Non-oriented electrical steel sheet having excellent fatigue property and method for manufacturing the same

Abstract

The application discloses an oriented electrical steel with excellent fatigue performance, which contains Fe and inevitable impurities, and further contains the following chemical elements with mass percentage as follows: 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 type inclusions with size of 1.5 microns or above in the oriented electrical steel is not more than 7 / mm 2 . Accordingly, the application also provides a manufacturing method of the oriented electrical steel with excellent fatigue performance. The oriented electrical steel has excellent fatigue performance, can meet the repeated starting, stable operation and deformation and fracture non-occurrence of a new energy automobile driving motor under complex working conditions. And when used as a stator material, it has the characteristics of low material high-frequency iron loss after stress relief annealing.

Description

TECHNICAL FIELD

[0001] The present application relates to a steel sheet and a manufacturing method thereof, and in particular, to an non-oriented electrical steel sheet and a manufacturing method thereof. BACKGROUND

[0002] In recent years, with the increasing demand for energy saving, environmental protection and low carbon emission in the global society, traditional fuel vehicles are gradually being replaced by new energy electric vehicles. The core component of electric vehicles, i.e. driving motor, requires high efficiency, light weight, high speed and high reliability.

[0003] Non-oriented electrical steel is an excellent soft magnetic material and is widely used in various motor cores. In order to adapt to high speed and high stability, higher and higher demands are put forward for the fatigue strength of the rotor. From the perspective of motor design, in order to improve the efficiency of the motor and reduce the magnetic flux leakage, the width of the magnetic bridge is designed to be thinner and thinner, and at the same time, the material needs to have high strength to ensure the stability and safety of the rotor during repeated operation, and abnormal working conditions such as deformation, fracture and sudden stop are not allowed. In addition, from the perspective of high power of the motor, the non-oriented silicon steel used as the stator material needs to have low high-frequency iron loss in order to reduce energy consumption.

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

[0005] Therefore, it is desirable to obtain a non-oriented electrical steel sheet with excellent fatigue performance and a manufacturing method thereof. SUMMARY

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

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

[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 type inclusions with a size of 1.5 μm or more in the non-oriented electrical steel is not more than 7 / mm 2 .

[0010] Accordingly, the present application also provides an oriented electrical steel with excellent fatigue performance, each chemical element mass percentage content of which 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 inevitable impurities.

[0012] The number of MgO.Al2O3 spinel type inclusions with a size of 1.5 μm or more in the non-oriented electrical steel is not more than 7 / mm 2 .

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

[0014] C: In the non-oriented electrical steel described in the present application, carbon is a harmful element that can form too much carbide, resulting in iron loss degradation. Therefore, the present application controls the carbon content to be not more than 0.0025%. However, since the C element is an element that must be contained in steel, its content cannot be 0. In the present application, it is desirable to control its upper limit, and it is desirable that the lower the content is, the better.

[0015] Si: In the non-oriented electrical steel described in the present application, the Si element is the main alloying element in electrical steel, which can increase the electrical resistivity of the steel plate and reduce the material iron loss, and the silicon solid solution in the matrix can improve the strength and fatigue limit of the steel plate. When the Si element content is less than 3.1%, the strength of the steel plate is limited, and the fatigue strength of the material cannot be guaranteed to be above 455 MPa; 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 application, the mass percentage content of the Si element is controlled to be between 3.1-3.8%.

[0016] Mn: In the non-oriented electrical steel described in the present application, the Mn element can increase the electrical resistivity of the material, thereby reducing the iron loss, and forming MnS by combining with residual S elements in the steel to improve the precipitate morphology in the steel. However, when the Mn element addition amount exceeds 0.95%, the iron loss reduction is limited, and the magnetic induction will be degraded. Therefore, in the non-oriented electrical steel described in the present application, the mass percentage content of the Mn element is controlled to be between 0.14-0.95%.

