High-magnetic-induction oriented silicon steel and manufacturing method therefor

Abstract

Disclosed in the present invention is a high-magnetic-induction oriented silicon steel. In addition to Fe and other inevitable impurities, the high-magnetic-induction oriented silicon steel further contains the following chemical elements in percentage by mass: less than or equal to 0.005% of C, 3.0-3.8% of Si, 0.010-0.035% of Als, and 0.05-0.20% of Mn. The other inevitable impurities comprise less than or equal to 0.005% of N, less than or equal to 0.005% of S, less than or equal to 0.005% of V, and less than or equal to 0.005% of Ti. The average size of the secondary grains of the high-magnetic-induction oriented silicon steel is 6-16 mm, and the percentage of the area of the secondary grains having the average deviation angle in the range of 0° to 3° to the area of all the secondary grains is greater than 50%. Correspondingly, the present invention further provides a manufacturing method for the high-magnetic-induction oriented silicon steel.

Description

A high magnetic induction oriented silicon steel and its manufacturing method Technical Field The present invention relates to a steel and its manufacturing method, and particularly to an oriented silicon steel and its manufacturing method. Background Art Oriented silicon steel is a soft magnetic material with excellent magnetic properties, which is composed of grains called Goss texture. The Goss texture is represented by Miller indices as {110}<001>. The {110} crystal plane of the grains is parallel to the rolling plane, and the <001> crystal direction of the grains is parallel to the rolling direction. The <001> crystal direction of iron has the best easy magnetization performance under a directional magnetic field. By making full use of magnetocrystalline anisotropy, the best magnetic properties of polycrystalline materials can be achieved. The transformer core made of oriented silicon steel can significantly save materials and electric energy due to its extremely high magnetic induction intensity and extremely low iron loss under the working condition of a directional magnetic field. Generally, the iron loss P 17 / 50 and the magnetic induction intensity B8 are usually used to characterize the magnetic property level of oriented silicon steel. Among them, P 17 / 50 represents the iron loss of a unit kg sample when the magnetic induction intensity is 1.7T and the frequency is 50Hz; B8 represents the magnetic induction intensity corresponding to a magnetic field strength of 800A / m. These two parameters can effectively reflect the advantages and disadvantages of the magnetic properties of oriented silicon steel under different magnetic fields and frequency conditions. Existing preparation processes all need to control the evolution of the whole process organization, texture and inhibitor through complex processes to obtain a finished plate with abnormal growth of Goss grains. The manufacturing process of oriented silicon steel can be classified into a single cold rolling method and a double cold rolling method according to the rolling process. Among them, the single cold rolling method is used to prepare high magnetic induction oriented silicon steel with AlN and MnS as the main inhibitors, and the double cold rolling method is used to prepare ordinary oriented silicon steel with MnS and Cu2S as the main inhibitors. It can also be classified into a low-temperature slab heating process and a high-temperature slab heating process according to the slab heating temperature. Among them, the slab heating temperature of the low-temperature slab heating process is lower than 1250°C. Since the low-temperature slab heating process can produce high magnetic induction oriented silicon steel at a lower cost, this process has developed rapidly and gradually become the mainstream. In the low-temperature slab heating process, the inhibitors come from both the inclusions already existing in the slab. This part of the inhibitors is called the primary inhibitor, which has an important influence on primary recrystallization and thus also affects the magnetic properties of the final product; and also from the inclusions formed through nitriding treatment after decarburization annealing. This part of the inhibitors is called the secondary inhibitor, which promotes secondary recrystallization together with the primary inhibitor. Although it is difficult to control the inhibitors through the low-temperature slab heating process and the annealing process window is narrow, with the application of some improved processes, such as adding auxiliary inhibitors, controlling the morphology of inclusions, and using rapid induction heating, the product grade of this process has been continuously improved. To improve the efficiency of transformers, the fundamental measure is to improve the magnetic properties of the core material, which requires the core material to have low iron loss and high magnetic induction intensity. Among them, the iron loss depends not only on the material itself but also on the operating frequency and magnetic induction intensity of the material in the alternating magnetic field. For the magnetic induction intensity, its value is mainly affected by the Goss grain orientation degree of the material. The grain orientation degree refers to the arrangement direction and degree of the grains in the material. Generally speaking, the higher the Goss grain orientation degree, the higher the magnetic induction intensity of the oriented silicon steel. The iron loss of oriented silicon steel is mainly composed of hysteresis loss and eddy current loss, and the eddy current loss accounts for the main part. Common techniques for reducing the iron loss of oriented silicon steel include: improving the grain orientation degree, reducing the strip thickness, and scribing to refine the magnetic domains. However, with the continuous progress of the manufacturing technology of oriented silicon steel, improving the grain orientation degree and scribing to refine the magnetic domains have entered a relatively mature stage, and the improvement effect on the magnetic properties is limited. Therefore, reducing the strip thickness has become the main means to reduce the iron loss of oriented silicon steel at present. The strip thickness has a significant impact on the total core loss. By reducing the strip thickness, the eddy current loss can be effectively suppressed, thereby significantly reducing the total core loss. As the number of laminations increases, the total loss of the equal-volume core decreases rapidly. It should be noted that if the strip thickness is too thin, it may lead to a sharp increase in manufacturing costs, and the magnetic properties will also deteriorate significantly due to the increase in hysteresis loss. Therefore, when choosing to reduce the strip thickness, it is necessary to comprehensively consider the balance between manufacturing costs and magnetic properties. Although reducing the strip thickness can