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

Abstract

The invention discloses a non-oriented electrical steel with excellent fatigue performance, which contains Fe and inevitable impurities, and further contains the following chemical elements in percentage by mass: less than or equal to 0.0025% of C, 3.1-3.8% of Si, 0.14-0.95% of Mn, 0.25-1.05% of Al, 0.0003-0.01% of Ca, less than or equal to 0.015% of P, less than or equal to 0.015% of S and the balance of Fe. In the non-oriented electrical steel, the number of MgO.Al2O3 spinel type inclusions with the size of 1.5 microns or above is not more than 7 / mm < 2 >. Correspondingly, the invention also provides a manufacturing method of the non-oriented electrical steel with excellent fatigue performance. The non-oriented electrical steel has excellent fatigue performance, can meet the requirement that a new energy automobile driving motor is repeatedly started and stably runs under complex working conditions, and does not deform or break. And when the material is used as a stator material, the material has the characteristic of low high-frequency iron loss after stress relief annealing.

Description

Technical Field

[0001] The present invention 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, light weight, high speed and high reliability.

[0003] Non-oriented electrical steel is an excellent soft magnetic material, widely used in various motor cores. In order to adapt to high speed and high stability, higher and higher requirements are placed on the fatigue strength of the rotor. From the perspective of motor design, in order to improve motor efficiency and reduce magnetic leakage, the width of the magnetic bridge is becoming thinner and thinner. The material also requires high strength to ensure sufficient stability and safety of the rotor during repeated operation, without deformation, fracture, or sudden cessation of operation. From the perspective of high power motor, non-oriented silicon steel used as the core stator material is required to have 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. Summary of the invention

[0006] One of the purposes of the present invention is to provide a non-oriented electrical steel sheet with excellent fatigue performance, which can meet the requirements of repeated starting and stable operation of new energy vehicle drive motors under complex working conditions without deformation or fracture. When used as a stator material, it has the characteristics of low high-frequency iron loss after stress relief annealing.

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

[0008] C≤0.0025%, Si: 3.1-3.8%, Mn: 0.14-0.95%, Al: 0.25-1.05%, Ca: 0.0003%-0.01%;

[0009] The number of MgO﹒Al2O3 spinel inclusions with a size of 1.5 μm or more in the non-oriented electrical steel is no more than 7 / mm 2 .

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

[0011] C≤0.0025%, Si: 3.1-3.8%, Mn: 0.14-0.95%, Al: 0.25-1.05%, Ca: 0.0003%-0.01%; the balance is Fe and unavoidable impurities.

[0012] The number of MgO﹒Al2O3 spinel inclusions with a size of 1.5 μm or more in the non-oriented electrical steel is no more than 7 / 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 of the present invention, carbon is a harmful element, which will form excessive carbides and cause iron loss degradation. Therefore, the present invention controls the carbon content to not exceed 0.0025%. However, since the C element is an element that must be contained in steel, its content will not be 0. In the present invention, it is expected to control its upper limit, and it is expected that its content is as low as possible.

[0015] Si: In the non-oriented electrical steel described in the present invention, Si element is the main alloying element in the electrical steel, which can increase the resistivity of the steel plate and reduce the iron loss of the material. At the same time, silicon solid solution in the matrix can improve the strength and fatigue limit of the steel plate. When the Si element content is lower than 3.1%, the improvement of the strength of the steel plate is limited, and the fatigue strength of the material cannot be guaranteed to be above 455MPa; when the Si element content exceeds 3.8%, the steel plate will become brittle, making it difficult to process. Therefore, in the non-oriented electrical steel described in the present invention, the mass percentage of Si element is controlled between 3.1-3.8%.

[0016] Mn: In the non-oriented electrical steel of the present invention, the Mn element can increase the resistivity of the material, thereby reducing the iron loss, and at the same time combine with the residual S element in the steel to form MnS, improving the morphology of the precipitates in the steel. However, when the addition amount of the Mn element exceeds 0.95%, the iron loss is limited and the magnetic induction will deteriorate. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of the Mn element is controlled between 0.14-0.95%.

