Low-frequency ultra-high magnetic induction strength oriented electrical steel, preparation method and application thereof

Abstract

This invention relates to a low-frequency ultra-high magnetic induction intensity oriented electrical steel, its preparation method, and its applications, belonging to the field of electrical steel technology. The chemical composition of the ingot of the low-frequency ultra-high magnetic induction intensity oriented electrical steel of this invention, by mass percentage, includes C: 0.02–0.05%, Si: 0.05–1.0%, Co: 0.3–2.2%, Cr: 0.03–0.12%, Als: 0.03–0.08%, N: 0.02–0.05%, Dy: 0.006–0.009%, Bi: 0.008–0.015%, with the remainder being Fe and unavoidable impurities, and the Dy:Bi ratio being (0.5–1):1. The oriented electrical steel of this invention possesses ultra-high magnetic induction intensity, and when applied to low-frequency transformers, it can significantly reduce the losses, weight, and volume of low-frequency transformers.

Description

Technical Field

[0001] This invention belongs to the field of electrical steel technology, specifically relating to a low-frequency ultra-high magnetic induction intensity oriented electrical steel, its preparation method, and its application. Background Technology

[0002] By selecting a suitable transmission frequency between DC and the power frequency of 50Hz, the impact of line impedance on power transmission can be reduced, while retaining the advantages of AC transmission such as electromagnetic induction intensity strain pressure and current zero-crossing interruption. Flexible low-frequency (20Hz) AC transmission has become a beneficial supplement to power frequency AC and DC transmission and is an important development direction for future advanced power transmission technology.

[0003] The size, weight, and losses of low-frequency transformers are crucial factors affecting the economics of flexible low-frequency AC transmission projects. Under the same voltage level and capacity conditions, when the frequency decreases from 50Hz to 20Hz, a 220kV low-frequency transformer, compared to a power frequency transformer, increases in weight by approximately 70%, floor space by approximately 21%, volume by approximately 34%, and transformer load losses by approximately 33%. Currently, low-frequency transformers mainly suffer from large weight, large size, and high load losses. Especially for medium- to long-distance offshore wind power low-frequency transmission applications, the limited area and load-bearing capacity of offshore substation platforms make it imperative to reduce the size, weight, and load losses of low-frequency transformers.

[0004] The magnetic properties of grain-oriented electrical steel used in low-frequency transformer cores are the most critical factors limiting its weight, volume, and load losses. The magnetic induction intensity B of existing ordinary grain-oriented electrical steel... 800 The typical range is 1.82–1.87 T. The magnetic induction intensity B of existing high magnetic induction intensity oriented electrical steels... 800 The typical range is 1.88–1.93 T. Currently, there is a need to innovate and develop ultra-high magnetic induction intensity oriented electrical steel materials to increase the working magnetic flux density of transformer cores, thereby reducing the product of core cross-sectional area and coil turns, and thus reducing the loss, weight, and volume of low-frequency transformers. Summary of the Invention

[0005] Therefore, the present invention provides a low-frequency ultra-high magnetic induction intensity oriented electrical steel, its preparation method and application. The oriented electrical steel of the present invention has ultra-high magnetic induction intensity. When applied to low-frequency transformers, it can reduce the loss, weight and volume of low-frequency transformers by more than 10% compared with existing demonstration low-frequency transformers.

[0006] To this end, the present invention provides the following technical solution.

[0007] In a first aspect, the present invention provides a low-frequency ultra-high magnetic induction intensity oriented electrical steel, wherein the chemical composition of the oriented electrical steel billet, by mass percentage, includes C: 0.02-0.05%, Si: 0.05-1.0%, Co: 0.3-2.2%, Cr: 0.03-0.12%, Als: 0.03-0.08%, N: 0.02-0.05%, Dy: 0.006-0.009%, Bi: 0.008-0.015%, with the remainder being Fe and unavoidable impurities, and the Dy:Bi ratio being (0.5-1):1.