reduce the iron loss, there are also some challenges and limitations. One is the reduction in the number of effective Goss crystal nuclei: as the strip thickness decreases, its specific surface area increases significantly, and the number of effective Goss crystal nuclei will decrease accordingly. At the same time, the coarsening and decomposition of the inhibitor during the annealing process are aggravated, and the inhibition effect weakens. This will have an adverse impact on the secondary recrystallization process, and thus affect the magnetic properties of the product. The second is the control of the cold rolling reduction rate: in order to obtain the desired primary recrystallization texture, it is necessary to ensure an appropriate cold rolling reduction rate. However, if the strip thickness is too thin, it will lead to a reduction in the thickness of the hot coil, which will increase the difficulty of hot rolling shape control and the stability of hot rolling production will deteriorate. The third is the decrease in the production efficiency of the hot-rolled sheet annealing unit: reducing the thickness of the hot-rolled sheet will lead to a significant decrease in the production efficiency of the annealing unit. When the thickness of the hot-rolled sheet is reduced from 2.6 mm to 1.8 mm, the unit efficiency is reduced by about 30%. Due to the above problems, on the premise of ensuring product quality and production stability, the finished product thickness of the existing oriented silicon steel preparation process mostly ranges from 0.23 to 0.30 mm, and it is difficult to further reduce the thickness. In addition, in order to achieve the desired inhibitor distribution state, annealing of hot-rolled sheets has become an essential process step in the production of high magnetic induction oriented silicon steel. During the annealing of hot-rolled sheets, the hot-rolled pickled sheet is rapidly heated to about 1120 °C, held for 2 to 4 minutes, air-cooled to about 900 °C, water-cooled through the water, or subjected to a two-stage treatment of air-cooling followed by holding for 2 minutes and then water-cooling through the water. After annealing, the recrystallized grains on the surface of the hot-rolled sheet grow, and a certain amount of martensite structure is generated during the rapid cooling process. Mechanical twins are also produced due to the rapid cooling and phase transformation stresses. These factors all increase the difficulty of cold rolling. Due to reasons such as hot-rolled sheet annealing and a large reduction ratio in the first pass, existing high magnetic induction oriented silicon steel requires a twenty-high reversing mill with high rolling stress for cold rolling, which makes it difficult to improve the rolling efficiency. In recent years, several new manufacturing technologies for oriented silicon steel have been developed to efficiently manufacture thin-gauge high magnetic induction oriented silicon steel. For example, the Chinese patent document with the publication number CN116460139A, publication date July 21, 2023, and title "An ultra-thin high magnetic induction oriented silicon steel and its rolling method" discloses an ultra-thin high magnetic induction oriented silicon steel and its rolling method. In this technical solution, the final finished product thickness obtained is 0.12 to 0.20 mm. The main difference between this method and the existing preparation process for high magnetic induction oriented silicon steel lies in the rolling process, which changes the reversible rolling used in the existing single cold rolling to a combined rolling of tandem cold rolling and reversible rolling. The work roll diameter of the tandem cold rolling is 300 to 500 mm, and the total reduction ratio is 60 to 91%; the work roll diameter of the reversible rolling is 70 to 150 mm, and the total reduction ratio is 10 to 50%. Compared with the existing preparation process, this technical solution only adjusts the cold rolling method, has limited effects on reducing the manufacturing cost of thin-gauge oriented silicon steel and improving the magnetic properties of the product, and does not solve the problem of difficult cold rolling after annealing of the existing oriented silicon steel hot-rolled sheet. Another example is that the Chinese patent with the publication number CN114134423A, publication date March 4, 2022, and title "A super-short process rare earth oriented silicon steel and its preparation method" discloses a solution for preparing oriented silicon steel by a thin strip continuous casting process. The production process of this technical solution includes: molten steel smelting, thin strip continuous casting, cold rolling, primary recrystallization annealing, coating an isolation agent, secondary recrystallization annealing, etc. A 2 to 2.5 mm thick cast strip can be directly obtained, and the finished product thickness of the prepared oriented silicon steel is 0.20 to 0.35 mm, and the iron loss P 17 / 50 is 0.9 to 1.1 W / kg, and the magnetic induction intensity B8 is 1.87 to 1.95 T. Compared with the existing process, this technical solution cancels important processes such as continuous casting, rough rolling, hot tandem rolling, and normalizing in the conventional process, and has obvious cost advantages, but the production stability and product magnetic properties of the thin strip continuous casting technology need to be improved. Summary of the Invention One of the objectives of the present invention is to provide a grain-oriented electrical steel, by precisely controlling the steel composition and microstructure, especially the size and proportion of grains in the grain-oriented electrical steel, so as to improve the magnetic induction of the grain-oriented electrical steel. The present invention also provides a manufacturing method for high magnetic induction grain-oriented electrical steel. Through a reasonable process route design, on the premise of canceling the hot-rolled sheet annealing step, a thin-gauge high magnetic induction grain-oriented electrical steel can be obtained, thereby reducing the manufacturing cost while improving the magnetic properties of the product. To achieve the above objectives, the present invention provides a high magnetic induction grain-oriented electrical steel, which, in addition to containing Fe and other inevitable impurities, also contains chemical elements with the following mass percentages: C ≤ 0.005%; Si: 3.0 - 3.8%; Als: 0.010 - 0.035%; Mn: 0.05 - 0.20%; Among them, among other inevitable impurity elements, N ≤ 0.005%, S ≤ 0.005%, V ≤ 0.005%, Ti ≤ 0.005%. The average size of the secondary grains of the above high magnetic induction grain-oriented electrical steel is 6 - 16 mm; among them, the area percentage of secondary grains with an average deviation angle (α + β) / 2 in the range of 0° - 3° among all secondary grains > 50%. In the present invention, the average deviation angle is (α + β) / 2. In the formula, α is the rolling direction deviation angle, which is the

