Non-oriented electrical steel sheet having high frequency, low iron loss and excellent fatigue performance, and manufacturing method therefor

Abstract

The present disclosure relates to a non-oriented electrical steel sheet having a high frequency, low iron loss and excellent fatigue performance. In addition to Fe and inevitable impurities, the non-oriented electrical steel sheet further comprises the following chemical elements in percentage by mass: 0<C≤0.0045%, Si: 2.65-3.75%, Mn: 0.10-1.04%, and Al: 0.10-1.85%. The number of Al2O3 inclusions larger than 2.0 µm in size in the non-oriented electrical steel sheet does not exceed 4 per mm2. In addition, the present disclosure also relates to a manufacturing method for the non-oriented electrical steel sheet. The non-oriented electrical steel sheet has the advantages of a high frequency and low iron loss, so that motor loss can be reduced and motor efficiency can be improved, and the non-oriented electrical steel sheet has excellent fatigue performance, so that high-speed and stable operation of motor cores and rotors within a temperature range from room temperature to 150°C can be satisfied, without deformation or breakage.

Description

Non-oriented electrical steel sheet with high frequency, low iron loss and excellent fatigue performance and its manufacturing method Technical Field

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

[0002] With the rapid development of the new energy vehicle market, the requirements for energy conservation and environmental protection of various types of motors are becoming increasingly higher, especially high-speed motors and new energy vehicle drive motors, which are constantly developing towards high efficiency, miniaturization and low loss.

[0003] Non-oriented silicon steel is an excellent soft magnetic material, widely used in various motor cores such as generators, drive motors, compressors, micro motors, industrial motors, etc.

[0004] For non-oriented silicon steel materials, it is hoped that the material loss is as low as possible, especially the loss above medium frequency. At the same time, it is also hoped that it has excellent fatigue performance to ensure that the motor rotor does not suffer from aging deformation or even the risk of fracture at weak locations such as the magnetic bridge during repeated starting and stopping and high-speed operation.

[0005] In this regard, Chinese patent publication CN105331879A, published on February 17, 2016, and entitled "Non-oriented silicon steel for high-power-density motors and production method," discloses a non-oriented silicon steel comprising 3.25-3.45% Si, 0.05-0.10% Mn, and 0.04-0.06% Sn, with no added Al alloy. The manufacturing process for this non-oriented silicon steel includes smelting and continuous casting of low-Al pure steel into billets, heating the billets, hot rolling, normalizing, primary cold rolling, and annealing the finished product. This non-oriented silicon steel exhibits an iron loss (P1.0 / 400) of ≤17.0 W / kg and a room-temperature fatigue limit strength of ≥400 MPa.

[0006] Summary of the Invention

[0007] One of the objectives of the present disclosure is to provide a non-oriented electrical steel sheet with low iron loss and excellent fatigue performance at high frequencies. This low iron loss at high frequencies reduces motor losses and improves motor efficiency. Furthermore, this non-oriented electrical steel sheet exhibits excellent high-temperature fatigue performance, enabling stable, high-speed operation of motor cores and rotors within the rated operating temperature range of room temperature to 150°C (rated ambient temperature) without deformation or fracture.

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

[0009] 0 < C ≤ 0.0045%, Si: 2.65 - 3.75%, Mn: 0.10 - 1.04%, Al: 0.10 - 1.85%;

[0010] The number of Al2O3 inclusions with a size of 2.0 μm or more in the non-oriented electrical steel sheet does not exceed 4 per mm 2 .

[0011] Preferably, the mass percentage content of each chemical element of the non-oriented electrical steel sheet of the present disclosure is:

[0012] 0 < C ≤ 0.0045%, Si: 2.65 - 3.75%, Mn: 0.10 - 1.04%, Al: 0.10 - 1.85%; the balance is Fe and inevitable impurities.

[0013] Preferably, the non-oriented electrical steel sheet of the present disclosure further contains Ca and / or REM, and in terms of mass percentage, Ca: 0.0005 - 0.0060% and / or REM: 0.0005 - 0.0120%.

[0014] Preferably, the non-oriented electrical steel sheet of the present disclosure further contains at least one of Nb, V, Cu, Mo, Ni, Co, Cr, Sn, Sb, Zr, and the total mass percentage content thereof is 0.0095 - 1.05%.