[0008] Secondly, the present invention provides a method for preparing the above-mentioned low-frequency ultra-high magnetic induction intensity oriented electrical steel, comprising the following steps:

[0009] Step 1: Smelting;

[0010] Step 2: Casting to obtain a billet;

[0011] Step 3: Hot-roll the cast billet to obtain a hot-rolled plate;

[0012] Step 4: Perform a cold rolling process on the hot-rolled plate;

[0013] Step 5: Decarburization annealing;

[0014] Step 6: Obtain cold-rolled sheet by secondary cold rolling;

[0015] Step 7: Perform electric pulse heat treatment on the cold-rolled sheet;

[0016] Step 8: Annealing.

[0017] Furthermore, step 1 includes: smelting the raw materials by circulating degassing in a vacuum smelting furnace, controlling the refining start and end temperature range to be 1510-1580℃, and controlling the content of each of the unnecessary impurity elements such as Ti, V, and Nb to be less than 0.001%.

[0018] Further, step 2 includes: casting the vacuum-smelted molten steel in an inert gas protective environment to obtain a cast billet, the chemical composition of which, by mass percentage, is: C: 0.02-0.05%, Si: 0.05-1.0%, Co: 0.3-2.2%, Cr: 0.03-0.12%, Als: 0.03-0.08%, N: 0.02-0.05%, Dy: 0.006-0.009%, Bi: 0.008-0.015%, with the remainder being Fe and unavoidable impurities, and the mass percentage ratio of Dy to Bi being (0.5-1):1.

[0019] Furthermore, step 3 satisfies at least one of the following conditions:

[0020] (1) Before hot rolling, the billet is kept at 1100℃~1220℃ for ≥2h;

[0021] (2) The hot rolling includes multiple rolling passes, with the temperature of the last rolling pass being ≥900℃;

[0022] (3) After hot rolling, the plate is cooled to 400-500℃ and then rolled to obtain a hot-rolled plate;

[0023] (4) The thickness of the hot-rolled plate is 1.6 to 2.1 mm.

[0024] Furthermore, step 4 satisfies at least one of the following conditions:

[0025] (1) Before a cold rolling process, the hot-rolled plate is also pickled;

[0026] (2) A single cold rolling process includes multiple rolling passes, and each pass is followed by an aging treatment; preferably, the aging treatment temperature is 180-250°C and the aging time is 1-3 min.

[0027] Furthermore, step 5 satisfies at least one of the following conditions:

[0028] (1) The decarburization annealing is carried out in a mixed atmosphere of N2 and H2; preferably, the volume ratio of N2 to H2 is (3-5):1;

[0029] (2) The decarburization annealing temperature is 760-800℃ and the time is 1-5 min;

[0030] (3) The product after one cold rolling is rapidly heated to the decarburization annealing temperature, with a heating rate ≥ 500℃ / min.

[0031] Furthermore, step 7 satisfies at least one of the following conditions:

[0032] (1) The surface temperature of the cold-rolled sheet is controlled at 500-600℃ by electrical pulse;

[0033] (2) The electric pulse heat treatment time is 5 to 30 seconds;

[0034] (3) An induced magnetic field is applied throughout the electrical pulse heat treatment process; preferably, the induced magnetic field is a transverse DC magnetic field with a magnitude of 1000-1500 A / m. Transverse refers to the direction perpendicular to the rolling direction of the steel strip or the direction perpendicular to the long side of the steel strip.

[0035] (4) The electrical pulse frequency is 200–400 Hz, and the pulse current density amplitude is 250–350 A / mm. 2 .

[0036] Furthermore, step 8 satisfies at least one of the following conditions:

[0037] (1) Before annealing, a release agent is coated on the surface of the product in step 7 and then dried; preferably, the release agent includes MgO;

[0038] (2) Annealing was carried out in an H2 atmosphere;

[0039] (3) The annealing temperature is 5 to 50°C below the transformation temperature of α-ferrite phase and γ-austenite phase (the temperature at which α and γ phases (two states) transform into each other), preferably 5 to 30°C.

[0040] (4) Insulation time: 2 to 20 hours.

[0041] Furthermore, at least one of the following conditions must be met:

[0042] (1) The interval between the end time of hot rolling and the start time of a single cold rolling shall not exceed 96 hours;

[0043] (2) The total reduction rate of the first cold rolling is controlled at 60-75%, and the total reduction rate of the second cold rolling is controlled at 55-65%.

