.015%.

[0014] Preferably, the non-oriented electrical steel sheet of the present disclosure further contains at least one of Mo, Ni, Co, Cu, and Cr, and the total mass percentage thereof is 0.015 - 1.85%.

[0015] Preferably, the number of Al2O3 inclusions with a size of 1.5 μm or more in the non-oriented electrical steel sheet of the present disclosure does not exceed 3 per mm 2 , more preferably does not exceed 2 per mm 2 .

[0016] Preferably, in the non-oriented electrical steel sheet of the present disclosure, the inevitable impurities include P, S, N, and Ti, and by mass percentage, P ≤ 0.024%, S ≤ 0.0025%, N ≤ 0.0035%, Ti ≤ 0.0018%.

[0017] Preferably, the mass percentage of Sn in the non-oriented electrical steel sheet of the present disclosure is: 0.0065 - 0.25%.

[0018] Preferably, the fatigue strength S of the non-oriented electrical steel sheet of the present disclosure at 150°C 150 ≥ 465 MPa.

[0019] Preferably, the fatigue strength S of the non-oriented electrical steel sheet of the present disclosure at 150°C 150 and the fatigue strength S at 25°C 25 The ratio S 150 / S 25 Satisfies: 1.0 < S 150 / S 25 ≤ 1.12.

[0020] Preferably, the thickness of the non-oriented electrical steel sheet of the present disclosure is 0.20 - 0.35 mm.

[0021] The present disclosure also provides a method for processing non-oriented electrical steel sheets, which comprises the following steps performed in sequence: smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, final annealing, and coating with an insulating coating, wherein in the RH refining step: the circulating air volume V1 during the decarburization process and the circulating air volume V0 at the end of decarburization satisfy the following conditions: V1 / V0≥1.12, and V0≥135Nm 3 / h; after decarburization, the free oxygen content in the molten steel shall not exceed 225ppm.

[0022] In the method disclosed herein, the heating temperature and the finishing temperature during the hot rolling step are not particularly limited and can be temperatures conventionally used in the art. In one embodiment, the heating temperature of the slab is 1150°C, and the finishing temperature of the coil is 800°C. In one embodiment, the coiling temperature is 625°C. In one embodiment, the thickness of the hot-rolled plate is 2.0-2.5 mm.

[0023] In the method disclosed herein, the holding temperature and holding time in the normalizing annealing step are not particularly limited and can be the temperature and time conventionally used in the art. In one embodiment, the holding temperature of the normalizing annealing is 950° C. and the holding time is 5 minutes.

[0024] In the method disclosed herein, cold rolling is performed using a single cold rolling process or a double cold rolling process.

[0025] In the method disclosed herein, the annealing temperature and holding time in the final annealing step are not particularly limited and can be the temperature and duration conventionally used in the art. In one embodiment, the annealing temperature of the final annealing is 790° C. In one embodiment, the holding time of the final annealing is 45 seconds.

[0026] The non-oriented electrical steel sheet produced by the method disclosed in the present invention has excellent high-temperature fatigue performance and can meet the requirements of driving a motor to rotate at high speed within the range of room temperature to 150° C. without deformation or fracture. DETAILED DESCRIPTION

[0027] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0028] As used herein, the term "and / or" refers to and encompasses any and all possible combinations of more than one of the listed items.

[0029] In this paper, the number of Al2O3 inclusions was statistically analyzed using a field emission scanning electron microscope. Photographs were taken under backscattered electron imaging for more than 20 fields of view, and the number of Al2O3 oxides with a size of 2.0 μm or more in the field of view was counted and expressed in units of "number / mm 2” Calculate the distribution density.

[0030] In this paper, fatigue strength S 25 and fatigue strength S 150 The test was carried out in accordance with ISO 1099-2006 Metallic materials fatigue test - Axial force control method. The test environment temperatures were 25±5°C and 150±3°C respectively. The fatigue limit (fatigue strength) was calculated based on a survival rate of 50%.