[0015] Preferably, the non-oriented electrical steel sheet of the present disclosure further contains Sn, and in terms of mass percentage, the content of Sn is: 0.0035% - 0.25%.

[0016] Preferably, in the non-oriented electrical steel sheet of the present disclosure, the inevitable impurities include P, S, N, and Ti, and in terms of mass percentage, P ≤ 0.02%, S ≤ 0.0055%, N ≤ 0.0035%, Ti ≤ 0.0025%.

[0017] Preferably, the thickness of the non-oriented electrical steel sheet of the present disclosure is 0.15 - 0.35 mm.

[0018] Preferably, the average grain size of the non-oriented electrical steel sheet of the present disclosure is 45 - 165 μm. [[ID=--]]

[0019] Preferably, the iron loss P of the non-oriented electrical steel sheet of the present disclosure 1.0 / 600 ≤ 36 - ([Si] + 1.2 × [Al]) / 5t, where t represents the thickness of the steel sheet in mm, and [Si] and [Al] are respectively substituted with the values before the percentage sign of the mass percentage content of Si and Al in the steel.

[0020] Preferably, the fatigue strength S of the non-oriented electrical steel sheet of the present disclosure at 25 °C 25≥365MPa, fatigue strength S at 150℃ 150 ≥294MPa, preferably S 150 ≥330MPa.

[0021] Preferably, the fatigue strength S of the non-oriented electrical steel sheet of the present disclosure at 150°C is 150 Fatigue strength S at 25°C 25 Ratio S 150 / S 25 Satisfy: 0.80≤S 150 / S 25 ≤1.0.

[0022] The non-oriented electrical steel sheet disclosed in the present invention can obtain excellent iron loss P by reasonable chemical composition design combined with inclusion and grain size control. 10 / 600 Performance (low iron loss at high frequency), which can reduce the loss of high-speed drive motors, improve motor efficiency, save a lot of electricity, and is also conducive to motor miniaturization design and material saving.

[0023] The present disclosure also provides a method for manufacturing a non-oriented electrical steel sheet, comprising the following steps performed in sequence: smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, final annealing, and coating with an insulating coating; wherein, in the RH refining step, the circulating air blowing volume V1 during the decarburization process and the circulating air blowing volume V0 at the end of decarburization satisfy the following conditions: V1 ≥ V0 + 12[Al], wherein [Al] represents the Al content in the molten steel (substitute the mass percentage of the Al element in the molten steel before the percentage sign), and V0 ≥ 140 Nm 3 / h; after decarburization, the ratio [O] / [C] of the free oxygen content [O] to the carbon content [C] in the molten steel is less than 21.5.

[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 1180°C, and the finishing temperature of the coil is 780°C. In one embodiment, the coiling temperature is 660°C. In one embodiment, the thickness of the hot-rolled plate is 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 980° C. and the holding time is 10 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] In the method disclosed herein, the annealing temperature and holding time in the final annealing step are not particularly limited, and the temperature and holding time conventionally used in the art can be used. In one embodiment, the holding time of the final annealing is 50 seconds. In one embodiment, the annealing temperature of the final annealing is 830-990°C. DETAILED DESCRIPTION

[0028] 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.

[0029] As used herein, the term "and / or" refers to and encompasses any and all possible combinations of more than one of the listed items.

[0030] In this paper, the number of Al2O3 inclusions was statistically analyzed using a field emission scanning electron microscope. Photographs were taken under backscattered electron imaging for more than 20 fields of view, and the number of Al2O3 oxides with a size of 2.0 μm or more in the field of view was counted and expressed in units of "number / mm 2 ” Calculate the distribution density.

[0031] In this paper, the average grain size was determined using the area method of the national standard "GBT6394-2017 Method for Determination of Average Grain Size of Metals".

[0032] In this paper, the iron loss P 1.0 / 600 (The iron loss value at the excitation frequency of 600Hz 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)".

[0033] In this paper, fatigue strength S 25 and fatigue strength S 150 The measurement was carried out in accordance with GB-T 3075-2008 Axial Force Control Method for Fatigue Test of Metallic Materials. The test environment temperatures were 25±5°C and 150±3°C, respectively. The fatigue limit (fatigue strength) was calculated based on a survival rate of 50%.

