Thin-gauge non-oriented silicon steel and its production method, motor iron core and its manufacturing method

Abstract

The present invention discloses a thin-gauge non-oriented silicon steel, a production method thereof, and a motor core and a manufacturing method thereof. The production method comprises: heating the steel billet to 1080-1120°C and holding the temperature for 150-200 minutes, first rough rolling to obtain a 35-45mm intermediate billet, and then finishing rolling and coiling to obtain a 2.30-3.00mm hot-rolled coil; the finishing rolling has a starting temperature of 970±20°C, a final rolling temperature of 850±20°C, a reduction ratio of more than 92%, and a coiling temperature of 700±20°C; pickling and cold rolling are performed without normalization to obtain a 0.15-0.35mm cold-rolled strip; the total cold rolling reduction is ≥86%; after a single annealing, cooling, and coating, a finished steel plate is obtained; the annealing temperature is 830-870°C and the temperature is held for 60-90 seconds. In this way, the same piece of non-oriented silicon steel can meet the needs of both the stator and rotor cores, reducing the manufacturing cost of the stator and rotor cores and avoiding material waste.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material preparation, and relates to a production method of thin-gauge non-oriented silicon steel for motor stator and rotor cores, and also relates to a motor core and a manufacturing method thereof. Background Art

[0002] The drive motor is one of the three core components of an electric vehicle. Its driving characteristics directly determine key performance indicators such as hill climbing, acceleration, and top speed. It is a crucial component of electric vehicles. Based on electromagnetic induction, the electric vehicle drive motor uses the stator to generate a rotating magnetic field, which acts on the rotor to generate magnetoelectric power, driving the vehicle.

[0003] Non-oriented silicon steel is an important material used to manufacture the core components of motors - stator and rotor cores, and iron loss is one of the important magnetic performance parameters of non-oriented silicon steel.

[0004] Based on research, there are two main ways to reduce iron loss: increasing the resistivity of the steel sheet and reducing its thickness. Increasing the Si and Al content in non-oriented silicon steel can increase the steel sheet's resistivity, thereby reducing its iron loss. However, as the Si and Al content increases, the rollability of the steel sheet decreases, hindering smooth production. Therefore, reducing iron loss by increasing the Si and Al content has certain limitations. Reducing the thickness of the steel sheet not only directly reduces iron loss, but also increases the steel sheet's resistivity, thereby indirectly reducing iron loss. Therefore, as the speed and frequency of the motor increase, reducing the thickness of the non-oriented silicon steel is the most effective method for reducing iron loss.

[0005] In particular, given that the stator core has higher requirements for magnetic properties, reducing iron loss by reducing the thickness of the steel plate is an important research direction for non-oriented silicon steel used in stator cores.

[0006] Furthermore, in drive motors, as speed and frequency increase, the rotor core requires higher structural strength to overcome the challenges of high centrifugal forces. To ensure structural strength, the rotor core must be made of relatively thick non-oriented silicon steel or non-oriented silicon steel with higher mechanical strength.

[0007] Obviously, in terms of thickness, the rotor core and the stator core have different requirements for the thickness of non-oriented silicon steel - the rotor core requires a thicker steel plate based on structural strength requirements, and the stator core requires a thinner steel plate based on iron loss requirements.

[0008] On the other hand, the high mechanical strength required for the rotor core is usually achieved through solid solution strengthening, precipitation strengthening, dislocation strengthening and grain refinement. For example: 1. Adding a large amount of alloying elements such as Cu, Cr, Ni, Nb, V, Ti, etc. to the composition; 2. Using incomplete recrystallization annealing or secondary cold rolling. However, these methods will destroy the magnetic properties and cause the iron loss of the steel plate to increase.

[0009] Due to the aforementioned reasons, existing technologies for manufacturing high-speed drive motors for electric vehicles generally require separate non-oriented silicon steel sheets for the rotor core and stator core. This involves using a thin non-oriented silicon steel sheet for the stator core and a thick non-oriented silicon steel sheet, or a thin non-oriented silicon steel sheet with poor magnetic properties, for the rotor core. This not only increases the manufacturing cost of the motor but also results in a significant waste of non-oriented silicon steel materials.

[0010] So far, there has never been a corresponding product in the field of non-oriented silicon steel that can meet the application requirements of stator core and rotor core at the same time. Summary of the Invention

[0011] In order to solve the technical problem that existing non-oriented silicon steel cannot simultaneously meet the application requirements of stator core and rotor core, the purpose of the present invention is to provide a non-oriented silicon steel and a production method thereof, especially a thin-gauge non-oriented silicon steel for motor stator and rotor core and a production method thereof.

[0012] In order to solve the technical problem that the same non-oriented silicon steel sheet cannot be used to produce the stator core and the rotor core, the present invention also aims to provide a motor core and a method for manufacturing the motor core.

[0013] To achieve the above-mentioned purpose, an embodiment of the present invention provides a method for producing non-oriented silicon steel. The production method comprises:

[0014] Steelmaking process: Molten steel is refined and cast into billets with a thickness of 200-240mm. After leaving the continuous casting machine, the billets are kept at a temperature range of 600-900℃ for 3-8 hours. The chemical composition of the billets, in mass percentage, includes: C ≤ 0.0025%, S ≤ 0.0020%, Si 3.00-3.40%, Al 0.50-1.00%, Mn 0.30-0.80%, P ≤ 0.015%, Nb ≤ 0.003%, V ≤ 0.003%, Ti ≤ 0.003%, Cr ≤ 0.02%, Ni ≤ 0.02%, Cu ≤ 0.02%, N ≤ 0.0020%. The rest is Fe and unavoidable inclusions.

[0015] Hot rolling process: After heating the steel billet to 1080-1120℃ and holding it for 150-200min, it is first rough rolled to obtain an intermediate billet with a thickness of 35-45mm. Then, it is finished rolled and coiled to obtain a hot-rolled coil with a thickness of 2.30-3.00mm. The starting rolling temperature of the finishing rolling is 970±20℃, the final rolling temperature is 850±20℃, the finishing reduction is controlled at more than 92%, and the coiling temperature is 700±20℃.

[0016] Cold rolling process: The hot-rolled coil is pickled and cold-rolled once without normalization to obtain cold-rolled strip with a thickness of 0.15-0.35 mm. The total cold rolling reduction is ≥86%.