[0031] In the non-oriented electrical steel sheet disclosed herein, the design principles of each chemical element are as follows:

[0032] C: In the non-oriented electrical steel sheet of the present disclosure, carbon is an impurity element. When the carbon content exceeds 0.0028%, excessive carbide precipitation occurs, resulting in deteriorated iron loss. However, since C is an essential element in steel, its content cannot be zero. The present disclosure contemplates limiting its upper limit, with the lower the content, the better.

[0033] Si: In the non-oriented electrical steel sheet disclosed herein, the Si element can significantly increase the resistivity of the steel sheet and reduce the iron loss of the material. At the same time, silicon can also improve the high-temperature fatigue strength of the steel sheet. When the Si element content is lower than 3.05%, the improvement in fatigue strength is limited, and the fatigue strength of the material at 150°C cannot be guaranteed to be above 465MPa. When the Si element content exceeds 3.95%, the difficulty of cold rolling the material increases sharply, making it difficult to stably mass-produce, and the magnetic induction of the material will also deteriorate. Therefore, in the non-oriented electrical steel sheet disclosed herein, the mass percentage of the Si element is controlled between 3.05-3.95%, preferably 3.15-3.55%.

[0034] Mn: In the non-oriented electrical steel sheet disclosed herein, Mn increases the material's resistivity, improves iron loss, and combines with S to form MnS, improving the morphology of precipitates in the steel. However, when Mn addition exceeds 0.65%, the hardness of the steel strip increases, hindering cold rolling. Therefore, in the non-oriented electrical steel sheet disclosed herein, the mass percentage of Mn is controlled between 0.12% and 0.65%, preferably between 0.25% and 0.45%.

[0035] Al: In the non-oriented electrical steel sheets disclosed herein, Al increases the material's resistivity and reduces iron loss. When Al content exceeds 1.15%, the magnetic induction of the finished product deteriorates significantly. When Al content is less than 0.14%, iron loss is not significantly improved. Therefore, in the non-oriented electrical steel sheets disclosed herein, the mass percentage of Al is controlled between 0.14% and 1.15%, preferably between 0.45% and 0.95%.

[0036] Sn: In the non-oriented electrical steel sheets disclosed herein, Sn can segregate at grain boundaries, inhibit oxidation within the steel sheet, and improve the favorable texture of the finished annealed microstructure. However, excessive Sn addition may increase surface defects in the steel. Therefore, in the non-oriented electrical steel sheets disclosed herein, the Sn content is controlled within a range of 0.0035% to 0.25% by weight. In some more preferred embodiments, the Sn content can be controlled within a range of 0.0065% to 0.25% by weight.

[0037] In order to further improve the properties of the non-oriented electrical steel sheet disclosed herein, appropriate amounts of Ca and rare earth elements (REM) may be preferably added to the steel.

[0038] Ca: In the non-oriented electrical steel sheets disclosed herein, the Ca element reacts with the sulfur and oxygen in the steel to form structurally stable CaS and CaO, improving the morphology and distribution of inclusions in the molten steel, reducing the formation of fine inclusions, and thus helping to reduce iron loss. However, when the Ca content is too high, it can lead to the formation of excessive oxide inclusions, affecting the surface quality of the steel sheet. Therefore, in the non-oriented electrical steel sheets disclosed herein, the mass percentage of the Ca element can be controlled between 0.0002% and 0.0065%. In some more preferred embodiments, the mass percentage of the Ca element can be controlled between 0.0005% and 0.0065%.

[0039] REM: In the nonoriented electrical steel sheets disclosed herein, rare earth elements (REMs) readily combine with harmful elements such as sulfur and oxygen. Appropriate addition of REMs can purify the molten steel, promote the growth of fine inclusions, and improve the recrystallized grain structure of the finished steel sheets. However, excessive REM content can cause surface defects and degrade magnetic properties. Therefore, in the nonoriented electrical steel sheets disclosed herein, the REM content can be controlled within a range of 0.0002% to 0.015% by weight. In more preferred embodiments, the REM content can be controlled within a range of 0.0005% to 0.008% by weight.

