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

Abstract

The invention discloses high-magnetic-induction oriented silicon steel, which contains Fe and other inevitable impurities, and further contains the following chemical elements in percentage by mass: less than or equal to 0.005% of C; 3.0 to 3.8 percent of Si; the content of Als is 0.010 to 0.035 percent; mn: 0.05 to 0.20%; the rare earth element is at least one of Ce and La, and the formula of Ce + La is 0.003-0.3%; wherein in other inevitable impurity elements, N is smaller than or equal to 0.005%, S is smaller than or equal to 0.005%, V is smaller than or equal to 0.005%, and Ti is smaller than or equal to 0.005%. Correspondingly, the invention further provides a manufacturing method of the high-magnetic-induction oriented silicon steel. The annealing temperature of the hot-rolled plate can be reduced or annealing of the hot-rolled plate can be omitted, the thin-gauge high-magnetic-induction oriented silicon steel can be efficiently produced through the cold continuous rolling method, and the magnetic performance of the product is improved while the manufacturing cost is reduced.

Description

Technical Field

[0001] The present invention relates to a steel type and a manufacturing method thereof, and more particularly to an oriented silicon steel and a manufacturing method thereof. Background Art

[0002] Oriented silicon steel is a soft magnetic material with excellent magnetic properties, which is composed of grains called Goss texture. The Goss texture is expressed 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 under the working condition of a directional magnetic field due to its extremely high magnetic induction intensity and extremely low iron loss.

[0003] 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, where 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 intensity of 800A / m. These two parameters can effectively reflect the magnetic property advantages and disadvantages of oriented silicon steel under different magnetic field and frequency conditions.

[0004] Existing preparation processes all need to control the evolution of the whole process organization, texture and inhibitors through complex processes to obtain a finished plate with abnormal growth of Goss grains. Oriented silicon steel can be classified into a single cold rolling method and a double cold rolling method according to the process flow. 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.

[0005] 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 existing in the slab, and this part of the inhibitors is called primary inhibitors, which have an important impact on primary recrystallization and thus also affect the magnetic properties of the final product; they also come from the nitriding treatment after decarburization annealing, and this part of the inhibitors is called secondary inhibitors, which promote secondary recrystallization together with the primary inhibitors. Although the inhibitor control of the low-temperature slab heating process is difficult and the annealing process window is narrow, with the application of some improved processes, such as adding auxiliary inhibitors, controlling the inclusion morphology, and using rapid induction heating, the product grade of this process has been continuously improved.

[0006] 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 is determined not only by the material itself but also by the working frequency of the material in the alternating magnetic field and the influence of the magnetic induction intensity, etc. 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 grain-oriented silicon steel.

[0007] The iron loss of grain-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 grain-oriented silicon steel include: increasing 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 grain-oriented silicon steel, increasing 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 grain-oriented silicon steel.

[0008] 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.

[0009] 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 inhibitor force weakens. This will have an adverse effect 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 hot coil thickness, 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: the reduction in the hot-rolled sheet thickness will lead to a significant decrease in the production efficiency of the annealing unit. When the hot-rolled sheet thickness 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 grain-oriented silicon steel preparation process is mostly between 0.23 and 0.30 mm, and it is difficult to further reduce.

[0010] In addition, in order to achieve the desired inhibitor distribution state, annealing of hot-rolled sheets has become an essential process step in the preparation of high magnetic induction oriented electrical steel. During the annealing of hot-rolled sheets, the hot-rolled pickled sheets are rapidly heated to about 1120 °C, held for 2 - 4 minutes, air-cooled to about 900 °C, water-cooled through the water, or processed in a two-stage manner with an additional 2-minute holding followed by water-cooling. After annealing, the recrystallized grains on the surface layer of the hot-rolled sheets grow, and a certain amount of martensite structure is formed during the rapid cooling process. Mechanical twins are also generated 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 electrical steel requires a 20-high reversible rolling mill with high rolling stress for cold rolling, which makes it difficult to improve the rolling efficiency.

[0011] In order to manufacture thin-gauge high magnetic induction oriented electrical steel efficiently, several new manufacturing technologies for oriented electrical steel have been developed in recent years.

[0012] For example, Chinese Patent Document with Publication No. CN116460139A, Publication Date of July 21, 2023, and Title of "An Ultra-Thin High Magnetic Induction Oriented Electrical Steel and Its Rolling Method" discloses an ultra-thin high magnetic induction oriented electrical steel and its rolling method. In this technical solution, the final finished product thickness obtained is 0.12 - 0.20 mm. The main difference between this method and the existing preparation process of high magnetic induction oriented electrical steel lies in the rolling process, where the reversible rolling used in the existing single cold rolling is changed to a combined rolling of tandem cold rolling plus reversible rolling. The work roll diameter of the tandem cold rolling is 300 - 500 mm, and the total reduction ratio is 60 - 91%; the work roll diameter of the reversible rolling is 70 - 150 mm, and the total reduction ratio is 10 - 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 electrical steel and improving the magnetic properties of the product, and does not solve the problem of difficult cold rolling after annealing of existing oriented electrical steel hot-rolled sheets.

