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

Abstract

A non-oriented electrical steel sheet with excellent fatigue performance, comprising, in addition to Fe and unavoidable impurities, the following chemical elements in percentage by mass: 0<C≤0.0025％; Si: 3.10-3.80%; Mn: 0.14-0.95%; Al: 0.25-1.05%; and Ca: 0.0003-0.01%, wherein the number of MgO·Al2O3 spinel-type inclusions having a size of 1.5 μm or more in the non-oriented electrical steel sheet is not more than 7 pieces / mm2. The non-oriented electrical steel sheet has excellent fatigue performance, and can meet the requirements of repeated startup and stable operation of a new energy automobile driving motor under complex working conditions without deformation and breakage. Moreover, when the non-oriented electrical steel sheet is used as a stator material, the non-oriented electrical steel sheet has the characteristic of low iron loss at high frequencies after stress relief annealing.

Description

Non-oriented electrical steel sheet with excellent 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] In recent years, with the increasing global demand for energy conservation, environmental protection and low carbon emissions, traditional fuel vehicles are gradually being replaced by new energy electric vehicles. The core components of electric vehicles, drive motors, require high efficiency, lightweight, high speed and high reliability.

[0003] Non-oriented electrical steel sheet is an excellent soft magnetic material widely used in various motor cores. To accommodate high speeds and high stability, rotor fatigue strength is increasingly demanded. From a motor design perspective, to improve efficiency and reduce magnetic flux leakage, the width of the magnetic shielding bridge is becoming increasingly thinner. This also requires high material strength to ensure sufficient stability and safety during repeated rotor operation, preventing deformation, fracture, sudden stoppages, and other abnormal operating conditions. To achieve higher motor power, the non-oriented silicon steel used in the stator core must exhibit low high-frequency iron loss to reduce energy consumption.

[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 with excellent fatigue performance and a method for manufacturing the same.

[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 fatigue performance. This non-oriented electrical steel sheet possesses excellent fatigue performance, enabling it to meet the requirements of repeated startups and stable operation of new energy vehicle drive motors under complex operating conditions without deformation or fracture. Furthermore, when used as a stator material, this non-oriented electrical steel sheet exhibits low iron loss at high frequencies after stress relief annealing.

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

[0009] C≤0.0025%, Si: 3.10-3.80%, Mn: 0.14-0.95%, Al: 0.25-1.05%, Ca: 0.0003%-0.01%;

[0010] The number of MgO-Al2O3 spinel inclusions with a size of 1.5 μm or more in the non-oriented electrical steel sheet is no more than 7 per mm 2 .

[0011] Preferably, the number of MgO﹒Al2O3 spinel type inclusions with a size of 1.5 μm or more in the non-oriented electrical steel sheet disclosed herein is no more than 5 per mm. 2 .

[0012] More preferably, the number of MgO﹒Al2O3 spinel type inclusions with a size of 1.5 μm or more in the non-oriented electrical steel sheet disclosed herein is no more than 3 / mm 2 .

[0013] Preferably, the mass percentage of each chemical element in the non-oriented electrical steel sheet disclosed herein is:

[0014] C≤0.0025%, Si: 3.10-3.80%, Mn: 0.14-0.95%, Al: 0.25-1.05%, Ca: 0.0003%-0.01%; the balance is Fe and unavoidable impurities.

[0015] Preferably, the non-oriented electrical steel sheet of the present disclosure further contains Ge, Bi and / or REM, and in terms of mass percentage, 0<Ge≤0.02%, 0<Bi≤0.01% and / or REM: 0.0004-0.015%.

[0016] Preferably, the non-oriented electrical steel sheet of the present disclosure further contains Sn and / or Sb, and the total amount of Sn and Sb is 0.0055%-0.15% by mass.

[0017] Preferably, the non-oriented electrical steel sheet of the present disclosure further contains at least one of Ni, Co, Zr, Nb, Cu and Cr, and the total mass percentage of the at least one of Ni, Co, Zr, Nb, Cu and Cr is 0.01-2.5%.

[0018] Preferably, in the non-oriented electrical steel sheet of the present disclosure, unavoidable impurities include P, S, N, Ti and O, and, in terms of mass percentage, P≤0.025%, S≤0.0025%, N≤0.0035%, Ti≤0.002%, and O≤0.002%.

