Method for producing grain-oriented silicon steel and grain-oriented silicon steel

Abstract

The application discloses a method for preparing oriented silicon steel and the oriented silicon steel, and the method comprises the following steps: continuously casting molten steel through a crystallizer to obtain a casting blank, wherein a unidirectional pulse current is applied to the molten steel in the crystallizer; hot-rolling the casting blank to obtain a hot-rolled coil; and carrying out subsequent treatment on the hot-rolled coil to obtain the oriented silicon steel. The unidirectional pulse current applied to the molten steel in the crystallizer can change the type and content of the metallographic structure in the casting blank, so that less or no banded structure is generated when the casting blank is subjected to a subsequent rolling process, thereby improving the magnetic properties and internal quality, such as linear crystal defects, of the prepared oriented silicon steel.

Description

Technical Field

[0001] This application belongs to the field of steel product preparation technology, specifically relating to a method for preparing oriented silicon steel and oriented silicon steel. Background Technology

[0002] Oriented silicon steel refers to Si-Fe soft magnetic material with a {110} texture (i.e., Goss texture) of about 3% by mass of Si element. It is a functional material for high-end power equipment and is widely used in ultra-high voltage power transmission, advanced large generators and other fields.

[0003] Currently, the main production processes for grain-oriented silicon steel include continuous casting, plastic forming (hot rolling, cold rolling), and heat treatment (normalizing, decarburizing annealing, high-temperature annealing). Among these technologies, the resulting grain-oriented silicon steel exhibits significant linear defects and low magnetic properties. Summary of the Invention

[0004] In view of this, this application provides a method for preparing oriented silicon steel and oriented silicon steel, aiming to provide a preparation method and product that can produce oriented silicon steel with good magnetic properties and internal quality.

[0005] In a first aspect, embodiments of this application provide a method for preparing grain-oriented silicon steel, comprising:

[0006] Molten steel is continuously cast through a crystallizer to obtain a billet, wherein a unidirectional pulse current is applied to the molten steel in the crystallizer;

[0007] The cast billet is hot-rolled to obtain a hot-rolled coil;

[0008] The hot-rolled coils are then further processed to obtain oriented silicon steel.

[0009] According to one embodiment of this application, the current intensity of the unidirectional pulse current is -2000A to 0A, and the frequency of the unidirectional pulse current is 1HZ to 100HZ.

[0010] According to one embodiment of this application, the current of the unidirectional pulse current is from 0A to 2000A, and the frequency of the unidirectional pulse current is from 1HZ to 100HZ.

[0011] According to one embodiment of this application, the voltage of the unidirectional pulse current is -30 to 0V.

[0012] According to one embodiment of this application, the method of applying a unidirectional pulse current to molten steel in a crystallizer includes: one side connected to a power source is connected to the molten steel in the crystallizer via an electrode, and the other side connected to the power source is connected to a straightening roller in continuous casting via a wire.

[0013] According to one embodiment of this application, the electrode is inserted into the molten steel in the crystallizer to a depth of 10 cm to 400 cm.

[0014] According to one embodiment of this application, the electrode includes any one of a cermet electrode, a graphite electrode, and an electrode made of the same material as the crystallizer nozzle.

[0015] According to one embodiment of this application, the conductor includes a cross-section ≥100mm². 2 Metal wires.

[0016] According to one embodiment of this application, the volume fraction of the equiaxed crystal structure in the billet is 30%-70%; the volume fraction of the columnar crystal structure in the billet is 30%-70%. According to one embodiment of this application, the composition of the molten steel, by mass percentage, includes: C ≤ 0.0050%, Si: 2.8%-3.8%, Mn: 0.05%-0.2%, P ≤ 0.010%, S ≤ 0.0030%, N ≤ 0.0040%, Als: 0.5%-1.3%, Ti, Nb, and V ≤ 0.0020% respectively; the remainder is Fe and other unavoidable impurity elements.

[0017] Secondly, embodiments of this application provide an oriented silicon steel, which is prepared by the method described in the first aspect.

