Non-oriented electrical steel for electric vehicle drive motors and its manufacturing method

Abstract

The present invention discloses a non-oriented electrical steel for electric vehicle drive motors. The non-oriented electrical steel further contains the following chemical elements in the following mass %: C≦0.003%, Si: 3.0-4.5%, Al: 0.15-2.5%, and Mn: 0.15-2.5% in addition to Fe and unavoidable impurities. The magnetic induction strength B of the non-oriented electrical steel for electric vehicle drive motors is 50M is 1.60T or more, where B 50M =(B 50L +B 50C +2B 50X ) / 4, where B 50L is the magnetic induction strength in the rolling direction when the non-oriented electrical steel is magnetized under a magnetic field of 5000 A / m; B 50C is the magnetic induction strength in the direction perpendicular to the rolling direction when the non-oriented electrical steel is magnetized under a magnetic field of 5000 A / m; and B 50X is the minimum value of magnetic induction strength at different angles relative to the rolling direction when the non-oriented electrical steel is magnetized in a magnetic field of 5000 A / m. The present invention further discloses a method for producing the non-oriented electrical steel.

Description

[Technical Field]

[0001] Technical Field The present invention relates to steel and a method for manufacturing the same, and more particularly to non-oriented electrical steel and a method for manufacturing the same. [Background technology]

[0002] background In recent years, countries around the world have increasingly paid attention to reducing carbon dioxide emissions, protecting the environment and saving energy. Traditional fuel-powered vehicles are gradually being replaced by electric vehicles, the market for and user demand for electric vehicles are also increasing, and more and more automobile companies have begun to invest in the research, development and manufacturing of electric vehicles.

[0003] Currently, in order to make electric vehicles more competitive, many automobile manufacturers are constantly increasing the requirements for electric vehicle traction motors, which must have characteristics such as compact size, high power density, and high rotational speed, while also increasing the operating frequency range from 400 Hz to several thousand Hz.

[0004] To meet the requirements of such traction motors, the non-oriented silicon steel used as the motor core material must have low core loss at high frequencies to ensure efficient energy conversion; it must also have sufficient strength to prevent the motor rotor from deforming or breaking during high-speed rotation; and it must also have excellent magnetic induction strength to meet the high torque requirements during motor startup or acceleration. In addition to the requirement for excellent magnetic induction strength in the longitudinal direction (rolling direction) and transverse direction (direction perpendicular to the rolling direction), magnetic performance in other directions, particularly in the direction of minimum magnetic value, also has an important impact on motor performance. In other words, it is desirable for the magnetic induction strength in the direction of minimum magnetic value to be very good.

[0005] To meet this demand, some researchers are currently conducting extensive research and achieving some results, but the practical application results are not ideal: For example, a Chinese patent document with publication number CN106435358A, published on February 22, 2017, entitled "Method for Producing High-Strength Non-Oriented Silicon Steel for New Energy Vehicle Drive Motors" discloses a high-strength non-oriented silicon steel for new energy vehicle drive motors, and uses a thin strip continuous casting process and a low-temperature annealing process to obtain a non-oriented silicon steel with a yield strength of 600 to 780 MPa through NbC precipitation and fine grain structure strengthening. However, the non-oriented silicon steel sheet obtained by this technical solution has relatively high iron loss at high frequencies and a low P at 400 Hz. 10 / 400 reaches 28.0 to 38.2 W / kg, and the iron loss further increases at 600 Hz, and at the same time, there is no report on controlling the magnetic anisotropy.

[0006] As another example, a Chinese patent document, Publication No. CN111471941A, published on July 31, 2020, entitled "High-Strength Non-Oriented Silicon Steel with a Yield Strength of 600 MPa for New Energy Vehicle Drive Motor Rotors and Its Manufacturing Method," discloses a high-strength non-oriented silicon steel with the chemical composition: Si: 2.8%-3.5%, Mn: 0.35%-0.65%, and Als: 0.35%-0.65% (wt%); solid solution strengthening is performed by adding any two elements selected from Cr, Nb, Ti, Ni, and V, with a content range of 0.05%-0.55%. This technical solution strengthens the {111} plane structure to obtain a product with a yield strength of 600 MPa or more, but the iron loss P of the product is low. 10 / 400 The loss is high at 22.6 to 30.4 W / kg, and the loss increases as the frequency increases to 600 Hz.