[0034] The non-oriented electrical steel sheet disclosed in the present invention contains Al element. In the manufacturing process of the non-oriented electrical steel sheet disclosed in the present invention, during the RH refining process, aluminum particles or aluminum ingots are added to the ladle for deoxidation treatment. Aluminum will quickly combine with the free oxygen in the molten steel to form Al2O3 oxide, which has a high melting point and hard particles. When such inclusions gather and grow to a certain size, and are not floated up and removed, and remain in the finished steel plate, they will hinder the movement of magnetic domains during the magnetization process of the material, degrade the iron loss of the steel plate, and greatly harm the fatigue performance of the material. Moreover, the larger the size of the inclusions and the more there are, the more likely the steel plate will generate stress concentration around the large-particle Al2O3 inclusions under repeated alternating stress, generate microcracks, and the more serious the degradation of fatigue performance. The inventors found that when the number of Al2O3 inclusions with a size of 2.0 μm or more in the non-oriented electrical steel sheet does not exceed 4 / mm 2 When the temperature is 0.5000°C, the non-oriented electrical steel sheet can have better iron loss and fatigue properties.

[0035] In the non-oriented electrical steel sheet disclosed herein, the design principles of each chemical element are as follows:

[0036] C: In the non-oriented electrical steel sheets of the present disclosure, carbon is a harmful impurity element that combines with other alloying elements to form carbides and precipitate, degrading iron loss. However, since C is an essential element in steel, its content cannot be zero. The present disclosure aims 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 be below 0.0045%. In some more preferred embodiments, the mass percentage of C can be controlled to be below 0.0030%.

[0037] Si: In the non-oriented electrical steel sheet disclosed herein, Si element can significantly increase the resistivity of the steel sheet and reduce the iron loss of the material. At the same time, silicon can also improve the high temperature fatigue strength of the steel sheet. In order to achieve the fatigue strength S at 150°C 150 To meet the requirements of a minimum of 294 MPa and low iron loss, the silicon content must be above 2.65%. However, the Si content should not be too high, as this significantly increases the difficulty of cold rolling the material and hinders stable mass production. Therefore, in the non-oriented electrical steel sheet disclosed herein, the mass percentage of Si is controlled between 2.65-3.75%, preferably between 2.90-3.45%.

[0038] Mn: In the nonoriented electrical steel sheet disclosed herein, Mn increases the material's resistivity. Mn also combines with S in the steel to form MnS, improving the morphology of precipitates. Therefore, it is necessary to add at least 0.10% Mn. However, when the Mn addition exceeds 1.04%, the hardness of the strip increases, hindering cold rolling. Therefore, in the nonoriented electrical steel sheet disclosed herein, the mass percentage of Mn is controlled between 0.10% and 1.04%, preferably between 0.55% and 1.00%.

[0039] Al: In the non-oriented electrical steel sheet disclosed herein, Al can increase the material's resistivity and reduce iron loss. To achieve the desired effect, Al can be added at a concentration of 0.10% or more. However, when Al addition exceeds 1.85%, production becomes more difficult and the steelmaking process generates a large amount of aluminum oxide, which not only degrades the performance of the finished product but also easily clogs the casting nozzle, impacting production. Therefore, in the non-oriented electrical steel sheet disclosed herein, the mass percentage of Al is controlled between 0.10% and 1.85%, preferably between 0.55% and 1.5%.

[0040] In order to further improve the properties of the non-oriented electrical steel sheet disclosed herein, appropriate amounts of Ca and rare earth elements (REM) may be preferably added to the steel.

[0041] Ca: In the non-oriented electrical steel sheets disclosed herein, Ca reacts with S and O in the steel to form structurally stable CaS and CaO, improving the morphology and distribution of inclusions in the molten steel, reducing the formation of fine inclusions, and ultimately reducing iron loss. However, excessive Ca content can lead to the formation of excessive oxide inclusions, affecting the surface quality of the steel sheets. Therefore, in the non-oriented electrical steel sheets disclosed herein, the mass percentage of Ca can be controlled between 0.0005% and 0.0060%.

[0042] REM: In the nonoriented electrical steel sheets disclosed herein, rare earth elements (REM) readily combine with harmful elements such as sulfur and oxygen. 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 cause surface defects and degrade magnetic properties. Therefore, in the nonoriented electrical steel sheets disclosed herein, the REM content can be controlled within a range of 0.0005% to 0.0120% by weight. In more preferred embodiments, the REM content can be controlled within a range of 0.0008% to 0.0120% by weight.