[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. In order to achieve the effect of reducing the iron loss, the addition amount is generally more than 0.25%. However, when the addition amount of Al element is too high, on the one hand, it will increase the MgO﹒Al2O3 type inclusions in the steel, deteriorate the electromagnetic properties and fatigue properties of the product, and on the other hand, the surface steel defects in the production process will also increase. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of Al element is controlled between 0.25-1.05%.

[0018] Ca: In the non-oriented electrical steel of the present invention, adding calcium alloy during RH refining can improve the characteristics and distribution of inclusions in the molten steel, especially for MgO﹒Al2O3 spinel inclusions, which gradually transforms them into low-melting-point CaO﹒MgO﹒Al2O3 composite inclusions, which is conducive to the removal of inclusions. However, the addition amount should not be too high, otherwise a large amount of CaO, Al2O3, and SiO2 inclusions will be formed, resulting in poor magnetic properties. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of Ca element is controlled between 0.0003% and 0.01%.

[0019] For the non-oriented electrical steel with excellent fatigue performance described in the present invention, MgO﹒Al2O3 spinel inclusions are hard and have a high melting point, which greatly harms the fatigue performance of the steel plate, especially large particle 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 inclusions, becoming one of the important crack sources of fatigue fracture. Therefore, the number of MgO﹒Al2O3 spinel inclusions with a size of more than 1.5 microns in the non-oriented electrical steel control steel plate described in the present invention does not exceed 7 / mm 2 .

[0020] Furthermore, in the non-oriented electrical steel of the present invention, it also contains at least one of: 0<Ge≤0.02wt%, 0<Bi≤0.01wt%, and REM: 0.0004-0.015wt%.

[0021] 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, appropriate amounts of Ge, Bi and rare earth elements may be preferably added to the steel. Among them:

[0022] Ge: In the non-oriented electrical steel of the present invention, Ge element can increase the resistivity of the material, improve the texture of the annealed plate, reduce the iron loss, and inhibit the oxidation of the material during the annealing process. However, considering the cost, the addition amount should not exceed 0.02%. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of Ge element is controlled between 0<Ge≤0.02%.

[0023] Bi: In the non-oriented electrical steel of the present invention, adding Bi in an appropriate amount can improve the texture of the steel plate and increase the magnetic induction. However, when the Bi content is too high, it will cause serious grain boundary segregation and refine the grain structure. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of Bi is controlled between 0<Bi≤0.01%.

[0024] 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. Adding a proper amount 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 REM is too high, it will cause steel defects on the surface of the steel plate. Therefore, in the non-oriented electrical steel described in the present invention, the mass percentage of REM is controlled between 0.0004-0.015%. In some more preferred embodiments, the mass percentage of REM can be controlled between 0.0006-0.01%.

[0025] Furthermore, in the non-oriented electrical steel of the present invention, it also contains at least one of Sn and Sb, and satisfies Sn+Sb: 0.0055%-0.15wt%.

[0026] 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, the steel may also contain Sn and Sb elements.

[0027] Sn and Sb are grain boundary segregation elements, which can inhibit oxidation in the steel plate and improve the favorable texture of the finished annealed structure, but excessive addition of Sn and Sb can 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 Sn and Sb is controlled between 0.0055% and 0.15%.

[0028] Furthermore, the non-oriented electrical steel of the present invention further contains at least one of Ni, Co, Zr, Nb, Cu and Cr, and the total mass percentage of the at least one of the at least one of the Ni, Co, Zr, Nb, Cu and Cr is controlled within a range of 0.01-2.5%.

[0029] In the non-oriented electrical steel of the present invention, Ni, Co, Zr, Nb, Cu and Cr elements 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 between 0.01-2.5%.

[0030] Furthermore, in some more preferred embodiments of the non-oriented electrical steel of the present invention, the number of MgO﹒Al2O3 spinel type inclusions with a size of 1.5 μm or more in the non-oriented electrical steel does not exceed 5 / mm. 2 .