[0007] Based on this, the present inventors have designed and hope to obtain a novel non-oriented electrical steel for electric vehicle drive motors and a manufacturing method thereof that meets the needs of the market and users and differs from the above-mentioned existing technical solutions. Summary of the Invention [Means for solving the problem]

[0008] overview One of the objectives of the present invention is to provide a non-oriented electrical steel for electric vehicle traction motors. This non-oriented electrical steel has the characteristics of high strength, low core loss at high frequencies, high magnetic induction strength, and small magnetic anisotropy, and has good prospects for development and application value. The non-oriented electrical steel can be used effectively to prepare traction motors for new energy vehicles, and can effectively meet market requirements for high rotational speed, miniaturization, high torque, etc. of electric vehicle traction motors.

[0009] In order to achieve the above object, the present invention provides a non-oriented electrical steel for electric vehicle drive motors, and the non-oriented electrical steel sheet contains, in addition to Fe and unavoidable impurities, the following chemical elements in mass %: C≦0.003%, Si: 3.0~4.5%, Al: 0.15~2.5%, Mn: 0.15~2.5%; The non-oriented electrical steel has a magnetic induction strength B of ≥ 1.60T. 50M where B 50M =(B 50L +B 50C +2B 50X ) / 4, where B 50L is the magnetic induction strength in the rolling direction of non-oriented electrical steel when magnetized under a magnetic field of 5000 A / m, and B 50C is the magnetic induction strength perpendicular to the rolling direction of non-oriented electrical steel when magnetized under a magnetic field of 5000 A / m, and B 50X is the minimum value of magnetic induction strength at an angle different from the rolling direction of non-oriented electrical steel when magnetized in a magnetic field of 5000 A / m.

[0010] Preferably, in the non-oriented electrical steel for electric vehicle drive motors according to the invention, the chemical elements, in mass %, are as follows: C≦0.003%, Si: 3.0 to 4.5%, Al: 0.15 to 2.5%, Mn: 0.15 to 2.5%; the balance being Fe and unavoidable impurities.

[0011] In the non-oriented electrical steel for electric vehicle drive motors according to the present invention, the design principles of each chemical element are as follows: C: C is an impurity element that is detrimental to the magnetic properties of non-oriented silicon steel. Therefore, the C content must be strictly controlled to 0.003% or less. That is, the C content in the steel must satisfy the following condition: C≦0.003%.

[0012] In some embodiments, in order to obtain better performance effect, the C element content in mass % is preferably controlled as follows: C≦0.002%.

[0013] Si: Adding an appropriate amount of Si to steel can increase the resistivity and reduce core loss of non-oriented electrical steel sheets; at the same time, Si acts as a solid-solution strengthening element, improving the strength of the steel sheet. Therefore, to maximize the beneficial effects of Si and enable the steel to achieve high yield strength and low core loss at high frequencies, the Si content in the steel must be 3.0% or more. However, it should be noted that the Si content in the steel should not be too high. If the Si content in the steel exceeds 4.5%, the ordered phase Fe3Si or FeSi will appear, rapidly deteriorating the room-temperature plasticity of the material, making industrial large-scale cold-rolled production impossible, and the magnetic induction strength will also deteriorate. Based on this premise and considering the effect of Si content on steel performance, the Si content (by mass%) in the non-oriented electrical steel for electric vehicle traction motors according to the present invention is controlled to 3.0-4.5%, specifically, for example, 3.3-4.2%, 3.5-4.0%, or 3.8%.

[0014] Al: Al is also an effective element for increasing resistivity and reducing iron loss. Considering the effect of this element on iron loss improvement, it is necessary to add 0.15% or more of Al to the steel. However, the Al content in the steel should not be too high. Excessive addition of Al reduces the magnetic induction strength of the steel, makes steelmaking and casting difficult, and leads to deterioration of the cold workability of the steel sheet. Therefore, the amount of Al added to the steel should not exceed 2.5%. Based on this premise, in the non-oriented electrical steel for electric vehicle drive motors according to the present invention, the Al content by mass is controlled to 0.15 to 2.5%, specifically, for example, 0.2 to 2.0%, 0.5 to 1.8%, 0.8 to 1.5%, or 1.0 to 1.2%.