[0043] In order to further improve the properties of the non-oriented electrical steel sheet disclosed herein, the steel may preferably contain at least one of Nb, V, Cu, Mo, Ni, Co, Cr, Sn, Sb, and Zr, and the total mass percentage of the contained elements is 0.0095-1.05%.

[0044] The present inventors have found that when the non-oriented electrical steel sheet of the present invention contains Sn element and the content thereof is 0.0035%-0.25%, the performance of the non-oriented electrical steel sheet of the present invention can be further improved.

[0045] Sn: In the non-oriented electrical steel sheets disclosed herein, Sn can segregate at grain boundaries, inhibit oxidation within the steel sheet, and improve the favorable texture of the finished annealed microstructure. However, excessive Sn addition may increase surface defects in the steel. Therefore, in the non-oriented electrical steel sheets disclosed herein, the mass percentage of Sn can be controlled between 0.0035% and 0.25%. In some more preferred embodiments, the mass percentage of Sn can be controlled between 0.0065% and 0.25%.

[0046] In addition to the Sn element, one or more elements selected from Nb, V, Cu, Mo, Ni, Co, Cr, Sb, and Zr may be further added. Among them, Nb, V, and Zr elements can be dissolved into the matrix to improve the strength of the material. Cu, Mo, Ni, Co, and Cr elements increase the resistivity of the material, reduce losses, and also play a certain role in solid solution strengthening. The Sb element segregates at the grain boundaries, inhibits oxidation within the steel plate, and improves the favorable texture of the finished annealed structure. In some embodiments, one or more of the above elements may be selected for addition, and the total amount added may be controlled between 0.0095% and 1.05%.

[0047] In the non-oriented electrical steel sheet disclosed herein, P, S, N and Ti are all impurity elements in the non-oriented electrical steel sheet. Where 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.

[0048] 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 0.02% by weight. In some more preferred embodiments, the P content can be controlled to be below 0.015% by weight.

[0049] S: In the non-oriented electrical steel sheet of the present disclosure, S is a harmful impurity element. It combines with Mn to form sulfides, hindering grain growth and significantly degrading 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 0.0055%. In some more preferred embodiments, the mass percentage of S can be controlled to below 0.0040%.

[0050] N: In the nonoriented electrical steel sheets of the present disclosure, if the N content is too high, it will combine with various elements in the steel to form a large number of fine nitrides, hindering grain growth and degrading magnetic properties. Therefore, in the nonoriented electrical steel sheets of the present disclosure, the N content can be controlled to below 0.0035% by weight. In some more preferred embodiments, the N content can be controlled to below 0.0030% by weight.

[0051] 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, hindering grain growth during recrystallization and degrading iron loss. Therefore, in the non-oriented electrical steel sheets disclosed herein, the Ti content can be controlled to below 0.0025% by weight. In some more preferred embodiments, the Ti content can be controlled to below 0.0020% by weight.

[0052] In the non-oriented electrical steel sheet disclosed herein, when the grain size is too small, while the material has high tensile strength and fatigue strength, high-frequency iron loss is severely degraded. When the grain size is too large, the material strength is reduced, the magnetic domain size is increased, and eddy current loss is increased. Therefore, the non-oriented electrical steel sheet disclosed herein has an average grain size controlled between 45 and 165 μm, preferably between 65 and 135 μm.

[0053] When the fatigue strength S of the non-oriented electrical steel sheet of the present disclosure at 25°C (ambient temperature) is 25 ≥365MPa, and fatigue strength S at 150℃ 150 When the tensile strength is ≥294MPa, better fatigue performance can be achieved. High-speed motor rotor cores made of this non-oriented electrical steel sheet can ensure long-term stable operation in the operating temperature range from room temperature to 150°C without sudden failure, deformation or fracture.

[0054] The present disclosure also provides a method for manufacturing the non-oriented electrical steel sheet of the present disclosure, comprising the steps of: smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, final annealing (continuous annealing) and coating an insulating coating; wherein, in the RH refining step, the circulating air blowing volume V1 during the decarburization process and the circulating air blowing volume V0 at the end of decarburization satisfy the following conditions: V1 ≥ V0 + 12 [Al], wherein [Al] represents the Al content in the molten steel (substitute the mass percentage of the Al element in the molten steel before the percentage sign), and V0 ≥ 140 Nm 3 / h; after decarburization, the ratio of the free oxygen content [O] to the carbon content [C] in the molten steel [O] / [C] is 21.5 or less, preferably 18.6 or less.