[0031] Furthermore, among the inevitable impurities of the non-oriented electrical steel of the present invention, P≤0.025%, S≤0.0025%, N≤0.0035%, Ti≤0.002%, and O≤0.002%.

[0032] In the non-oriented electrical steel of the present invention, P, S, N, Ti and O 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:

[0033] 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 0.025%, and in some more preferred embodiments, the mass percentage of the P element can be controlled to be below 0.02%.

[0034] S: In the non-oriented electrical steel of the present invention, S element is a harmful impurity element. If the residual content of S element is too high, a large amount of sulfide precipitates will be formed, which will hinder the growth of grains and lead to the deterioration of iron loss of steel plates. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of S element can be controlled to be less than 0.0025%.

[0035] N: In the non-oriented electrical steel of the present invention, N is a harmful impurity element, which will combine with various elements in the steel to form a large number of fine nitrides, deteriorating the magnetic properties. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of N can be controlled to be less than 0.0035%, and in some more preferred embodiments, the mass percentage of N can be controlled to be less than 0.0030%.

[0036] Ti: In the non-oriented electrical steel of the present invention, the Ti element is a harmful impurity element for the non-oriented silicon steel. It reacts with carbon and nitrogen to precipitate titanium carbide and titanium nitride to pin the grain boundaries, hinder the growth of grains in the recrystallization process, and deteriorate the iron loss. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of the Ti element can be controlled to be less than 0.002%. In some more preferred embodiments, the mass percentage of the Ti element can be controlled to be less than 0.0015%.

[0037] O: In the non-oriented electrical steel of the present invention, oxygen is a harmful impurity element, and the steelmaking process needs to be strictly controlled, otherwise a large amount of oxide inclusions will be formed, which will deteriorate the electromagnetic properties. Therefore, in the non-oriented electrical steel of the present invention, the mass percentage of P element can be controlled to be below 0.002%.

[0038] Furthermore, in the non-oriented electrical steel of the present invention, when it is not subjected to stress relief annealing, its fatigue strength at room temperature (eg, 25° C.) is ≥455 MPa.

[0039] When the room temperature fatigue strength of the non-oriented electrical steel with excellent fatigue performance is 1×10 7 When the pressure is not less than 455MPa under repeated stress cycles, high fatigue strength non-oriented silicon steel can meet the requirements of material fatigue performance for driving motor rotors under complex working conditions of repeated start-stop and high speed. In particular, the rotor magnetic bridge in permanent magnet motors has a narrower and narrower design width to limit magnetic leakage. At this time, the non-oriented silicon steel used as the rotor has a sufficiently high fatigue strength to ensure that the rotor does not deform or break under the centrifugal force generated by high-speed rotation, and operates stably and efficiently.

[0040] Furthermore, in the non-oriented electrical steel of the present invention, after stress relief annealing, the proportion of grains with a size of 115 μm or more in the steel plate exceeds 95%, and the iron loss P 1.0 / 400 ≤12.5W / kg.

[0041] Therefore, in this embodiment, the non-oriented electrical steel after stress relief annealing has the characteristic of low high-frequency iron loss, and thus can be used as a stator material.

[0042] Accordingly, another object of the present invention is to provide a method for manufacturing a non-oriented electrical steel sheet with excellent performance. The non-oriented electrical steel obtained by the method has excellent fatigue performance, can meet the requirements of repeated starting and stable operation of the drive motor of new energy vehicles under complex working conditions without deformation and fracture. At the same time, it also has the characteristics of low high-frequency iron loss after stress relief annealing, so it can be used as a stator material.

[0043] In order to achieve the above-mentioned object of the invention, the present invention proposes a method for manufacturing non-oriented electrical steel, which comprises the steps of: smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, continuous annealing and insulating coating;

[0044] In the RH refining step: MgO in the refining slag is controlled to be ≤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 is controlled to meet the following conditions: 140≤V≤245-1.6×T×[Al] 2 , where [Al] is the total aluminum content in the molten steel, the unit parameter is wt.%, and T is the aluminum deoxidation time during RH refining, the unit parameter is min.