[0017] Primary annealing: The cold-rolled strip is subjected to primary annealing, cooling, and coating to obtain a finished steel plate. The annealing temperature is 830-870°C and the temperature is maintained for 60-90 seconds.

[0018] Preferably, in the hot rolling process: the steel billet is fed into a heating furnace for heating, the furnace entry temperature is ≥450°C, the preheating temperature is 950-1000°C, the heating and soaking temperature is 1080-1120°C, and the total heating and soaking time is 150-200 minutes.

[0019] Preferably, in the cold rolling process, the first cold rolling reduction rate is 32-34%, the last cold rolling reduction rate is 20-25%, and the remaining cold rolling reduction rates are 25-30%.

[0020] Preferably, the production method further comprises,

[0021] Stamping process: stamping the finished steel plate to obtain a series of thin sheets;

[0022] Secondary annealing process: first, a series of thin sheets are laminated and pressed, and then secondary annealing is performed; alternatively, a series of thin sheets are secondary annealed first, and then laminated and pressed; wherein, during the secondary annealing: the heating rate is ≤5°C / min, the annealing temperature is 900~940°C, and the holding time is 90~120min.

[0023] Preferably, in the secondary annealing process: after the heat preservation is completed, the cooling rate is controlled to be ≤3°C / min.

[0024] Preferably, in the stamping process: a series of pairs of rotor sheets and stator sheets are stamped out from the finished steel plate, with each pair of rotor sheets and stator sheets being concentrically distributed; the stator sheets enter the secondary annealing process to prepare the stator core;

[0025] The production method further comprises a rotor core preparation step: a series of rotor sheets are assembled into a rotor core by lamination press-fitting.

[0026] To achieve the above-mentioned object of the invention, an embodiment of the present invention provides a non-oriented silicon steel, characterized in that its chemical composition, in percentage by mass, includes: C≤0.0025%, S≤0.0020%, Si 3.00-3.40%, Al 0.50-1.00%, Mn 0.30-0.80%, P≤0.015%, Nb≤0.003%, V≤0.003%, Ti≤0.003%, Cr≤0.02%, Ni≤0.02%, Cu≤0.02%, N≤0.0020%, and the rest is Fe and unavoidable inclusions;

[0027] The non-oriented silicon steel is a steel plate with a thickness of 0.15-0.35 mm, an average grain size of 20-40 μm, and an iron loss of P 1.0 / 400 ≤22.0W / kg, magnetic induction intensity B 5000 ≥1.62T, yield strength ≥550MPa, tensile strength ≥650MPa, elongation ≥12%.

[0028] Preferably, after secondary annealing, the average grain size of the non-oriented silicon steel is 90-120 μm, and the iron loss P is 1.0 / 400 ≤19.0W / kg, magnetic induction intensity B 5000 ≥1.63T;

[0029] Among them, during the secondary annealing: the heating rate is ≤5°C / min, the annealing temperature is 900~940°C, and the heat preservation time is 90~120min.

[0030] Preferably, the non-oriented silicon steel is a steel plate with a thickness of 0.35 mm and an iron loss P of 1.0 / 400 ≤22.0W / kg, magnetic induction intensity B 5000 ≥1.64T, and after secondary annealing, its iron loss P 1.0 / 400 ≤19.0W / kg, magnetic induction intensity B 5000 ≥1.65T;

[0031] Alternatively, the non-oriented silicon steel is a steel plate with a thickness of 0.30 mm, and its iron loss P 1.0 / 400 ≤18.0W / kg, magnetic induction intensity B 5000 ≥1.63T, and after secondary annealing, its iron loss P 1.0 / 400 ≤15.0W / kg, magnetic induction intensity B 5000 ≥1.64T;

[0032] Alternatively, the non-oriented silicon steel is a steel plate with a thickness of 0.25 mm, and its iron loss P 1.0 / 400 ≤16.0W / kg, magnetic induction intensity B 5000 ≥1.63T, and after secondary annealing, its iron loss P 1.0 / 400≤13.0W / kg, magnetic induction intensity B 5000 ≥1.64T;

[0033] Alternatively, the non-oriented silicon steel is a steel plate with a thickness of 0.20 mm, and its iron loss P 1.0 / 400 ≤15.0W / kg, magnetic induction intensity B 5000 ≥1.62T, and after secondary annealing, its iron loss P 1.0 / 400 ≤12.0W / kg, magnetic induction intensity B 5000 ≥1.63T;

[0034] Alternatively, the non-oriented silicon steel is a steel plate with a thickness of 0.15 mm, and its iron loss P 1.0 / 400 ≤14.0W / kg, magnetic induction intensity B 5000 ≥1.62T, and after secondary annealing, its iron loss P 1.0 / 400 ≤11.0W / kg, magnetic induction intensity B 5000 ≥1.63T.

[0035] To achieve the above-mentioned object of the invention, an embodiment of the present invention provides a method for manufacturing a motor core, characterized in that the manufacturing method includes:

[0036] Stamping process: stamping the non-oriented silicon steel to obtain a series of thin sheets;

[0037] Secondary annealing process: first, a series of thin sheets are laminated and pressed, and then secondary annealing is performed; alternatively, a series of thin sheets are secondary annealed first, and then laminated and pressed; wherein, during the secondary annealing: the heating rate is ≤5°C / min, the annealing temperature is 900~940°C, and the holding time is 90~120min.

[0038] To achieve the above-mentioned purpose, an embodiment of the present invention provides a motor core. The motor core includes a laminated rotor core and a laminated stator core;

[0039] The laminated rotor core and the laminated stator core are both made of non-oriented silicon steel with a thickness of 0.15-0.35 mm, and the chemical composition, in mass percentage, includes: C≤0.0025%, S≤0.0020%, Si 3.00-3.40%, Al 0.50-1.00%, Mn 0.30-0.80%, P≤0.015%, Nb≤0.003%, V≤0.003%, Ti≤0.003%, Cr≤0.02%, Ni≤0.02%, Cu≤0.02%, N≤0.0020%, and the rest is Fe and unavoidable inclusions;

[0040] The average grain size of the non-oriented silicon steel sheets of the laminated rotor core is 20-40 μm, and the iron loss P 1.0 / 400≤22.0W / kg, magnetic induction intensity B 5000 ≥1.62T, yield strength ≥550MPa, tensile strength ≥650MPa, elongation ≥12%;

[0041] The average grain size of the non-oriented silicon steel sheets of the laminated stator core is 90-120 μm, and the iron loss P 1.0 / 400 ≤19.0W / kg, magnetic induction intensity B 5000 ≥1.63T.