[0001] deviation angle of the crystal orientation of the grain relative to the rolling direction (RD) in the rolling plane (RD-TD plane). In high magnetic property grain-oriented electrical steel, it is usually desired that the

[0001] crystal orientation of the crystal is consistent with, or very close to, the rolling direction. The smaller the α angle, the better the magnetic properties. β is the rolling plane tilt angle, which is the tilt angle of the

[0001] crystal orientation of the grain relative to the rolling plane. β has an optimal value of about 2°, at which time the total loss reaches the minimum. The higher the area percentage of secondary grains with an average deviation angle in the range of 0° - 3° among all secondary grains, the better the magnetic properties of the grain-oriented electrical steel. In the present invention, the area percentage of secondary grains with an average deviation angle in the range of 0° - 3° among all secondary grains > 50%, indicating that the grain-oriented electrical steel of the present invention has excellent magnetic properties. Preferably, in the high magnetic induction grain-oriented electrical steel described in the present invention, the mass percentages of its various chemical elements are: C ≤ 0.005%; Si: 3.0 - 3.8%; Als: 0.010 - 0.035%; Mn: 0.05 - 0.20%; The remainder is Fe and other inevitable impurities; among other inevitable impurity elements, N ≤ 0.005%, S ≤ 0.005%, V ≤ 0.005%, and Ti ≤ 0.005%. In the high magnetic induction oriented silicon steel described in the present invention, the design principles of each chemical element are as follows: C: In the high magnetic induction oriented silicon steel described in the present invention, excessive C will precipitate fine and dispersed ε carbide particles in the material, resulting in magnetic aging phenomenon, that is, the magnetic properties of the material change with the service time. Therefore, C is a residual element in the present invention. During the production process of oriented silicon steel, C needs to be purified and removed in processes such as decarburization annealing and high-temperature annealing. Based on this, in the high magnetic induction oriented silicon steel described in the present invention, the mass percentage content of the C element is limited to C ≤ 0.005%. Si: In the high magnetic induction oriented silicon steel described in the present invention, Si is a basic element in the oriented silicon steel, which can increase the resistivity and reduce the iron loss. It should be noted that when the mass percentage content of the Si element in the steel is less than 3.0%, the resistivity of the material will decrease, and the eddy current loss of the oriented silicon steel cannot be effectively reduced; correspondingly, the content of the Si element in the steel should not be too high. When the mass percentage content of the Si element in the steel is higher than 3.8%, due to the tendency of Si to segregate along the grain boundaries, it will increase the brittleness of the steel plate, make the rollability worse, and also make the recrystallized structure and inhibitors unstable, resulting in imperfect secondary recrystallization. Based on this, in the high magnetic induction oriented silicon steel described in the present invention, the mass percentage content of the Si element is controlled between 3.0% and 3.8%. Acid-soluble aluminum Als: In the high magnetic induction oriented silicon steel described in the present invention, Als can form a secondary inhibitor during the subsequent nitriding treatment of the material, which can act together with the primary inhibitor to form sufficient pinning strength to promote secondary recrystallization. However, it should be noted that when the mass percentage content of Als in the steel is less than 0.010%, the pinning strength of the inhibitor will be insufficient, the directional inhibition effect will be weakened, the secondary recrystallization will be incomplete, and even the secondary recrystallization cannot occur; if the mass percentage content of Als in the steel is higher than 0.035%, the nitrides of Als will coarsen, the inhibitor effect will decrease, and the magnetic properties of the material will deteriorate. Based on this, in the high magnetic induction oriented silicon steel described in the present invention, the mass percentage content of Als is controlled between 0.010% and 0.035%. Mn: In the high magnetic induction oriented silicon steel described in the present invention, the Mn element is similar to the Si element, and both can increase the resistivity and reduce the eddy current loss. In addition, the Mn element can also expand the γ phase region, with the effect of improving the hot rolling plasticity and structure, thereby effectively improving the hot rolling workability of the material. However, it should be noted that when the mass percentage content of the Mn element in the steel is less than 0.05%, the above-mentioned effects cannot be effectively exerted; if the mass percentage content of the added Mn element in the steel is higher than 0.20%, an α and γ mixed duplex structure is likely to appear, resulting in phase transformation stress during annealing and generating the γ phase, causing unstable secondary recrystallization. Based on this, in the high magnetic induction oriented silicon steel described in the present invention, the mass percentage content of the Mn element is controlled between 0.05% and 0.20%. S and N: In the high magnetic induction oriented silicon steel described in the present invention, excessive S or N will precipitate fine and dispersed MnS, Fe 16 N4 and other particles in the material, resulting in the phenomenon of magnetic aging, that is, the magnetic properties of the material change with the service time. Therefore, S and N are impurity elements in the present invention. During the production process of oriented silicon steel, S and N need to be purified and removed in processes such as decarburization annealing and high-temperature annealing. Based on this, in the high magnetic induction oriented silicon steel described in the present invention, the mass percentage content of the S element is limited to S ≤ 0.005%, and the mass percentage content of the N element is limited to N ≤ 0.005%. V and Ti: In the high magnetic induction oriented silicon steel described in the present invention, V and Ti are impurity elements. The V element will form VN after the material is nitrided, affecting the secondary recrystallization and being unfavorable to the magnetic properties of the material. Since the Ti element can preferentially precipitate TiN, MnS will precipitate attached to TiN, and then AlN will precipitate attached to MnS, thus easily forming coarse MnS + AlN composite inclusions, which is also unfavorable to the magnetic properties of the material. In addition, reducing the content of Ti and V can also reduce the harmful inclusions of TiN and VN in the finished product. Based on this, in the high magnetic induction oriented silicon steel described in the present invention, the mass percentage content of the Ti element is limited to Ti ≤ 0.005%, and the mass percentage content of the V element is limited to V ≤ 0.005%. Preferably, in the high magnetic induction oriented silicon steel described in the present invention, it also contains at least one of the following chemical elements: P: 0.01 - 0.08%; Cr: 0.01 - 0.40%, Sn: 0.03 - 0.30%, Cu: 0.01 - 0.40%, 0 < Sb ≤ 0.1%, 0 < Bi ≤ 0.1%, 0 < Nb ≤ 0.1%, 0 < Mo ≤ 0.1%. In the high magnetic induction oriented silicon steel described in the present invention, the above-mentioned various chemical elements can further improve the performance of the high magnetic induction oriented silicon steel described in the present invention, and the design principle is as follows: P: In the high magnetic induction oriented silicon steel of the present invention, in some preferred embodiments, P is a grain boundary segregation element, which can act as an auxiliary inhibitor. During the secondary recrystallization process, even at a high temperature of about 1000 °C, the P element still has the effect of grain boundary segregation. It can delay the premature oxidation and decomposition of AlN, which is beneficial to secondary recrystallization. At the same time, the P element can also increase the resistivity of the material and reduce the eddy current loss. However, it should be noted that when the mass