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

Abstract

The invention discloses a non-oriented electrical steel with excellent high-temperature fatigue performance, which contains Fe and inevitable impurities, and also contains the following chemical elements in percentage by mass: less than or equal to 0.0028% of C, 3.05-3.95% of Si, 0.12-0.65% of Mn, 0.14-1.15% of Al, 0.0035-0.25% of Sn, less than or equal to 0.025% of P, less than or equal to 0.025% of S, less than or equal to 0.025% of S, less than or equal to 0.025% of P, less than or equal to 0.025% of Wherein the number of Al2O3 inclusions with the size of 1.5 microns or above is not more than 4.5 per mm < 2 >. The manufacturing method of the non-oriented electrical steel comprises the steps of smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, continuous annealing and insulating coating. In the RH refining step, after decarburization is finished, the content of free oxygen in molten steel is controlled not to exceed 225 ppm; and after the aluminum material is added, the circulation blowing amount V1 and the circulation blowing amount V0 after decarburization are controlled to meet the conditions that V1 / V0 is larger than or equal to 1.12, and V0 is larger than or equal to 135 Nm < 3 > / h.

Description

Technical Field

[0001] The present invention relates to a steel plate and a manufacturing method thereof, and in particular to a non-oriented electrical steel plate and a manufacturing method thereof. 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 the 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 that the rotor has sufficient stability and safety during repeated operation, and does not experience abnormal operating conditions such as deformation, breakage, sudden stop, etc.

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

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

[0006] One of the objects of the present invention is to provide a non-oriented electrical steel with excellent high temperature fatigue performance, which can meet the requirements of driving a motor to rotate at high speed in the range of room temperature to 150°C without deformation or fracture.

[0007] In order to achieve the above object, the present invention provides a non-oriented electrical steel with excellent high temperature fatigue performance, which contains Fe and inevitable impurities, and further contains the following chemical elements in the following mass percentages:

[0008] C≤0.0028%, Si: 3.05-3.95%, Mn: 0.12-0.65%, Al: 0.14-1.15%, Sn: 0.0035-0.25%;

[0009] The number of Al2O3 inclusions with a size of 1.5 μm or more in the non-oriented electrical steel does not exceed 4.5 / mm 2 .

[0010] Accordingly, the present invention also provides a non-oriented electrical steel with excellent high temperature fatigue performance, wherein the mass percentage of each chemical element is:

[0011] 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 unavoidable impurities;

[0012] The number of Al2O3 inclusions with a size of 1.5 μm or more in the non-oriented electrical steel does not exceed 4.5 / mm 2 .

[0013] In the non-oriented electrical steel of the present invention, the design principles of each chemical element are as follows:

[0014] C: In the non-oriented electrical steel described in the present invention, carbon is an impurity element. When the carbon content exceeds 0.0028%, excessive carbide precipitation will be formed, resulting in deteriorated iron loss. However, since C is an element that must be contained in steel, its content will not be 0. The present invention hopes to control its upper limit, and hopes that its content is as low as possible.

[0015] Si: In the non-oriented electrical steel described in the present invention, the Si element can significantly increase the resistivity of the steel plate and reduce the iron loss of the material. At the same time, silicon can also improve the high-temperature fatigue strength of the steel plate. When the Si element content is lower than 3.05%, the improvement in fatigue strength is limited, and it cannot guarantee that the fatigue strength of the material is above 465MPa under an ambient temperature of 150°C. When the Si element content exceeds 3.95%, the difficulty of cold rolling processing of the material increases sharply, and it is difficult to stably mass produce, and the magnetic induction of the material will also deteriorate. Therefore, in the non-oriented electrical steel described in the present invention, the mass percentage of the Si element is controlled between 3.05-3.95%.

[0016] Mn: In the non-oriented electrical steel of the present invention, the Mn element can increase the resistivity of the material, improve the iron loss, and can be combined with the S element to form MnS, improving the morphology of the precipitates in the steel. When the addition amount of the Mn element exceeds 0.65%, the hardness of the strip increases, which is not conducive to cold rolling. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of the Mn element is controlled between 0.12-0.65%.

[0017] Al: In the non-oriented electrical steel of the present invention, Al element can increase the resistivity of the material and reduce the iron loss. When the Al element exceeds 1.15%, the magnetic induction of the finished product deteriorates seriously, and when the Al element is less than 0.14%, it does not have the effect of significantly improving the iron loss. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of Al element is controlled between 0.14-1.15%.