[0019] Preferably, the fatigue strength of the non-oriented electrical steel sheet of the present disclosure at 25° C. before stress relief annealing is ≥ 455 MPa.

[0020] When the room temperature (25°C) fatigue strength of the non-oriented electrical steel sheet of the present invention is 1×10 7When subjected to a stress of no less than 455 MPa under repeated load cycles, this high fatigue strength non-oriented silicon steel can meet the material fatigue performance requirements of drive motor rotors under complex operating conditions, repeated starts and stops, and high speeds. This is particularly true for the rotor magnetic bridges in permanent magnet motors, where the width of the bridges is increasingly narrow to limit magnetic leakage. The non-oriented silicon steel used in these rotors possesses sufficiently high fatigue strength to prevent deformation or fracture under the centrifugal forces generated by high-speed rotation, ensuring stable and efficient operation.

[0021] Preferably, in the non-oriented electrical steel sheet of the present disclosure, after stress relief annealing, the grain structure with a size of 115 μm or more in the steel sheet exceeds 95%.

[0022] Preferably, the iron loss P of the non-oriented electrical steel sheet disclosed in the present invention after stress relief annealing is 1.0 / 400 ≤12.5W / kg.

[0023] The present disclosure also provides a method for manufacturing a non-oriented electrical steel sheet, comprising the steps of smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, continuous annealing, and applying an insulating coating. In the RH refining step, the MgO content in the refined slag is ≤5 wt%; Ca is added to modify inclusions in the molten steel, gradually transforming MgO﹒Al2O3 spinel inclusions into CaO﹒MgO﹒Al2O3 composite inclusions; and the circulating air volume V satisfies the following conditions: 140≤V≤245-1.6×T×[Al] 2 , where [Al] represents the Al content in the molten steel (substitute the value before the percentage sign for the mass percentage of the Al element in the molten steel), and T represents the aluminum deoxidation time in minutes during the RH refining process (substitute the value before the min unit sign).

[0024] 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.

[0025] 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 900° C. and the holding time is 5 minutes.

[0026] In the method of the present disclosure, cold rolling may be performed using a single cold rolling process or a double cold rolling process.

[0027] Preferably, in the method disclosed herein, during the continuous annealing step, the holding temperature is 720-850°C and the holding time is 10-75 seconds. Under the above-mentioned continuous annealing process conditions, high tensile strength and fatigue performance can be achieved through grain refinement while also maintaining the high-frequency and low iron loss properties of non-oriented silicon steel.

[0028] Preferably, the method of the present disclosure further comprises a stress relief annealing step after the steps of continuous annealing and coating the insulating coating, and in the stress relief annealing step, the annealing temperature is 745-855° C. and the holding time is 60-180 min.

[0029] The non-oriented electrical steel sheets produced using the disclosed method exhibit excellent fatigue performance, enabling them to meet the requirements of repeated startups and stable operation of new energy vehicle drive motors under complex operating conditions without deformation or fracture. Furthermore, after stress-relief annealing, the non-oriented electrical steel sheets exhibit high-frequency and low iron loss characteristics, making them suitable for use as stator materials. DETAILED DESCRIPTION

[0030] 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.

[0031] As used herein, the term "and / or" refers to and encompasses any and all possible combinations of more than one of the listed items.

[0032] In this paper, the number of MgO﹒Al2O3 spinel 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 MgO﹒Al2O3 oxides with a size of 1.5μm or more in the field of view was counted and expressed in units of "pieces / mm 2 ” Calculate the distribution density.

[0033] In this paper, fatigue strength was measured according to ISO 1099-2006 Metallic materials fatigue test method of axial force control, and the test environment temperature was 25±5℃.

[0034] In this paper, the grain size distribution was statistically analyzed according to the national standard "GB / T 36165-2018 Determination of average grain size of metals - Electron backscatter diffraction (EBSD) method".

[0035] In this paper, the iron loss P 1.0 / 400 (The iron loss value at the excitation frequency of 400Hz and magnetic flux density of 1.0T) is measured using the square circle method of the standard "GB / T10129-2019 Measurement method of medium frequency magnetic properties of electrical steel strip (sheet)".