[0015] Mn: Mn can increase the resistivity of steel. At the same time, Mn can react with S to form MnS, thereby improving the electromagnetic performance of steel. Therefore, to achieve the beneficial effects of Mn, it is necessary to add 0.15% or more Mn to steel. However, it should be noted that the Mn content in steel should not be too high. A Mn content exceeding 2.5% in steel can lead to a decrease in the plasticity of the steel and, as a result, strip breakage during cold rolling. Based on this, to achieve the beneficial effects of Mn, the Mn content in the non-oriented electrical steel for electric vehicle drive motors described in the present invention is controlled to 0.15-2.5% by mass, specifically, for example, 0.2-2.0%, 0.5-1.8%, 0.8-1.5%, or 1.0-1.2%.

[0016] The non-oriented electrical steel for electric vehicle drive motors designed according to the present invention not only has high strength, low iron loss at high frequencies, and high magnetic induction strength, but also small magnetic anisotropy. It has a yield strength of ≥ 440 MPa, iron loss P 10 / 600 ≦30W / kg, and magnetic induction strength B 50M ≥ 1.60T.

[0017] Regarding iron loss, as new energy electric vehicle drive motors are rapidly developing toward miniaturization and high efficiency, it is required to minimize the iron loss of non-oriented electrical steel at high frequencies. The non-oriented electrical steel of the present invention has low iron loss, and its iron loss P under the conditions of a magnetic flux density of 1.0 T and a frequency of 600 Hz is 10 / 600 is ≦30W / kg.

[0018] Regarding yield strength, rotors for electric vehicle drive motors must have high reliability during high-speed operation. In particular, when the rotational speed exceeds 15,000 rpm, the core material must have sufficient strength to avoid deformation or breakage. The non-oriented electrical steel of the present invention has a high yield strength, and its yield strength is ≥ 440 MPa.

[0019] Regarding magnetic induction strength, the direction of magnetization of the steel sheet constantly changes during the operation of an electric vehicle drive motor. In motor design, the non-oriented electrical steel used must not only have excellent magnetic induction strength in the longitudinal direction (rolling direction) and transverse direction (direction perpendicular to the rolling direction), but magnetic performance in other directions, especially magnetic induction strength in the direction of the minimum magnetic performance value, also has an important impact on motor performance.

[0020] Magnetic induction strength B of the non-oriented electrical steel according to the present invention 50M is ≧1.60T, and B 50M =(B 50L +B 50C +2B 50X ) / 4, thereby satisfying the above requirements for magnetic induction strength of electric vehicle drive motors and providing a non-oriented electrical steel with small magnetic anisotropy.

[0021] Preferably, in the non-oriented electrical steel for electric vehicle drive motors according to the present invention, C≦0.002%.

[0022] Preferably, in the non-oriented electrical steel for electric vehicle drive motors according to the present invention, the unavoidable impurities are P≦0.03%, S≦0.003%, N≦0.005%, and O≦0.0030%.

[0023] In the non-oriented electrical steel for electric vehicle drive motors described in the present invention, the elements P, S, N, and O are all impurity elements in the non-oriented electrical steel sheet. As far as technical conditions permit, the content of impurity elements in the steel should be reduced as much as possible to obtain steel with better performance and better quality.

[0024] P: In the present invention, P is a grain boundary segregation element. In a composition system where Si≧3.0%, if the content of the impurity element P in the steel exceeds 0.03%, the brittleness of the electrical steel sheet increases and rolling of the electrical steel sheet becomes difficult. Therefore, in the non-oriented electrical steel for electric vehicle drive motors described in the present invention, the content of the P element is controlled to P≦0.03% by mass. In some preferred embodiments, it can be further controlled to P≦0.02%, or P≦0.01%, or P≦0.005%.

[0025] S: In the present invention, S is an element that is harmful to magnetic properties. The S element combines with Mn to form fine MnS, which inhibits grain growth during finish annealing and deteriorates the magnetic properties of the steel sheet. Therefore, in the non-oriented electrical steel for electric vehicle drive motors described in the present invention, the S element content is controlled to S≦0.003% by mass.

[0026] N: In the present invention, N is an element that is detrimental to magnetic performance. N forms fine nitrides with elements such as Al, Ti, Nb, and V, inhibiting grain growth. Therefore, in the non-oriented electrical steel for electric vehicle drive motors described in the present invention, the N content is controlled to N≦0.005% by mass. In some preferred embodiments, it can be further controlled to N≦0.0035%.

[0027] O: In the present invention, O is a harmful element. In a composition system where Si is 3.0% or more, the cold workability of the material is very sensitive to oxygen segregation at grain boundaries. At the same time, the resulting oxides of silicon, aluminum, manganese, etc. also deteriorate the magnetic performance of the material. Therefore, in the non-oriented electrical steel for electric vehicle drive motors described in the present invention, the content of the O element is controlled so that O is ≦0.0030% by mass.