[0018] Sn: In the non-oriented electrical steel of the present invention, the Sn element can be segregated at the grain boundary, inhibit oxidation in the steel plate, and improve the favorable texture of the finished annealed structure, but excessive addition may lead to an increase in surface defects of the steel. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of the Sn element is controlled between 0.0035% and 0.25%, and in some more preferred embodiments, the mass percentage of the Sn element can be controlled between 0.0065% and 0.25%.

[0019] Furthermore, the non-oriented electrical steel of the present invention further contains Ca: 0.0002-0.0065wt% and REM: 0.0002-0.015wt%.

[0020] In the above technical solution of the present invention, in order to further optimize the performance of the non-oriented electrical steel of the present invention, an appropriate amount of Ca element and rare earth elements may be preferably added to the steel. Among them:

[0021] Ca: In the non-oriented electrical steel of the present invention, the Ca element can react with S and O in the steel to generate CaS and CaO with stable structure, improve the morphology and distribution of inclusions in the molten steel, reduce the formation of fine inclusions, and help reduce iron loss. However, when the Ca content is too high, it will lead to the formation of too many oxide inclusions, affecting the surface quality of the steel plate. Therefore, in the non-oriented electrical steel of the present invention, 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%.

[0022] REM: In the non-oriented electrical steel described in the present invention, rare earth elements are easily combined with harmful elements such as sulfur and oxygen. The appropriate addition of rare earth elements can purify the molten steel, promote the growth of fine inclusions, and improve the recrystallized grain structure of the finished steel plate. However, when the REM content is too high, it will cause steel defects on the surface of the steel plate and deteriorate the magnetic properties. Therefore, in the non-oriented electrical steel described in the present invention, the mass percentage of REM can be controlled between 0.0002% and 0.015%. In some more preferred embodiments, the mass percentage of REM can be controlled between 0.0005% and 0.008%.

[0023] Furthermore, the non-oriented electrical steel of the present invention may also contain at least one of Mo, Ni, Co, Cu and Cr, and the total mass percentage of the at least one of the Mo, Ni, Co, Cu and Cr is controlled within the range of 0.015-1.85%.

[0024] The Mo, Ni, Co, Cu and Cr elements in the non-oriented electrical steel of the present invention can increase the resistivity of the steel plate, reduce the loss and improve the material strength. One or more of them can be selected when adding, and the total addition amount can be controlled within 0.015-1.85%.

[0025] Furthermore, in some more preferred embodiments of the non-oriented electrical steel of the present invention, the number of Al2O3 inclusions with a size of 1.5 μm or more does not exceed 3 / mm 2 .

[0026] Generally speaking, during the RH refining process of non-oriented electrical steel, during the aluminum deoxidation and aluminum alloying treatment, aluminum will combine with free oxygen in the molten steel to generate a large amount of Al2O3 inclusions. Such inclusions are hard and have a high melting point, which are extremely harmful to the fatigue performance of the steel plate, especially large-particle Al2O3 inclusions with a size of more than 1.5μm. 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. Based on this, the present invention controls the content of Al2O3 inclusions with a size of more than 1.5μm to an upper limit of no more than 4.5 / mm 2 , more preferably 3 / mm 2 the following.

[0027] Furthermore, among the inevitable impurities of the non-oriented electrical steel of the present invention, P≤0.024%, S≤0.0025%, N≤0.0035%, and Ti≤0.0018%.

[0028] In the non-oriented electrical steel of the present invention, P, S, N and Ti are all impurity elements in the non-oriented electrical steel sheet. Under the condition that technical conditions permit, in order to obtain steel with better performance and better quality, the content of impurity elements in the steel should be reduced as much as possible. Among them:

[0029] P: In the non-oriented electrical steel of the present invention, the P element is easy to segregate at the grain boundary, increasing the brittleness of the material. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of the P element can be controlled to be below 0.024%, and in some more preferred embodiments, the mass percentage of the P element can be controlled to be below 0.02%.

[0030] S: In the non-oriented electrical steel of the present invention, when the S element content is too high, it will react with the Mn element to form a large amount of sulfide precipitates, especially in the stress relief annealing process, which hinders the growth of grains and significantly deteriorates the iron loss of the steel plate. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of the S element can be controlled to be less than 0.0025%.

[0031] N: In the non-oriented electrical steel of the present invention, 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 the growth of grains and deteriorating magnetic properties. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of the N element can be controlled to be less than 0.0035%. In some more preferred embodiments, the mass percentage of the N element can be controlled to be less than 0.0030%.

[0032] Ti: In the non-oriented electrical steel described in the present invention, Ti reacts with carbon and nitrogen to precipitate titanium carbide and titanium nitride to pin the grain boundaries, hinder the grain growth during the recrystallization process, and deteriorate the iron loss. Therefore, its mass percentage can be controlled not to exceed 0.002%, preferably below 0.0015%.