[0036] In the non-oriented electrical steel sheet disclosed herein, the design principles of each chemical element are as follows:

[0037] C: In the non-oriented electrical steel sheets of the present disclosure, carbon is a harmful element, forming excessive carbides and causing deterioration in iron loss. However, since C is an essential element in steel, its content cannot be zero. In the present disclosure, it is desirable to control its upper limit, with the lower the content, the better. Therefore, in the non-oriented electrical steel sheets of the present disclosure, the mass percentage of C is controlled to no more than 0.0025%.

[0038] Si: In the non-oriented electrical steel sheet disclosed herein, Si is the main alloying element in electrical steel, which can increase the resistivity of the steel sheet and reduce the iron loss of the material. At the same time, silicon is dissolved in the matrix to improve the strength and fatigue limit of the steel sheet. When the Si content is lower than 3.1%, the effect on improving the strength of the steel sheet is limited, and the fatigue strength of the material cannot be guaranteed to be above 455 MPa. When the Si content exceeds 3.8%, the steel sheet will become brittle, making it difficult to process. Therefore, in the non-oriented electrical steel sheet disclosed herein, the mass percentage of Si is controlled between 3.10-3.80%, preferably between 3.32-3.80%.

[0039] Mn: In the non-oriented electrical steel sheet disclosed herein, Mn increases the material's resistivity, thereby reducing iron loss. Furthermore, Mn combines with residual S in the steel to form MnS, improving the morphology of precipitates in the steel. However, when Mn addition exceeds 0.95%, the iron loss reduction effect is limited and the magnetic induction deteriorates. Therefore, in the non-oriented electrical steel sheet disclosed herein, the mass percentage of Mn is controlled between 0.14% and 0.95%, preferably between 0.25% and 0.62%.

[0040] Al: In the non-oriented electrical steel sheet disclosed herein, Al can increase the material's resistivity and reduce iron loss. To achieve this iron loss reduction, the Al addition generally needs to exceed 0.25%. However, excessive Al addition can increase MgO and Al₂O₃ inclusions in the steel, degrading the product's electromagnetic and fatigue properties. It can also increase surface defects during production. Therefore, in the non-oriented electrical steel sheet disclosed herein, the Al content is controlled within a range of 0.25-1.05% by weight, preferably 0.35-0.90%.

[0041] Ca: In the nonoriented electrical steel sheet disclosed herein, the addition of a calcium alloy during the RH refining process can improve the characteristics and distribution of inclusions in the molten steel. This improves the properties and distribution of MgO / Al2O3 spinel inclusions, particularly by gradually transforming them into low-melting-point CaO / MgO / Al2O3 composite inclusions, thus facilitating their removal. However, the amount of Ca added should not be too high, as this will result in the formation of a large number of CaO, Al2O3, and SiO2 inclusions, leading to poor magnetic properties. Therefore, in the nonoriented electrical steel sheet disclosed herein, the mass percentage of Ca is controlled between 0.0003% and 0.01%, preferably between 0.0005% and 0.01%.

[0042] In the non-oriented electrical steel sheets disclosed herein, MgO﹒Al2O3 spinel inclusions are hard and have a high melting point, significantly damaging the fatigue performance of the steel sheets. This is especially true for large inclusions larger than 1.5 μm. Under repeated alternating loads, stress and strain concentrations can occur around these large inclusions, becoming a significant source of fatigue cracking. The inventors have discovered that when the number of MgO﹒Al2O3 spinel inclusions larger than 1.5 μm in a non-oriented electrical steel sheet does not exceed 7 per mm, the fatigue life of the steel sheet will be significantly improved. 2 When the temperature is 0.5000°, the non-oriented electrical steel sheet can have excellent fatigue properties.

[0043] In order to further improve the properties of the non-oriented electrical steel sheet disclosed herein, appropriate amounts of Ge, Bi and rare earth elements (REM) may be preferably added to the steel.

[0044] Ge: In the non-oriented electrical steel sheet disclosed herein, Ge can increase the material's resistivity, improve the annealed sheet's texture, reduce iron loss, and inhibit oxidation during the annealing process. However, for cost considerations, the Ge addition level should not exceed 0.02%. Therefore, in the non-oriented electrical steel sheet disclosed herein, the Ge content by weight is controlled within the range of 0 < Ge ≤ 0.02%.