[0028] Preferably, in the non-oriented electrical steel for electric vehicle drive motors according to the present invention, the unavoidable impurities are P≦0.02% and N≦0.0035%.

[0029] Preferably, the non-oriented electrical steel for electric vehicle drive motors according to the present invention further contains, by mass %, 0.0005% to 0.010% B.

[0030] In the present invention, in order to further optimize the performance of the designed non-oriented electrical steel for electric vehicle drive motors, it is preferable to further add an appropriate amount of B element to the steel.

[0031] B: B is a grain boundary strengthening element, which enhances the grain boundary bonding ability of high-silicon compositions, thereby improving the cold-rolling processability of the material. However, it is important to note that an appropriate amount of B must be added to the steel. Excessive addition of B refines the grain structure and does not contribute to magnetic performance. Therefore, the B content should not exceed 0.010%; and if the B content in the steel is less than 0.0005%, the grain boundary strengthening effect cannot be achieved. Therefore, in the non-oriented electrical steel for electric vehicle drive motors described in this invention, it is preferable to add 0.0005% to 0.010% of B.

[0032] Preferably, the non-oriented electrical steel for electric vehicle drive motors according to the present invention further contains at least one element selected from Co, Ni, Sn, Sb, Cu and Cr in a total amount of 0.020 to 4.0 mass %.

[0033] In the present invention, it is preferable to further add Co, Ni, Sn, Sb, Cu, Cr or a combination thereof to the non-oriented electrical steel for electric vehicle drive motors.

[0034] Sn and Sb are both grain boundary segregating elements; on the one hand, they inhibit the diffusion of trace oxygen along grain boundaries during the normalizing process of hot-rolled steel sheets, preventing oxidation and plastic deformation of the steel sheets. On the other hand, Sn and Sb can improve the {100} surface structure and Goss structure during the final annealing process, which are beneficial to magnetic performance. Elements such as Co, Ni, Cu, and Cr can play a role in solid solution strengthening and can also increase the resistivity and core loss performance of steel.

[0035] In the present invention, in order to exert the beneficial effects of the above elements, it is preferable to add at least one selected from Co, Ni, Sn, Sb, Cu, and Cr, and the total mass% of these elements is controlled to be 0.020% or more. If the total mass% of these elements exceeds 4.0%, the improving effects provided by these elements tend to saturate, and the manufacturing cost increases. Therefore, the total mass% of these elements should not exceed 4.0%.

[0036] Preferably, the non-oriented electrical steel for electric vehicle drive motors according to the present invention has a thickness of 0.1 to 0.3 mm. This is because: by reducing the thickness, eddy current loss in iron loss at high frequencies can be effectively reduced, so the thickness of the finished steel sheet is preferably 0.30 mm or less; and from the perspective of drive motor production efficiency, if the steel sheet used is too thin, production efficiency will decrease, so it is preferable to control the thickness of the finished steel sheet to 0.10 mm or more.

[0037] Preferably, the non-oriented electrical steel for electric vehicle drive motors according to the present invention has a yield strength of ≥ 440 MPa and an iron loss P 10 / 600 ≦30W / kg.

[0038] Another object of the present invention is to provide a method for producing the above-mentioned non-oriented electrical steel for electric vehicle drive motors, which is simple and easy to implement, and by this method, it is possible to obtain a non-oriented electrical steel sheet having excellent mechanical and electromagnetic properties.

[0039] In order to achieve the above object of the invention, the present invention provides a method for producing a non-oriented electrical steel for an electric vehicle drive motor, comprising the following steps: (1) Preparing the casting slab; (2) The cast slab is hot-rolled to obtain a hot-rolled sheet with a thickness of 1.5 to 2.2 mm; (3) Normalizing and annealing the hot-rolled sheet at a normalizing temperature of 820°C to 950°C; (4) Cold rolling to obtain cold-rolled sheet; (5) Continuously anneal the cold-rolled sheet in a continuous annealing furnace; (6) Apply an insulating coating.

[0040] In this invention, the inventors have optimized the chemical composition design of the steel and defined a rational manufacturing process. After continuously casting slabs according to the designed chemical composition, the slabs must be sequentially subjected to the following process steps: hot rolling, normalizing annealing, cold rolling (for example, single cold rolling or double cold rolling with intermediate annealing), final continuous annealing, and coating with an insulating coating. This effectively produces a non-oriented electrical steel for electric vehicle drive motors with excellent overall performance. This non-oriented electrical steel for electric vehicle drive motors can be used to effectively manufacture electric vehicle drive motors and has the properties of high strength, low core loss at high frequencies, high magnetic induction, and small magnetic anisotropy.