[0042] Compared with the prior art, the present invention has the following beneficial effects: the same piece of non-oriented silicon steel can meet the needs of both the stator core and the rotor core. Compared with the current situation in which the non-oriented silicon steel products used for the stator core and the rotor core must be prepared separately in the conventional technology, not only the manufacturing cost of the motor and its stator and rotor core is greatly reduced, but also the full utilization of the non-oriented silicon steel material is greatly realized, thereby avoiding material waste; in addition, the design based on chemical composition, grain size, performance and other aspects can also make the production process of the non-oriented silicon steel simple and easy to implement, improve the rollability, avoid the conventional normalizing treatment, and save energy and reduce consumption. DETAILED DESCRIPTION

[0043] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0044] An embodiment of the present invention provides a thin-gauge non-oriented silicon steel, which can meet the use requirements of the rotor core and the requirements of the stator core for the base material, that is, can meet the use requirements of the stator core.

[0045] The chemical composition of the non-oriented silicon steel includes, by mass percentage, C≤0.0025%, S≤0.0020%, Si3.00~3.40%, Al 0.50~1.00%, Mn 0.30~0.80%, P≤0.015%, Nb≤0.003%, V≤0.003%, Ti≤0.003%, Cr≤0.02%, Ni≤0.02%, Cu≤0.02%, N≤0.0020%, and the rest is Fe and unavoidable inclusions.

[0046] The functions of the various chemical elements in this embodiment are described in detail below.

[0047] Si, Al: Si and Al can increase the resistivity of the steel plate, thereby reducing iron loss. In addition, Si and Al can improve the strength of the steel plate; however, an increase in Si and Al content will cause difficulty in cold rolling; in one embodiment of the present application, the Si content is controlled between 3.00~3.40%, and the Al content is controlled between 0.50~1.00%.

[0048] Mn: Mn can improve the microstructure and texture of hot-rolled plates, strengthen the (100) and (110) components, and weaken the (111) component, which is beneficial to improving magnetic properties. In addition, Mn easily forms MnS with S, and coarse MnS is beneficial to grain growth and reducing iron loss. In addition, Mn can also improve the strength of steel plates. In one embodiment of the present application, the Mn content is controlled between 0.30% and 0.80%.

[0049] Nb, V, Ti, Cr, Ni, and Cu: Adding Nb, V, Ti, Cr, Ni, and Cu to non-oriented silicon steel can improve strength, but this can also increase iron loss and reduce magnetic induction. In one embodiment of the present application, Nb is controlled to be ≤ 0.003%, V ≤ 0.003%, Ti ≤ 0.003%, Cr ≤ 0.02%, Ni ≤ 0.02%, and Cu ≤ 0.02%. Specifically, in one embodiment, alloying elements such as Nb, V, Ti, Cr, Ni, and Cu may not be intentionally added during the steelmaking process, and these elements may exist as impurities in the molten steel. Alternatively, in another embodiment, during the steelmaking process, any one or more alloying elements such as Nb, V, Ti, Cr, Ni, and Cu may be added, and the following conditions are satisfied: Nb≤0.003%, V≤0.003%, Ti≤0.003%, Cr≤0.02%, Ni≤0.02%, and Cu≤0.02%. In this case, the content of any one or more of Nb, V, Ti, Cr, Ni, and Cu is not zero.

[0050] C, S, N: C, S, and N are all harmful elements in non-oriented silicon steel, which will lead to increased iron loss and reduced magnetic induction intensity. In order to meet the requirements of low iron loss and high magnetic induction intensity for ultra-thin non-oriented silicon steel used in the stator core of high-speed drive motors of electric vehicles, in one embodiment of the present application, C is controlled to be ≤0.0025%, S ≤0.0020%, and N ≤0.0020%.

[0051] P: P is a residual element that is detrimental to magnetic properties and causes difficulty in cold rolling. In one embodiment of the present application, P is controlled to be ≤ 0.015%.

[0052] The non-oriented silicon steel is a steel plate with a thickness of 0.15~0.35mm. In this way, this thin-gauge non-oriented silicon steel can not only directly reduce the iron loss, but also cause the resistivity of the steel plate to increase, thereby indirectly reducing the iron loss. Therefore, the non-oriented silicon steel of one embodiment of the present application has low iron loss.

[0053] Furthermore, the non-oriented silicon steel hot-rolled coil is sequentially pickled and cold-rolled once without normalization. This process controls the fibrous microstructure of the hot-rolled coil, significantly improving the rollability of the steel sheet compared to the equiaxed microstructure after conventional normalization. This allows for a certain degree of increase in the Si, Mn, and Al contents, thereby enhancing mechanical strength and reducing iron loss. Simultaneously, a single cold-rolling process allows for the production of high-alloy non-oriented silicon steel with a thin gauge of 0.15-0.35 mm. Furthermore, by combining grain size with Si, Al, and Mn contents, this method not only meets the high mechanical property requirements of the non-oriented silicon steel used in electric vehicle drive motor rotor cores but also facilitates the preparation of electric vehicle drive motor stator cores. In particular, it lays the foundation for obtaining coarse grains after secondary annealing to further reduce iron loss.

[0054] In one embodiment of the present application, the iron loss P of the non-oriented silicon steel is 1.0 / 400 ≤22.0W / kg, magnetic induction intensity B 5000 ≥1.62T, yield strength ≥550MPa, tensile strength ≥650MPa, elongation ≥12%.

[0055] Based on the above settings and controls in terms of chemical composition, thickness, grain size and properties (including magnetic properties and mechanical properties), the non-oriented silicon steel of one embodiment of the present application can not only meet the requirements of the rotor core for low iron loss, high magnetic induction intensity and high strength without the need for a large amount of alloying elements, that is, the non-oriented silicon steel can be used to prepare the rotor core, for example, by stamping and laminating to obtain a laminated rotor core, and the obtained rotor core has the properties of low iron loss, high magnetic induction intensity and high strength; at the same time, the non-oriented silicon steel can also meet the requirements of the stator core for the base material, that is, the non-oriented silicon steel can be used to prepare the stator core, for example, by stamping, lamination and then annealing, or annealing and then lamination to obtain a laminated stator core, and the obtained stator core has the properties of ultra-low iron loss and high magnetic induction intensity.