percentage content of the P element in the steel is less than 0.01%, the above effects cannot be effectively exerted; but when the mass percentage content of the P element in the steel is higher than 0.08%, it will not only reduce the nitriding efficiency but also make the cold rolling workability worse. Therefore, in the high magnetic induction oriented silicon steel of the present invention, in some preferred embodiments, the mass percentage content of added P can preferably be set to 0.01 - 0.08%. Cr: In the high magnetic induction oriented silicon steel of the present invention, in some preferred embodiments, adding the Cr element can not only increase the resistivity but also be beneficial to improving the mechanical properties of the material, and can significantly improve the surface quality by promoting the oxidation of the steel plate. In order to give full play to the role of the Cr element, the mass percentage content of the Cr element in the steel is usually higher than 0.01%. However, when the Cr content in the steel is higher than 0.40%, a dense oxide layer will be formed during the decarburization process, which will affect the decarburization and nitriding efficiency. Therefore, in the high magnetic induction oriented silicon steel of the present invention, in some preferred embodiments, the mass percentage content of added Cr can preferably be set to 0.01 - 0.40%. Sn: In the high magnetic induction oriented silicon steel of the present invention, in some preferred embodiments, Sn is a grain boundary segregation element, which has the role of an auxiliary inhibitor. It can effectively compensate for the problem of the decrease in the inhibitory force caused by the coarsening of AlN inclusions due to the increase in the Si content in the steel or the thinning of the strip thickness, etc., and can expand the process window, which is beneficial to the stability of the magnetic properties of the product. However, considering that when the mass percentage content of Sn is less than 0.03%, the above effects cannot be effectively obtained; and when the mass percentage content of Sn is higher than 0.30%, it will not only affect the decarburization efficiency but also cause poor surface quality, and the magnetic properties will not be improved, and it will also lead to an increase in manufacturing costs. Therefore, in the high magnetic induction oriented silicon steel of the present invention, in some preferred embodiments, the mass percentage content of added Sn can preferably be set to 0.03 - 0.30%. Cu: In the high magnetic induction oriented electrical steel described in the present invention, in some preferred embodiments, Cu is added because: similar to the Mn element, the Cu element can expand the γ-phase region and contribute to obtaining fine AlN inclusions. In addition to expanding the γ-phase region, the Cu element can preferentially combine with the S element to form Cu2S compared with Mn, which is beneficial to suppressing the change in the primary grain size. Considering that when the mass percentage content of the Cu element added to the steel is less than 0.01%, its above functions cannot be exerted; however, if the mass percentage content of the Cu element added to the steel is higher than 0.40%, the manufacturing cost will increase and the magnetic properties will not be improved. Therefore, in the high magnetic induction oriented electrical steel described in the present invention, in some preferred embodiments, the mass percentage content of the added Cu can preferably be set to 0.01 - 0.40%. Sb and Bi: In the high magnetic induction oriented electrical steel described in the present invention, in some preferred embodiments, Sb and Bi are added because: Sb and Bi are also grain boundary segregation elements and both have the function of auxiliary inhibitors, which can improve the grain boundary migration conditions of Goss nuclei, contribute to expanding the process window, and improving the finished product magnetic induction. However, when the mass percentage content of Sb and Bi in the steel is higher than 0.1%, it will not only affect the decarburization efficiency, but also cause poor surface quality and the magnetic properties will not be significantly improved, increasing the manufacturing cost. Therefore, in the high magnetic induction oriented electrical steel described in the present invention, in some preferred embodiments, the mass percentage content of Sb can preferably be set to less than 0.1%, and the mass percentage content of Bi can also preferably be set to less than 0.1%. Nb and Mo: In the high magnetic induction oriented electrical steel described in the present invention, in some preferred embodiments, Nb and Mo are added because: Nb and Mo are both effective grain refinement microalloying elements, which can promote the formation of fine and uniform primary grain sizes, and at the same time, the formed carbonitrides can also be used as auxiliary inhibitors, reducing the difficulty of adjusting the morphology of the primary inhibitor. However, when the mass percentage content of Nb and Mo exceeds 0.1%, it has a strong inhibitory effect on recrystallization and the secondary recrystallization is imperfect. Therefore, in the high magnetic induction oriented electrical steel described in the present invention, in some preferred embodiments, the mass percentage content of Nb can preferably be set to less than 0.1%, and the mass percentage content of Mo can preferably be set to less than 0.1%. Preferably, the thickness of the high magnetic induction oriented electrical steel described in the present invention is 0.13 - 0.20 mm. Unless otherwise specified, the "high magnetic induction oriented electrical steel" in the present invention refers to the finished product of oriented electrical steel. Preferably, in the high magnetic induction oriented electrical steel described in the present invention, the area percentage of secondary grains with a size < 6 mm or > 16 mm in all secondary grains < 15%. In the present invention, the secondary grain size of the oriented electrical steel is preferably between 6 - 16 mm, which helps to improve the magnetic induction intensity, reduce the iron loss, and improve the stability of product performance. Preferably, the iron loss P of the high magnetic induction oriented silicon steel of the present invention 17 / 50 ≤0.86 + 2×finished product plate thickness - 16×Si, the magnetic induction intensity B8≥2.14 - 6.5×Si, where the unit of the finished product plate thickness is mm, and the element symbol Si in the formula is substituted with the mass percentage content of the Si element in the finished product steel plate, and the unit of P 17 / 50 is W / kg, and the unit of B8 is T. The above formula is an empirical formula obtained through optimization in the actual production process. By reasonably controlling the Si content in the oriented silicon steel, the present invention can better balance the iron loss and magnetic induction. The oriented silicon steel that meets the above-defined iron loss and magnetic induction intensity has better comprehensive performance. Another object of the present invention is to provide a manufacturing method of the above high magnetic induction oriented silicon steel. By using this method in combination with the above-mentioned component ratio, thin-gauge high magnetic induction oriented silicon steel can be obtained on the premise of canceling the hot-rolled sheet annealing step, thereby reducing the manufacturing cost and improving the magnetic properties of the product at the same time. To achieve the above object, the present invention proposes a manufacturing method of high magnetic induction oriented silicon steel, which includes the following steps: (1) Smelting and casting to obtain a slab; (2) Heating the slab; (3) Hot rolling; (4) First cold rolling (5) Intermediate annealing; (6) Second cold rolling; (7) Decarburization annealing, nitriding treatment, and coating with an isolation agent coating. The average primary grain size of the obtained decarburized annealed sheet is 6 - 18 μm, and the proportion of Goss grains with an average deviation angle (α + β) / 2 less than 15° is greater than 1.5%; (8) High-temperature annealing; (9) Coating with an insulating coating and skin pass annealing. In the manufacturing method of the present invention, the morphology of the inhibitor can be adjusted in the step (5) intermediate annealing, rather than in the