[0055] The method disclosed in the present invention controls the number of large-sized Al2O3 harmful inclusions in steel by controlling process parameters. During the RH refining and decarburization process, a KTB oxygen gun is used to blow oxygen into the vacuum chamber to react with CO gas and molten steel. In this process, it is necessary to strictly control the decarburization reaction according to the ratio of free oxygen and carbon content in the molten steel to ensure that the blown-in oxygen is used for decarburization and avoid increasing the free oxygen in the molten steel, thereby controlling the oxygen content of the molten steel within a suitable range at the end of decarburization. Otherwise, it will directly lead to high difficulty in subsequent aluminum deoxidation and produce a large amount of Al2O3 oxide inclusions. After the decarburization process of the RH refining process is completed, the ratio of the free oxygen content [O] in the molten steel at this time to the carbon content [C] in the molten steel at this time is controlled to meet the relationship: [O] / [C]≤21.5.

[0056] In addition, the present invention also achieves the removal of large-sized inclusions by reasonably controlling the circulating air blowing volume during the RH refining process. The key is to make the circulating air blowing volume V0 ≥ 140Nm at the end of decarburization. 3 / h, and after adding aluminum particles or aluminum ingots, the circulating air blowing volume V1 during the decarburization process and the circulating air blowing volume V0 at the end of decarburization meet the relationship: V1 ≥ V0 + 12 [Al], where [Al] is the total Al content in the molten steel (that is, the value before the percentage sign of the mass percentage of the Al element in the steel grade). The present disclosure achieves that the number of Al2O3 inclusions with a size of 2.0 μm or more in the steel plate does not exceed 4 / mm by differentially controlling the circulating air blowing volume at different times during the RH refining process, so that Al2O3 inclusions flow with the molten steel and float rapidly to be removed, thereby achieving a goal of not more than 4 Al2O3 inclusions with a size of 2.0 μm or more in the steel plate / mm 2 .

[0057] The non-oriented electrical steel sheet and the manufacturing method thereof disclosed in the present invention have the following advantages and beneficial effects:

[0058] The non-oriented electrical steel sheet disclosed herein has excellent fatigue performance, which can ensure that the high-speed motor rotor core made of the non-oriented electrical steel sheet disclosed herein can operate stably for a long time in the operating temperature range from room temperature to 150°C without sudden failure, deformation or fracture.

[0059] Through reasonable chemical composition design, process control, especially the control of inclusions and grain size, the non-oriented electrical steel sheet disclosed in the present invention can achieve excellent iron loss P 10 / 600 Performance, in order to reduce the high-frequency iron loss of non-oriented silicon steel, and is conducive to reducing the loss of high-speed drive motors, can improve the working efficiency of the motor, save a lot of electricity, and is also conducive to the miniaturization design of the motor and save materials.

[0060] 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.

[0061] Examples 1-8 and Comparative Examples 1-5

[0062] The non-oriented electrical steel sheets of Examples 1-8 and Comparative Examples 1-5 were prepared by the following steps:

[0063] (1) Blast furnace molten iron undergoes molten iron pretreatment and converter smelting.

[0064] (2) Decarburization, deoxidation, and alloying are performed by RH refining. In the RH refining step: after adding aluminum material, the annular air volume V1 during the decarburization process and the annular air volume V0 at the end of decarburization are such that: V1 ≥ V0 + 12 [Al], where [Al] represents the Al content in the molten steel, and V0 ≥ 140 Nm 3 / h; after decarburization is completed, the ratio [O] / [C] of the free oxygen content [O] to the carbon content [C] in the molten steel is set to be below 21.5. Table 2 shows the specific process parameters of each embodiment and comparative example in this step.

[0065] (3) After refining, the molten steel is continuously cast to obtain continuous casting slabs. The chemical element compositions of the continuous casting slabs of the embodiments and comparative examples are shown in Table 1.

[0066] (4) Hot rolling: The heating temperature of the slab is 1180°C, the final rolling temperature of the coil is 780°C, and the coiling temperature is 660°C to obtain a hot-rolled plate with a thickness of 2.5 mm.

