A grain control method for oriented electrical steel

Abstract

The present invention relates to the technical field of oriented electrical steel, and in particular to a method for controlling grains of oriented electrical steel. The method for controlling grains of oriented electrical steel comprises the following steps: S1: setting an expected contour pattern on the surface of a steel plate after decarburization and nitriding annealing; S2: thinning the surface nitriding layer of the area on the surface of the steel plate where the expected contour pattern is set and / or applying pressure to the area on the surface of the steel plate where the expected contour pattern is set, so as to generate compressive stress in the pattern area on the surface of the steel plate; S3: uniformly coating a high-temperature annealing separator on the surface of the steel plate and drying it, and performing high-temperature annealing on the steel plate; S4: pickling and cleaning the steel plate until the steel plate presents a clear grain structure. The present application provides a method for controlling grains of oriented electrical steel, which thins the surface nitriding layer of the steel plate, thereby weakening the inhibitory force on grain growth, and applies pressure within the set contour on the surface of the steel plate, which can increase the driving force for the growth of primary recrystallized grains, and achieves precise control of the finished product grain size to grow differentially with the surrounding grains according to the set contour, presenting an artistic grain pattern.

Description

Technical Field

[0001] The present invention relates to the technical field of oriented electrical steel, and in particular to a grain control method for oriented electrical steel. Background Art

[0002] Grain-oriented electrical steel is primarily used in transformer cores. Its key performance indicator is electromagnetic properties, and the final grain orientation is a key determinant of these properties. Grain-oriented electrical steel undergoes primary recrystallization during the decarburization and nitriding annealing process, followed by secondary recrystallization during the high-temperature annealing process, resulting in a large (centimeter-scale) grain structure in the finished product. Precise grain size control has been a focus of ongoing research in the field of grain-oriented electrical steel for many years, and its effectiveness depends primarily on the precise matching of driving and restraining forces. Excessively large grain size significantly increases specific total loss, while too small a grain size can lead to the appearance of stray grains with orientations other than Gaussian. These stray grains, deviating from the precise Gaussian texture, negatively impact magnetic induction. Given the extremely stringent process requirements for grain-oriented electrical steel throughout the entire process, even the slightest process deviation can cause the grain size to deviate from the target. Therefore, the ability to control grain size directly reflects the depth of secondary recrystallization research, the ability to manufacture products with superior magnetic properties, and the company's competitiveness. Summary of the Invention

[0003] The present application provides a method for controlling grain size of oriented electrical steel, which reflects the research level of oriented electrical steel manufacturers on secondary recrystallization, their ability to manufacture products with excellent magnetic properties, and improves the competitiveness of the enterprises.

[0004] The present application provides a method for controlling grain size of oriented electrical steel, which comprises the following steps:

[0005] S1: Setting the desired profile pattern on the surface of the steel plate after decarburization and nitriding annealing;

[0006] S2: thinning the surface nitriding layer of the area on the surface of the steel plate where the expected profile pattern is set and / or applying pressure to the area on the surface of the steel plate where the expected profile pattern is set, so as to generate compressive stress on the surface of the steel plate;

[0007] S3: evenly coating a high-temperature annealing release agent on the surface of the steel plate and drying the same to perform high-temperature annealing on the steel plate;

[0008] S4: pickling and cleaning the steel plate until the steel plate exhibits a clear grain structure.

[0009] In some embodiments, in step S2, the surface nitriding layer in the area on the surface of the steel plate where the expected profile pattern is set is thinned by 5-30 μm.

[0010] In some embodiments, in step S2, the surface nitrided layer in the area of ​​the steel plate surface where the expected profile pattern is set is removed by a corrosive agent.

[0011] In some embodiments, in step S2, the surface nitrided layer in the area where the expected contour pattern is set on the surface of the steel plate is removed by shot blasting, sand blasting, high-pressure water or laser etching.

[0012] In some embodiments, in step S2, the pressure applied to the area on the surface of the steel plate where the expected contour pattern is set is in a range of 0.1-10 MPa.

[0013] In some embodiments, in step S2, pressure is applied to the area of ​​the steel plate surface where the expected contour pattern is set by shot blasting, shot blasting, sand blasting, high-pressure water, hammering, or laser etching.

[0014] In some embodiments, in step S3, the steel plate may be coated on one side or both sides with a high temperature annealing separator, wherein the high temperature annealing separator is MgO and / or Al2O3.

[0015] In some embodiments, in step S3, the single-side coating thickness of the high-temperature annealing isolation agent is 10-50 μm, and the drying temperature of the high-temperature annealing isolation agent after coating is 600-800° C.