[0033] Furthermore, in the non-oriented electrical steel of the present invention, the mass percentage of Sn is 0.0065-0.25%.

[0034] Furthermore, in the non-oriented electrical steel of the present invention, the fatigue strength S 150 ≥465MPa, and the fatigue strength S at 25℃ 25 Satisfaction: Satisfaction relationship: 1.0<S 150 / S 25 ≤1.12.

[0035] Meeting the above conditions can, on the one hand, meet the requirements of repeated starting and high speed of the drive motor for material fatigue performance, ensuring that the material does not fail, deform or break during operation. On the other hand, at a rated working environment temperature of 150°C, the fatigue strength of the non-oriented electrical steel of the present invention is further improved, and the ratio to the fatigue strength at 25°C is not less than 1.02, ensuring that the drive motor rotor can repeatedly and stably operate at high speed within 150°C.

[0036] Furthermore, the thickness of the non-oriented electrical steel of the present invention is 0.20-0.35 mm.

[0037] Another object of the present invention is to provide a method for manufacturing non-oriented electrical steel with excellent high-temperature fatigue performance. The non-oriented electrical steel manufactured by this method has excellent high-temperature fatigue performance and can meet the requirements of driving the motor to rotate at high speed in the range of room temperature to 150°C without deformation or fracture.

[0038] In order to achieve the above object, the present invention provides a method for manufacturing non-oriented electrical steel with excellent high temperature fatigue performance, which comprises the steps of: smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, continuous annealing and insulation coating; wherein:

[0039] In the RH refining step: after decarburization, the free oxygen content in the molten steel is controlled not to exceed 225ppm; after adding aluminum, the circulating air volume V1 and the circulating air volume V0 at the end of decarburization are controlled to meet the following conditions: V1 / V0≥1.12, and V0≥135Nm 3 / h.

[0040] In the method for manufacturing non-oriented electrical steel of the present invention, after the decarburization in the RH refining process is completed, the free oxygen content of the molten steel is controlled to be no more than 225ppm, which can prevent the free oxygen content in the molten steel from being too high at this stage, resulting in an increase in subsequent oxidized inclusions.

[0041] In the method for manufacturing non-oriented electrical steel described in the present invention, the removal of large-particle-sized inclusions can be achieved by controlling the circulating air blowing amount during the RH refining process. During the RH refining process, air is blown into the molten steel to drive the molten steel to circulate between the ladle and the vacuum chamber. In this process, inclusions flow and float up with the molten steel and are captured by the slag layer, thereby achieving purification of the molten steel.

[0042] In the method for producing non-oriented electrical steel of the present invention, the circulating air blowing volume V0 during the decarburization process and before the end of decarburization is greater than 135 Nm 3 / h, after adding aluminum particles or aluminum ingots, the circulating air blowing volume V1 and V0 meet the relationship: V1 / V0≥1.12. The flow of molten steel is controlled by the circulating air blowing volume, and the residence time and movement of inclusions in the molten steel are controlled. This process allows the Al2O3 oxide inclusions generated by the reaction of aluminum with free oxygen in steel to have time to aggregate and grow, and quickly float up to be captured and removed by the slag layer.

[0043] By means of the above, the present invention can achieve the control of the number of Al2O3 inclusions with a size of 1.5 microns or more in the steel plate to no more than 4.5 / mm. 2 .

[0044] In the manufacturing method described in the present invention, hot rolling, normalizing annealing, cold rolling, continuous annealing and insulating coating are not particularly improved compared to conventional processes, and conventional process parameters in the art can be used, so they are not particularly limited or described here.

[0045] The non-oriented electrical steel and the method for manufacturing the same according to the present invention have the following advantages and beneficial effects:

[0046] In the non-oriented electrical steel for driving motor with excellent high temperature fatigue performance described in the present invention, the fatigue strength S 150 Not less than 465MPa or above, and the fatigue strength S at 25℃ 25 Satisfaction relationship: 1.0<S 150 / S 25≤1.12, which can meet the material fatigue performance requirements of repeated starting and high speed of the drive motor, and ensure that the material will not fail, deform or break during the operation process.

[0047] In the non-oriented electrical steel for drive motor with excellent high-temperature fatigue performance described in the present invention, at a rated working environment temperature of 150°C, the fatigue strength of the non-oriented electrical steel of the present invention is further improved, and the ratio of the fatigue strength at 25°C is in the range of 1.0-1.12, ensuring that the rotor of the drive motor can repeatedly and stably operate at high speed within 150°C. DETAILED DESCRIPTION

[0048] The non-oriented electrical steel and the method for manufacturing the same according to the present invention will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0049] Examples 1-10 and Comparative Examples 1-6

[0050] The non-oriented electrical steels of Examples 1-10 and Comparative Examples 1-6 were prepared by the following steps:

[0051] (1) Blast furnace molten iron is pretreated and smelted in a converter.