[0017] Al: In the non-oriented electrical steel described in the present application, the Al element can increase the material resistivity and reduce the iron loss. In order to achieve the effect of reducing the iron loss, the general addition amount is more than 0.25%. However, when the addition amount of the Al element is too high, on the one hand, the MgO-Al2O3 type inclusions in the steel will increase, which will deteriorate the electromagnetic performance and fatigue performance 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 described in the present application, the mass percentage of the Al element is controlled to be between 0.25-1.05%.

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

[0019] For the non-oriented electrical steel with excellent fatigue performance described in the present application, MgO-Al2O3 spinel type inclusions are hard and have high melting point, which is extremely harmful to the fatigue performance of the steel sheet, especially large particle inclusions with a size of 1.5 μm or more, which will produce stress concentration and strain concentration around the large particle inclusions under the action of repeated alternating load, becoming one of the important crack sources of fatigue fracture. Therefore, in the non-oriented electrical steel described in the present application, the number of MgO-Al2O3 spinel type inclusions with a size of 1.5 μm or more in the steel sheet is controlled to be not more than 7 / mm 2 .

[0020] Further, in the non-oriented electrical steel described in the present application, it also contains at least one of: 0

[0021] In the above technical solution of the present application, in order to further optimize the performance of the non-oriented electrical steel described in the present application, an appropriate amount of Ge element, Bi element and rare earth element can also be added to the steel. Among them:

[0022] Ge: In the non-oriented electrical steel described in the present application, the Ge element can increase the material resistivity, improve the annealing plate texture, reduce the iron loss, and at the same time can inhibit the internal oxidation during the material annealing process. However, considering the cost, the addition amount should not be more than 0.02%. Therefore, in the non-oriented electrical steel described in the present application, the mass percentage of the Ge element is controlled to be between 0

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

[0024] REM: In the non-oriented electrical steel described in the present application, rare earth elements are easy to combine with sulfur and oxygen, which are harmful elements. Appropriate addition of rare earth elements can purify the molten steel, promote the growth of small inclusions, and improve the recrystallized grain structure of the finished steel plate. However, when the content of 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 application, the mass percentage of REM is controlled between 0.0004-0.015%, and in some more preferred embodiments, the mass percentage of REM can be controlled between 0.0006-0.01%.

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

[0026] In the above technical solutions of the present application, in order to further optimize the performance of the non-oriented electrical steel described in the present application, the steel can also contain Sn element and Sb element. Among them:

[0027] Sn element and Sb element are grain boundary segregation elements, which can inhibit the oxidation of the steel plate and improve the beneficial texture of the annealed structure of the finished product. However, excessive addition of Sn element and Sb element can cause an increase in steel surface defects. Therefore, in the non-oriented electrical steel described in the present application, the mass percentage of Sn element and Sb element is controlled between 0.0055%-0.15%.

[0028] Further, in the non-oriented electrical steel described in the present application, it also contains at least one of Ni, Co, Zr, Nb, Cu, Cr, and the total mass percentage of these elements is controlled between 0.01-2.5%.

[0029] In the non-oriented electrical steel described in the present application, Ni, Co, Zr, Nb, Cu, and Cr elements can increase the resistivity of the steel plate, reduce the loss, and improve the strength of the material. When added, one or more of them can be selected, and the total addition amount can be controlled between 0.01-2.5%.

[0030] Further, in some more preferred embodiments of the non-oriented electrical steel described in the present application, the number of MgO·Al2O3 spinel type inclusions with a size of 1.5 μm or more in the non-oriented electrical steel is not more than 5 / mm 2 .

[0031] Further, in the unavoidable impurities of the non-oriented electrical steel described in the present application, P≤0.025%, S≤0.0025%, N≤0.0035%, Ti≤0.002%, O≤0.002%.

[0032] In the non-oriented electrical steel described in the present application, the P element, the S element, the N element, the Ti element and the O element are all impurity elements in the non-oriented electrical steel plate, and the content of the impurity elements in the steel should be as low as possible to obtain a steel with better performance and quality under the condition of the technology. Among them:

[0033] P: In the non-oriented electrical steel described in the present application, the P element is easy to segregate at the grain boundary, increasing the brittleness of the material. Therefore, in the non-oriented electrical steel described in the present application, the mass percentage content of P element can be controlled below 0.025%, and in some more preferred embodiments, the mass percentage content of P element can be controlled below 0.02%.