conventional hot-rolled sheet annealing process. This change can cancel the hot-rolled sheet annealing process and greatly reduce the cold rolling difficulty. In the decarburized sheet of the existing high magnetic induction oriented silicon steel, the proportion of Goss grains with an average deviation angle (α + β) / 2 less than 15° is usually less than 1.5%. The reduction of the strip thickness will cause the problem of insufficient effective Goss crystal nuclei, which will have an adverse effect on the magnetic properties of the product. The present invention adopts a double cold rolling process including a primary cold rolling and a secondary cold rolling, which can better regulate the primary recrystallization structure, texture and primary inhibitor, so that the decarburized plate in step (7) can more easily obtain a high proportion of Goss grains, which means that the present invention can increase the number of effective Goss nuclei to solve the problem caused by the thinning of the strip thickness, thereby improving the magnetic properties of the product. Preferably, in step (2) of the manufacturing method described in the present invention, the slab heating temperature is in the range of 1140°C to 1250°C. Preferably, in step (4) of the manufacturing method of the present invention, the primary cold rolling adopts cold tandem rolling, and the reduction rate thereof is 50 to 75%. Preferably, in step (6) of the manufacturing method of the present invention, the secondary cold rolling adopts cold tandem rolling, and the reduction rate thereof is 60 to 85%. Although in the present invention, the cold rolling steps (4) and / or (6) may also adopt conventional reversible rolling, from the perspective of improving rolling efficiency and yield rate, cold tandem rolling is preferably adopted. In addition, in the manufacturing method of the present invention, by adopting the cold rolling reduction rate of the two cold rollings in step (4) and step (6), it is not only conducive to the formation of fine and uniform recrystallized grains in the decarburized plate, but also conducive to increasing the number ratio of Goss grains. In addition, since the rolling efficiency and yield rate of cold rolling are significantly superior to reversible rolling, the overall cold rolling efficiency in the present invention is also significantly improved. Preferably, in step (5) of the manufacturing method of the present invention, the maximum temperature of the intermediate annealing is 900-1050°C. In the manufacturing method of the present invention, the total oxygen content of the sample after annealing can be controlled to be ≤600ppm, and the C element content can be ≥300ppm. This is conducive to the stable production of the secondary cold rolling in step (6), and promotes the formation of a strong γ texture, which is conducive to the formation of a complete secondary recrystallization. In one embodiment of the present invention, the manufacturing method further comprises a hot-rolled plate annealing step after step (3) and before step (4), and the hot-rolled plate annealing temperature is ≤1000°C. As described above, in the manufacturing method of the present invention, after hot rolling, hot rolling annealing can be performed directly without cold rolling, thereby reducing the process flow, improving production efficiency, and reducing production costs. However, in some embodiments, hot rolling annealing can also be performed after the hot rolling step, but the annealing temperature of the hot-rolled plate needs to be ≤1000°C. This is because when the maximum annealing temperature is higher than 1000°C, it will cause the surface grains of the hot-rolled plate to coarsen, which is not conducive to the stable production of the subsequent cold rolling in step (4). Preferably, in step (7) of the manufacturing method of the present invention, the decarburizing annealing temperature is 800-900 °C, the decarburizing annealing time is 80-170 s, and the heating rate is 30-150 °C / s. Preferably, in step (7) of the manufacturing method of the present invention, the nitrogen content of the decarburized annealing sheet after nitriding treatment is 160-260 ppm. In the manufacturing method of the present invention, nitrogen combines with the original aluminum in the steel through nitriding treatment to form secondary inhibitors of fine and dispersed particles such as AlN, (Al,Si)N, (Al,Si,Mn)N, etc. During the subsequent high-temperature annealing process, the secondary inhibitors and the primary inhibitors jointly promote the secondary recrystallization process. The high magnetic induction oriented silicon steel described in the present invention has the following advantages and beneficial effects compared with the prior art: The solution of the present invention obtains an oriented silicon steel with good comprehensive performance through reasonable control of steel composition, secondary grain size and proportion of the steel sheet, etc. The manufacturing method of the high magnetic induction oriented silicon steel in the present invention has the following beneficial effects: The high magnetic induction oriented silicon steel described in the present invention can significantly reduce the annealing temperature of the hot rolled sheet or even cancel the annealing of the hot rolled sheet by adopting the two-pass cold rolling method to adjust the primary recrystallization structure, texture and precipitation of primary inhibitors, as well as appropriate composition and process design, so as to realize the efficient production of thin-gauge high magnetic induction oriented silicon steel by the continuous cold rolling method. Compared with the prior art, the present invention can solve the problem of insufficient number of effective Goss crystal nuclei after the strip thickness is reduced, which is beneficial to improving the magnetic properties of the final product. Therefore, it is possible to produce thin-gauge high magnetic induction oriented silicon steel without further reducing the thickness of the hot rolled sheet, thus avoiding a series of problems caused by the production of thin-gauge hot coils by conventional hot rolling lines. At the same time, canceling the annealing of the hot rolled sheet and realizing the efficient production of thin-gauge high magnetic induction oriented silicon steel by the continuous cold rolling method can significantly reduce the manufacturing cost. Specific Embodiments The following will further explain and illustrate the high magnetic induction oriented silicon steel and its manufacturing method described in the present invention with specific embodiments. However, this explanation and illustration shall not unduly limit the technical solution of the present invention. First, the various detection means of the embodiments and comparative examples of this case are described as follows: (1) The average primary grain size is the grain size of the decarburized sheet after treatment measured by the equivalent circle diameter specified in GB / T 36165-2018. (2) The finished product secondary grain size is the grain size of the finished product sheet after pickling measured by the intercept method specified in GB / T 6394-2017. (3) The Gaussian orientation deviation angle is measured by EBSD (electron backscatter diffraction), including the rolling direction deviation angle α and the rolling plane inclination angle β. (4) The P 17 / 50 and B8 of the non-notch product steel are obtained by the method of measuring the magnetic properties of electrical steel sheets (strips) with Epstein square coils as specified in Standard GB / T 3655-2022. (5) The P 17 / 50 and B8 of the notched product steel are obtained by the method of measuring the magnetic properties of electrical steel sheets (strips) with a single-sheet tester as specified in Standard GB / T 13789-2022. Examples 1-6 and Comparative Examples 1-5 The high magnetic induction oriented silicon steel of Examples 1-6 and the comparative steel of Comparative Examples 1-5 are manufactured according to the following steps carried out in sequence: (1) Smelting and casting: Smelting is carried out using a converter or an electric furnace, and continuously cast into a slab with a thickness of 230 mm. (2) Slab heating: Control the slab heating temperature to 1140 °C and the heating time to 200 min. (3) Hot rolling: Rolled into a hot-rolled sheet with a thickness of 1.8 mm, 2.4 mm or 2.6 mm, as shown in Table 1-1. (4) Prepare