[0056] Therefore, the non-oriented silicon steel of one embodiment of the present application can be used as the base material of both the rotor core and the stator core, and can simultaneously meet the needs of the stator core and the rotor core for the non-oriented silicon steel finished steel plates that have been annealed once after cold rolling. Compared with the current situation in which the non-oriented silicon steel finished steel plates that have been annealed once after cold rolling used for the stator core and the non-oriented silicon steel finished steel plates that have been annealed once after cold rolling used for the rotor core in conventional technology must be prepared separately, not only the manufacturing cost of the motor and its stator and rotor cores is greatly reduced, but also the full utilization of the non-oriented silicon steel material is greatly realized. For example, in one area of the steel plate, the outer periphery can constitute the annular thin slices of the stator core, and the center can constitute the thin slices of the rotor core, thereby avoiding material waste. In addition, based on the design of chemical composition, grain size, performance, etc., the production process of the non-oriented silicon steel can be simple and easy to implement, the rollability is improved, the conventional normalizing treatment is eliminated, and energy is saved and consumption is reduced.

[0057] In one embodiment, the average grain size of the non-oriented silicon steel is 20-40 μm.

[0058] Furthermore, in one embodiment of the present application, the non-oriented silicon steel has an average grain size of 90-120 μm and an iron loss of P after secondary annealing based on the chemical composition, thickness, average grain size and performance. 1.0 / 400 ≤19.0W / kg, magnetic induction intensity B 5000 ≥1.63T. It can be seen that after the secondary annealing treatment, the average grain size of the non-oriented silicon steel can be greatly increased, the iron loss is reduced, and it can be used as a stator core material.

[0059] In the secondary annealing process, the heating rate is ≤5°C / min, the annealing temperature is 900-940°C, and the holding time is 90-120 minutes. Of course, the annealing process of this embodiment is not limited to this, and other feasible annealing conditions can also be used for annealing.

[0060] In addition, the structure of the non-oriented silicon steel is a completely recrystallized structure, that is, the proportion of recrystallized grains is 100%.

[0061] In one embodiment, the non-oriented silicon steel is a steel plate with a thickness of 0.35 mm and an iron loss P of 1.0 / 400 ≤22.0W / kg, magnetic induction intensity B 5000 ≥1.64T, and after the above secondary annealing treatment, its iron loss P 1.0 / 400 ≤19.0W / kg, magnetic induction intensity B 5000 ≥1.65T.

[0062] Alternatively, in a modified embodiment, the non-oriented silicon steel is a steel plate with a thickness of 0.30 mm, and its iron loss P 1.0 / 400≤18.0W / kg, magnetic induction intensity B 5000 ≥1.63T, and after the above secondary annealing treatment, its iron loss P 1.0 / 400 ≤15.0W / kg, magnetic induction intensity B 5000 ≥1.64T;

[0063] Alternatively, in another embodiment, the non-oriented silicon steel is a steel plate with a thickness of 0.25 mm, and its iron loss P is 1.0 / 400 ≤16.0W / kg, magnetic induction intensity B 5000 ≥1.63T, and after the above secondary annealing treatment, its iron loss P 1.0 / 400 ≤13.0W / kg, magnetic induction intensity B 5000 ≥1.64T;

[0064] Alternatively, in another embodiment, the non-oriented silicon steel is a steel plate with a thickness of 0.20 mm, and its iron loss P is 1.0 / 400 ≤15.0W / kg, magnetic induction intensity B 5000 ≥1.62T, and after the above secondary annealing treatment, its iron loss P 1.0 / 400 ≤12.0W / kg, magnetic induction intensity B 5000 ≥1.63T;

[0065] Alternatively, in another embodiment, the non-oriented silicon steel is a steel plate with a thickness of 0.15 mm, and its iron loss P 1.0 / 400 ≤14.0W / kg, magnetic induction intensity B 5000 ≥1.62T, and after the above secondary annealing treatment, its iron loss P 1.0 / 400 ≤11.0W / kg, magnetic induction intensity B 5000 ≥1.63T.

[0066] Furthermore, an embodiment also provides a method for producing the non-oriented silicon steel, which produces the non-oriented silicon steel product described above through a process route of steelmaking, hot rolling, cold rolling, and primary annealing.

[0067] The following is a detailed introduction to each process.

[0068] <Steelmaking Process>

[0069] In this process, molten steel is refined and cast into billets with a thickness of 200-240 mm. After leaving the continuous casting machine, the billets are kept at a temperature range of 600-900°C for 3-8 hours.

[0070] In this process, by refining molten steel, the chemical composition of the obtained steel billet is controlled to be the same as the range of the chemical composition of the non-oriented silicon steel introduced above. For example, the chemical composition of the steel billet includes, by mass percentage, C≤0.0025%, S≤0.0020%, Si 3.00~3.40%, Al 0.50~1.00%, Mn 0.30~0.80%, P≤0.015%, Nb≤0.003%, V≤0.003%, Ti≤0.003%, Cr≤0.02%, Ni≤0.02%, Cu≤0.02%, N≤0.0020%, and the rest is Fe and unavoidable inclusions.

[0071] In this way, the present application can control the metallographic structure of the hot-rolled plate to be a fibrous metallographic structure through the design and control of the chemical composition, combined with the subsequent hot rolling process, which significantly improves the toughness of the conventional equiaxed crystal metallographic structure after normalization, laying the foundation for the subsequent realization of a single cold rolling without normalization, and creating conditions for the subsequent realization of the high strength requirements of non-oriented silicon steel for the rotor core of the electric vehicle drive motor and the low iron loss requirements of non-oriented silicon steel for the stator core.

[0072] In this process, the specific method of refining molten steel can adopt the conventional process of molten iron KR desulfurization, converter smelting, and vacuum refining to prepare molten steel that meets the above-mentioned chemical composition. It can be implemented in a feasible manner known in the art, and this application does not limit it.

[0073] Similarly, in this process, the molten steel is cast into steel billets through continuous casting technology, wherein the specific continuous casting technology can also be implemented in a feasible manner known in the art, and this application does not limit it.