[0016] In some embodiments, in step S3, when the heating temperature of the high temperature annealing is below 1100°C, the heating rate is 10-25°C / h, the maximum heating temperature is 1200°C, and the holding time is 20-30h.

[0017] In some embodiments, the method for controlling grain size of grain-oriented electrical steel further comprises:

[0018] S4: applying an anti-rust coating on the surface of the steel plate.

[0019] The beneficial effects of this application are as follows:

[0020] During the decarburization and nitriding annealing process, nitrogen atoms penetrate into the surface of the steel plate to form a nitriding layer, which is converted into an inhibitor during the high-temperature annealing process and gradually diffuses to the center layer of the steel plate to achieve uniform distribution in the thickness direction. The present application provides a method for controlling the grain size of oriented electrical steel. After the decarburization and nitriding annealing process, the surface nitriding layer in the area where the expected contour pattern is set on the surface of the steel plate is thinned, thereby greatly weakening the inhibitory force on grain growth during the secondary recrystallization process in the high-temperature annealing process, and applying pressure in the area where the expected contour pattern is set on the surface of the steel plate to generate compressive stress on the surface of the steel plate, which can increase the driving force for the growth of the primary recrystallization grains. By controlling the inhibitory force and the driving force, the finished grain size can be precisely controlled, so that the grains grow differently in the set direction to show the artistic effect of the grain contour, which represents the company's precise control ability over high-performance oriented silicon steel and improves the company's competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention.

[0022] Figure 1 The grain structure of the oriented electrical steel provided in this embodiment is Figure 1 ;

[0023] Figure 2 The grain structure of the oriented electrical steel provided in this embodiment is Figure 2 ;

[0024] Figure 3 The grain structure of the oriented electrical steel provided in this embodiment is Figure 3 ;

[0025] Figure 4 The grain structure of the oriented electrical steel without adopting the technical solution of this embodiment is shown as follows: Figure 1 ;

[0026] Figure 5 The grain structure of the oriented electrical steel without adopting the technical solution of this embodiment is shown as follows: Figure 2 ;

[0027] Figure 6 The grain structure of the oriented electrical steel without adopting the technical solution of this embodiment is shown as follows: Figure 3 . DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments 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.

[0029] Grain-oriented electrical steel undergoes primary recrystallization during the decarburization and nitriding annealing process, followed by secondary recrystallization during the high-temperature annealing process, forming the finished grain structure. Precise grain size control has been a focus of ongoing research in the field of grain-oriented electrical steel for many years, and its degree of occurrence depends primarily on the precise matching of driving and inhibiting forces. The driving force primarily originates from the primary recrystallized grain structure, while the inhibiting force primarily originates from inhibitors in the steel sheet. When the driving and inhibiting forces are precisely matched, "Goss" nuclei with a specific orientation preferentially engulf surrounding grains during the high-temperature annealing process, leading to abnormal growth in secondary recrystallization. Grains grow from 0.02 mm to over 10 mm, forming a large-grain structure dominated by Goss orientations and exhibiting excellent unidirectional magnetic conductivity. When the driving force increases or the inhibiting force decreases, grains of various orientations in the primary recrystallized structure tend to grow simultaneously. The preferential growth advantage of Goss-oriented grains disappears, resulting in a finished structure with small grains less than 2 mm in diameter. If the grain size is too large, the specific total loss value will increase significantly. If the grain size is too small, stray grains with orientations other than Gaussian orientations will easily appear. These stray grains deviate from the precise Gaussian texture, which is not conducive to improving the magnetic induction value. Due to the extremely stringent process requirements for the entire process of oriented electrical steel, even the slightest process deviation may cause the grain size to deviate from the target value. At the same time, if the grains grow differentially in the set direction, they will show the artistic effect of the grain outline. The final presentation of the grain pattern can intuitively demonstrate the company's ability to control the grain size and improve the company's competitiveness. In order to obtain grain art boards that reflect the characteristics of the combination of oriented electrical steel grain control technology and art, it is necessary to develop a new process for controlling the directional growth of oriented electrical steel grains according to the expected outline.