[0044] Furthermore, the magnetic induction intensity value B of the prepared grain-oriented electrical steel under a low-frequency condition of 20Hz was measured. 800 The value is 1.99–2.02 T, B 10000 The value is 2.13 to 2.18 T.

[0045] Thirdly, the present invention provides an application of the above-mentioned low-frequency ultra-high magnetic induction intensity oriented electrical steel or the low-frequency ultra-high magnetic induction intensity oriented electrical steel prepared according to the method in a low-frequency transformer.

[0046] Preferably, the low frequency is 20Hz to 50Hz.

[0047] The technical solution of this invention has the following advantages:

[0048] 1. The chemical composition of the billet of the ultra-high magnetic induction strength oriented electrical steel of the present invention, by mass percentage, includes C: 0.02-0.05%, Si: 0.05-1.0%, Co: 0.3-2.2%, Cr: 0.03-0.12%, Als: 0.03-0.08%, N: 0.02-0.05%, Dy: 0.006-0.009%, Bi: 0.008-0.015%, with the remainder being Fe and unavoidable impurities, and the Dy:Bi ratio being (0.5-1):1.

[0049] This invention reduces the mass percentage of the nonferromagnetic element Si from 3.0-3.2% in existing commercially available formulations to 0.05-1.0%, limits the content of other nonferromagnetic elements, and further adds a new ferromagnetic element Co to the original Fe matrix, controlling its mass percentage to be 0.3-2.2%. This results in the intrinsic magnetic saturation magnetic induction intensity of the grain-oriented electrical steel exceeding the limit value under the original composition system, with a saturation magnetic induction intensity B... s The engine capacity has been significantly increased from 2.03T to over 2.13T.

[0050] Als (acid-soluble aluminum) and N serve as the main sources of the inhibitory particles AlN. Meanwhile, the mass percentages of special inhibitory elements Dy and Bi are 0.006–0.009% and 0.008–0.015%, respectively. The mass percentage ratio of Dy and Bi, which exist in the form of interstitial atoms, is controlled to be 0.5–1. Bi tends to agglomerate at grain boundaries, while Dy can promote the fine dispersion and stepwise division of Bi elemental particles. The combined effect of these two elements can inhibit the growth of primary recrystallized grains, thereby promoting the abnormal growth of Goss-oriented grains, improving the orientation degree of electrical steel, and thus improving the magnetic properties of the steel.

[0051] 2. The preparation method of the ultra-high magnetic induction strength oriented electrical steel of the present invention includes the following steps: Step 1, smelting; Step 2, casting to obtain a billet; Step 3, hot rolling the billet to obtain a hot-rolled plate; Step 4, cold rolling the hot-rolled plate once; Step 5, decarburizing and annealing; Step 6, cold rolling a second time to obtain a cold-rolled plate; Step 7, electro-pulse heat treatment of the cold-rolled plate; Step 8, annealing.

[0052] The method for preparing grain-oriented electrical steel in this invention is energy-efficient and low-energy-consumption. During the hot rolling stage, since MnS is not included in the composition system (the solution temperature of MnS in equilibrium is 1320℃), the billet heating temperature is reduced to 1100℃~1220℃, thus reducing energy consumption. The normalizing process between hot and cold rolling is eliminated. In existing grain-oriented electrical steel preparation, normalizing is mainly used for microstructure adjustment. In this invention, the reduced Si content improves the brittleness and edge cracking problems of the steel plate. By controlling the ratio of austenite and ferrite phases during hot rolling deformation and using a two-stage cold rolling method, the microstructure control objective can be achieved even without the energy-intensive normalizing process. Electrical pulse treatment replaces the conventional initial recrystallization heat treatment, completing the initial recrystallization in a very short time of 5~30s, while the traditional process of heating-holding-cooling takes several hours. In summary, by reducing the hot rolling temperature, eliminating the normalizing process, and introducing electrical pulse treatment to replace the traditional initial recrystallization annealing, the method for preparing grain-oriented electrical steel in this invention is energy-efficient and high-energy-consumption.