[0052] (2) Decarburization, deoxidation and alloying treatment are carried out during RH refining: after decarburization, the free oxygen content in the molten steel is controlled to be no more than 225 ppm; after adding aluminum material, the circulating air volume V1 and the circulating air volume V0 at the end of decarburization are controlled to meet the following conditions: V1 / V0 ≥ 1.12, and V0 ≥ 135 Nm 3 Table 2 shows the specific process parameters of each embodiment and comparative example in this step.

[0053] (3) After refining, the molten steel is continuously cast to obtain a continuous casting slab, the chemical element composition ratio of which is shown in Table 1-1 and Table 1-2.

[0054] (4) Hot rolling: The heating temperature of the slab can be 1150°C, the final rolling temperature of the steel coil can be 800°C, and the coiling temperature can be 625°C to obtain a hot-rolled plate with a thickness of 2.0-2.5 mm.

[0055] (5) Normalizing annealing: For example, the normalizing holding temperature may be 950° C., and the holding time may be 5 min.

[0056] (6) Cold rolling to obtain a finished product with a thickness of 0.20-0.35 mm: Examples 2 and 6 adopt a double cold rolling process, while the other examples and comparative examples adopt a single cold rolling process.

[0057] (7) Final annealing and application of insulating coating: For example, the annealing temperature may be 790° C. and the holding time may be 45 s.

[0058] Table 1-1 and Table 1-2 list the mass percentages of chemical elements in the non-oriented electrical steels of Examples 1-10 and the comparative steel sheets of Comparative Examples 1-6.

[0059] Table 1-1. (wt%, the balance is Fe and inevitable impurities other than P, S, N, and Ti)

[0060] serial number C Si Mn Al Sn Ca REM Example 1 0.0018 3.95 0.25 0.14 0.0035 / / Example 2 0.0017 3.55 0.45 0.95 0.08 0.0065 0.0002 Example 3 0.0022 3.74 0.30 0.55 0.015 / / Example 4 0.0014 3.56 0.52 1.15 0.085 0.0003 0.0015 Example 5 0.0013 3.42 0.55 1.09 0.02 0.0005 0.0005 Example 6 0.0016 3.31 0.65 0.45 0.06 / / Example 7 0.0015 3.05 0.25 0.75 0.25 / / Example 8 0.0021 3.15 0.35 0.61 0.0065 0.0002 0.015 Example 9 0.0013 3.25 0.12 1.00 0.0045 0.0006 0.001 Example 10 0.0010 3.50 0.45 0.95 0.005 / / Comparative Example 1 0.0023 3.35 0.35 1.00 0.055 / / Comparative Example 2 0.0018 3.45 0.56 0.55 0.004 0.0005 / Comparative Example 3 0.0020 3.75 0.25 0.45 0.095 0.004 0.009 Comparative Example 4 0.0020 3.04 0.55 0.13 / / / Comparative Example 5 0.0037 2.85 0.25 2.00 0.005 / / Comparative Example 6 0.0021 3.40 0.1 0.005 0.003 / /

[0061] Table 1-2. (wt%, the balance is Fe and inevitable impurities other than P, S, N, and Ti)

[0062]

[0063]

[0064] Table 2 lists the specific process parameters of the non-oriented electrical steels of Examples 1-10 and the comparative steel sheets of Comparative Examples 1-6 in the RH refining step.

[0065] Table 2.

[0066]

[0067] In order to verify the implementation effect of the present invention, the non-oriented electrical steels of the final finished products of Examples 1-10 and the comparative steel sheets of Comparative Examples 1-6 were sampled respectively, and these non-oriented electrical steel sheets were tested, and the obtained test results are listed in the following Table 3. The relevant performance testing methods are as follows:

[0068] Fatigue performance test: The test is carried out in accordance with GB-T 3075-2008 Axial force control method for fatigue test of metal materials and ISO1099-2006 Axial force control method for fatigue test of metal materials. The maximum capacity of the 10kN servo-type fatigue testing machine is used. The test condition parameters can be set as follows: the test environment temperature is 25±5℃ and 150±3℃, the waveform is controlled by a sine wave, the stress ratio R=0.1, the frequency is 20-30Hz, and the maximum number of cycles is 1.0×10 7 Second-rate.