[0018] Compared with the prior art, this application has at least the following beneficial effects:

[0019] The method provided in this application applies a unidirectional pulsed current to molten steel in a crystallizer, which can change the type and content of the metallographic structure in the billet, so that less or no banded structure is generated when the billet undergoes subsequent rolling processes, thereby improving the magnetic properties and internal quality of the obtained grain-oriented silicon steel, such as reducing linear defects. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0021] Figure 1 A schematic diagram of the installation of the unidirectional pulse current device according to Embodiment 1 of this application is shown;

[0022] Figure 2 The diagram shows the voltage-frequency relationship of a unidirectional pulse current applied according to Embodiment 1 of this application;

[0023] Figure 3 The diagram shows the current-frequency relationship of a unidirectional pulse current applied according to Embodiment 1 of this application;

[0024] Figure 4 A microstructure diagram of the cast billet of Embodiment 2 of this application is shown;

[0025] Figure 5 A microstructure diagram of the cast billet of Embodiment 3 of this application is shown;

[0026] Figure 6 A microstructure diagram of the billet of Comparative Example 1 of this application is shown.

[0027] Among them, 1. high-frequency power supply, 2. crystallizer, and 3. tension leveling machine roller conveyor. Detailed Implementation

[0028] To make the purpose, technical solution, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the embodiments described in this specification are merely for explaining this application and are not intended to limit it.

[0029] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0030] In the description of this application, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more.

[0031] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0032] Oriented silicon steel refers to steel with {110} <001> 3% Si-Fe soft magnetic material with Goss texture is a functional material for high-end power equipment and is widely used in ultra-high voltage power transmission, advanced large generators, and other fields. The production process of grain-oriented silicon steel is complex and requires strict manufacturing techniques. The main preparation processes include: plastic processing (hot rolling, cold rolling) and heat treatment processes (normalizing, decarburizing annealing, high-temperature annealing).

[0033] Research has revealed that the well-developed columnar crystal structure in continuously cast slabs of grain-oriented silicon steel can cause severe internal cracks and central segregation, leading to coarse banded structures in hot-rolled plates. Ultimately, this results in surface defects such as line crystal defects on the grain-oriented silicon steel surface. Line crystal defects (also known as linear defects) are a type of defect in crystal structure, typically manifesting as linear regions arranged along a certain direction within the crystal, where the atomic arrangement or structure is abnormal, including dislocations, slip lines, and fractures.

[0034] To obtain grain-oriented silicon steel with better internal quality, necessary measures (such as electromagnetic stirring and adding nucleating agents) are usually adopted during production to control the quality of grain-oriented silicon steel. However, these measures still cannot significantly improve its internal quality and have many limitations.

[0035] Method for preparing grain-oriented silicon steel

[0036] In a first aspect, embodiments of this application provide a method for preparing grain-oriented silicon steel, comprising:

[0037] Molten steel is continuously cast through a crystallizer to obtain a billet, wherein a unidirectional pulse current is applied to the molten steel in the crystallizer;

[0038] The cast billet is hot-rolled to obtain a hot-rolled coil;

[0039] The hot-rolled coils are then further processed to obtain oriented silicon steel.

[0040] Research has shown that applying an electric current to the molten steel before solidification of grain-oriented silicon steel allows for precise control of grain size, resulting in better steel products. Electrical pulse treatment in the tundish can improve yield and production efficiency, and ensure the electromagnetic properties of the steel meet national standards. However, even with electrical pulse treatment in the tundish, the molten steel temperature remains above the solidus temperature, thus having little effect on improving the solidification structure of the billet.

[0041] Further research revealed that applying a pulsed current before or during the solidification of oriented silicon steel can effectively reduce columnar crystals and increase equiaxed crystals in the billet, thus mitigating compositional segregation. It can also refine the grain size. When the integral numbers of columnar and equiaxed crystals in the billet are within a suitable range, the formation of coarse banded structures detrimental to steel properties in the hot-rolled plate can be avoided. Furthermore, the unidirectional pulsed current introduced by the internal quality control does not affect the magnetic properties of the oriented silicon steel.

[0042] According to the embodiments of this application, hot rolling can be understood as: cold rolling or hot rolling raw materials to the required thickness to form a silicon steel sheet. This step results in poor grain orientation, but it is the basis for subsequent orientation processes.