[0045] In the process of manufacturing non-oriented silicon steel, refined slag needs to be added during the RH refining process. At the same time, in order to reduce the loss of ladle lining, a certain amount of MgO will be contained in the slag. For Al-containing non-oriented silicon steel, during aluminum deoxidation and aluminum alloying treatment, the molten steel circulates and the refined slag will be partially drawn into the molten steel. At this time, the MgO in the slag will react with the acid-soluble aluminum and Al2O3 inclusions in the molten steel to generate MgO﹒Al2O3 spinel-type harmful inclusions.

[0046] However, as mentioned above, MgO﹒Al2O3 spinel inclusions are hard and have a high melting point, which greatly harms the fatigue performance of steel plates, especially large particle inclusions with a size of more than 1.5μm. Under repeated alternating loads, stress concentration and strain concentration will occur around the large particle inclusions, becoming one of the important crack sources of fatigue fracture. Therefore, in order to obtain non-oriented silicon steel with excellent fatigue performance, in addition to adopting a specific chemical composition design, the present invention also controls large-sized MgO﹒Al2O3 harmful inclusions in steel through a specific process. Among them:

[0047] In the manufacturing method of the present invention, the MgO content in the refined slag is controlled to be no more than 5wt%, so that the Mg content can be reduced from the source, thereby reducing the reaction between MgO and acid-soluble aluminum in molten steel.

[0048] In addition, in the manufacturing method of the present invention, calcium is added during the refining process to modify the inclusions in the molten steel, so that the MgO﹒Al2O3 spinel inclusions are gradually transformed into low-melting-point CaO﹒MgO﹒Al2O3 composite inclusions, which are easy to flow with the molten steel and be adsorbed and removed by the top slag.

[0049] In addition, in the manufacturing method described in the present invention, the refining process adopts a reasonable circulating air blowing volume V (its unit parameter is Nm 3 / h), 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 floating removal will be low. The circulating air volume cannot be too high either, especially for Al-containing non-oriented silicon steel. Too high a blowing volume will cause serious slag rolling, and will not be conducive to the polymerization and growth of MgO﹒Al2O3 inclusions and their floating removal. The setting range of the circulating air volume V of the present invention is closely related to the Al content and the aluminum deoxidation treatment time, and the specific range satisfies the formula: 140≤V≤245-1.6×T×[Al] 2 , where [Al] is the total aluminum content of the molten steel, in wt.%, and T is the aluminum deoxidation time during the RH refining process, in min.

[0050] Through the above means, the number of MgO﹒Al2O3 spinel inclusions with a size of more than 1.5μm in non-oriented electrical steel products can be controlled to no more than 7 / mm 2In some more preferred embodiments, the number of MgO﹒Al2O3 spinel inclusions with a size of 1.5 μm or more in the non-oriented electrical steel does not exceed 5 / mm 2 .

[0051] Furthermore, in the continuous annealing step of the method for manufacturing non-oriented electrical steel of the present invention, the holding temperature is 720-850° C., and the holding time is 10-75 s.

[0052] Under the above-mentioned continuous annealing process conditions, high tensile strength and fatigue performance can be obtained through grain refinement strengthening, while taking into account the high frequency and low iron loss performance of non-oriented silicon steel.

[0053] Furthermore, after the continuous annealing and insulation coating steps, the method for manufacturing non-oriented electrical steel of the present invention further includes a stress relief annealing step: the annealing temperature is 745° C.-855° C., and the holding time is 60-180 min.

[0054] The non-oriented electrical steel and the method for manufacturing the same according to the present invention have the following advantages and beneficial effects:

[0055] The non-oriented electrical steel of the present invention has excellent fatigue properties. In some embodiments, the room temperature fatigue strength is 1×10 7 The fatigue strength is not less than 455MPa under repeated stress cycles, and it has sufficiently high fatigue strength to ensure that the rotor does not deform or break under the centrifugal force generated by high-speed rotation, and operates stably and efficiently. Therefore, it can meet the requirements of new energy vehicle drive motors for repeated starting and stable operation under complex working conditions without deformation or breakage.