[0034] S: In the non-oriented electrical steel described in the present application, the S element is a harmful impurity element, and if the residual content of S element is too high, a large amount of sulfide precipitates will be formed, hindering the grain growth and causing the deterioration of the iron loss of the steel plate. Therefore, in the non-oriented electrical steel described in the present application, the mass percentage content of S element can be controlled below 0.0025%.

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

[0036] Ti: In the non-oriented electrical steel described in the present application, Ti element is a harmful impurity element for non-oriented silicon steel, which reacts with carbon and nitrogen to precipitate titanium carbide and titanium nitride, pinning the grain boundary and hindering the grain growth during the recrystallization process, deteriorating the iron loss. Therefore, in the non-oriented electrical steel described in the present application, the mass percentage content of Ti element can be controlled below 0.002%, and in some more preferred embodiments, the mass percentage content of Ti element can be controlled below 0.0015%.

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

[0038] Further, in the non-oriented electrical steel according to the present application, the fatigue strength of the steel at room temperature (e.g. 25℃) is ≥ 455 MPa when the steel has not been subjected to a stress relief annealing.

[0039] When the fatigue strength of the non-oriented electrical steel according to the present application at room temperature is not less than 455 MPa under 1x10 7 When the fatigue strength of the non-oriented electrical steel according to the present application at room temperature is not less than 455 MPa under 1x10

[0040] Further, in the non-oriented electrical steel according to the present application, after the steel has been subjected to a stress relief annealing, the fraction of grains having a size of 115 μm or more is more than 95% in the steel sheet, and the iron loss P 1.0 / 400 ≤ 12.5 W / kg.

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

[0042] Correspondingly, another object of the present application is to provide a method for manufacturing a non-oriented electrical steel sheet having excellent performance. The non-oriented electrical steel manufactured by the method has excellent fatigue performance, and can meet the requirements of a new energy automobile driving motor under complex working conditions, i.e. repeated start-up and stable operation without deformation or fracture. Meanwhile, the non-oriented electrical steel has a low high-frequency iron loss after the stress relief annealing, and can be used as a stator material.

[0043] In order to achieve the above objects, the present application provides a method for manufacturing a non-oriented electrical steel, which comprises the following steps: smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, continuous annealing and insulation coating;

[0044] In the RH refining step: the MgO content in the refining slag is controlled to be ≤ 5 wt.%; and Ca is added to modify the inclusions in the molten steel, so that the MgO-Al2O3 spinel type inclusions are gradually converted into CaO-MgO-Al2O3 composite inclusions; and the circulation blowing amount V is controlled to satisfy: 140 ≤ V ≤ 245-1.6xTx[Al] 2 wherein [Al] is the total aluminum content in the molten steel, and the unit parameter is wt.%, and T is the aluminum deoxidization time during the RH refining process, and the unit parameter is min.

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

[0046] However, as described above, the MgO·Al2O3 spinel type inclusions are hard and have a high melting point, which is extremely harmful to the fatigue performance of the steel plate. In particular, large particle inclusions with a size of 1.5 μm or more can cause stress concentration and strain concentration around the large particle inclusions under repeated alternating loads, and become 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 the use of a specific chemical composition design, the present application also controls the large size MgO·Al2O3 harmful inclusions in the steel through a specific process. Among them:

[0047] In the manufacturing method described in the present application, the MgO content in the refining slag is controlled to be not more than 5 wt.%, which can reduce the Mg content from the source, thereby reducing the reaction of MgO with acid-soluble aluminum in the molten steel.

[0048] In addition, in the manufacturing method described in the present application, calcium treatment is added during the refining process, which can denature the inclusions in the molten steel, so that the MgO·Al2O3 spinel type inclusions gradually change into low-melting-point CaO·MgO·Al2O3 composite inclusions, which are easy to flow with the molten steel and are easily absorbed and removed by the top slag.