[0040] In order to further improve the performance of the non-oriented electrical steel sheet disclosed herein, the steel may preferably contain at least one of Mo, Ni, Co, Cu, and Cr, and the total weight percentage of these elements may be controlled within a range of 0.015-1.85%. In the non-oriented electrical steel sheet disclosed herein, Mo, Ni, Co, Cu, and Cr elements can increase the resistivity of the steel sheet, reduce losses, and enhance the material strength. Therefore, one or more of these elements may be selected for addition, and the total amount of these elements may be controlled within a range of 0.015-1.85%.

[0041] During the manufacturing process of the non-oriented electrical steel sheet disclosed in the present invention, during the RH refining process, during the aluminum deoxidation and aluminum alloying treatment, aluminum will combine with the free oxygen in the molten steel to generate a large amount of Al2O3 inclusions. Such inclusions are hard and have a high melting point, and are extremely harmful to the fatigue performance of the steel sheet, especially large-particle Al2O3 inclusions with a size of 1.5μm or more. Under the action of repeated alternating loads, stress concentration and strain concentration will occur around the large-particle Al2O3 inclusions, becoming one of the important crack sources of fatigue fracture. The inventors have found that when the number of Al2O3 inclusions with a size of 1.5μm or more in the non-oriented electrical steel sheet does not exceed 4.5 / mm 2 When the temperature is 0.05°C, the non-oriented electrical steel sheet can have better high temperature fatigue performance.

[0042] In the non-oriented electrical steel sheet disclosed herein, P, S, N and Ti are all impurity elements in the non-oriented electrical steel sheet. When technical conditions permit, in order to obtain steel with better performance and higher quality, the content of impurity elements in the steel should be reduced as much as possible.

[0043] P: In the non-oriented electrical steel sheet of the present disclosure, the P element tends to segregate at grain boundaries, increasing the material's brittleness. Therefore, the P content in the non-oriented electrical steel sheet of the present disclosure can be controlled to be below 0.024% by weight. In some more preferred embodiments, the P content can be controlled to be below 0.02% by weight.

[0044] S: In the non-oriented electrical steel sheet disclosed herein, if the S content is too high, it will react with Mn to form a large amount of sulfide precipitates. This, particularly during stress relief annealing, hinders grain growth and significantly degrades the iron loss of the steel sheet. Therefore, in the non-oriented electrical steel sheet disclosed herein, the S content can be controlled to below 0.0025% by weight.

[0045] N: In the nonoriented electrical steel sheets of the present disclosure, when the N content is too high, it will combine with various elements in the steel to form a large number of fine nitrides, hindering grain growth and degrading magnetic properties. Therefore, in the nonoriented electrical steel sheets of the present disclosure, the N content can be controlled to be below 0.0035% by weight. In some more preferred embodiments, the N content can be controlled to be below 0.0030% by weight.

[0046] Ti: In the nonoriented electrical steel sheet disclosed herein, Ti reacts with carbon and nitrogen to precipitate titanium carbide and titanium nitride, which pin grain boundaries, hindering grain growth during recrystallization and degrading iron loss. Therefore, the mass percentage of Ti in the nonoriented electrical steel sheet disclosed herein can be controlled to below 0.0018%, preferably below 0.0015%.

[0047] In some embodiments, the fatigue strength S of the non-oriented electrical steel sheet of the present disclosure at 150°C is 150 ≥465MPa, and S 150 With S 25 Ratio S 150 / S 25 Satisfied: 1.0<S 150 / S 25 ≤1.12. When the above conditions are met, on the one hand, the fatigue performance requirements of the material under repeated starting and high speed of the drive motor can be met, ensuring that the material does not fail, deform, or break during operation. On the other hand, the fatigue strength of the non-oriented electrical steel sheet disclosed in the present invention is further improved at a rated operating ambient temperature of 150°C, and the ratio to the fatigue strength at 25°C is not less than 1.02. This ensures that the drive motor rotor can repeatedly and stably operate at high speeds below 150°C.