[0045] Bi: In the non-oriented electrical steel sheets disclosed herein, adding an appropriate amount of Bi can improve the steel's texture and enhance its magnetic induction. However, excessive Bi content can lead to severe grain boundary segregation and refine the grain structure. Therefore, in the non-oriented electrical steel sheets disclosed herein, the mass percentage of Bi is controlled within the range of 0 < Bi ≤ 0.01%.

[0046] REM: In the nonoriented electrical steel sheets disclosed herein, rare earth elements (REM) easily combine with harmful elements such as sulfur and oxygen. The appropriate addition of REM can purify the molten steel, promote the growth of fine inclusions, and improve the recrystallized grain structure of the finished steel sheet. However, excessive REM content can lead to surface defects. Therefore, in the nonoriented electrical steel sheets disclosed herein, the REM content is controlled to be between 0.0004% and 0.015% by weight. In some more preferred embodiments, the REM content can be controlled to be between 0.0006% and 0.01% by weight.

[0047] In order to further improve the properties of the non-oriented electrical steel sheet disclosed herein, the steel may further contain Sn element and / or Sb element.

[0048] Sn and Sb are grain boundary segregating elements that inhibit oxidation within the steel sheet and improve the texture of the finished annealed microstructure. However, excessive addition of Sn or Sb can increase surface defects in the steel. Therefore, in the non-oriented electrical steel sheet disclosed herein, the combined content of Sn and Sb is controlled between 0.0055% and 0.15% by weight.

[0049] In order to further improve the performance of the non-oriented electrical steel sheet disclosed herein, the steel may further contain at least one of Ni, Co, Zr, Nb, Cu, and Cr, and the total weight percentage of the elements contained is controlled to be 0.01-2.5%. In the non-oriented electrical steel sheet disclosed herein, Ni, Co, Zr, Nb, Cu, and Cr elements can increase the resistivity of the steel sheet, reduce losses, and enhance the material strength. When adding, one or more of these elements can be selected, and the total amount of these elements can be controlled to be between 0.01-2.5%.

[0050] In the non-oriented electrical steel sheet disclosed herein, P, S, N, Ti and O 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.

[0051] 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 0.025% by weight. In some more preferred embodiments, the P content can be controlled to be below 0.02% by weight.

[0052] S: In the non-oriented electrical steel sheet of the present disclosure, S is a harmful impurity element. If the residual S content is too high, a large amount of sulfide precipitates will form, hindering grain growth and causing deterioration in the iron loss of the steel sheet. Therefore, in the non-oriented electrical steel sheet of the present disclosure, the mass percentage of S can be controlled to below 0.0025%.

[0053] N: In the non-oriented electrical steel sheets of the present disclosure, N is a harmful impurity element that combines with various elements in the steel to form a large number of fine nitrides, degrading magnetic properties. Therefore, in the non-oriented 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.

[0054] Ti: In the non-oriented electrical steel sheets disclosed herein, Ti is a harmful impurity element in non-oriented silicon steel. Ti reacts with carbon and nitrogen to precipitate titanium carbide and titanium nitride, which pin grain boundaries, hinder grain growth during recrystallization, and degrade iron loss. Therefore, in the non-oriented electrical steel sheets disclosed herein, the Ti content can be controlled to below 0.002% by weight. In some more preferred embodiments, the Ti content can be controlled to below 0.0015% by weight.

[0055] O: In the non-oriented electrical steel sheets disclosed herein, oxygen is a harmful impurity element and requires strict control during the steelmaking process. Otherwise, a large amount of oxide inclusions will form, degrading electromagnetic properties. Therefore, in the non-oriented electrical steel sheets disclosed herein, the mass percentage of O can be controlled to below 0.002%.

[0056] In a preferred embodiment, the non-oriented electrical steel sheet of the present disclosure has a grain size of 115 μm or more in the steel sheet after stress relief annealing, and the iron loss P is greater than 95%. 1.0 / 400 ≤12.5W / kg. This non-oriented electrical steel sheet has the characteristics of high frequency and low iron loss, and is suitable for use as a stator material.

[0057] The present disclosure also provides a method for manufacturing a non-oriented electrical steel sheet, comprising the steps of smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, continuous annealing, and coating an insulating coating. In the RH refining step, MgO in the refined slag is ≤5 wt%; Ca is added to modify inclusions in the molten steel, gradually transforming MgO﹒Al2O3 spinel inclusions into CaO﹒MgO﹒Al2O3 composite inclusions; and the circulating air volume V satisfies the following conditions: 140≤V≤245-1.6×T×[Al] 2, where [Al] represents the Al content in the molten steel (substitute the value before the percentage sign for the mass percentage of the Al element in the molten steel), and T represents the aluminum deoxidation time in minutes during the RH refining process (substitute the value before the min unit sign).