[0049] In addition, in the manufacturing method described in the present application, a reasonable circulating blowing amount V (the unit parameter is Nm 3 / h) is used in the refining process. The circulating blowing amount cannot be too low, otherwise the molten steel flow is not sufficient, the steel-slag reaction is not sufficient, and the removal efficiency of the inclusions is not high. The circulating blowing amount also cannot be too high, especially for Al-containing non-oriented silicon steel, too high blowing amount can cause serious slag entrainment, which is also not conducive to the aggregation and removal of MgO·Al2O3 inclusions. The circulating blowing amount V set range has a close relationship with the Al content and the aluminum deoxidation treatment time, and the specific range satisfies the formula: 140≤V≤245-1.6×T×[Al] 2 , wherein [Al] is the total aluminum content of the molten steel, the unit is wt.%, and T is the aluminum deoxidation time in the RH refining process, the unit parameter is min.

[0050] Through the above means, the number of MgO·Al2O3 spinel type inclusions with a size of 1.5 μm or more in the non-oriented electrical steel product can be controlled to be not more than 7 / mm 2In some more preferred embodiments, the number of MgO.Al2O3 spinel type inclusions with a size of 1.5 pm or more in the non-oriented electrical steel is not more than 5 per mm 2 .

[0051] Further, in the continuous annealing step of the method for manufacturing the non-oriented electrical steel according to the present application, the holding temperature is 720-850℃ and the holding time is 10-75s.

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

[0053] Further, after the continuous annealing and insulation coating step of the method for manufacturing the non-oriented electrical steel according to the present application, a stress relief annealing step is further included: the annealing temperature is 745℃-855℃ and the holding time is 60-180min.

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

[0055] The non-oriented electrical steel according to the present application has excellent fatigue performance, and in some embodiments, its room temperature fatigue strength under 1x10 7 times repeated stress cycle conditions is not less than 455MPa, which has a high enough fatigue strength to ensure that the rotor does not deform or break under the action of centrifugal force generated by high-speed rotation, and operates stably and efficiently, so as to meet the requirements of the new energy automobile driving motor under complex working conditions.

[0056] When used as a stator material, the non-oriented electrical steel according to the present application has the characteristics of low high-frequency iron loss after stress relief annealing, and in some embodiments, the proportion of grain structures with a grain size of 115pm or more is more than 95%, which is fully grown, and the iron loss P 1.0 / 400 is significantly reduced, with a maximum value of not more than 12.5W / kg. DETAILED DESCRIPTION

[0057] The non-oriented electrical steel and the method for manufacturing the same according to the present application will be further explained and described below in conjunction with specific examples, but the explanation and description do not constitute an improper limitation on the technical solutions of the present application.

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

[0059] The non-oriented electrical steel of Examples 1-10 and Comparative Examples 1-5 is prepared by the following steps:

[0060] (1) The molten iron from the blast furnace is pretreated and smelted in a converter.

[0061] (2) In the RH refining process of decarburization, deoxidation, and alloying treatment: control the MgO content in the refining slag ≤5wt%; and add Ca to modify the inclusions in the molten steel, so that the MgO-Al2O3 spinel type inclusions gradually change into CaO-MgO-Al2O3 complex inclusions; control the circulation blowing amount V to satisfy: 140≤V≤245-1.6×T×[Al] 2 , wherein [Al] is the total aluminum content in the molten steel, the unit parameter is wt.%, and T is the aluminum deoxidation time during the RH refining process, the unit parameter is min; wherein the MgO content in the refining slag, the circulation blowing amount V, and the aluminum deoxidation time T in each example and comparative example are shown in Table 2.

[0062] (3) After the refining is completed, the molten steel is subjected to continuous casting to obtain a continuous casting slab, and the chemical element composition ratio 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 steel coil finishing rolling temperature can be 800°C, and the coiling temperature can be 625°C, to obtain a hot-rolled plate with a thickness of 2.0-2.5mm.