[0048] The present disclosure also provides a method for manufacturing a non-oriented electrical steel sheet, which comprises the steps of: smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, final annealing (continuous annealing) and coating an insulating coating; wherein, in the RH refining step, the circulating air blowing volume V1 during the decarburization process and the circulating air blowing volume V0 at the end of decarburization satisfy the following conditions: V1 / V0≥1.12, and V0≥135Nm 3 / h; after decarburization, the free oxygen content in the molten steel shall not exceed 225ppm.

[0049] In the manufacturing method of the non-oriented electrical steel sheet disclosed herein, by controlling the free oxygen content in the molten steel after decarburization in the RH refining process to no more than 225 ppm, it is possible to prevent the subsequent increase of oxidized inclusions caused by excessive free oxygen content in the molten steel at this stage.

[0050] In the disclosed method for manufacturing non-oriented electrical steel sheet, large inclusions can be removed by controlling the circulating air blowing rate during the RH refining process. During the RH refining process, air is blown into the molten steel, driving it to circulate between the ladle and the vacuum chamber. This causes inclusions to rise with the molten steel and be captured by the slag layer, thus purifying the molten steel.

[0051] In the method for producing the non-oriented electrical steel sheet disclosed herein, the circulating air blowing volume V0 at the end of decarburization is set to 135 Nm 3 / h or more, and after adding aluminum granules or ingots, the circulating air volume V1 and V0 at this time are adjusted to meet the relationship: V1 / V0 ≥ 1.12. The circulating air volume is used to control the flow of molten steel, thereby controlling the residence time and movement of inclusions in the molten steel. By adopting these process conditions, Al2O3 oxide inclusions generated by the reaction of aluminum with free oxygen in the steel have sufficient time to aggregate and grow, and then quickly float up to be captured by the slag layer and removed.

[0052] By using the above technical means, the number of Al2O3 inclusions with a size of 1.5 microns or more in the steel plate can be reduced to no more than 4.5 / mm 2 .

[0053] In the manufacturing method disclosed herein, the steps of hot rolling, normalizing annealing, cold rolling, final annealing and coating of an insulating coating are not particularly limited, and conventional process parameters in the art may be used.

[0054] The non-oriented electrical steel sheet and the manufacturing method thereof disclosed in the present invention have the following advantages and beneficial effects:

[0055] The non-oriented electrical steel sheet disclosed in the present invention can meet the requirements of repeated starting and high speed of the driving motor on material fatigue performance, and ensure that the material will not fail, deform or break during the operation process.

[0056] The non-oriented electrical steel sheet disclosed herein has excellent fatigue performance at a rated operating ambient temperature of 150° C., which can ensure that the rotor of the driving motor can repeatedly and stably operate at high speed below 150° C.

[0057] The non-oriented electrical steel sheet and the manufacturing method thereof disclosed herein will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an undue limitation to the technical solution disclosed herein.

[0058] Examples 1-10 and Comparative Examples 1-6

[0059] The non-oriented electrical steel sheets of Examples 1-10 and Comparative Examples 1-6 were prepared by the following steps:

[0060] (1) Blast furnace molten iron undergoes molten iron pretreatment and converter smelting.

[0061] (2) Decarburization, deoxidation and alloying are carried out in RH refining. In the RH refining step: after adding aluminum material, the circulating air volume V1 during the decarburization process and the circulating air volume V0 at the end of decarburization are satisfied: V1 / V0≥1.12, and V0≥135Nm 3 After decarburization, the free oxygen content in the molten steel is not more than 225 ppm. Table 2 shows the specific process parameters of each embodiment and comparative example in this step.