[0058] During the RH refining process of non-oriented silicon steel, refined slag is added. To reduce ladle lining wear, the slag contains a certain amount of MgO. For non-oriented silicon steel containing Al, during aluminum deoxidation and aluminum alloying, the molten steel circulates, and some of the refined slag is drawn into the molten steel. At this point, the MgO in the slag reacts with the acid-soluble aluminum and Al2O3 inclusions in the molten steel, forming harmful inclusions such as MgO-Al2O3 spinel.

[0059] However, as mentioned above, MgO﹒Al2O3 spinel inclusions are hard and have a high melting point, significantly damaging the fatigue performance of steel plates, especially large inclusions larger than 1.5μm. Under repeated alternating loads, stress and strain concentrations can occur around these large inclusions, becoming a significant source of fatigue cracks. Therefore, to achieve non-oriented silicon steel with excellent fatigue performance, this disclosure not only employs a specific chemical composition design but also employs a specific process to control the presence of large, harmful MgO﹒Al2O3 inclusions in the steel.

[0060] In the manufacturing method disclosed herein, the MgO content in the refined slag in the RH refining step is controlled to be no more than 5 wt %, which can reduce the Mg content from the source, thereby reducing the reaction between MgO and acid-soluble aluminum in molten steel.

[0061] Furthermore, in the manufacturing method disclosed herein, calcium is added during the refining process to modify the inclusions in the molten steel, gradually transforming the MgO﹒Al2O3 spinel inclusions into low-melting-point CaO﹒MgO﹒Al2O3 composite inclusions, which are easily transported with the molten steel and removed by adsorption by the top slag.

[0062] In addition, in the manufacturing method disclosed in the present invention, the refining process adopts a suitable circulating air blowing volume V (its unit parameter is Nm 3 The circulating air volume cannot be too low, otherwise the molten steel will not flow sufficiently, the steel-slag reaction will not be sufficient, and the efficiency of inclusion removal by floating up will be low. The circulating air volume cannot be too high either, especially for non-oriented silicon steel containing Al. Too high a volume will cause severe slag roll-up and will not be conducive to the aggregation, growth, and floating removal of MgO and Al2O3 inclusions. The range of the circulating air volume V used in the method disclosed herein is closely related to the Al content and the aluminum deoxidation treatment time, and satisfies the following conditions: 140≤V≤245-1.6×T×[Al] 2, where [Al] represents the total aluminum content in the molten steel, in wt.%, and T represents the aluminum deoxidation time during the RH refining process, in min.

[0063] By using the above technical means, it can be achieved that the number of MgO﹒Al2O3 spinel inclusions with a size of 1.5μm or more in non-oriented electrical steel sheet products does not exceed 7 / mm 2 .

[0064] The non-oriented electrical steel sheet and the manufacturing method thereof disclosed in the present invention have the following advantages and beneficial effects:

[0065] The non-oriented electrical steel sheet disclosed herein has excellent fatigue properties. In some embodiments, its room temperature fatigue strength is 1×10 7 The fatigue strength of the non-oriented electrical steel sheet disclosed herein is not less than 455 MPa under repeated stress cycles. This ensures that the rotor does not deform or break under the centrifugal force generated by high-speed rotation, ensuring stable and efficient operation. This meets the requirements of new energy vehicle drive motors for repeated startup and stable operation under complex operating conditions without deformation or breakage.

[0066] The non-oriented electrical steel sheet disclosed herein, when used as a stator material, has the characteristic of low high-frequency iron loss after stress relief annealing. In some embodiments, after stress relief annealing, the grain size of the steel sheet with a grain size of 115 μm or more accounts for more than 95%, the grains are fully grown, and the iron loss P is 1.0 / 400 Significantly decreased (P 1.0 / 400 ≤12.5W / kg).

[0067] 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.

[0068] Examples 1-10 and Comparative Examples 1-5

[0069] The non-oriented electrical steel sheets of Examples 1-10 and Comparative Examples 1-5 were prepared by the following steps:

[0070] (1) Blast furnace molten iron undergoes molten iron pretreatment and converter smelting.