a cold-rolled sheet with a finished thickness of 0.18 mm according to the process shown in Table 1-1. Among them, Examples 1-6 and Comparative Examples 3-5 adopt the two-pass cold rolling process described in the present invention, without annealing the hot-rolled sheet, and intermediate annealing is carried out between the first cold rolling and the second cold rolling. The intermediate annealing adopts the open-coil continuous annealing method, and the intermediate annealing and its maximum temperature are controlled according to the process shown in Table 1-1, and the annealing time is 220 s; Comparative Examples 1-2 adopt the conventional one-pass cold rolling process, control the maximum temperature of the hot-rolled sheet annealing to 1150 °C, and control the annealing time to 250 s. (5) Decarburization annealing: The decarburization annealing temperature is 835 °C, the decarburization annealing time is 125 s, and the heating rate in the heating section is 115 °C / s. The [C] content in the steel plate is reduced to less than 30 ppm, and the primary grain size and the proportion of Goss grain quantity shown in Table 1-2 are obtained through detection. (6) Nitriding treatment: Control the nitrogen content of the decarburized annealed sheet to be 180-250 ppm. (7) Coating with MgO coating: Coat the MgO coating on the steel plate. (8) High-temperature annealing: Carry out a 20-hour purification annealing under the condition of a conventional reducing atmosphere and a high-temperature annealing temperature of 1200 °C to reduce the [S] and [N] contents in the steel to less than 40 ppm. (9) Coating with insulating coating and flat annealing: After coating with insulating coating and hot stretching flat annealing, the finished product is obtained. The finished product contains chemical components with the following mass percentages: Si 3.22%, C 0.0016%, Als 0.0334%, N 0.0012%, Mn 0.088%, S 0.0013%, V 0.0025%, Ti 0.0015%. Elements such as P, Cr, Sn, Cu, Sb, Bi, Nb, and Mo are not deliberately added in the finished product steel plate, and their contents are below the detection limit. The various indexes of the secondary grains of the measured finished product are listed in Table 1-2. Table 1-1 Table 1-2 lists the average primary grain size of the decarburized plates involved in Examples 1-6 and Comparative Examples 1-5, the proportion of Goss grains in the decarburized plates, the average secondary grain size, the proportion of the average deviation angle in the range of 0° to 3°, the proportion of secondary grain sizes <6 mm or >16 mm, the finished product P 17 / 50 and the finished product B 8。 Table 1-2 It can be seen from Table 1-1 and Table 1-2 that in Examples 1-6, the two-pass cold rolling method described in the present invention is used to prepare 0.18 mm grain-oriented silicon steel, which can obtain a suitable primary grain size, and the proportion of Goss grains with an average deviation angle (α + β) / 2 less than 15° in the decarburized plate is higher. At the same time, the various indexes of the secondary grains also meet the requirements, and the magnetic properties of the obtained products are more excellent. Its iron loss P 17 / 50 are all lower than the reference iron loss of 0.705 W / kg calculated based on the formula 0.86 + 2× finished product plate thickness - 16×Si, and the magnetic induction intensity B8 is higher than the reference magnetic induction of 1.931 T calculated based on the formula 2.14 - 6.5×Si. In Comparative Examples 1-2, the conventional one-pass cold rolling method is used to prepare 0.18 mm grain-oriented silicon steel. In Comparative Examples 3-5, the two-pass cold rolling method is used but the intermediate annealing temperature does not meet the requirements of the present invention. The average primary grain size of the decarburized plates or the proportion of Goss grains in the decarburized plates in Comparative Examples 1-5 do not meet the requirements of the present invention, and the obtained iron loss and / or magnetic induction are inferior to the reference values calculated above. Examples 7-10 and Comparative Examples 6-13 The high magnetic induction grain-oriented silicon steel of Examples 7-10 and the comparative steel of Comparative Examples 6-13 are manufactured according to the following steps carried out in sequence: (1) Smelting and casting: Using a converter or an electric furnace for smelting and continuously casting into a slab with a thickness of 230 mm. (2) Slab heating: Controlling the slab heating temperature at 1190 °C and the heating time at 160 min. (3) Hot rolling: The hot-rolled sheet with a thickness of 2.6 mm is rolled by hot rolling. (4) First cold tandem rolling: Cold roll for the first time to the thickness shown in Table 2-1. (5) Intermediate annealing: Anneal for 180 s by the method of uncoiling continuous annealing, control the maximum temperature of intermediate annealing according to Table 2-1, and obtain the total oxygen content and C element content of the intermediate annealed sheet shown in Table 2-1. (6) Second cold tandem rolling: Cold roll for the second time until the thickness of the steel sheet reaches 0.15 mm. (7) Decarburizing annealing: Control the decarburizing annealing temperature according to Table 2-1, the decarburizing annealing time is 100 s, the heating rate in the heating section is 80 °C / s, reduce the [C] content in the steel sheet to below 30 ppm, and detect the primary grain size and the proportion of Goss grain quantity shown in Table 2-2. (8) Nitriding treatment: Control the nitrogen content of the decarburized annealed sheet according to Table 2-1. (9) Coating with MgO coating: Coat the MgO coating on the steel sheet. (10) High-temperature annealing: Carry out purification annealing for 18 hours under the condition of a conventional reducing atmosphere with a high-temperature annealing temperature of 1170 °C, and reduce the [S] and [N] contents in the steel to below 50 ppm. (11) Insulating coating and skin pass annealing: Obtain the finished product after coating the insulating coating and hot stretch skin pass annealing. The obtained finished product contains the following chemical components by mass percentage: Si 3.39%, C 0.0007%, Als 0.0275%, N 0.0017%, Mn 0.183%, S 0.0008%, V 0.0031%, Ti 0.0010%. Elements such as P, Cr, Sn, Cu, Sb, Bi, Nb, and Mo are not deliberately added in the finished product steel sheet, and their contents are below the detection limit. The indexes of the secondary grains of the finished product are listed in Table 2-2. Table 2-1 Table 2-2 As can be seen from Table 2-1 and Table 2-2, although Examples 7-10 and Comparative Examples 6-13 both use the two-stage cold rolling method described in the present invention to prepare 0.15 mm grain-oriented silicon steel, the reduction ratios of the first cold rolling, the reduction ratio of the second cold rolling, the maximum temperature of intermediate annealing, the total oxygen content of the intermediate annealed sheet, the C element content of the intermediate annealed sheet, the nitriding amount of the decarburized sheet, the average primary grain size of the decarburized sheet, the proportion of Goss grain quantity in the decarburized sheet, and the indexes of the secondary grains in Examples 7-10 all meet the requirements of this case. Therefore, the iron loss P 17 / 50They are all lower than the reference iron loss of 0.618 W / kg calculated based on the formula 0.86 + 2×finished plate thickness - 16×Si, and the magnetic induction intensity B8 is all higher than the reference magnetic induction of 1.920 T calculated based on the formula 2.14 - 6.5×Si. On the contrary, the iron loss and / or magnetic induction of Comparative Examples 6-13 are inferior to the reference values obtained from the above calculations. Examples 11-22 and Comparative Examples 14-21 The high magnetic induction oriented silicon steel of Examples 11-22 and the comparative steel of Comparative Examples 14-21 were manufactured according to the following steps carried out in sequence: (1) Smelting and casting: Smelt using a converter or an electric furnace and continuously cast into a slab with a thickness of 230 mm. (2) Slab heating: Control the slab heating temperature at 1200 °C and the heating time at 250 min. (3) Hot rolling: Hot roll into a hot rolled sheet with a thickness of 2.3 mm. (4) First tandem cold rolling: Cold roll for the first time to obtain a steel sheet with a thickness of 0.75 mm, and