[0062] (3) After refining, the molten steel is continuously cast to obtain a continuous casting slab. The chemical element composition of the continuous casting slabs of each embodiment and comparative example is shown in Table 1-1 and Table 1-2.

[0063] (4) Hot rolling: The heating temperature of the slab is 1150°C, the final rolling temperature of the coil is 800°C, and the coiling temperature is 625°C to obtain a hot-rolled plate with a thickness of 2.0-2.5 mm.

[0064] (5) Normalizing annealing: The normalizing holding temperature is 950℃ and the holding time is 5 minutes.

[0065] (6) Cold rolling to obtain a finished product with a thickness of 0.20-0.35 mm. Example 2 and Example 6 adopt a double cold rolling process, while the other examples and comparative examples adopt a single cold rolling process.

[0066] (7) Final annealing and coating with insulating coating: annealing temperature is 790℃, and holding time is 45s.

[0067] Table 1-1 and Table 1-2 list the mass percentage content of various chemical elements in the non-oriented electrical steel sheets of Examples 1-10 and the comparative steel sheets of Comparative Examples 1-6.

[0068] Table 1-1. (wt%, the balance is Fe and other inevitable impurities)

[0069] Table 1-2. (wt%, the balance is Fe and other inevitable impurities)

[0070] Table 2 lists the specific process parameters of the non-oriented electrical steel sheets of Examples 1-10 and the comparative steel sheets of Comparative Examples 1-6 in the RH refining step.

[0071] Table 2.

[0072] Next, samples of the non-oriented electrical steel sheets of Examples 1-10 and the comparative steel sheets of Comparative Examples 1-6 were taken and tested. The test results are listed in Table 3 below. The relevant performance test methods are as follows:

[0073] Fatigue performance: The test was conducted in accordance with ISO 1099-2006 Metallic materials fatigue test method for axial force control. A servo-type fatigue testing machine with a maximum capacity of 10kN was used. The test conditions and parameters were set as follows: test environment temperature 25±5℃ and 150±3℃, sinusoidal control waveform, stress ratio R=0.1, frequency: 20-30Hz, and maximum number of cycles 1.0×10 7 Second-rate.

[0074] The number of Al2O3 inclusions: Statistical analysis was performed using a field emission scanning electron microscope. 20*20mm specimens were randomly cut from the base steel plate, ground to 1 / 2 of the thickness of the steel plate, and then mechanically or electrochemically polished. The specimens were then photographed under a backscattered electron image to confirm the presence of Al2O3 oxide inclusions and to count their number. More than 20 fields of view were photographed continuously, and the number of Al2O3 oxide inclusions larger than 1.5μm in size in the field of view was counted. The unit of measurement was "pieces / mm". 2 ” Calculate the distribution density.

[0075] Table 3

[0076] It can be seen from Table 3 above that the room temperature fatigue strength S of the steel grades of Examples 1-10 is 25 All are higher than 475MPa. The fatigue strength at 150℃ not only does not decrease, but further increases. 150 All above 500MPa, S 150 With S 25 Ratio S 150 / S 25 Therefore, the non-oriented electrical steel sheets of each embodiment meet the fatigue performance requirements of the drive motor when it is repeatedly started and operated at high speed, ensuring that the material does not fail, deform or break during operation.

[0077] In contrast, the process parameters of RH refining in Comparative Examples 1 to 3 are not within the scope of the present invention. In Comparative Example 1, the annular air blowing volume is too low, and the circulation rate of the molten steel is slowed down, resulting in insufficient floating and removal of Al2O3 oxide inclusions.

[0078] The free oxygen content of the steel liquid in Comparative Examples 2 and 3 is too high at the end of decarburization during the RH refining process, resulting in the generation of a large amount of Al2O3 when the aluminum ingot is added. At the same time, the circulating air volume V1 is not increased accordingly, causing the Al2O3 oxide to aggregate and grow, and not be fully floated up and removed, ultimately resulting in poor fatigue performance of the finished product.