[0043] In some embodiments, adding a unidirectional pulsed current to the molten steel in the crystallizer can significantly increase the equiaxed crystal ratio of the billet, thereby improving the internal quality of the grain-oriented silicon steel. In some embodiments, under the same continuous casting production conditions, the equiaxed crystal ratio of the as-cast microstructure of the billet without electrical pulse treatment is 30%, while after electrical pulse treatment, the equiaxed crystal ratio can reach 40% to 75%.

[0044] In some embodiments, the current intensity of the unidirectional pulse current is -2000A to 0A, and the frequency of the unidirectional pulse current is 1Hz to 100Hz. The unidirectional pulse current within the above range can exert a certain influence on the molten steel in the crystallizer, improve the conformation of the solidification structure of the billet, and thus affect the microstructure of the billet; and the unidirectional pulse current intensity within this range will not cause serious damage to the relevant instruments on the continuous casting platform.

[0045] In some embodiments, the unidirectional pulse current is 0A to 2000A, and the frequency of the unidirectional pulse current is 0Hz to 100Hz. The unidirectional pulse current within the above range can exert a certain influence on the molten steel in the crystallizer, further improve the conformation of the solidification structure of the billet, thereby affecting the microstructure of the billet, reducing or avoiding linear defects on the surface of grain-oriented silicon steel, and improving its internal quality.

[0046] In some embodiments, the voltage of the unidirectional pulse current is -30 to 0V. Voltages within this range improve the safety of the continuous casting platform and reduce the degree of damage to related instruments on the platform. This is likely because the signal voltage detected by the monitoring equipment on the continuous casting machine is generally in the positive range, not in the negative range, and has little or no impact on production and instrumentation.

[0047] In some embodiments, applying a unidirectional pulse current to the molten steel in the crystallizer includes: one side connected to the power source is connected to the molten steel in the crystallizer via an electrode, and the other side connected to the power source is connected to the straightening roller in the continuous casting via a wire.

[0048] The technical solution of this application introduces a pulsed current into the continuous casting mold. At this time, the entire billet is in an energized state. How to reduce or avoid the impact of the pulsed current on the continuous casting instruments and meters is one of the key problems that urgently need to be solved. By connecting one side connected to the power supply to the molten steel in the mold through an electrode, and the other side connected to the power supply to the straightening rollers in the continuous casting process through a wire, the impact of the pulsed current on the relevant instruments and meters during the continuous casting process can be reduced or avoided, thus reducing the impact on the operation of related equipment.

[0049] In some embodiments, the electrode is inserted into the molten steel in the crystallizer to a depth of 10 cm to 400 cm. By controlling the depth of electrode insertion into the molten steel in the crystallizer, the solidification structure of the cast billet is positively regulated, while the adverse effects of mold flux entrapment are avoided.

[0050] In some embodiments, the electrode comprises any one of a cermet electrode, a graphite electrode, and an electrode made of the same material as the crystallizer nozzle. These electrodes can effectively transmit current and exhibit a certain degree of resistance to high temperatures, allowing for the stable application of unidirectional pulsed current to molten steel. In some embodiments, the surface of the graphite electrode is coated with a slag-resistant, insulating, and refractory protective layer.

[0051] In some embodiments, the electrode is heated to a red-hot state before use.

[0052] In some embodiments, the conductor includes a cross-section ≥100mm². 2 Metallic wires. Metallic wires include copper wires, aluminum wires, etc.

[0053] In some embodiments, the volume fraction of equiaxed grain structure in the billet is 30%-70%; the volume fraction of columnar grain structure in the billet is 30%-70%. The sum of the volume fractions of equiaxed grain structure and columnar grain structure in the billet is approximately 90%-95%. Equiaxed grains are grains whose size difference is small in all directions. Columnar grains exhibit directional properties; therefore, in alloys with poor plasticity, such as steel, a high proportion of columnar grains can easily lead to cracking during reheating. However, during steel production, columnar grains possess… <100> The characteristics of texture inheritance have certain advantages on the performance of steel. It can appropriately improve the magnetic properties of silicon steel. Equiaxed crystals can improve the processing performance of steel plates and avoid internal quality defects in steel, such as linear crystals, caused by subsequent continuous casting processes. Therefore, comprehensively controlling the volume fraction of equiaxed crystals and columnar crystals within the above range has a positive effect on the magnetic properties of steel.