[0074] Furthermore, in this process, after the steel billet leaves the continuous casting machine, the insulation treatment, especially the design of the insulation temperature and duration, is conducive to the full precipitation of MnS and AlN in the steel billet, creating conditions for the precise control of the recrystallization process and grain size during the subsequent cold rolling, primary annealing and high-temperature secondary annealing without normalization and preheating.

[0075] <Hot rolling process>

[0076] In this process, the steel billet is heated to 1080~1120℃ and kept warm for 150~200 minutes, then rough rolled to obtain an intermediate billet with a thickness of 35~45mm, and then finished rolled and coiled to obtain a hot-rolled coil with a thickness of 2.30~3.00mm.

[0077] Among them, the starting rolling temperature of the finishing rolling is 970±20℃, the final rolling temperature is 850±20℃, and the coiling temperature is 700±20℃.

[0078] In this way, on the basis of chemical composition, by controlling the heating temperature, the solid solution of coarse precipitates (MnS, AlN) in the ingot can be avoided, creating conditions for the control of subsequent microstructure and performance. Furthermore, combined with the control of finishing deformation, temperature and coiling temperature, a hot-rolled coil with a fibrous metallographic structure can be obtained, which has significantly improved toughness compared to the conventional equiaxed metallographic structure after normalization, laying the foundation for the subsequent cold rolling without normalization, and creating conditions for the precise control of the recrystallization process and grain size during the primary annealing and high-temperature secondary annealing.

[0079] Preferably, during the hot rolling process, the steel slab is heated in a heating furnace with an entry temperature ≥ 450°C, a preheating temperature of 950-1000°C, a heating and soaking temperature of 1080-1120°C, and a total heating and soaking time of 150-200 minutes. This not only meets the lower heating temperature requirements described above, but also prevents hot-rolled edge cracking caused by rapid heating by setting the entry and preheating temperatures. Of course, within the basic technical principles of this application, if the issue of hot-rolled edge cracking is not a concern, the entry and preheating temperatures are not limited to these.

[0080] <Cold rolling process>

[0081] In this process, the hot-rolled coil is pickled and cold-rolled once in sequence without normalization to obtain a cold-rolled strip with a thickness of 0.15-0.35 mm.

[0082] In this process, the total cold rolling reduction is ≥86%.

[0083] In this way, on the basis of the previous hot rolling, combined with the large reduction rate of cold rolling, a large number of dislocation defects are provided for the cold-rolled strip, which is conducive to a large number of nucleations during the first annealing, forming a fine-grained structure with high strength, and then the high strength requirements of non-oriented silicon steel for the rotor core of new energy high-speed motors are achieved with the help of the subsequent first annealing process, and the foundation is laid for the subsequent realization of the low iron loss requirements of non-oriented silicon steel for the stator core through the secondary annealing process.

[0084] Preferably, in this process, the first cold rolling pass has a reduction of 32-34%, the final pass has a reduction of 20-25%, and the remaining passes have a reduction of 25-30%. This not only allows high-silicon, high-aluminum steel to be directly cold-rolled without preheating, leveraging the hot-rolled fibrous metallographic structure, but also effectively ensures cold-rolling stability and plate quality. Of course, this application is not limited to this.

[0085] In addition, in this process, the specific operation of pickling can be implemented in a feasible manner known in the art and is not limited in this application.

[0086] <Primary Annealing Process>

[0087] In this process, the cold-rolled strip is annealed, cooled and coated once to obtain the non-oriented silicon steel product.

[0088] The annealing temperature is 830-870°C and held for 60-90 seconds to ensure full recrystallization of the steel. Compared to similar high-silicon, high-aluminum steels, the annealing temperature is 100-200°C lower, ensuring fine grains after the primary annealing process. This achieves the high strength requirements of non-oriented silicon steel for rotor cores in new energy high-speed motors and creates conditions for subsequent secondary annealing.

[0089] Specifically, on the basis of the previous hot rolling and cold rolling, combined with the design of the annealing temperature, the steel plate can be fully recrystallized in one annealing, that is, the finished steel plate has a fully recrystallized structure, and the average recrystallized grain size can be controlled, for example, the average recrystallized grain size in the finished steel plate is 20-40 μm. In this way, the finished steel plate can not only meet the performance requirements of high-strength non-oriented silicon steel for electric vehicle drive motor rotor cores (for example, a laminated rotor core can be directly produced after stamping), but also meet the requirements of non-oriented silicon steel base material for electric vehicle drive motor stator cores (for example, the grain structure can create conditions for subsequent secondary annealing to obtain a low iron loss grain structure). For example, a laminated stator core can be obtained by stamping, annealing after lamination, or laminating after annealing, and the obtained stator core has the performance of ultra-low iron loss and high magnetic induction intensity.

[0090] During the primary annealing, a weak reducing protective atmosphere may be used, for example, a protective atmosphere of N2 and H2, wherein the volume percentage of H2 is 20-30% and the remainder is N2.

[0091] Furthermore, the production method also includes a stamping process and a secondary annealing process located after the primary annealing process; and from another perspective, this stamping and secondary annealing process is a process of using the non-oriented silicon steel finished product to manufacture a motor core, that is, one embodiment also provides a method for manufacturing a motor core.

[0092] The stamping process and secondary annealing process are introduced in detail below.

[0093] <Stamping process>

[0094] In this process, the non-oriented silicon steel (or the non-oriented silicon steel product obtained in the primary annealing process) is punched to obtain a series of thin sheets.

[0095] <Secondary Annealing Process>

[0096] In this process, a series of thin sheets are first laminated and pressed, and then subjected to secondary annealing to obtain a non-oriented silicon steel core; alternatively, a series of thin sheets are first subjected to secondary annealing and then laminated and pressed to obtain a non-oriented silicon steel core.

[0097] Among them, during the secondary annealing: the heating rate is ≤5°C / min, the annealing temperature is 900~940°C, and the holding time is 90~120min.

[0098] In this way, the grains of the non-oriented silicon steel obtained by stamping, lamination and subsequent secondary annealing, or lamination after secondary annealing, are significantly grown compared to the non-oriented silicon steel product before stamping. For example, the average grain size of the recrystallized steel grows from 20~40μm to 90~120μm, so that the non-oriented silicon steel obtained after secondary annealing has lower iron loss, thereby producing a non-oriented silicon steel core with low iron loss.