control the reduction ratio of the first tandem cold rolling at 67.4%. (5) Intermediate annealing: Adopt the open-coil continuous annealing method, control the maximum intermediate annealing temperature at 975 °C, the intermediate annealing time at 120 s, and obtain the total oxygen content of the sample after intermediate annealing at 261-594 ppm and the C element content at 308-939 ppm. (6) Second tandem cold rolling: Cold roll for the second time to obtain a steel sheet with a thickness of 0.19 mm, and control the reduction ratio of the second tandem cold rolling at 74.7%. (7) Decarburization annealing: The decarburization annealing temperature is 835 °C, the decarburization annealing time is 125 s, and the heating rate in the heating section is 115 °C / s. Reduce the [C] content in the steel sheet to below 50 ppm to obtain the primary grain size and the proportion of Goss grain quantity shown in Table 4. (8) Nitriding treatment: Control the nitrogen content of the decarburized annealed sheet at 190-250 ppm. (9) Coating with MgO coating: Coat the MgO coating on the steel sheet. (10) High-temperature annealing: Carry out purification annealing for 25 hours under the condition of a conventional reducing atmosphere with a high-temperature annealing temperature of 1180 °C to reduce the [S] and [N] contents in the steel to below 50 ppm. (11) Insulating coating and skin pass annealing: After coating the insulating coating and hot-stretching skin pass annealing, obtain the finished product with the chemical compositions shown in Table 3-1 and Table 3-2. The indexes of the secondary grains of the finished product are listed in Table 4. Table 3-1. (wt%, the balance is Fe and other inevitable impurity elements except N, S, V, Ti) Table 3-2 (Content of Optionally Added Elements, wt%) Table 4 Combined with Table 3-1, Table 3-2 and Table 4, it can be seen that for the slab compositions, average primary grain sizes of decarburized slabs, proportions of Goss grain numbers in decarburized slabs, and various indicators of secondary grains of the high magnetic induction oriented silicon steels in Examples 11-22 of the present invention all meet the ranges defined in the claims of this case. Therefore, their iron losses P 17 / 50 are all lower than the reference iron losses obtained by calculating based on the formula 0.86 + 2 × finished product plate thickness - 16 × Si, and the magnetic induction intensity B8 is all higher than the reference magnetic induction obtained by calculating based on the formula 2.14 - 6.5 × Si. On the contrary, the iron losses and / or magnetic inductions of Comparative Examples 14-21 are inferior to the reference values obtained by the above calculations. Examples 23-29 and Comparative Examples 22-28 The high magnetic induction oriented silicon steels of Examples 23-29 and the comparative steels of Comparative Examples 22-28 are manufactured according to the following steps carried out in sequence: (1) Smelting and casting: Smelt using a converter or an electric furnace and continuously cast into a 230-mm thick slab. (2) Slab heating: Control the slab heating temperature at 1250 °C and the heating time at 120 min. (3) Hot rolling: Hot roll into a hot-rolled sheet with a thickness of 2.5 mm, and anneal some of the hot-rolled sheets according to Table 5-1. (4) First cold tandem rolling: Obtain a steel sheet with a thickness of 0.75 mm by first cold rolling, and control the reduction ratio of the first cold tandem rolling at 70.0%. (5) Intermediate annealing: Carry out intermediate annealing according to the intermediate annealing method, intermediate annealing maximum temperature, and intermediate annealing time shown in Table 5-1, where the uncoiling continuous annealing time is 220 s and the coil annealing time in a bell-type furnace is 12 h, to obtain a total oxygen content of 350-450 ppm and a C element content of 450-550 ppm for the sample after intermediate annealing. (6) Second cold tandem rolling: Obtain a steel sheet with a thickness of 0.13 mm by second cold rolling, and control the reduction ratio of the second cold tandem rolling at 82.7%. (7) Decarburizing annealing: Control the heating section heating rate, decarburizing annealing temperature, and decarburizing annealing time according to Table 5-1 to reduce the [C] content in the steel sheet to below 30 ppm, and obtain the primary grain size and proportion of Goss grain numbers shown in Table 5-2. (8) Nitriding treatment: Control the nitrogen content of the decarburized annealing sheet at 200-230 ppm. (9) Coating with MgO coating: Coat the MgO coating on the steel sheet. (10) High-temperature annealing: Under the condition of a conventional reducing atmosphere and a high-temperature annealing temperature of 1200 °C, a purification annealing is carried out for 20 hours to reduce the [S] and [N] contents in the steel to below 30 ppm. (11) Insulating coating and leveling annealing: After applying the insulating coating and performing hot-stretching leveling annealing, the finished product is obtained. The obtained finished product contains chemical components with the following mass percentages: Si 3.17%, C 0.0009%, Als 0.0254%, N 0.0019%, Mn 0.144%, S 0.0027%, V 0.0025%, Ti 0.0015%, Sn 0.065%, Cu 0.12%. Elements such as P, Cr, Sb, Bi, Nb, and Mo are not deliberately added in the finished product steel plate, and their contents are below the detection limit. The indicators of the secondary grains of the finished product are listed in Table 5-2. Table 5-1 Table 5-2 As can be seen from Table 5-1 and Table 5-2, although both Examples 23-29 and Comparative Examples 22-28 use the two-pass cold rolling method described in the present invention to prepare grain-oriented silicon steel with a finished thickness of 0.13 mm, the hot-rolled plate annealing and the highest annealing temperature, intermediate annealing and the highest annealing temperature, the heating section heating rate of decarburization annealing, decarburization annealing temperature, decarburization annealing time, as well as the average primary grain size of the decarburized plate, the proportion of Goss grain number in the decarburized plate, and the indicators of the secondary grains in Examples 23-29 all meet the requirements of this case. Therefore, its iron loss P 17 / 50 is lower than the reference iron loss of 0.613 W / kg calculated based on the formula 0.86 + 2 × finished plate thickness - 16 × Si, and the magnetic induction intensity B8 is higher than the reference magnetic induction of 1.934 T calculated based on the formula 2.14 - 6.5 × Si. On the contrary, the iron loss and / or magnetic induction of Comparative Examples 22-28 are inferior to the reference values obtained from the above calculations, and even rolling difficulties lead to strip breakage. In addition, the present invention also uses the method of laser scribing on the finished product samples with a thickness of 0.13 mm in Examples 23-29 in Table 5-2 to refine the magnetic domains of the finished product, and the comparison results of the iron loss before and after scribing are listed in Table 6. Table 6 As can be seen from Table 6, the iron loss of each example after scribing has decreased compared to its original iron loss. In summary, it can be seen that the high-magnetic-induction grain-oriented silicon steel and its manufacturing method described in the present invention have significant advantages and beneficial effects compared with the prior art, can improve product quality, reduce manufacturing costs, and avoid common problems, and have good application prospects. It should be pointed out that the composition design and manufacturing process described in the present invention are not only applicable to thin-gauge oriented silicon steel with a thickness of 0.13 to 0.20 mm, but also applicable to oriented silicon steel with a conventional thickness, such as oriented silicon steel with a thickness of 0.23 to 0.30 mm. For oriented silicon steel with a conventional thickness, the prominence of the problem described in the present invention may be relatively low, but since the manufacturing principles of oriented silicon steels of different thicknesses are similar, it can be considered that the technical solution proposed in the present invention is also applicable to the manufacturing of oriented silicon steel with a conventional thickness. It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them. It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