[0054] In some embodiments, the composition of the molten steel, by mass percentage, includes: C ≤ 0.0050%, Si: 2.8%–3.8%, Mn: 0.05%–0.2%, P ≤ 0.010%, S ≤ 0.0030%, N ≤ 0.0040%, Als: 0.5%–1.3%, Ti, Nb, and V ≤ 0.0020% respectively; the remainder being Fe and other unavoidable impurity elements. This composition of the molten steel contributes to the magnetic properties of grain-oriented silicon steel, and controlling the proportions of Ti, Ni, V, and N elements helps improve the internal quality of the grain-oriented silicon steel.

[0055] In some embodiments, post-processing may include the following steps:

[0056] Annealing: High-temperature annealing improves grain orientation. The annealing temperature and time are adjusted according to the specific material requirements. Annealing promotes grain growth, thereby achieving a columnar crystal structure.

[0057] Orientation hot rolling: After annealing, the grains are hot rolled again, this time at a high temperature. This process helps to further optimize grain orientation, making them more aligned along a predetermined direction and improving magnetic permeability.

[0058] Magnetic field treatment: A strong magnetic field is applied during hot rolling to further control grain orientation. Magnetic field treatment can be performed during hot rolling or annealing.

[0059] Cutting and shaping: The grain-oriented silicon steel sheet is cut into the required shapes and sizes for use in subsequent manufacturing processes. This can be done according to specific application requirements.

[0060] In some embodiments, after cutting and shaping, the grain-oriented silicon steel may include the following steps:

[0061] Coating treatment: Sometimes an insulating or organic coating is applied to the surface of oriented silicon steel to improve surface properties and magnetic properties.

[0062] Heat treatment: Appropriate heat treatment can further optimize grain orientation and magnetic properties. This may involve annealing or other heat treatment processes.

[0063] Secondly, embodiments of this application provide an oriented silicon steel, which is prepared by the method described in the first aspect.

[0064] Example

[0065] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0066] Example 1

[0067] This embodiment provides a method for preparing grain-oriented silicon steel, including:

[0068] Molten steel is continuously cast through a crystallizer to obtain a billet. A unidirectional pulsed current is applied to the molten steel in the crystallizer. The chemical composition of the molten steel, by mass percentage, includes: C ≤ 0.0050%, Si: 2.8%–3.8%, Mn: 0.05%–0.2%, P ≤ 0.010%, S ≤ 0.0030%, N ≤ 0.0040%, Als: 0.5%–1.3%, and Ti, Nb, and V ≤ 0.0020% respectively. The billet is then hot-rolled to obtain a hot-rolled coil.

[0069] The hot-rolled coils are then further processed to obtain oriented silicon steel.

[0070] Apply a unidirectional pulse current to the molten steel in the crystallizer, see details. Figure 1 Connect the high-frequency power supply 1 to a 380V three-wire four-phase power circuit breaker, using 2 to 4 wires ≥10mm². 2 Cable connection; connect the negative output terminal of the high-frequency power supply with 2-4 cables ≥100mm². 2 The cable is connected to the leveling machine roller 3, and the positive output of the high-frequency power supply is connected by 2 to 4 wires ≥100mm. 2 The cable and the molten steel inserted into crystallizer 2 are connected to the electrode connector, and the installation method is as follows: Figure 1 As shown; during operation, after heating the electrodes to a red-hot state, turn on the high-frequency power switch, insert the electrodes into the crystallizer at a depth of 10-400 cm below the molten steel surface, and fix the electrodes in place; after rectifying the pulse current, filter out the positive pulse current, retain the negative current, and adjust the voltage to -30 to 0V. See the voltage-time diagram below. Figure 2 The current is adjusted to 1000A and the frequency to 1-100Hz. After production is completed, the high-frequency power switch is turned off, and the electrodes are removed from the crystallizer. After passing through the crystallizer, the molten steel undergoes foot rolling, zero-segment positioning, etc., and after the above-mentioned hot rolling and post-treatment, the preparation of grain-oriented silicon steel is completed.

[0071] Example 2

[0072] The difference between this embodiment and Embodiment 1 is the voltage; the voltage is as follows: Figure 3 As shown.