[0041] In the hot rolling process of step (2) according to the present invention, to obtain a thin-gauge hot-rolled sheet, the thickness of the hot-rolled sheet obtained by hot rolling must be controlled to between 1.5 mm and 2.2 mm or less. This is because: by reducing the thickness of the hot-rolled sheet and reducing the reduction rate of the cold rolling, the structural components of the cold-rolled sheet can be improved and the strength of undesirable structures (γ fiber structures) can be reduced. However, care must be taken because making the hot-rolled sheet too thin increases the difficulty of production and deteriorates the sheet shape, which is disadvantageous in suppressing thickness variation within a single sheet. Therefore, the thickness of the hot-rolled sheet must be controlled to be 1.5 mm or more.

[0042] Therefore, in the normalizing annealing process of step (3) according to the present invention, the hot-rolled sheet can be transported to a horizontal continuous annealing furnace for normalizing, and the normalizing annealing temperature is strictly controlled between 820°C and 950°C. The normalizing treatment can improve the magnetic induction strength of the final product. However, if the temperature is too low, the effect of improving the magnetic induction strength cannot be obtained. Therefore, in the present invention, the normalizing annealing temperature is controlled to 820°C or higher. Furthermore, from the viewpoint of workability, in a high-silicon composition system, particularly a normalized sheet with a Si+Al content exceeding 4.5%, the grain size of the steel sheet is too large, making the strip steel prone to breakage during cold rolling and making production difficult. Therefore, in the present invention, the normalizing annealing temperature is controlled to 950°C or lower, and the holding time can be preferably controlled to 3 minutes or less.

[0043] Preferably, in step (3) of the manufacturing method according to the present invention, the unit tension F of the steel strip in the annealing furnace used for normalizing annealing is expressed by the relational expression (2): 1.5≦F≦(3.8+0.3d) / ([Si] 2 × T), where d is the thickness of the hot-rolled sheet in mm, T is the normalizing annealing temperature in °C, [Si] is the mass% of silicon in the hot-rolled sheet, and F is in N / mm 2 is.

[0044] The above phrase "[Si] is the mass % of silicon element in the hot-rolled sheet" means that if the content of [Si] is, for example, 3.0%, 3.0% is substituted into relational expression (2).

[0045] In the present invention, by controlling the small tension in the annealing furnace, the uniform recrystallization nucleation and growth of grains in various directions of the strip steel during annealing can be promoted, the magnetic performance in other directions can be improved, and the magnetic anisotropy can be reduced, thereby achieving a high magnetic induction strength B 50M can be obtained.

[0046] In the present invention, the normalizing annealing temperature is controlled to be 820°C to 950°C, and the unit tension F in the annealing furnace is set to satisfy the relational formula (2), thereby controlling the grain structure of non-oriented electrical steel based on the conventional continuous annealing process, so that the average grain size D is 20 to 105 μm, and the average grain size D and the standard deviation of grain size distribution S can satisfy the following relational formula (1): 0.78≦S / D<1.0 (1).

[0047] If the average grain size D of the non-oriented electrical steel and the relationship between the average grain size D and the standard deviation S of the grain size distribution do not satisfy the above conditions, the core loss and yield strength of the non-oriented electrical steel will deteriorate, and the distribution of the grain structure will be unreasonable, which will result in an increase in magnetic anisotropy and magnetic induction B. 50M If the average grain size of the non-oriented electrical steel is less than 20 μm, the yield strength is improved, but the iron loss P 10 / 600 The S / D ratio may be worse and may exceed 30 W / kg; if the average grain size of non-oriented electrical steel exceeds 105 μm, the yield strength decreases. Alternatively, the S / D ratio may be 0.80 to 0.90, or 0.82 to 0.87.

[0048] In the present invention, the setting range of the value of unit tension F of the steel strip in the annealing furnace is related to the silicon content [Si] in the steel, the normalizing annealing temperature T, and the hot-rolled sheet thickness d; here, the higher the Si element content [Si] in the steel, the higher the normalizing annealing temperature T, and the thinner the hot-rolled sheet thickness d, the smaller the upper limit of the value of unit tension F of the steel strip in the annealing furnace. This is because: the higher the Si element content [Si] in the steel, especially when it exceeds 3.5%, the greater the risk of brittle fracture of the steel strip; and the higher the normalizing annealing temperature T and the thinner the hot-rolled sheet thickness d, the more easily the steel deforms in the high-temperature zone.