Claims

1. An oriented electrical steel, characterized in that, In addition to containing Fe and other inevitable impurities, the grain-oriented electrical steel also contains chemical elements with the following mass percentages: C ≤ 0.005%; Si: 3.0 - 3.8%; Als: 0.010 - 0.035%; Mn: 0.05 - 0.20%. Among other inevitable impurity elements, N ≤ 0.005%, S ≤ 0.005%, V ≤ 0.005%, Ti ≤ 0.005%. Among them, the average secondary grain size of the grain-oriented electrical steel is 6 - 16 mm; the area percentage of secondary grains with an average deviation angle (α + β) / 2 in the range of 0° - 3° among all secondary grains > 50%, where α is the rolling direction deviation angle and β is the rolling plane inclination angle.

2. The grain-oriented electrical steel according to claim 1, wherein, The mass percentages of the chemical elements in the grain-oriented electrical steel are: C ≤ 0.005%; Si: 3.0 - 3.8%. Als: 0.010 - 0.035%; Mn: 0.05 - 0.20%. The balance is Fe and other inevitable impurities; among other inevitable impurity elements, N ≤ 0.005%, S ≤ 0.005%, V ≤ 0.005%, Ti ≤ 0.005%.

3. The grain-oriented electrical steel according to claim 1 or 2, characterized in that, The grain-oriented electrical steel also contains at least one of the following chemical elements: P: 0.01 - 0.08%; Cr: 0.01 - 0.40%, Sn: 0.03 - 0.30%, Cu: 0.01 - 0.40%, 0 < Sb ≤ 0.1%, 0 < Bi ≤ 0.1%, 0 < Nb ≤ 0.1%, 0 < Mo ≤ 0.1%.

4. The grain-oriented electrical steel according to claim 1 or 2, characterized in that, The thickness of the grain-oriented electrical steel is 0.13 - 0.20 mm.

5. The grain-oriented electrical steel according to claim 1 or 2, characterized in that, The area percentage of secondary grains with a size < 6 mm or > 16 mm among all secondary grains < 15%.

6. The grain-oriented electrical steel according to claim 1 or 2, characterized in that, The iron loss P of the oriented silicon steel 17 / 50 ≤0.86+2×finished plate thickness-16×Si, magnetic induction intensity B8≥2.14-6.5×Si, where the unit of finished plate thickness is mm. When calculating, the element symbol Si in the formula is substituted into the mass percentage of Si element in the finished steel plate, P 17 / 50 The unit of is W / kg, and the unit of B8 is T.

7. The manufacturing method of the grain-oriented electrical steel according to any one of claims 1-6, characterized in that, The manufacturing method includes the following steps: (1) Smelting and casting to obtain a slab. (2) Heating the slab. (3) Hot rolling. (4) First cold rolling (5) Intermediate annealing. (6) Second cold rolling (7) Decarburizing annealing, nitriding treatment, and coating with an isolation agent coating. The average primary grain size of the obtained decarburized annealed sheet is 6 - 18 μm, and the proportion of Goss grains with an average deviation angle (α + β) / 2 less than 15° is greater than 1.5%. (8) High-temperature annealing. (9) Coating with an insulating coating and skin pass annealing.

8. The manufacturing method according to claim 7, characterized in that, In step (2), the slab heating temperature is in the range of 1140°C - 1250°C.

9. The manufacturing method according to claim 7, characterized in that, In step (4), the first cold rolling uses tandem cold rolling, and its reduction rate is 50 - 75%.

10. The manufacturing method according to claim 7, characterized in that, In step (5), the maximum temperature of the intermediate annealing is 900 - 1050°C.

11. The manufacturing method according to claim 7, characterized in that, In step (6), the second cold rolling uses tandem cold rolling, and its reduction rate is 60 - 85%.

12. The manufacturing method according to claim 7, characterized in that, The manufacturing method also includes a hot rolled sheet annealing step after step (3) and before step (4), and the hot rolled sheet annealing temperature ≤ 1000°C.

13. The manufacturing method according to claim 7, characterized in that, In step (7), the decarburizing annealing temperature is 800 - 900°C, the decarburizing annealing time is 80 - 170 s, and the heating rate is 30 - 150°C / s.

14. The manufacturing method according to claim 7, characterized in that, In step (7), the nitrogen content of the decarburized annealed sheet after nitriding treatment is 160 - 260 ppm.

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