[0099] In one embodiment, the secondary annealing process may be performed in a bell annealing furnace or a continuous annealing furnace, but is not limited thereto.

[0100] The secondary annealing may be performed in a weakly reducing protective atmosphere, such as a protective atmosphere of N2 and H2, wherein the volume percentage of H2 is 20-30% and the remainder is N2.

[0101] Furthermore, in one embodiment, in the stamping process, a series of pairs of rotor sheets and stator sheets can be stamped out from the non-oriented silicon steel product, and each pair of rotor sheets and stator sheets are concentrically distributed.

[0102] The stator sheets enter the secondary annealing process to prepare a stator core.

[0103] The rotor sheets then enter the rotor core preparation process, which specifically involves assembling a series of rotor sheets into a rotor core through lamination press-fitting.

[0104] In this way, not only can the rotor core and the stator core be prepared by stamping the same non-oriented silicon steel plate product, but also each time a rotor sheet is punched out around a center of a circle, a stator sheet surrounding the rotor sheet will be punched out around the center of the circle (that is, the rotor sheet just utilizes the steel plate in the center area of the circular stator sheet), which can achieve full utilization of the non-oriented silicon steel material, greatly improve the utilization rate of the material, avoid material waste, and reduce the production cost of the motor.

[0105] As mentioned above, in the first annealing process, the thickness of the non-oriented silicon steel product obtained is 0.15~0.35mm. Therefore, the thickness of each rotor sheet and stator sheet obtained in the stamping process is the same as the thickness of the non-oriented silicon steel, which is also between 0.15~0.35mm.

[0106] In one embodiment, after the secondary annealing is completed, the cooling rate may be controlled to be ≤3° C. / min.

[0107] For example, in an embodiment in which a secondary annealing is performed on the stator core laminations, the stator core laminations may be cooled in an annealing furnace, and the cooling rate of the annealing furnace is controlled to be ≤3°C / min, so that the cooling rate of the stator core laminations is ≤3°C / min. Alternatively, in an embodiment in which a secondary annealing is performed on a series of stator sheets, the stator sheets may be cooled in an annealing furnace, and the cooling rate of the annealing furnace is controlled to be ≤3°C / min, so that the cooling rate of the stator sheets is ≤3°C / min.

[0108] It is understandable that in this application, the order of the various processes is not limited by the order in which they are described in the technical introduction. For example, the "rotor core preparation process" and the "stator core preparation process" can be implemented simultaneously, or the rotor core preparation process can be performed first and then the stator core preparation process, or the stator core preparation process can be performed first and then the rotor core preparation process. For another example, the "stamping process" can be performed completely before the "rotor core preparation process" and the "stator core preparation process", or it can be performed simultaneously with the "rotor core preparation process" and the "stator core preparation process" (for example, lamination while stamping). These changes in the implementation order do not deviate from the technical purpose of this application.

[0109] Furthermore, an embodiment of the present application also provides a motor core, which includes a laminated rotor core and a laminated stator core.

[0110] The laminated rotor core and the laminated stator core can be made of the non-oriented silicon steel mentioned above, respectively, and the specific preparation process can adopt the manufacturing method or the production method mentioned above.

[0111] The chemical composition of the non-oriented silicon steel sheets of the laminated rotor core and the laminated stator core can be completely the same, for example, they are made from the same non-oriented silicon steel plate; or they can be different, for example, they are made from two different non-oriented silicon steel plates.

[0112] The average grain size of the non-oriented silicon steel sheets of the laminated rotor core is 20-40 μm, and the iron loss P 1.0 / 400 ≤22.0W / kg, magnetic induction intensity B 5000 ≥1.62T, yield strength ≥550MPa, tensile strength ≥650MPa, elongation ≥12%. This shows that the laminated rotor core has excellent magnetic properties and high mechanical strength, meeting the rotor strength requirements of electric vehicle drive motors at high speeds.

[0113] The average grain size of the non-oriented silicon steel sheets of the laminated stator core is 90-120 μm, and the iron loss P 1.0 / 400≤19.0W / kg, magnetic induction intensity B 5000 ≥1.63 T. It can be seen that the laminated stator core has more excellent magnetic properties and can meet the requirements of electric vehicle drive motors in terms of stator iron loss at high speeds.

[0114] Specifically, in one embodiment, the non-oriented silicon steel sheets of the laminated rotor core and the laminated stator core are both steel plates with a thickness of 0.35 mm, and the iron loss P of the laminated rotor core is 1.0 / 400 ≤22.0W / kg, magnetic induction intensity B 5000 ≥1.64T, iron loss P of laminated stator core 1.0 / 400 ≤19.0W / kg, magnetic induction intensity B 5000 ≥1.65T.

[0115] Alternatively, in a variation, the non-oriented silicon steel sheets of the laminated rotor core and the laminated stator core are both steel plates with a thickness of 0.30 mm, and the iron loss P of the laminated rotor core is 1.0 / 400 ≤18.0W / kg, magnetic induction intensity B 5000 ≥1.63T, iron loss P of laminated stator core 1.0 / 400 ≤15.0W / kg, magnetic induction intensity B 5000 ≥1.64T;

[0116] Alternatively, in another embodiment, the non-oriented silicon steel sheets of the laminated rotor core and the laminated stator core are both steel plates with a thickness of 0.25 mm, and the iron loss P of the laminated rotor core is 1.0 / 400 ≤16.0W / kg, magnetic induction intensity B 5000 ≥1.63T, iron loss P of laminated stator core 1.0 / 400 ≤13.0W / kg, magnetic induction intensity B 5000 ≥1.64T;

[0117] Alternatively, in another embodiment, the non-oriented silicon steel sheets of the laminated rotor core and the laminated stator core are both steel plates with a thickness of 0.20 mm, and the iron loss P of the laminated rotor core is 1.0 / 400 ≤15.0W / kg, magnetic induction intensity B 5000 ≥1.62T, iron loss P of laminated stator core 1.0 / 400 ≤12.0W / kg, magnetic induction intensity B 5000 ≥1.63T;

[0118] Alternatively, in another embodiment, the non-oriented silicon steel sheets of the laminated rotor core and the laminated stator core are both steel plates with a thickness of 0.15 mm, and the iron loss P of the laminated rotor core is 1.0 / 400 ≤14.0W / kg, magnetic induction intensity B 5000≥1.62T, iron loss P of laminated stator core 1.0 / 400 ≤11.0W / kg, magnetic induction intensity B 5000 ≥1.63T.