[0053] 3. In the method of this invention, the total reduction rate of the first cold rolling is controlled at 60-75%, and the total reduction rate of the second cold rolling is controlled at 55-65%. Limiting the reduction rates of the two cold rolling passes within the range of this invention effectively ensures the quality of the sheet shape and a favorable texture composition. It avoids an excessively high reduction rate in the first cold rolling pass, which would result in too few Goss nuclei after the initial recrystallization, hindering the improvement of magnetic properties; and it also avoids an excessively low reduction rate in the first cold rolling pass and an excessively high reduction rate in the second cold rolling pass, which would be detrimental to the adjustment of the microstructure and texture composition. A reasonable distribution of the reduction rates across the cold rolling passes ensures the sheet quality of the electrical steel and a favorable texture composition.

[0054] 4. The method for preparing oriented electrical steel provided by the present invention uses electrical pulse treatment instead of conventional initial recrystallization heat treatment, which accelerates the recrystallization process, shortens the preparation process, and simultaneously achieves {110} <001> Goss, {100} <110> {111} <110> {111} <112> {113} <161> Fine-tuning the texture composition during the initial recrystallization process is beneficial for improving the magnetic induction intensity of the final oriented electrical steel.

[0055] Under the pulse current density amplitude, temperature, DC magnetic field strength, and pulse duration conditions specified in this invention, the proportion of Goss texture after the electrical pulse can exceed 5%, which is conducive to the subsequent high-temperature annealing stage {110} <001> This provides a good foundation for the complete secondary recrystallization of Goss-oriented grains.

[0056] 5. The method for preparing oriented electrical steel provided by the present invention, wherein the high-temperature annealing temperature range is limited to 5 to 50°C below the transformation temperature of α-ferrite phase and γ-austenite phase, so as to avoid the phase transformation from destroying the preferred grain orientation. After high-temperature annealing, a sharp preferred oriented electrical steel sheet is obtained, which greatly improves the magnetic induction intensity.

[0057] The magnetic induction intensity B of existing ordinary grain-oriented electrical steel 800 The value is 1.82–1.87 T, B 10000 Approximately 2.01T; Existing high magnetic induction strength oriented electrical steel B 800 The value is 1.88–1.93 T, B 10000 Approximately 2.02T. The magnetic induction intensity value B of the oriented electrical steel in this invention... 800 The value is 1.99–2.02 T, B 10000 The saturation magnetic induction intensity (in B) of the grain-oriented electrical steel in this invention is 2.13–2.18 T. 10000 (Calculation) It breaks through the existing limit value of 3% Si oriented electrical steel.

[0058] 6. The interval between the end of hot rolling and the start of a single cold rolling cycle shall not exceed 96 hours. This is to avoid prolonged storage of hot-rolled plates, which can cause the dissolved C and N atoms in the steel to precipitate and form an unstable second phase. This weakens the ability of C and N atoms to pin dislocations during subsequent cold rolling, and increases the size of AlN inhibitor particles precipitated after annealing, resulting in reduced magnetic properties. Detailed Implementation

[0059] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0060] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0061] Example 1

[0062] This embodiment provides a method for preparing low-frequency ultra-high magnetic induction intensity oriented electrical steel, including the following steps:

[0063] 1) Vacuum smelting: The raw materials are smelted by circulating degassing in a vacuum smelting furnace. The refining start temperature is controlled at 1560℃ and the end temperature is controlled at 1550℃. The content of each of the unnecessary Ti, V and Nb impurity elements is controlled to be less than 0.001wt%.

[0064] 2) Casting: The molten steel after vacuum smelting is poured in an inert gas protective environment to obtain a cast billet, the composition of which is shown in Table 1.

[0065] Table 1 Chemical composition of the cast billet (wt.%)

[0066] C Si Co Cr Als N Dy Bi Fe and impurities 0.045 0.099 1.596 0.082 0.035 0.031 0.008 0.012 margin

[0067] 3) After holding the billet at 1170℃ for 3 hours, hot rolling is carried out. Hot rolling includes five rolling passes. The temperature of the last rolling pass is controlled to be no less than 900℃. After the last rolling pass is completed, water is sprayed to cool it down to 450℃. The billet is then rolled to obtain a hot-rolled plate with a thickness of 2.0mm.