[0064] (5) Normalization heat treatment: for example, the normalizing holding temperature can be 900°C, and the holding time can be 5min.

[0065] (6) Cold rolling to a finished thickness of 0.25-0.30mm: among them, the steel coil of Example 3 and Example 4 adopts a secondary cold rolling process.

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

[0067] (8) Stress relief annealing: the annealing temperature is 745°C-855°C, and the holding time is 60-180min. The annealing temperature and holding time in each example and comparative example are shown in Table 2.

[0068] Table 1-1 and Table 1-2 list the mass percentage of each chemical element of the non-oriented electrical steel of Examples 1-10 and the comparative steel plates of Comparative Examples 1-5.

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

[0070]

[0071]

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

[0073]

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

[0075]

[0076]

[0077] To verify the implementation effect of the present application, samples of the final finished non-oriented electrical steel of Examples 1-10 and the comparative steel sheets of Comparative Examples 1-5 were taken, and tests were performed on these non-oriented electrical steel sheets, and the test results obtained are listed in Table 3 below. Among them, the relevant performance test means are as follows:

[0078] Fatigue performance test, according to GB-T 3075-2008 Metal Materials Fatigue Test Axial Force Control Method and ISO 1099-2006 Metal Materials Fatigue Test Axial Force Control Method, using a maximum capacity of 10kN servo fatigue testing machine, the test condition parameters can be set as follows: test environment temperature 25±5℃, according to sine wave control waveform, stress ratio R=0.1, frequency: 20-30Hz, maximum cycle number is 1.0x10 7 .

[0079] Statistical analysis of MgO-Al2O3 oxide inclusions in non-oriented electrical steel: 20*20mm samples were randomly cut from the base steel sheet, ground to the position of 1 / 2 thickness of the steel sheet, mechanically polished or electrochemically polished, and then photographed under backscattered electron image to confirm the presence or absence of Al2O3 oxide inclusions and calculate the number, more than 20 fields of view were continuously photographed, the number of Al2O3 oxide with a size of more than 1.5μm in the field of view was counted, and the distribution density was calculated in units of "pieces / mm 2 ".

[0080] Statistical analysis of grain size of steel sheet, according to GB / T 36165-2018 Metal Average Grain Size Determination Electron Backscattered Diffraction (EBSD) Method, 20*20mm samples were randomly cut from the sample sheet after stress relief annealing, ground to the position of 1 / 2 thickness of the steel sheet, mechanically polished or electrochemically polished, and the field of view contained at least 500 grains, the grain size distribution was counted, and the proportion of grain structure with a size of more than 115μm was calculated.

[0081] Iron loss P1.0 / 400 (Which represents the iron loss value under the condition of 1.0T, 400HZ) Test: square method based on the standard "GB / T10129-2019 Electrical steel strip (sheet) Method for measuring the magnetic properties at medium frequency".

[0082] Table 3.

[0083]

[0084] As can be seen from the above Table 3, the examples 1-10 of the present application control the chemical composition, and at the same time control the MgO content of the refining slag in the RH refining process and the process of circulating gas blowing amount in the RH refining process are all within the design range of the present application, so that the number of MgO·Al2O3 spinel type inclusions with a size of 1.5μm or more in the non-oriented electrical steel obtained is not more than 5 / mm 2 , and the fatigue strength at room temperature is higher than 465MPa, and the high-frequency iron loss P 1.0 / 400 of the stress relief annealing is less than 12.12W / kg. Thus, the non-oriented electrical steel can guarantee excellent fatigue performance, and can meet the repeated start-up and stable operation of the new energy automobile driving motor under complex working conditions without deformation and fracture. After stress relief annealing, it can be used as a stator material.

[0085] In contrast, in the comparative examples 1 and 2, although the chemical composition is within the scope of the present application, the MgO content of the refining slag is relatively high, and the circulating gas blowing amount is relatively small, resulting in a relatively high density of MgO·Al2O3 oxide inclusions in the final product, and the fatigue strength under the condition of 1.0x10 7 times of cycles is lower than 455MPa.