[0079] The chemical composition content of the steels in Comparative Examples 4-6 is not within the scope of the present invention, and the final fatigue strength is low, which cannot meet the performance requirements.

[0080] All publications, patent applications, patents, and other references mentioned in this disclosure are incorporated by reference in their entirety.

[0081] Although the present disclosure has been illustrated and described with reference to certain preferred embodiments thereof, it should be understood by those skilled in the art that the above description is provided to further illustrate the present disclosure in conjunction with specific embodiments thereof, and that the present disclosure is not limited to these descriptions. Those skilled in the art may make various changes in form and detail, including simple deductions or substitutions, without departing from the spirit and scope of the present disclosure.

Claims

1. Non-oriented electrical steel sheet, characterized in that: In addition to Fe and inevitable impurities, the non-oriented electrical steel sheet contains the following chemical elements in the following mass percentages: 0 < C ≤ 0.0028%, Si: 3.05 - 3.95%, Mn: 0.12 - 0.65%, Al: 0.14 - 1.15%, Sn: 0.0035 - 0.25%. The number of Al2O3 inclusions with a size of 1.5 μm or more in the non-oriented electrical steel sheet does not exceed 4.5 / mm 2 .

2. The non-oriented electrical steel sheet according to claim 1, characterized in that: The mass percentages of its chemical elements are: 0 < C ≤ 0.0028%, Si: 3.05 - 3.95%, Mn: 0.12 - 0.65%, Al: 0.14 - 1.15%, Sn: 0.0035 - 0.25%; the balance is Fe and inevitable impurities.

3. The non-oriented electrical steel sheet according to claim 1 or 2, characterized in that: The non-oriented electrical steel sheet also contains Ca and / or REM, and in terms of mass percentage, Ca: 0.0002 - 0.0065% and / or REM: 0.0002 - 0.015%.

4. The non-oriented electrical steel sheet according to any one of claims 1 to 3, characterized in that: The non-oriented electrical steel sheet also contains at least one of Mo, Ni, Co, Cu, and Cr, and the total mass percentage thereof is 0.015 - 1.85%.

5. The non-oriented electrical steel sheet according to any one of claims 1 to 4, characterized in that: The number of Al2O3 inclusions with a size of 1.5 μm or more in the non-oriented electrical steel sheet does not exceed 3 / mm 2 , preferably no more than 2 / mm 2 .

6. The non-oriented electrical steel sheet according to any one of claims 1 to 5, characterized in that: The inevitable impurities include P, S, N, and Ti, and in terms of mass percentage, P ≤ 0.024%, S ≤ 0.0025%, N ≤ 0.0035%, Ti ≤ 0.0018%.

7. The non-oriented electrical steel sheet according to any one of claims 1 to 6, characterized in that: The mass percentage of Sn is: 0.0065 - 0.25%.

8. The non-oriented electrical steel sheet according to any one of claims 1 to 7, characterized in that: The fatigue strength S of the non-oriented electrical steel sheet at 150°C 150 ≥465MPa, preferably, S 150 With S 25 Ratio S 150 / S 25 Satisfied: 1.0<S 150 / S 25 ≤1.

12.

9. The non-oriented electrical steel sheet according to any one of claims 1 to 8, characterized in that: The thickness of the non-oriented electrical steel sheet is 0.20 - 0.35 mm.

10. A method for manufacturing the non-oriented electrical steel sheet according to any one of claims 1 to 9, which comprises the following steps carried out in sequence: smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, final annealing, and coating with an insulating coating, characterized in that In the RH refining step: the circulation gas flow rate V1 during the decarburization process and the circulation gas flow rate V0 at the end of decarburization satisfy: V1 / V0≥1.12, and V0≥135Nm 3 / h; After decarburization, the free oxygen content in the molten steel shall not exceed 225ppm.

11. The method according to claim 10, characterized in that The cold rolling is carried out by a single cold rolling process or a double cold rolling process.

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