[0071] (2) Decarburization, deoxidation, and alloying are performed through RH refining. In the RH refining step: MgO in the incoming slag is controlled to be ≤5wt%; Ca is added to modify the inclusions in the molten steel, gradually transforming the MgO﹒Al2O3 spinel inclusions into CaO﹒MgO﹒Al2O3 composite inclusions; and the circulating air volume V is controlled to meet the following conditions: 140≤V≤245-1.6×T×[Al] 2Wherein [Al] is the total aluminum content in the molten steel, expressed in wt.%, and T is the aluminum deoxidation time during RH refining, expressed in minutes. The MgO content in the refined slag, the circulating air volume V, and the aluminum deoxidation time T for each of the Examples and Comparative Examples are shown in Table 2.

[0072] (3) After refining, the molten steel is continuously cast to obtain a continuous casting slab. The chemical element compositions of the continuous casting slabs of each embodiment and comparative example are shown in Table 1-1 and Table 1-2.

[0073] (4) Hot rolling: The heating temperature of the slab is 1150℃, the final rolling temperature of the coil is 800℃, and the coiling temperature is 625℃ to obtain a hot-rolled plate with a thickness of 2.0-2.5mm.

[0074] (5) Normalizing annealing: The normalizing holding temperature is 900℃ and the holding time is 5 minutes.

[0075] (6) Cold rolling to a finished product thickness of 0.25-0.30 mm. The steel coils of Examples 3 and 4 were subjected to a double cold rolling process, while the remaining Examples and Comparative Examples were subjected to a single cold rolling process.

[0076] (7) Continuous annealing and coating with insulating coating: The holding temperature of continuous annealing is 720-850°C and the holding time is 10-75 seconds. The holding temperatures and holding times of the embodiments and comparative examples are shown in Table 2.

[0077] (8) Stress relief annealing: the annealing temperature is 745°C-855°C, and the holding time is 60-180 min. The annealing temperature and holding time of each embodiment and comparative example are shown in Table 2.

[0078] 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 1-5.

[0079] Table 1-1. (wt%, the balance is Fe and other inevitable impurities)

[0080] Table 1-2. (wt%, the balance is Fe and other inevitable impurities)

[0081] Table 2 lists the specific process parameters in each step of the manufacturing method of the non-oriented electrical steel sheets of Examples 1-10 and the comparative steel sheets of Comparative Examples 1-5.

[0082] Table 2.

[0083] Next, samples of the non-oriented electrical steel sheets of Examples 1-10 and the comparative steel sheets of Comparative Examples 1-5 were taken and tested. The test results are listed in Table 3 below. The relevant performance test methods are as follows:

[0084] 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 can be set as follows: test environment temperature 25±5℃, sinusoidal control waveform, stress ratio R=0.1, frequency: 20-30Hz, maximum number of cycles 1.0×10 7 Second-rate.

[0085] MgO﹒Al2O3 inclusion count: 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 the thickness of the steel plate, and mechanically or electrochemically polished. The specimens were then photographed under a backscattered electron image to confirm the presence of Al2O3 oxide inclusions and count them. Over 20 consecutive views were taken, and the number of MgO﹒Al2O3 oxide inclusions larger than 1.5μm in size was counted. The number was expressed as "individuals / mm 2 ” Calculate the distribution density.

[0086] Grain size: Grain size distribution is calculated according to the national standard "GB / T 36165-2018 Metals—Determination of Average Grain Size—Electron Backscatter Diffraction (EBSD) Method." 20 x 20 mm specimens are randomly cut from stress-relief annealed samples, ground to half the thickness of the steel plate, and mechanically or electrochemically polished. The field of view contains at least 500 grains. The grain size distribution is calculated, and the proportion of grains larger than 115 μm is calculated.

[0087] Iron loss P 1.0 / 400 (Iron loss value at magnetic flux density of 1.0T and excitation frequency of 400Hz): Measured using the square circle method of the standard "GB / T10129-2019 Measurement method of medium frequency magnetic properties of electrical steel strip (sheet)".

[0088] Table 3.