[0049] However, in the technical solution designed by the present invention, it should be noted that if the value of the unit tension F of the steel strip in the annealing furnace is too low, the steel strip will be deviated and damaged. Therefore, in the present invention, the value of the unit tension F of the steel strip in the annealing furnace is set to 1.5 N / mm 2 The control is performed so that the above is true.

[0050] Compared with the prior art, the non-oriented electrical steel for electric vehicle drive motors and the manufacturing method thereof according to the present invention have the following advantages and beneficial effects: The present inventors have optimized the chemical element composition ratio and related manufacturing process of the non-oriented electrical steel for electric vehicle drive motors described in the present invention. The non-oriented electrical steel for electric vehicle drive motors manufactured by this manufacturing method has the properties of high strength, low core loss at high frequencies, high magnetic induction strength, and also has the properties of small magnetic anisotropy.

[0051] The non-oriented electrical steel for electric vehicle drive motors designed in this invention has a yield strength of 440 MPa or more and an iron loss P 10 / 600 ≦30W / kg, and magnetic induction strength B 50M ≧1.60T. This non-oriented electrical steel for electric vehicle drive motors can be used to effectively prepare drive motors for new energy vehicles, and can effectively meet the market requirements for high rotation speed, miniaturization, high torque, etc. of electric vehicle drive motors, which has good promotion prospects and application value.

[0052] Detailed explanation The non-oriented electrical steel for electric vehicle traction motors and its manufacturing method according to the present invention will be further described and illustrated with reference to specific examples below, but the description and illustrations should not be construed as unduly limiting the technical solutions of the present invention.

[0053] Examples 1 to 10 and Comparative Examples 1 to 6 Table 1 shows the mass % of each chemical element in the non-oriented electrical steels for electric vehicle drive motors of Examples 1 to 10 and the comparative steel sheets of Comparative Examples 1 to 6.

[0054] [Table 1]

[0055] The non-oriented electrical steels for electric vehicle drive motors of Examples 1 to 10 and the comparative steel sheets of Comparative Examples 1 to 6 were produced by the following steps: (1) A cast slab is prepared according to the chemical composition shown in Table 1. (2) Hot rolling: The resulting cast slab is hot rolled to obtain a hot rolled sheet having a thickness of 1.5 to 2.2 mm. (3) Normalizing: The obtained hot-rolled sheet is transported to a horizontal continuous annealing furnace and normalized. The normalizing temperature is controlled to 820°C to 950°C, the normalizing holding time is controlled to 90 seconds, and the unit tension F of the strip steel in the annealing furnace is determined by the following formula: 1.5≦F≦(3.8+0.3d) / ([Si] 2 × T), where d is the thickness of the hot-rolled sheet in mm, T is the normalizing annealing temperature in °C, [Si] is the silicon content (mass%) in the hot-rolled sheet, and F is in N / mm 2 is. (4) Cold rolling: Single cold rolling, or first cold rolling + intermediate annealing + second cold rolling is carried out to achieve the target thickness and obtain a cold-rolled sheet. (5) The cold-rolled sheet is continuously annealed in a continuous annealing furnace. (6) Apply an insulating coating.

[0056] It should be noted that in the present invention, the chemical compositions and related process parameters of the non-oriented electrical steels for electric vehicle drive motors in Examples 1 to 10 all meet the control requirements of the design specifications according to the present invention; however, in Comparative Examples 1 to 6, although the comparative steels of Comparative Examples 1 to 6 are also prepared by the above-mentioned process steps, there are parameters in their chemical element compositions and / or related process parameters that do not comply with the design of the present invention.

[0057] Table 2 shows the specific process parameters and final product thicknesses of the non-oriented electrical steels for electric vehicle drive motors of Examples 1 to 10 and the comparative steel sheets of Comparative Examples 1 to 6 in the above manufacturing process.

[0058] [Table 2]

[0059] The final non-oriented electrical steels for electric vehicle drive motors of Examples 1 to 10 and the comparative steel sheets of Comparative Examples 1 to 6 were sampled, and the mechanical properties, magnetic induction and iron loss of the steel sheet samples of Examples 1 to 10 and Comparative Examples 1 to 6 were tested. The yield strength, magnetic induction strength B 50M and iron loss P 10 / 600 The test results obtained are shown in Table 3 below.