[0069] Statistics of Al2O3 oxide inclusions: Statistical analysis was performed using a field emission scanning electron microscope. 20*20 mm samples were randomly cut from the substrate steel plate, ground to 1 / 2 thickness of the steel plate, and mechanically or electrochemically polished. Then, photographs were taken under the backscattered electron image to confirm the presence of Al2O3 oxide inclusions and count the number. More than 20 fields of view were taken continuously to count the number of Al2O3 oxides with a size of more than 1.5 μm in the field of view, and the unit was "pieces / mm 2 ” Calculate the distribution density.

[0070] Table 3

[0071]

[0072] It can be seen from Table 3 that the key process parameters such as the steelmaking chemical composition control of the steel grades in Examples 1-10, the free oxygen content in the molten steel at the end of decarburization during the RH refining process, the annular air blowing volume V0 at the end of decarburization, and the annular air blowing volume V1 after adding the aluminum ingot are controlled within the design range of the present invention. Therefore, the room temperature fatigue strength S of each embodiment is 25 All of them are higher than 475MPa. The fatigue strength at an ambient temperature of 150℃ not only does not decrease, but further increases. 150 All above 523MPa, S 150 With S 25 The ratios are all within the range of 1.02-1.12, which can ensure that the non-oriented electrical steel sheets of each embodiment meet the material fatigue performance requirements of repeated starting and high speed of the driving motor, and ensure that the material does not fail, deform or break during the operation process.

[0073] In contrast, in Comparative Examples 1-3, although the chemical composition is within the scope of the present invention, the RH refining control process is 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 the inability to fully float and remove Al2O3 oxide inclusions.

[0074] The free oxygen content of the molten steel in Comparative Examples 2 and 3 is too high at the end of decarburization in the RH refining process, resulting in a large amount of Al2O3 being generated 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 fully float up and be removed, ultimately resulting in poor fatigue performance of the finished product.

[0075] Although the RH refining process of the steel types in Comparative Examples 4-6 is within the scope of the present invention, the chemical composition does not meet the requirements of the present invention, so the corresponding final fatigue strength is low and does not meet the requirements of the present invention.

[0076] It should be noted that the prior art in the protection scope of the present invention is not limited to the embodiments given in the present application documents. All prior art that does not contradict the scheme of the present invention, including but not limited to prior patent documents, prior public publications, prior public uses, etc., can be included in the protection scope of the present invention.

[0077] In addition, the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0078] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

Claims

1. A non-oriented electrical steel having excellent high temperature fatigue performance, comprising Fe and unavoidable impurities, characterized in that: It also contains the following chemical elements in the following mass percentages: 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 does not exceed 4.5 / mm 2 .

2. The non-oriented electrical steel according to claim 1, characterized in that: The mass percentage of each chemical element is: 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 unavoidable impurities.

3. The non-oriented electrical steel according to claim 1 or 2, characterized in that: It also contains Ca: 0.0002-0.0065 wt %, REM: 0.0002-0.015 wt %.

4. The non-oriented electrical steel according to claim 1 or 2, characterized in that: It also contains at least one of Mo, Ni, Co, Cu and Cr, and the total mass percentage of the contents is controlled within the range of 0.015-1.85%.

5. The non-oriented electrical steel according to claim 1 or 2, characterized in that: The number of Al2O3 inclusions with a size of 1.5 μm or more in the non-oriented electrical steel does not exceed 3 / mm 2 .

6. The non-oriented electrical steel according to claim 1 or 2, characterized in that: Among the inevitable impurities, P≤0.024%, S≤0.0025%, N≤0.0035%, and Ti≤0.0018%.

7. The non-oriented electrical steel according to claim 1 or 2, characterized in that: The mass percentage of Sn is: 0.0065-0.25%.

8. The non-oriented electrical steel according to claim 1 or 2, characterized in that: Its fatigue strength S at 150°C ambient temperature 150 ≥465MPa, and the fatigue strength S at 25℃ 25 Satisfied: 1.0<S 150 / S 25 ≤1.

12.

9. The non-oriented electrical steel according to claim 1 or 2, characterized in that: Its thickness is 0.20-0.35mm.

10. A method for producing non-oriented electrical steel according to any one of claims 1 to 9, comprising the steps of smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, continuous annealing and insulation coating; characterized in that: In the RH refining step: after decarburization, the free oxygen content in the molten steel is controlled not to exceed 225ppm; after adding aluminum, the circulating air volume V1 and the circulating air volume V0 at the end of decarburization are controlled to meet the following conditions: V1 / V0≥1.12, and V0≥135Nm 3 / h.

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