[0119] The detailed description listed above is only a specific description of the feasible implementation methods of the present invention. The specific implementation methods of the present invention are introduced below through several specific examples.

[0120] These embodiments respectively provide a non-oriented silicon steel product, specifically a finished steel plate that is subjected to one-time annealing after cold rolling.

[0121] The chemical composition of the steel plates is shown in Table 1.

[0122] [Table 1]

[0123]

[0124] The production methods of each non-oriented silicon steel product are as follows:

[0125] (1) Molten steel is refined and cast into billets with chemical compositions as shown in Table 1. After leaving the continuous casting machine, the billets are kept at a temperature range of 600-900°C for 3-8 hours;

[0126] (2) The steel slab is heated in a heating furnace, and then subjected to rough rolling to obtain an intermediate slab, which is then subjected to finish rolling and coiling to obtain a hot-rolled coil. The thickness of the steel slab, heating temperature, holding time, thickness of the intermediate slab, start rolling temperature of finish rolling, final rolling temperature, coiling temperature, and thickness of the hot-rolled coil are shown in Table 2.

[0127] [Table 2]

[0128]

[0129] (3) The hot rolled coil is pickled and cold rolled once in sequence without normalization to obtain a cold rolled strip; and then subjected to a primary annealing, cooling and coating to obtain a finished steel plate; wherein the thickness, primary annealing temperature and holding time of the cold rolled strip are shown in Table 3 respectively;

[0130] The finished steel plates of each embodiment were subjected to performance testing, including: using the standard GB / T 228.1-2021 "Tensile testing of metallic materials - Part 1 - Room temperature test methods" to test the tensile strength Rm, yield strength Re, and elongation δ; using the national standard GB / T3655-2008 "Method for measuring magnetic properties of electrical steel sheets (strips) using Epstein square rings" to test the iron loss and magnetic induction intensity; and using the national standard GB / T 4335-2013 "Determination of ferrite grain size of cold-rolled low-carbon steel sheets" to measure the grain size. The results are shown in Table 3.

[0131] [Table 3]

[0132]

[0133] (4) The finished steel sheets of each embodiment were stamped and subjected to secondary annealing, with a heating rate of ≤5°C / min, an annealing temperature of 900~940°C, and a holding time of 90~120min. After completion, the non-oriented silicon steel sheets after stamping were subjected to performance testing, including: using the national standard GB / T 3655-2008 "Method for measuring magnetic properties of electrical steel sheets (strips) using Epstein square rings" to test iron loss and magnetic induction intensity; and using the national standard GB / T 4335-2013 "Method for determining the ferrite grain size of cold-rolled low-carbon steel sheets" to measure grain size. The results are shown in Table 4.

[0134] [Table 4]

[0135]

[0136] From Table 3 and Table 4, it can be seen that in the present application, the non-oriented silicon steel product has high mechanical strength, and when used in the preparation of the rotor core, it can meet the high strength requirement of the rotor core; at the same time, after the secondary annealing of the non-oriented silicon steel product, the grain coarsening can be achieved, so that the obtained secondary annealed steel plate has the characteristics of low iron loss, which meets the high requirements of the stator core in terms of low iron loss; that is, the non-oriented silicon steel plate of the present application can not only meet the requirements of the rotor core for low iron loss, high magnetic induction intensity and high strength, but also meet the requirements of the stator core for the base material, that is, it can have the performance of ultra-low iron loss and high magnetic induction intensity after annealing, so it can simultaneously meet the needs of the stator core and the rotor core for the non-oriented silicon steel finished steel plate that is annealed once after cold rolling.

Claims

1. A method for producing non-oriented silicon steel, characterized in that: The production method comprises, Steelmaking process: Molten steel is refined and cast into billets with a thickness of 200-240mm. After leaving the continuous casting machine, the billets are kept at a temperature range of 600-900℃ for 3-8 hours. The chemical composition of the billets, in mass percentage, includes: C ≤ 0.0025%, S ≤ 0.0020%, Si 3.00-3.40%, Al 0.50-1.00%, Mn 0.30-0.80%, 0<P ≤ 0.015%, Nb ≤ 0.003%, V ≤ 0.003%, Ti ≤ 0.003%, Cr ≤ 0.02%, Ni ≤ 0.02%, Cu ≤ 0.02%, N ≤ 0.0020%, and the rest is Fe and unavoidable inclusions. Hot rolling process: After heating the steel billet to 1080-1120℃ and holding it for 150-200min, it is first rough rolled to obtain an intermediate billet with a thickness of 35-45mm. Then, it is finished rolled and coiled to obtain a hot-rolled coil with a thickness of 2.30-3.00mm and a fibrous metallographic structure. The starting rolling temperature of the finishing rolling is 970±20℃, the final rolling temperature is 850±20℃, the finishing reduction is controlled at more than 92%, and the coiling temperature is 700±20℃. Cold rolling process: The hot-rolled coil is directly pickled and cold-rolled once without normalization to obtain cold-rolled strip with a thickness of 0.15-0.35mm; the total cold rolling reduction is ≥86%; Primary annealing: After the cold-rolled strip is subjected to primary annealing, cooling and coating, the finished steel plate is obtained; wherein, the annealing temperature is 830~870℃ and the temperature is kept for 60~90s; the average grain size of the finished steel plate is 20~40μm, and the iron loss P is 0. 1.0 / 400 ≤22.0W / kg, magnetic induction intensity B 5000 ≥1.62T, yield strength ≥550MPa, tensile strength ≥650MPa.

2. The method for producing non-oriented silicon steel according to claim 1, wherein: In the hot rolling process: the steel billet is sent to the heating furnace for heating, the furnace entry temperature is ≥450℃, the preheating temperature is 950~1000℃, the heating and soaking temperature is 1080~1120℃ and the total heating and soaking time is 150~200min.

3. The method for producing non-oriented silicon steel according to claim 1, wherein: In the cold rolling process: the first pass reduction rate of cold rolling is 32~34%, the last pass reduction rate is 20~25%, and the remaining passes reduction rate is 25~30%.