[0067] (5) Normalizing annealing: The normalizing holding temperature is 980℃ and the holding time is 10min.

[0068] (6) Cold rolling to obtain a finished product with a thickness of 0.15-0.35 mm. The steel coil of Example 3 adopts a double cold rolling process, while the other examples and comparative examples adopt a single cold rolling process.

[0069] (7) Final annealing and coating with insulating coating: The annealing holding time is 50s. The annealing temperatures of the embodiments and comparative examples are shown in Table 2.

[0070] Table 1 lists the mass percentage content of various chemical elements in the non-oriented electrical steel sheets of Examples 1-8 and the comparative steel sheets of Comparative Examples 1-5.

[0071] Table 2 lists the specific process parameters of the non-oriented electrical steel sheets of Examples 1-8 and the comparative steel sheets of Comparative Examples 1-5 in the RH refining step.

[0072] Table 2.

[0073] Next, samples of the non-oriented electrical steel sheets of Examples 1-8 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:

[0074] Fatigue performance: The test was conducted in accordance with GB-T 3075-2008 Axial Force Control Method for Fatigue Tests of Metallic Materials. The test conditions and parameters were set as follows: test environment temperature 25±5℃ and 150±3℃, sinusoidal control waveform, stress ratio R=0.1, test frequency: 50Hz, conditional fatigue limit cycle number 1.0×10 7 The fatigue limit (fatigue strength) is calculated based on a survival rate of 50%.

[0075] The number of Al2O3 inclusions: Statistical analysis was performed using a field emission scanning electron microscope. 20*20mm specimens were randomly cut from the base steel plate, ground to 1 / 2 of the thickness of the steel plate, and then mechanically or electrochemically polished. The specimens were then photographed under a backscattered electron image to confirm the presence of Al2O3 oxide inclusions and to count their number. More than 20 fields of view were photographed continuously, and the number of Al2O3 oxide inclusions larger than 2.0μm in size in the field of view was counted. The unit of measurement was "pieces / mm". 2 ” Calculate the distribution density.

[0076] Iron loss P 1.0 / 600 (Iron loss value at magnetic flux density of 1.0T and excitation frequency of 600Hz): Measured using the square circle method of the standard "GB / T10129-2019 Method for measuring medium frequency magnetic properties of electrical steel strip (sheet)".

[0077] Average Grain Size: The average grain size is calculated using the planimetric method according to the national standard "GBT6394-2017 Method for Determination of Average Grain Size of Metals." A small 15 x 20 mm specimen is cut from the finished annealed sheet. The cross section in the rolling direction serves as the observation surface. This is ground and mechanically polished. The observation surface is then etched with nital to reveal the grain boundaries. The grains are counted and the average grain size is calculated.

[0078] It can be seen from Table 3 above that in the non-oriented electrical steel sheets of Examples 1 to 8 of the present disclosure, the number of Al2O3 inclusions with a size of 2.0 μm or more does not exceed 4 / mm 2 The average grain size is between 45-165μm, and the fatigue strength at 25℃ is above 365MPa, and the fatigue strength at 150℃ is S 150 With S 25 Ratio S 150 / S 25 Between 0.8-1.0, while the iron loss P 1.0 / 600 Low and meets P 1.0 / 600 ≤36-([Si]+1.2*[Al]) / 5t. Therefore, the non-oriented electrical steel sheets of Examples 1-8 can reduce motor losses and improve motor efficiency, while having excellent fatigue properties and meeting the requirements for high-speed and stable operation of motor cores and motor rotors in the range of room temperature to 150°C without deformation or fracture.

[0079] In contrast, in Comparative Example 1, the free oxygen content [O] in the molten steel was too high at the end of decarburization, and the ratio of the free oxygen content [O] to the carbon content [C] in the molten steel was higher than 21.5, which made subsequent deoxidation difficult. Moreover, after the addition of aluminum ingots, a large amount of Al2O3 inclusions were generated, resulting in a density of large-sized Al2O3 oxide particles in the final product reaching 5 / mm. 2 , the fatigue performance at 25℃ is lower than 365MPa.