[0030] Based on this, an embodiment of the present application provides a method for controlling grain size of oriented electrical steel, comprising the steps of:

[0031] S1: Setting the desired profile pattern on the surface of the steel plate after decarburization and nitriding annealing;

[0032] Combine Figure 1-Figure 3 The outline pattern can be freely set, such as artistic patterns or Chinese characters, and the grains can grow according to the expected outline pattern, thus showing the sharp contrast of grain structure morphology in different areas of the same steel plate;

[0033] S2: thinning the surface nitriding layer in the area where the expected profile pattern is set on the surface of the steel plate and / or applying pressure to the area where the expected profile pattern is set on the surface of the steel plate to generate compressive stress on the surface of the steel plate;

[0034] Steps S1 and S2 are pretreatment steps in the grain-oriented electrical steel manufacturing process, following the decarburization and nitriding annealing steps, to pre-treat the steel plate surface with a desired profile pattern, applying a directional restraining force and a driving force. Specifically, in this embodiment, the surface nitrided layer in the area of ​​the steel plate surface designated with the desired profile pattern can be thinned by 5-30 μm. This portion of the surface nitrided layer can be removed using physical or chemical methods, such as shot blasting, sand blasting, high-pressure water, and laser etching. Alternatively, the surface nitrided layer can be removed chemically using an etchant, such as sulfuric acid or hydrochloric acid.

[0035] Furthermore, the pressure range of applying pressure to the area where the expected contour pattern is set on the surface of the steel plate can be 0.1-10Mpa, and the pressure can be applied to the area where the expected contour pattern is set on the surface of the steel plate by shot blasting, shot blasting, sand blasting, high-pressure water, hammering or laser etching.

[0036] S3: evenly coating the surface of the steel plate with a high-temperature annealing separator and drying the steel plate to perform high-temperature annealing on the steel plate;

[0037] The steel plate can be coated with a high-temperature annealing separator on one or both sides. The high-temperature annealing separator can be MgO and / or Al2O3. Preferably, the solute mass fraction of the high-temperature annealing separator slurry is 7% to 13%, the single-sided coating thickness is 10 to 50 μm, and the drying temperature after application of the high-temperature annealing separator is 600 to 800°C.

[0038] When the heating temperature of the high temperature annealing is below 1100°C, the heating rate is 10-25°C / h, the maximum heating temperature is 1200°C, and the holding time is 20-30h.

[0039] S4: The steel plate is pickled and cleaned until the steel plate exhibits a clear grain structure.

[0040] The acid medium for pickling the steel plate is low-temperature, low-concentration hydrochloric acid or sulfuric acid (temperature ≤ 50°C, concentration ≤ 20%) to corrode the steel plate until the surface is bright and the grain outline is clear, thereby obtaining oriented electrical steel with artistic patterns.

[0041] During the decarburization and nitriding annealing process, nitrogen atoms penetrate into the surface of the steel plate to form a nitriding layer, which is converted into an inhibitor during the high-temperature annealing process and gradually diffuses to the center layer of the steel plate to achieve uniform distribution in the thickness direction. The present application provides a method for controlling the grain size of oriented electrical steel. After the decarburization and nitriding annealing process, the surface nitriding layer in the area where the expected contour pattern is set on the surface of the steel plate is thinned, thereby greatly weakening the inhibitory force on grain growth during the secondary recrystallization process in the high-temperature annealing process, and applying pressure in the area where the expected contour pattern is set on the surface of the steel plate to generate compressive stress on the surface of the steel plate, which can increase the driving force for the growth of the primary recrystallization grains. By controlling the inhibitory force and the driving force, the finished grain size can be precisely controlled, so that the grains grow differently in the set direction to show the artistic effect of the grain contour, which represents the company's precise control ability over high-performance oriented silicon steel and improves the company's competitiveness.

[0042] It should be noted that in step S2, the surface nitriding layer in the area where the expected contour pattern is set on the surface of the steel plate is thinned to weaken the inhibitory force, and pressure is applied to the area where the expected contour pattern is set on the surface of the steel plate to enhance the driving force. Both can be implemented at the same time, or only one of them can be implemented, both of which can improve the control effect of the grain size of the finished product.

[0043] Combine Figures 1-6 The present invention removes the surface nitriding layer by thinning the surface layer of the set contour area on the decarburizing and nitriding plate by 5-30μm, thereby removing the inhibitor in the high-temperature annealing process and reducing the inhibitory force. By applying pressure to the surface layer of the steel plate in the set contour area, the driving force can be increased. Under the effect of the weakening of the inhibitory force or (and) the strengthening of the driving force, small grains with a diameter of less than 2mm are guided to grow differentially according to the preset contour pattern and the expected grain size during the high-temperature annealing process, achieving a clear contrast in the organizational morphology of different areas of the same steel plate, a strong artistic atmosphere, and "crystal flash changes" when illuminated, reflecting the characteristics of the complex, precise, and fine matching control of the oriented silicon steel process, showing the perfect combination of silicon steel process technology and art, and characterizing the precise control ability of high-performance oriented silicon steel.