[0056] When the non-oriented electrical steel of the present invention is used as a stator material, it has the characteristics of low high-frequency iron loss after stress relief annealing. In some embodiments, the grain size of 115 μm or more accounts for more than 95%, is fully grown, and the iron loss P 1.0 / 400 Significantly reduced, the maximum value does not exceed 12.5W / kg. DETAILED DESCRIPTION

[0057] 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.

[0058] Examples 1-10 and Comparative Examples 1-5

[0059] The non-oriented electrical steels of Examples 1-10 and Comparative Examples 1-5 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 treatment are carried out in RH refining: MgO in the refining slag is controlled to be ≤5wt%; and 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 is controlled to meet the following conditions: 140≤V≤245-1.6×T×[Al] 2 , wherein [Al] is the total aluminum content in the molten steel, and the unit parameter is wt.%, and T is the aluminum deoxidation time during RH refining, and the unit parameter is min; wherein the MgO content of the refined slag, the circulating air blowing volume V, and the aluminum deoxidation time T in each embodiment and comparative example are as shown in Table 2.

[0062] (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.

[0063] (4) Hot rolling: For example, the slab heating temperature can be 1150°C, the coil final rolling temperature 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.

[0064] (5) Normalization heat treatment: For example, the normalization holding temperature may be 900° C., and the holding time may be 5 min.

[0065] (6) Cold rolling each embodiment and comparative example to a finished product thickness of 0.25-0.30 mm: wherein the steel coils of embodiment 3 and embodiment 4 were subjected to a secondary cold rolling process.

[0066] (7) Continuous annealing and applying insulating coating: The holding temperature of continuous annealing is 720-850°C and the holding time is 10-75s. See Table 2 for the holding temperature and holding time in each embodiment and comparative example.

[0067] (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 in each embodiment and comparative example are shown in Table 2.

[0068] 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 1-5.

[0069] Table 1-1. (wt%, the balance is Fe and inevitable impurities other than P, S, N, Ti, and O)

[0070]

[0071]

[0072] Table 1-2. (wt%, the balance is Fe and inevitable impurities other than P, S, N, and Ti)

[0073]

[0074] Table 2 lists the specific process parameters in each step of the method for manufacturing the non-oriented electrical steel of Examples 1-10 and the comparative steel sheets of Comparative Examples 1-5.

[0075]

[0076]

[0077] 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 1-5 were sampled respectively, and these non-oriented electrical steel sheets were tested, and the test results are listed in the following Table 3. The relevant performance testing methods are as follows:

[0078] Fatigue performance test is carried out according to 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. A servo fatigue testing machine with a maximum capacity of 10kN is used. The test condition parameters can be set as follows: test environment temperature 25±5℃, waveform control according to sine wave, stress ratio R=0.1, frequency: 20-30Hz, maximum number of cycles is 1.0×10 7 Second-rate.

[0079] Statistics of MgO﹒Al2O3 oxide inclusions in non-oriented electrical steel: Statistical analysis was performed using a field emission scanning electron microscope. 20*20mm samples were randomly cut from the base steel plate, ground to 1 / 2 thickness of the steel plate, and mechanically polished or electrochemically polished. Then, photographed and observed under the backscattered electron image to confirm the presence of Al2O3 oxide inclusions and calculate the number. More than 20 fields of view were photographed continuously, and the number of Al2O3 oxides with a size of more than 1.5μm in the field of view was counted, and the unit was "pieces / mm 2 ” Calculate the distribution density.

[0080] The grain size of the steel plate is statistically analyzed according to the national standard "GB / T 36165-2018 Determination of the average grain size of metals - Electron backscatter diffraction (EBSD) method". 20*20mm specimens are randomly cut from the sample after stress relief annealing, ground to 1 / 2 thickness of the steel plate, and mechanically polished or electrochemically polished. The observation field contains at least 500 grains, and the grain size distribution is statistically analyzed, and the proportion of grains larger than 115μm is calculated.

[0081] Iron loss P1.0 / 400 (It represents the iron loss value under 1.0T, 400HZ conditions) Test: Based on the square circle method of the standard "GB / T10129-2019 Measurement method of medium frequency magnetic properties of electrical steel strip (sheet)".