[0089] It can be seen from Table 3 above that in the non-oriented electrical steel sheets of Examples 1-10 of the present disclosure, the number of MgO﹒Al2O3 spinel type inclusions with a size of 1.5 μm or more does not exceed 5 / mm 2 The fatigue strength at room temperature is higher than 465MPa, and the high-frequency iron loss P after stress relief annealing is 1.0 / 400Therefore, the non-oriented electrical steel sheets of Examples 1-10 have excellent fatigue properties, can meet the requirements of repeated starting and stable operation of new energy vehicle drive motors under complex working conditions without deformation or fracture, and can be used as stator materials after stress relief annealing.

[0090] In contrast, the MgO content of the refined slag in Comparative Examples 1 and 2 was too high, and the circulating air blowing volume was too small, resulting in a high density of MgO﹒Al2O3 oxide inclusions in the final product. 7 The fatigue strength under these conditions is less than 455MPa.

[0091] The chemical composition of the steels of Comparative Examples 3-5 is low in Si, Al or Mn, resulting in low final fatigue strength and high iron loss.

[0092] All publications, patent applications, patents, and other references mentioned in this disclosure are incorporated by reference in their entirety.

[0093] 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. A 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 ≤ 0.0025%, Si: 3.10 - 3.80%, Mn: 0.14 - 0.95%, Al: 0.25 - 1.05%, Ca: 0.0003% - 0.01%; The number of MgO﹒Al2O3 spinel type inclusions with a size of 1.5 μm or more in the non-oriented electrical steel sheet is no more than 7 pieces / mm 2 , preferably no more than 5 / mm 2 , preferably no more than 3 / mm 2 .

2. The non-oriented electrical steel sheet according to claim 1, characterized in that: The mass percentages of the chemical elements of the non-oriented electrical steel sheet are: 0 < C ≤ 0.0025%, Si: 3.10 - 3.80%, Mn: 0.14 - 0.95%, Al: 0.25 - 1.05%, Ca: 0.0003% - 0.01%; 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 further contains Ge, Bi, and / or REM, and, by mass percentage, 0 < Ge ≤ 0.02%, 0 < Bi ≤ 0.01%, and / or REM: 0.0004 - 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 further contains Sn and / or Sb, and, by mass percentage, the total amount of Sn and Sb is 0.0055% - 0.15%.

5. The non-oriented electrical steel sheet according to any one of claims 1 to 4, characterized in that: The non-oriented electrical steel sheet further contains at least one of Ni, Co, Zr, Nb, Cu, and Cr, and the total mass percentage thereof is 0.01 - 2.5%.

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, Ti, and O, and, by mass percentage, P ≤ 0.025%, S ≤ 0.0025%, N ≤ 0.0035%, Ti ≤ 0.002%, O ≤ 0.002%.

7. The non-oriented electrical steel sheet according to any one of claims 1 to 6, characterized in that: The fatigue strength of the non-oriented electrical steel sheet at 25°C before stress relief annealing is ≥ 455 MPa.

8. The non-oriented electrical steel sheet according to any one of claims 1 to 7, characterized in that: After stress relief annealing, the grain structure with a size of 115 μm or more in the steel sheet of the non-oriented electrical steel sheet exceeds 95%.

9. The non-oriented electrical steel sheet according to any one of claims 1 to 8, characterized in that: The iron loss P of the non-oriented electrical steel sheet after stress relief annealing 1.0 / 400 ≤12.5W / kg.

10. A method for manufacturing the non-oriented electrical steel sheet 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 coating an insulating coating, characterized in that In the RH refining step: MgO in the refining slag is ≤5wt%; Ca is added to modify the inclusions in the molten steel, so that the MgO﹒Al2O3 spinel inclusions are gradually transformed into CaO﹒MgO﹒Al2O3 composite inclusions; the circulating air volume V satisfies: 140≤V≤245-1.6×T×[Al] 2 , where [Al] represents the Al content in the molten steel (substitute the value before the percentage sign of the mass percentage of the Al element in the molten steel), and T represents the aluminum deoxidation time in minutes during the RH refining process (substitute the value before the min unit symbol).

11. The method according to claim 10, characterized in that In the continuous annealing step, the holding temperature is 720 - 850°C, and the holding time is 10 - 75 s.

12. The method according to claim 10 or 11, characterized in that The method further includes a stress relief annealing step after the continuous annealing and insulating coating steps, and, in the stress relief annealing step, the annealing temperature is 745 - 855°C, and the holding time is 60 - 180 min.

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