[0073] Example 3

[0074] The difference between this embodiment and Embodiment 1 is that the current intensity is different; the current is 900A.

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 1 is that no unidirectional pulse current was applied to the molten steel in the crystallizer.

[0077] Comparative Example 2

[0078] The difference between this comparative example and Example 1 is that a unidirectional pulse current is applied to the molten steel at the foot roller position.

[0079] Comparative Example 3

[0080] The difference between this comparative example and Example 1 is that a negative pulse current is applied to the molten steel at the zero-segment position.

[0081] Test section

[0082] The metallographic structure of the oriented silicon steel in the examples and comparative examples was examined using electron microscopy, and the results are shown in Table 1.

[0083] The magnetic properties of grain-oriented silicon steel were tested using the method of measuring the magnetic properties of electrical steel sheets (strips) with Epstein squares according to GB / T 3655-2008. The results are shown in Table 1.

[0084] Table 1

[0085]

[0086] As can be seen from the results in Table 1, applying a unidirectional pulse current to the molten steel in the crystallizer in the examples can improve the equiaxed crystal ratio of the billet. However, in Comparative Example 1, no unidirectional pulse current was applied to the molten steel in the crystallizer, resulting in a low equiaxed crystal ratio of the oriented silicon steel. In Comparative Examples 2 and 3, an electric pulse current was applied, and the equiaxed crystal ratio of the billet was improved to a certain extent.

[0087] Figure 4 The microstructure of the grain-oriented silicon steel billet treated with a 30Hz unidirectional pulsed current in Example 2 is shown, illustrating that the pulsed current treatment is beneficial to improving the equiaxed crystal ratio of the billet. Figure 5 The microstructure of the grain-oriented silicon steel billet treated with a unidirectional pulsed current of 900A and 30Hz in Example 3 is shown, illustrating that the billet has a higher equiaxed crystal ratio under high current pulsed current conditions. Figure 6 The microstructure of the grain-oriented silicon steel billet in Comparative Example 1, which was not treated with pulse, is shown, illustrating that the equiaxed crystal ratio of the billet without pulse treatment is low.

[0088] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing grain-oriented silicon steel, characterized in that, include: Molten steel is continuously cast through a crystallizer to obtain a billet. The composition of the molten steel, by mass percentage, includes: C ≤ 0.0050%, Si: 2.8%–3.8%, Mn: 0.05%–0.2%, P ≤ 0.010%, S ≤ 0.0030%, N ≤ 0.0040%, Als: 0.5%–1.3%, Ti, Nb, and V ≤ 0.0020% respectively; the remainder is Fe and other unavoidable impurity elements. A unidirectional pulsed current is applied to the molten steel in the crystallizer; the current intensity of the unidirectional pulsed current is 900 to 2000 A, the frequency of the unidirectional pulsed current is 1 Hz to 100 Hz, and the voltage of the unidirectional pulsed current is -30 to 0 V; the electrode is inserted into the molten steel in the crystallizer to a depth of 10 cm to 400 cm. The cast billet is hot-rolled to obtain a hot-rolled coil; The hot-rolled coils are then further processed to obtain oriented silicon steel.

2. The method according to claim 1, characterized in that, The method of applying a unidirectional pulse current to the molten steel in the crystallizer includes: one side connected to the power source is connected to the molten steel in the crystallizer through an electrode, and the other side connected to the power source is connected to the straightening roller in the continuous casting through a wire.

3. The method according to claim 2, characterized in that, The electrode includes any one of the following: a metal-ceramic electrode, a graphite electrode, and an electrode made of the same material as the crystallizer nozzle; And / or, The conductor includes conductors with a cross-section ≥100mm². 2 Metal wires.

4. The method according to claim 1, characterized in that, The volume fraction of the equiaxed crystal structure of the billet is 30%-70%; the volume fraction of the columnar crystal structure of the billet is 30%-70%.

5. The method according to claim 4, characterized in that, The average grain size of equiaxed crystals is 2000-4500 μm, while the average grain size of columnar crystals is 3000-7000 μm.

6. A type of grain-oriented silicon steel, characterized in that, It is prepared by the method described in any one of claims 1-5.

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