[0068] 4) After pickling the hot-rolled plate, perform a cold rolling process (on the same day as the hot rolling is completed) to the intermediate thickness. The total reduction rate of this process is controlled at 70%. The cold rolling process includes 5 rolling passes. After each rolling pass, an aging treatment is performed at an aging temperature of 200℃ for 2 minutes.

[0069] 5) Decarburization annealing: The cold-rolled sheet after one cold rolling is rapidly heated to carry out intermediate decarburization annealing. The decarburization annealing atmosphere is a mixture of N2 and H2 gas with a volume ratio of N2 to H2 of 4:1. The heating rate is ≥500℃ / min, the decarburization temperature is 780℃, and the annealing time is 2min.

[0070] 6) Secondary cold rolling: The decarburized annealed plate is cold rolled a second time to a final thickness of 0.27 mm. The total reduction rate of this process is controlled at 55% to obtain a cold-rolled plate.

[0071] 7) Electrical pulse heat treatment: The electrical steel sheet after secondary cold rolling is subjected to electrical pulse heat treatment with an electrical pulse frequency of 300Hz and a pulse current density amplitude of 300A / mm. 2 The surface temperature of the steel plate was controlled at 550℃, the electric pulse heat treatment time was 10s, and a 1000A / m induced magnetic field was applied simultaneously during the electric pulse process.

[0072] 8) High-temperature annealing: The steel plate after the electrical pulse treatment is coated with MgO release agent and dried. It is then further annealed in H2 atmosphere at a temperature of 860℃ for 10 hours. After furnace cooling, the oriented electrical steel plate is obtained.

[0073] The oriented electrical steel sheet prepared according to the above method was tested at a frequency of 20Hz according to GB / T 3655-2022. The measured magnetic induction intensity value B of the sample was... 800 It is 2.01T, B 10000 It is 2.16T.

[0074] Example 2

[0075] This embodiment provides a method for preparing low-frequency ultra-high magnetic induction intensity oriented electrical steel, including the following steps:

[0076] 1) Vacuum smelting: The raw materials are smelted by circulating degassing in a vacuum smelting furnace. The refining start temperature is controlled at 1550℃ and the end temperature is controlled at 1530℃. The content of each of the unnecessary Ti, V and Nb impurity elements is controlled to be less than 0.001wt%.

[0077] 2) Casting: The molten steel after vacuum smelting is poured into an inert gas protective environment to obtain a cast billet, the composition of which is shown in Table 2.

[0078] Table 2 Chemical composition of the cast billet (wt.%)

[0079] C Si Co Cr Als N Dy Bi Fe and impurities 0.039 0.079 0.502 0.031 0.079 0.048 0.006 0.008 margin

[0080] 3) After holding the billet at 1120℃ for 3 hours, hot rolling is carried out. Hot rolling includes five rolling passes. The temperature of the last rolling pass is controlled to be no less than 900℃. After the last rolling pass is completed, water is sprayed to cool it down to 500℃. The billet is then rolled to obtain a hot-rolled plate with a thickness of 1.8mm.

[0081] 4) After pickling the hot-rolled plate, perform a cold rolling process (the cold rolling is performed the day after the hot rolling is completed) to the intermediate thickness. The total reduction rate of this process is controlled at 63.9%. The cold rolling process includes 5 rolling passes. After each rolling pass, an aging treatment is performed. The aging temperature of the cold rolling is 180℃ and the aging time is 3min.

[0082] 5) Decarburization annealing: The cold-rolled sheet after one cold rolling is rapidly heated to carry out intermediate decarburization annealing. The decarburization annealing atmosphere is a mixture of N2 and H2 gas with a volume ratio of 3:1. The heating rate is 500℃ / min, the decarburization temperature is 760℃, and the annealing time is 5min.

[0083] 6) Secondary cold rolling: The decarburized annealed plate is cold rolled a second time to a final thickness of 0.23 mm. The total reduction rate of this process is controlled at 64.6% to obtain a cold-rolled plate.

[0084] 7) Electrical pulse heat treatment: The electrical steel sheet after secondary cold rolling is subjected to electrical pulse heat treatment with an electrical pulse frequency of 300Hz and a pulse current density amplitude of 260A / mm. 2 The surface temperature of the steel plate was controlled at 520℃, the electric pulse heat treatment time was 15s, and a 1500A / m induced magnetic field was applied simultaneously during the electric pulse process.