[0044] Table 1 lists the surface orientation pretreatment processes, various technical parameters and final grain pattern presentation effects of Examples 1-3 and Comparative Examples 1-3. Figure 1-3 , Comparative Examples 1-3 correspond to the attached Figure 4-6 , combined with Figures 1-6 As shown in Table 1, Examples 1-3 adopted the technical parameters of the directional pretreatment method in this embodiment, achieving the effect of distinct contrast in the organizational morphology of different regions of the same steel plate, while Comparative Examples 1-3 did not adopt the technical solution of this embodiment or the technical parameters in this embodiment, and did not achieve the expected effect.

[0045] Table 1

[0046]

[0047] Furthermore, the grain control method for grain-oriented electrical steel provided in the embodiment of the present application further includes:

[0048] S4: Apply anti-rust coating on the surface of the steel plate.

[0049] That is, after the steel plate is pickled and cleaned, it is coated with an anti-rust coating to prevent rust and extend the shelf life.

[0050] As described above, steps S1 and S2 are the steps of performing an orientation pretreatment of the steel plate according to the desired profile pattern after decarburization and nitriding annealing in the manufacturing process of grain-oriented electrical steel. Of course, before this, the manufacturing process of grain-oriented electrical steel also includes steelmaking, hot rolling, normalizing annealing, cold rolling, and decarburization and nitriding annealing. Specifically, the following steps are performed:

[0051] 1) Steelmaking, smelting composition: C: 0.055% to 0.085%; Si: 3.0% to 4.5%; Mn: 0.06% to 0.19%; P: 0.01% to 0.03%; S: 0.005% to 0.018%; Als: 0.020% to 0.035%; N: 0.0045% to 0.0145%; the rest is Fe and unavoidable impurity elements;

[0052] 2) heating the ingot to a temperature of 1000-1250° C. and hot rolling the steel plate to a thickness of 1.5-3.0 mm;

[0053] 3) Two-stage normalizing annealing, the first stage annealing temperature is 1000-1130℃, the second stage annealing temperature is 800-1000℃, and pickling is performed after normalizing to remove iron oxide scale;

[0054] 4) cold rolling the steel plate to a thickness of 0.35 to 0.18 mm;

[0055] 5) Decarburization and nitriding annealing: the carbon content of the steel plate does not exceed 30ppm and the nitrogen content is greater than 160ppm.

[0056] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0057] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for controlling grain size of oriented electrical steel, characterized in that: The grain control method of oriented electrical steel comprises the following steps: S1: setting a desired profile pattern on the surface of the steel plate after decarburization and nitriding annealing; S2: thinning the surface nitriding layer of the area on the surface of the steel plate where the expected contour pattern is set by 5-30 μm and / or applying pressure to the area on the surface of the steel plate where the expected contour pattern is set, so as to generate compressive stress in the pattern area on the surface of the steel plate; wherein the pressure range of applying pressure to the area on the surface of the steel plate where the expected contour pattern is set is 0.1-10 MPa; S3: uniformly coating a high temperature annealing separator on the surface of the steel plate and drying the steel plate to perform high temperature annealing on the steel plate; S4: pickling and cleaning the steel plate until the steel plate presents a clear grain structure.

2. The grain control method of grain oriented electrical steel according to claim 1, characterized in that: In step S2, a surface nitriding layer in a region of the steel plate surface where the expected profile pattern is set is thinned by using a corrosive agent.

3. The grain control method for oriented electrical steel according to claim 1, characterized in that: In step S2, the surface nitriding layer of the area on the surface of the steel plate where the expected contour pattern is set is thinned by shot peening, shot blasting, sand blasting, high-pressure water, hammering or laser etching.

4. The grain control method for grain oriented electrical steel according to claim 1, characterized in that: In step S2, pressure is applied to the area on the surface of the steel plate where the expected contour pattern is set by shot peening, shot blasting, sand blasting, high-pressure water, hammering or laser etching.

5. The grain control method for grain oriented electrical steel according to claim 1, characterized in that: In step S3, the steel plate is coated with a high temperature annealing separator on one side or both sides, and the high temperature annealing separator is MgO and / or Al2O3.

6. The grain control method of grain oriented electrical steel according to claim 5, characterized in that: In step S3, the single-side coating thickness of the high-temperature annealing isolation agent is 10-50 μm, and the drying temperature of the high-temperature annealing isolation agent after coating is 100-400° C.

7. The grain control method for grain oriented electrical steel according to claim 1, characterized in that: In step S3, when the heating temperature of the high temperature annealing is below 1100°C, the heating rate is 10-25°C / h, the maximum heating temperature is 1200°C, and the holding time is 20-30h.

8. The grain control method for grain oriented electrical steel according to claim 1, characterized in that: The grain control method of oriented electrical steel further comprises: S4: applying an anti-rust coating on the surface of the steel plate.

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