[0060] The relevant performance test methods are as follows: Grain size statistics of steel sheets: Using EBSD testing, each grain area is counted, and the average grain size D and grain size distribution standard deviation S are calculated.

[0061] Tensile test: The mechanical properties of the steel plates of each example and comparative example are tested according to the national standard "GB / T 228.1-2010 Metallic Material Tensile Test Part 1: Room Temperature Test Method" to obtain the yield strength of the steel plates of each example and comparative example.

[0062] Magnetic induction performance test: The magnetic induction performance test was carried out using the square method in accordance with the national standard "GB / T3655-2008 Method for measuring the magnetic properties of electrical steel sheets (strips) using Epstein squares." For each example and comparative example, the magnetic induction strength B in the rolling direction when magnetized under a magnetic field of 5000 A / m was measured. 50L , magnetic induction intensity perpendicular to the rolling direction B 50C , and the minimum value B of the magnetic induction strength of the steel sheet at an angle different from the rolling direction 50X get.

[0063] At the same time, the magnetic induction strength B of the steel sheet samples of Examples 1 to 10 and Comparative Examples 1 to 6 50M B obtained above 50L , B 50C and B 50X Based on Equation B 50M =(B 50L +B 50C +2B 50X ) / 4.

[0064] Iron loss performance test: The iron loss performance test was performed using the square method in accordance with the standard "GB / T10129-2019 Measurement method for medium-frequency magnetic properties of electromagnetic steel strips (sheets)." The iron loss P 10 / 600 get.

[0065] Table 3 shows the test results of the non-oriented electrical steels for electric vehicle drive motors of Examples 1 to 10 and the comparative steel sheets of Comparative Examples 1 to 6.

[0066] [Table 3]

[0067] Referring to Tables 1, 2, and 3 above, it can be seen that in the present invention, the non-oriented electrical steels for electric vehicle drive motors of Examples 1 to 4 are produced using a single cold rolling process, and the processes for controlling the chemical composition, hot-rolled sheet thickness, normalizing annealing temperature, and furnace tension are all within the design range of the present invention, and non-oriented silicon steels with small iron loss at high frequencies, excellent magnetic anisotropy, and high yield strength can be ultimately obtained.

[0068] The chemical composition design and process of the non-oriented electrical steel for electric vehicle drive motors in Examples 5 to 10 also meet the requirements of the present invention. In Examples 5 to 10, micro-alloying and double cold rolling, which are different from those in Examples 1 to 4, can further improve the performance of the final steel sheet.

[0069] As shown in Table 3 above, in the present invention, the non-oriented electrical steels for electric vehicle drive motors of Examples 1 to 10 have a yield strength of 448 to 565 MPa, a magnetic induction strength B of 1.632 to 1.662 T, and 50M , and iron loss P of 17.5 to 28.5 W / kg 10 / 600 The overall performance of the non-oriented electrical steels for electric vehicle drive motors of Examples 1 to 10 is significantly better than that of the comparative steel sheets of Comparative Examples 1 to 6. Comparative Examples 1 to 6 do not meet the conditions stipulated by the technical solution of the present invention, and therefore the implementation effects of Comparative Examples 1 to 6 are inferior to those of the present invention.

[0070] The five comparative examples prepared herein can be further analyzed and explained with reference to the data presented in Tables 1, 2 and 3 above.

[0071] In Comparative Examples 1 to 3, the chemical composition used for the steel is within the range designed in the present invention, but the normalizing annealing temperature used during production is low (Comparative Example 1), or the furnace tension F used is high (Comparative Example 2 and Comparative Example 3), resulting in a low magnetic induction strength B of the final product. 50M is poor.

[0072] In Comparative Examples 4 to 6, the manufacturing processes employed meet the design requirements of the present invention, but the chemical composition contains parameters that do not meet the design requirements of the present invention: the Si content or Al content in the steel is relatively low, which results in relatively high iron loss at high frequency and the yield strength of the finally prepared steel sheet is lower than 440 MPa.

[0073] It should be noted that the prior art part in the protection scope of the present invention is not limited to the embodiments described in the application documents, and all prior art parts that are not contrary to the solution means of the present invention, including but not limited to prior patent documents, prior publications, prior known uses, etc., may be included in the protection scope of the present invention.