[0082] Table 3.

[0083]

[0084] It can be seen from Table 3 that in Examples 1-10 of the present invention, the chemical composition is controlled, and the MgO content in the slag during the RH refining process and the circulating air blowing volume during the RH refining process are controlled within the design range of the present invention. Therefore, the number of MgO﹒Al2O3 spinel inclusions with a size of more than 1.5 μm in the obtained non-oriented electrical steel does not exceed 5 pieces / mm 2 The fatigue strength at room temperature is higher than 465MPa, and the high-frequency iron loss P 1.0 / 400 All are less than 12.12W / kg. Therefore, it can be ensured that the non-oriented electrical steel has excellent fatigue performance and can meet the requirements of repeated starting and stable operation of new energy vehicle drive motors under complex working conditions without deformation or fracture. After stress relief annealing, it can be used as a stator material.

[0085] In contrast, although the chemical compositions of Comparative Examples 1 and 2 are within the scope of the present invention, the MgO content of the refined slag is relatively high and the circulating air blowing volume is relatively small, resulting in a high inclusion density of MgO﹒Al2O3 oxides in the final product. 7 The fatigue strength under this condition is less than 455MPa.

[0086] The chemical compositions of Comparative Examples 3-5 are low in Si, Al or Mn, which results in low ultimate fatigue strength and high iron loss.

[0087] 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.

[0088] 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.

[0089] 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 fatigue properties, comprising Fe and unavoidable impurities, characterized in that: It also contains the following chemical elements in the following mass percentages: C≤0.0025%, Si: 3.1-3.8%, Mn: 0.14-0.95%, Al: 0.25-1.05%, Ca: 0.0003%-0.01%; The number of MgO﹒Al2O3 spinel inclusions with a size of 1.5 μm or more in the non-oriented electrical steel is no more than 7 / mm 2 .

2. The non-oriented electrical steel according to claim 1, characterized in that: The mass percentage of each chemical element is: C≤0.0025%, Si: 3.1-3.8%, Mn: 0.14-0.95%, Al: 0.25-1.05%, Ca: 0.0003%-0.01%; 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 at least one of: 0<Ge≤0.02wt%, 0<Bi≤0.01wt%, and REM: 0.0004-0.015wt%.

4. The non-oriented electrical steel according to claim 1 or 2, characterized in that: It also contains at least one of Sn and Sb, and satisfies Sn+Sb: 0.0055%-0.15wt%.

5. The non-oriented electrical steel according to claim 1 or 2, characterized in that: It also contains at least one of Ni, Co, Zr, Nb, Cu and Cr, and the total mass percentage of the at least one of the at least one of the Ni, Co, Zr, Nb, Cu and Cr is controlled within the range of 0.01-2.5%.

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

7. The non-oriented electrical steel according to claim 1 or 2, characterized in that: Among the inevitable impurities, P≤0.025%, S≤0.0025%, N≤0.0035%, Ti≤0.002%, and O≤0.002%.

8. The non-oriented electrical steel according to claim 1 or 2, characterized in that: When it is not subjected to stress relief annealing, its fatigue strength at room temperature is ≥455MPa.

9. The non-oriented electrical steel according to claim 1 or 2, characterized in that: After stress relief annealing, the proportion of grains larger than 115 μm in the steel plate exceeds 95%, and the iron loss P 1.0 / 400 ≤12.5W / kg.

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: MgO in the refining slag is controlled to be ≤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 is controlled to meet the following conditions: 140≤V≤245-1.6×T×[Al] 2 , where [Al] is the total aluminum content in the molten steel, the unit parameter is wt.%, and T is the aluminum deoxidation time during RH refining, the unit parameter is min.

11. The manufacturing 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 seconds.

12. The manufacturing method according to claim 10, characterized in that: After the continuous annealing and insulation coating steps, a stress relief annealing step is also included: the annealing temperature is 745° C.-855° C., and the heat preservation time is 60-180 minutes.

Images