[0080] The steels in Comparative Examples 2 and 3 did not meet the requirements of this disclosure for the circulating air volume (V0) at the end of decarburization during RH refining, and the circulating air volume (V1) after the addition of aluminum ingots. This resulted in insufficient removal of the large-sized Al₂O₃ generated during aluminum deoxidation, resulting in a high inclusion density and poor fatigue performance in the finished steel. Furthermore, the average grain size of Comparative Example 3 was less than 45 μm, further degrading iron loss.

[0081] The chemical composition of the steels in Comparative Examples 4 and 5 is low in Si or Al, which results in low final fatigue strength and low iron loss P. 1.0 / 600 Too high to achieve the expected performance.

[0082] All publications, patent applications, patents, and other references mentioned in this disclosure are incorporated by reference in their entirety.

[0083] Although the present disclosure has been illustrated and described with reference to certain preferred embodiments thereof, it should be understood by those skilled in the art that the above description is provided to further illustrate the present disclosure in conjunction with specific embodiments thereof, and that the present disclosure is not limited to these descriptions. Those skilled in the art may make various changes in form and detail, including simple deductions or substitutions, without departing from the spirit and scope of the present disclosure.

Claims

1. Non-oriented electrical steel sheet, characterized in that: In addition to Fe and inevitable impurities, the non-oriented electrical steel sheet contains the following chemical elements in the following mass percentages: 0 < C ≤ 0.0045%, Si: 2.65 - 3.75%, Mn: 0.10 - 1.04%, Al: 0.10 - 1.85%. The number of Al2O3 inclusions with a size of 2.0 μm or more in the non-oriented electrical steel sheet does not exceed 4 / mm 2 , preferably no more than 2 / 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 ≤ 0.0045%, Si: 2.65 - 3.75%, Mn: 0.10 - 1.04%, Al: 0.10 - 1.85%; 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 Ca and / or REM, and in terms of mass percentage, Ca: 0.0005 - 0.0060% and / or REM: 0.0005 - 0.0120%.

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 at least one of Nb, V, Cu, Mo, Ni, Co, Cr, Sn, Sb, Zr, and the total mass percentage thereof is 0.0095 - 1.05%.

5. The non-oriented electrical steel sheet according to claim 4, characterized in that: The non-oriented electrical steel sheet further contains Sn, and in terms of mass percentage, the content of Sn is: 0.0035% - 0.25%.

6. The non-oriented electrical steel sheet according to any one of claims 1 to 5, characterized in that: The inevitable impurities include P, S, N, and Ti, and in terms of mass percentage, P ≤ 0.02%, S ≤ 0.0055%, N ≤ 0.0035%, Ti ≤ 0.0025%.

7. The non-oriented electrical steel sheet according to any one of claims 1 to 6, characterized in that: The thickness of the non-oriented electrical steel sheet is 0.15 - 0.35 mm.

8. The non-oriented electrical steel sheet according to any one of claims 1 to 7, characterized in that: The average grain size of the non-oriented electrical steel sheet is 45 - 165 μm.

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 1.0 / 600 ≤36-([Si]+1.2×[Al]) / 5t, where t represents the thickness of the steel plate in mm, and [Si] and [Al] are substituted with the values ​​before the percentage sign of the mass percentage of Si and Al in the steel respectively.

10. The non-oriented electrical steel sheet according to any one of claims 1 to 9, characterized in that: The fatigue strength S of the non-oriented electrical steel sheet at 25°C 25 ≥365MPa, fatigue strength S at 150℃ 150 ≥294MPa, preferably, S 150 With S 25 Ratio S 150 / S 25 Satisfy: 0.80≤S 150 / S 25 ≤1.

0.

11. A method for manufacturing the non-oriented electrical steel sheet according to any one of claims 1 to 10, which comprises the following steps carried out in sequence: smelting, RH refining, casting, hot rolling, normalizing annealing, cold rolling, final annealing, and coating an insulating coating, characterized in that In the RH refining step: the annular air blowing volume V1 during the decarburization process and the annular air blowing volume V0 at the end of decarburization satisfy: V1 ≥ V0 + 12 [Al], 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 V0 ≥ 140 Nm 3 / h; after decarburization is completed, the ratio [O] / [C] of the free oxygen content [O] to the carbon content [C] in the molten steel is made to be less than 21.

5.

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

13. The method according to claim 11 or 12, characterized in that The annealing temperature of the final annealing is 830 - 990 °C.

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