[0074] Furthermore, the combinations of the technical features of the present invention are not limited to the combinations described in the claims or in the specific embodiments of the present invention, and all the technical features of the present invention can be freely combined in any way as long as they are not inconsistent with each other.

[0075] It should be noted that the above-described embodiments are merely specific examples of the present invention. It is clear that the present invention is not limited to the above-described embodiments, and various changes or modifications can be made. Such changes or modifications can be directly obtained or easily conceived by those skilled in the art from the disclosure of the present invention, and all of them are included in the scope of the present invention.

Claims

1. Non-oriented electrical steel for electric vehicle drive motors containing, in addition to Fe and unavoidable impurities, the following chemical elements in mass %: C≦0.003%, Si: 3.0~4.5%, Al: 0.15~2.5%, Mn: 0.15~2.5%; The non-oriented electrical steel for electric vehicle drive motors has a magnetic induction strength B of ≥ 1.60T. 50M where B 50M = (B 50L +B 50C +2B 50X ) / 4, where B 50L is the magnetic induction strength in the rolling direction of the non-oriented electrical steel when magnetized under a magnetic field of 5000 A / m, and B 50C is the magnetic induction strength perpendicular to the rolling direction of the non-oriented electrical steel when magnetized in a magnetic field of 5000 A / m, and B 50X is the minimum value of the magnetic induction strength of the non-oriented electrical steel at an angle different from the rolling direction when magnetized in a magnetic field of 5000 A / m.

2. 2. A non-oriented electrical steel for electric vehicle drive motors according to claim 1, comprising the following chemical elements in mass %: C≦0.003%, Si: 3.0 to 4.5%, Al: 0.15 to 2.5%, Mn: 0.15 to 2.5%; the balance is Fe and unavoidable impurities.

3. 3. The non-oriented electrical steel for electric vehicle drive motors according to claim 1, wherein C is ≦0.002%.

4. 3. The non-oriented electrical steel for electric vehicle drive motors according to claim 1, wherein the unavoidable impurities are P≦0.03%, S≦0.003%, N≦0.005%, and O≦0.0030%.

5. 5. The non-oriented electrical steel for electric vehicle drive motors according to claim 4, wherein, among the unavoidable impurities, P is ≦0.02% and N is ≦0.0035%.

6. 3. The non-oriented electrical steel for electric vehicle drive motors according to claim 1, further comprising B in an amount of 0.0005% by mass to 0.010% by mass.

7. 3. The non-oriented electrical steel for electric vehicle drive motors according to claim 1, further containing 0.020 to 4.0 mass% in total of at least one selected from Co, Ni, Sn, Sb, Cu, and Cr.

8. 3. The non-oriented electrical steel for electric vehicle drive motors according to claim 1, having a thickness of 0.1 to 0.3 mm.

9. 3. The non-oriented electrical steel for electric vehicle drive motors according to claim 1, having an average grain size D of 20 to 105 μm, and the average grain size D and the grain size distribution standard deviation S satisfy the following relational expression (1): 0.78≦S / D<1.0 (1).

10. Yield strength ≥ 440 MPa, and iron loss P 10／600 3. The non-oriented electrical steel for electric vehicle drive motors according to claim 1, having a strength of ≦30 W / kg.

11. A method for producing a non-oriented electrical steel for electric vehicle drive motors according to any one of claims 1 to 10, comprising the following steps: (1) Preparing a casting slab; (2) The cast slab is hot-rolled to obtain a hot-rolled sheet having a thickness of 1.5 to 2.2 mm; (3) Normalizing and annealing the hot-rolled sheet at a normalizing temperature of 820°C to 950°C; (4) Cold rolling to obtain cold-rolled sheet; (5) Continuously annealing the cold-rolled sheet in a continuous annealing furnace; (6) Apply an insulating coating.

12. The method according to claim 11, wherein in the step (3), normalizing annealing is performed using a horizontal continuous annealing furnace.

13. In step (3), the unit tension F of the strip steel in the annealing furnace for normalizing annealing is calculated according to the following formula (2): 1.5≦F≦(3.8+0.3d) / ([Si] 2 × T), where d is the thickness of the hot-rolled sheet in mm, T is the normalizing annealing temperature in °C, [Si] is the mass% of silicon in the hot-rolled sheet, and F is in N / mm 2 The method for producing a semiconductor device according to claim 11, wherein the control is performed so as to satisfy the following condition:

14. 12. The method according to claim 11, wherein in step (4), the cold rolling is a single cold rolling or a double cold rolling including an intermediate annealing.

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