4. The method for producing non-oriented silicon steel according to claim 1, wherein: The production method further comprises, Stamping process: stamping the finished steel plate to obtain a series of thin sheets; Secondary annealing process: first, a series of thin sheets are laminated and pressed, and then secondary annealing is performed; alternatively, a series of thin sheets are secondary annealed first, and then laminated and pressed; wherein, during the secondary annealing: the heating rate is ≤5°C / min, the annealing temperature is 900~940°C, and the holding time is 90~120min.

5. The method for producing non-oriented silicon steel according to claim 4, characterized in that: In the secondary annealing process: after the end of the heat preservation, the cooling rate is controlled to be ≤3℃ / min.

6. The method for producing non-oriented silicon steel according to claim 4, characterized in that: In the stamping process: a series of pairs of rotor sheets and stator sheets are stamped out from the finished steel plate, with each pair of rotor sheets and stator sheets being concentrically distributed; the stator sheets enter the secondary annealing process to prepare the stator core; The production method further comprises a rotor core preparation step: a series of rotor sheets are assembled into a rotor core by lamination press-fitting.

7. A non-oriented silicon steel, characterized in that: Its chemical composition, in percentage by mass, includes: C≤0.0025%, S≤0.0020%, Si 3.00~3.40%, Al 0.50~1.00%, Mn 0.30~0.80%, 0<P≤0.015%, Nb≤0.003%, V≤0.003%, Ti≤0.003%, Cr≤0.02%, Ni≤0.02%, Cu≤0.02%, N≤0.0020%, and the rest is Fe and unavoidable inclusions; The non-oriented silicon steel is a steel plate with a thickness of 0.15-0.35 mm, an average grain size of 20-40 μm, and an iron loss of P 1.0 / 400 ≤22.0W / kg, magnetic induction intensity B 5000 ≥1.62T, yield strength ≥550MPa, tensile strength ≥650MPa, elongation ≥12%.

8. The non-oriented silicon steel according to claim 7, characterized in that: After secondary annealing, the non-oriented silicon steel has an average grain size of 90-120 μm and an iron loss of P 1.0 / 400 ≤19.0W / kg, magnetic induction intensity B 5000 ≥1.63T; Among them, during the secondary annealing: the heating rate is ≤5°C / min, the annealing temperature is 900~940°C, and the heat preservation time is 90~120min.

9. The non-oriented silicon steel according to claim 7, characterized in that: The non-oriented silicon steel is a steel plate with a thickness of 0.35 mm and an iron loss of P 1.0 / 400 ≤22.0W / kg, magnetic induction intensity B 5000 ≥1.64T, and after secondary annealing, its iron loss P 1.0 / 400 ≤19.0W / kg, magnetic induction intensity B 5000 ≥1.65T; Alternatively, the non-oriented silicon steel is a steel plate with a thickness of 0.30 mm, and its iron loss P 1.0 / 400 ≤18.0W / kg, magnetic induction intensity B 5000 ≥1.63T, and after secondary annealing, its iron loss P 1.0 / 400 ≤15.0W / kg, magnetic induction intensity B 5000 ≥1.64T; Alternatively, the non-oriented silicon steel is a steel plate with a thickness of 0.25 mm, and its iron loss P 1.0 / 400 ≤16.0W / kg, magnetic induction intensity B 5000 ≥1.63T, and after secondary annealing, its iron loss P 1.0 / 400 ≤13.0W / kg, magnetic induction intensity B 5000 ≥1.64T; Alternatively, the non-oriented silicon steel is a steel plate with a thickness of 0.20 mm, and its iron loss P 1.0 / 400 ≤15.0W / kg, magnetic induction intensity B 5000 ≥1.62T, and after secondary annealing, its iron loss P 1.0 / 400 ≤12.0W / kg, magnetic induction intensity B 5000 ≥1.63T; Alternatively, the non-oriented silicon steel is a steel plate with a thickness of 0.15 mm, and its iron loss P 1.0 / 400 ≤14.0W / kg, magnetic induction intensity B 5000 ≥1.62T, and after secondary annealing, its iron loss P 1.0 / 400 ≤11.0W / kg, magnetic induction intensity B 5000 ≥1.63T.

10. A method for manufacturing a motor core, characterized in that: The manufacturing method comprises: Stamping step: stamping the non-oriented silicon steel according to claim 7 to obtain a series of thin sheets; Secondary annealing process: first, a series of thin sheets are laminated and pressed, and then secondary annealing is performed; alternatively, a series of thin sheets are secondary annealed first, and then laminated and pressed; wherein, during the secondary annealing: the heating rate is ≤5°C / min, the annealing temperature is 900~940°C, and the holding time is 90~120min.

11. The method for manufacturing a motor core according to claim 10, wherein: In the secondary annealing process: after the end of the heat preservation, the cooling rate is controlled to be ≤3℃ / min.

12. The method for manufacturing a motor core according to claim 10, wherein: In the stamping process: a series of pairs of rotor sheets and stator sheets are stamped out from the non-oriented silicon steel, and each pair of rotor sheets and stator sheets are distributed concentrically; the stator sheets enter the secondary annealing process to prepare the stator core; The manufacturing method further comprises a rotor core preparation step: assembling a series of rotor sheets into a rotor core by lamination press-fitting.

13. A motor core, characterized in that: It includes a laminated rotor core and a laminated stator core; The laminated rotor core and the laminated stator core are both made of non-oriented silicon steel with a thickness of 0.15-0.35 mm, and the chemical composition, in mass percentage, includes: C≤0.0025%, S≤0.0020%, Si 3.00-3.40%, Al 0.50-1.00%, Mn0.30-0.80%, 0<P≤0.015%, Nb≤0.003%, V≤0.003%, Ti≤0.003%, Cr≤0.02%, Ni≤0.02%, Cu≤0.02%, N≤0.0020%, and the rest is Fe and unavoidable inclusions; The average grain size of the non-oriented silicon steel sheets of the laminated rotor core is 20-40 μm, and the iron loss P 1.0 / 400 ≤22.0W / kg, magnetic induction intensity B 5000 ≥1.62T, yield strength ≥550MPa, tensile strength ≥650MPa, elongation ≥12%; The average grain size of the non-oriented silicon steel sheets of the laminated stator core is 90-120 μm, and the iron loss P 1.0 / 400 ≤19.0W / kg, magnetic induction intensity B 5000 ≥1.63T.

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