[0085] 8) High-temperature annealing: The steel plate after the electric pulse heat treatment is coated with MgO release agent on the top and bottom and dried. It is then further annealed in H2 atmosphere at a high temperature of 880℃ for 5 hours. After furnace cooling, the oriented electrical steel plate is obtained.

[0086] The oriented electrical steel sheet prepared according to the above method was tested at a frequency of 20Hz according to GB / T 3655-2022. The measured magnetic induction intensity value B of the sample was... 800 It is 1.99T, B 10000 It is 2.13T.

[0087] Example 3

[0088] This embodiment provides a method for preparing low-frequency ultra-high magnetic induction intensity oriented electrical steel, including the following steps:

[0089] 1) Vacuum smelting: The raw materials are smelted by circulating degassing in a vacuum smelting furnace. The refining start temperature is controlled at 1580℃ and the end temperature is controlled at 1570℃. The content of each of the unnecessary impurity elements such as Ti, V, and Nb is controlled to be less than 0.001wt%.

[0090] 2) Casting: The molten steel after vacuum smelting is poured into an inert gas protective environment to obtain a cast billet, the composition of which is shown in Table 3.

[0091] Table 3 Chemical composition of the cast billet (wt.%)

[0092] C Si Co Cr Als N Dy Bi Fe and impurities 0.022 0.051 2.103 0.109 0.046 0.035 0.008 0.015 margin

[0093] 3) After holding the billet at 1200℃ for 2 hours, hot rolling is carried out. Hot rolling includes five rolling passes. The temperature of the last rolling pass is controlled to be no less than 900℃. After the last rolling pass is completed, water is sprayed to cool it down to 490℃. The billet is then rolled to obtain a hot-rolled plate with a thickness of 2.1mm.

[0094] 4) After pickling the hot-rolled plate, perform a cold rolling process (on the same day as the hot rolling is completed) to the intermediate thickness. The total reduction rate of this process is controlled at 68%. The cold rolling process includes 5 rolling passes. After each rolling pass, an aging treatment is performed. The aging temperature is 220℃ and the aging time is 2min.

[0095] 5) Decarburization annealing: The cold-rolled sheet after one cold rolling is rapidly heated to carry out intermediate decarburization annealing. The decarburization annealing atmosphere is a mixture of N2 and H2 gas with a volume ratio of 5:1. The heating rate is 550℃ / min, the decarburization temperature is 800℃, and the annealing time is 2min.

[0096] 6) Secondary cold rolling: The decarburized annealed plate is cold rolled a second time to a final thickness of 0.30 mm. The total reduction rate of this process is controlled at 55% to obtain a cold-rolled plate.

[0097] 7) Electrical pulse heat treatment: The electrical steel sheet after secondary cold rolling is subjected to electrical pulse heat treatment with an electrical pulse frequency of 300Hz and a pulse current density amplitude of 320A / mm. 2 The surface temperature of the steel plate was controlled at 580℃, the electric pulse heat treatment time was 8s, and a 1200A / m induced magnetic field was applied simultaneously during the electric pulse process.

[0098] 8) High-temperature annealing: The steel plate after the electrical pulse treatment is coated with MgO release agent and dried. It is then further annealed in H2 atmosphere at a temperature of 870℃ for 20 hours. After furnace cooling, the oriented electrical steel plate is obtained.

[0099] The oriented electrical steel sheet prepared according to the above method was tested at a frequency of 20Hz according to GB / T 3655-2022. The measured magnetic induction intensity value B of the sample was... 800 It is 2.02T, B 10000 It is 2.18T.

[0100] Comparative Example 1

[0101] This comparative example is basically the same as Example 1, except that the Si content is 3% and the corresponding Fe content of the matrix element is reduced by 3%.

[0102] The oriented electrical steel sheet prepared in Comparative Example 1 was tested at a frequency of 20Hz according to GB / T 3655-2022, and the measured magnetic induction intensity value B was obtained. 800 It is 1.88T, B 10000 It is 1.96T.