[0086] The chemical composition of the comparative examples 3-5 is low in Si or Al or Mn, and the corresponding final fatigue strength is low, and the iron loss is also high.

[0087] It should be noted that the scope of protection of the present application is not limited to the examples given in the present application file, and all prior art that does not conflict with the scheme of the present application, including but not limited to prior patent documents, prior published publications, prior public use, etc., can be included in the scope of protection of the present application.

[0088] In addition, the combination of the technical features in the present case is not limited to the combination mode or the combination mode of the specific examples described in the claims of the present case, and all the technical features described in the present 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-mentioned embodiments are only specific embodiments of the present application. Obviously, the present application is not limited to the above-mentioned embodiments, and similar changes or modifications made in accordance with the disclosure of the present application are directly derived or easily thought of by those skilled in the art, and should all belong to the protection scope of the present application.

Claims

1. A non-oriented electrical steel with excellent fatigue properties, characterized in that, Its mass percentage content of each chemical element is as follows: C ≤ 0.0025%, Si: 3.1-3.8%, Mn: 0.14-0.95%, Al: 0.25-1.05%, Ca: 0.0003%-0.01%; balance is Fe and unavoidable impurities; The number of MgO·Al2O3 spinel-type inclusions with a size of 1.5μm or larger in the non-oriented electrical steel shall not exceed 7 per mm. 2 ; The non-oriented electrical steel, without stress-relief annealing, has a fatigue strength ≥455 MPa at room temperature; after stress-relief annealing, the proportion of grains larger than 115 μm in the steel sheet exceeds 95%, and the iron loss P 1.0 / 400 ≤12.5W / kg.

2. The non-oriented electrical steel as described in claim 1, characterized in that, It also contains at least one of the following: 0 < Ge ≤ 0.02 wt%, 0 < Bi ≤ 0.01 wt%, REM: 0.0004-0.015 wt%.

3. The non-oriented electrical steel as described in claim 1, characterized in that, It also contains at least one of Sn and Sb, and satisfies Sn+Sb: 0.0055%-0.15wt%.

4. The non-oriented electrical steel as described in claim 1, characterized in that, It also contains at least one of Ni, Co, Zr, Nb, Cu, and Cr, and its total mass percentage is controlled between 0.01% and 2.5%.

5. The non-oriented electrical steel as described in claim 1, characterized in that, The number of MgO·Al2O3 spinel-type inclusions with a size of 1.5μm or larger in the non-oriented electrical steel shall not exceed 5 per mm. 2 .

6. The non-oriented electrical steel as described in claim 1, characterized in that, Among the unavoidable impurities, P ≤ 0.025%, S ≤ 0.0025%, N ≤ 0.0035%, Ti ≤ 0.002%, and O ≤ 0.002%.

7. A method for manufacturing non-oriented electrical steel as described in any one of claims 1-6, comprising the steps of: smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, continuous annealing, and insulating coating; characterized in that: In the RH refining process: the MgO content in the refining slag is controlled to be ≤5 wt%; and Ca is added to modify inclusions in the molten steel, gradually transforming MgO·Al2O3 spinel-type inclusions into CaO·MgO·Al2O3 composite inclusions; the circulating gas flow rate V is controlled to satisfy: 140 ≤ V ≤ 245 - 1.6 × T × [Al] 2 Where [Al] is the total aluminum content in the molten steel, in wt.%, T is the aluminum deoxidation time during RH refining, in min, and the circulating air volume V is in Nm³. 3 / h.

8. The manufacturing method as described in claim 7, characterized in that, In the continuous annealing process, the holding temperature is 720-850℃ and the holding time is 10-75s.

9. The manufacturing method as described in claim 7, characterized in that, The continuous annealing and insulating coating steps are followed by a stress-relief annealing step: the annealing temperature is 745℃-855℃, and the holding time is 60-180min.

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