[0103] As can be seen from the magnetic induction intensity of the oriented electrical steel sheets obtained in Examples 1-3 and Comparative Example 1, the magnetic properties of the oriented electrical steel sheets obtained by the present invention are significantly improved. When applied to low-frequency transformers, they can significantly reduce the losses, weight and volume of low-frequency transformers.

[0104] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A low-frequency, ultra-high magnetic induction intensity oriented electrical steel, characterized in that, The chemical composition of the oriented electrical steel billet, by mass percentage, includes C: 0.02~0.05%, Si: 0.05~1.0%, Co: 0.3~2.2%, Cr: 0.03~0.12%, Als: 0.03~0.08%, N: 0.02~0.05%, Dy: 0.006~0.009%, Bi: 0.008~0.015%, with the remainder being Fe and unavoidable impurities, and the Dy:Bi ratio being (0.5~1):1; The preparation method of the low-frequency ultra-high magnetic induction intensity oriented electrical steel includes the following steps: Step 1: Smelting; Step 2: Casting to obtain a billet; Step 3: Hot-roll the cast billet to obtain a hot-rolled plate; Step 4: Perform a cold rolling process on the hot-rolled plate; Step 5: Decarburization annealing; Step 6: Obtain cold-rolled sheet by secondary cold rolling; Step 7: Perform electric pulse heat treatment on the cold-rolled sheet; Step 8: Annealing; The total reduction rate of the first cold rolling is controlled at 60-75%, and the total reduction rate of the second cold rolling is controlled at 55-65%. In step 4, a single cold rolling process includes multiple rolling passes, and an aging treatment is performed after each rolling pass. The aging treatment temperature is 180~250℃ and the aging time is 1~3min. In step 7, the surface temperature of the cold-rolled sheet is controlled at 500~600℃ using an electric pulse; the electric pulse heat treatment time is 5~30s; the electric pulse frequency is 200~400Hz; and the pulse current density amplitude is 250~350A / mm. 2 An induced magnetic field is applied throughout the entire electrical pulse heat treatment process. In step 8, the annealing temperature is 5 to 50°C below the transformation temperature of the α-ferrite phase and the γ-austenite phase.

2. The low-frequency ultra-high magnetic induction intensity oriented electrical steel according to claim 1, characterized in that, Step 3 satisfies at least one of the following conditions: (1) Before hot rolling, the billet is kept at 1100℃~1220℃ for ≥2h; (2) The hot rolling includes multiple rolling passes, with the temperature of the last rolling pass being ≥900℃; (3) After hot rolling, the plate is cooled to 400~500℃ and then rolled to obtain a hot-rolled plate; (4) The thickness of the hot-rolled plate is 1.6~2.1mm.

3. The low-frequency ultra-high magnetic induction intensity oriented electrical steel according to claim 1, characterized in that, In step 4, the hot-rolled plate is pickled before cold rolling.

4. The low-frequency ultra-high magnetic induction intensity oriented electrical steel according to claim 1, characterized in that, Step 5 satisfies at least one of the following conditions: (1) Decarburization annealing is carried out in a mixed atmosphere of N2 and H2; (2) The decarburization annealing temperature is 760~800℃ and the time is 1~5min; (3) The product after one cold rolling is rapidly heated to the decarburization annealing temperature, with a heating rate ≥ 500℃ / min.

5. The low-frequency ultra-high magnetic induction intensity oriented electrical steel according to claim 1, characterized in that, Step 8 satisfies at least one of the following conditions: (1) Before annealing, a release agent is coated on the surface of the product in step 7 and then dried; (2) Annealing is carried out in an H2 atmosphere; (3) The annealing holding time is 2~20h.

6. The low-frequency ultra-high magnetic induction intensity oriented electrical steel according to any one of claims 1-5, characterized in that, The interval between the end time of hot rolling and the start time of a single cold rolling cycle shall not exceed 96 hours.

7. The low-frequency ultra-high magnetic induction intensity oriented electrical steel according to any one of claims 1-5, characterized in that, The magnetic induction intensity value B of the prepared grain-oriented electrical steel under a low-frequency condition of 20Hz 800 The value is 1.99~2.02T, B 10000 The value is 2.13~2.18T.

8. The application of the low-frequency ultra-high magnetic induction intensity oriented electrical steel according to any one of claims 1-7 in low-frequency transformers.