[0013] Another example is that Chinese Patent with Publication No. CN114134423A, Publication Date of March 4, 2022, and Title of "A Ultra-Short Process Rare Earth Oriented Electrical Steel and Its Preparation Method" discloses a solution for preparing oriented electrical 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 and other processes. A 2 - 2.5 mm thick cast strip can be directly obtained, and the finished product thickness of the prepared oriented electrical steel is 0.20 - 0.35 mm, and the iron loss P 17 / 50 is 0.9 - 1.1 W / kg, and the magnetic induction intensity B8 is 1.87 - 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 of the thin strip continuous casting technology and the magnetic properties of the product need to be improved. Summary of the Invention

[0014] One of the objectives of the present invention is to provide a high magnetic induction oriented silicon steel, which can obtain a thin-gauge high magnetic induction oriented silicon steel on the premise of canceling the hot-rolled sheet annealing step through reasonable chemical composition design, thereby reducing the manufacturing cost and improving the magnetic properties of the product.

[0015] To achieve the above objective, the present invention provides a high magnetic induction oriented silicon steel, which contains Fe and other inevitable impurities. In addition, it also contains chemical elements with the following mass percentages:

[0016] C ≤ 0.005%;

[0017] Si: 3.0 - 3.8%;

[0018] Als: 0.010 - 0.035%;

[0019] Mn: 0.05 - 0.20%;

[0020] At least one of Ce and La, and Ce + La: 0.003 - 0.3%;

[0021] Among other inevitable impurity elements, N ≤ 0.005%, S ≤ 0.005%, V ≤ 0.005%, Ti ≤ 0.005%.

[0022] Further, in the high magnetic induction oriented silicon steel described in the present invention, the mass percentages of its various chemical elements are:

[0023] C ≤ 0.005%;

[0024] Si: 3.0 - 3.8%;

[0025] Als: 0.010 - 0.035%;

[0026] Mn: 0.05 - 0.20%;

[0027] At least one of Ce and La, and Ce + La: 0.003 - 0.3%;

[0028] 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%.

[0029] In the high magnetic induction oriented silicon steel described in the present invention, the design principles of its various chemical elements are as follows:

[0030] C: In the high magnetic induction oriented silicon steel of 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 belongs to residual elements in the present invention and 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 of the present invention, the mass percentage content of C element is limited to C≤0.005%.

[0031] Si: In the high magnetic induction oriented silicon steel of 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 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 Si element in the steel should not be too high. When the mass percentage content of Si element in the steel is higher than 3.8%, due to the tendency of Si to segregate along the grain boundaries, it will lead to an increase in the brittleness of the steel plate, poor rollability, and instability of the recrystallized structure and inhibitors, resulting in imperfect secondary recrystallization. Based on this, in the high magnetic induction oriented silicon steel of the present invention, the mass percentage content of Si element is controlled between 3.0 and 3.8%.

[0032] Als: In the high magnetic induction oriented silicon steel of the present invention, Als can form secondary inhibitors during the subsequent nitriding treatment of the material, which can act together with the primary inhibitors 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, and secondary recrystallization will be incomplete or even not 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 of the present invention, the mass percentage content of Als is controlled between 0.010 and 0.035%.

[0033] Mn: In the high magnetic induction oriented silicon steel of the present invention, the Mn element is similar to the Si element, both of which can increase the resistivity and reduce the eddy current loss. In addition, the Mn element can also expand the γ phase region, improve the hot rolling plasticity and structure, and effectively improve the hot rolling rollability of the material. However, it should be noted that when the mass percentage content of Mn element in the steel is less than 0.05%, the above effects cannot be effectively exerted; if the mass percentage content of Mn element added to the steel is higher than 0.20%, it is easy to appear α and γ mixed duplex structure, resulting in phase transformation stress and generation of γ phase during annealing, causing instability of secondary recrystallization. Based on this, in the high magnetic induction oriented silicon steel of the present invention, the mass percentage content of Mn element is controlled between 0.05 and 0.20%.

[0034] Ce and La: In the high magnetic induction oriented silicon steel described in the present invention, Ce and La elements can change the formation path of inclusions during the solidification of molten steel, thereby improving the precipitation morphology of inhibitors. By reducing the number of coarse MnS+AlN complex inclusions in the slab, the slab heating temperature can be reduced. They can also form Ce-S, La-S with S element in the molten steel and play an auxiliary inhibitor role as segregation elements, playing a role in improving magnetic properties. In the present invention, adding Ce and La helps to solve the problem that the inhibitor rapidly matures during high-temperature annealing of thin-gauge oriented silicon steel, resulting in weakened inhibition force. When the sum of the mass percentages of Ce and La is less than 0.003%, the above effects cannot be effectively exerted; however, if the sum of the mass percentages of Ce and La exceeds 0.3%, it has a strong inhibitory effect on recrystallization and the secondary recrystallization is imperfect. Based on this, in the high magnetic induction oriented silicon steel described in the present invention, the sum of the mass percentages of Ce and La elements is controlled between 0.003% and 0.3%.

[0035] 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 magnetic aging phenomenon, that is, the magnetic properties of the material change with the service time. Therefore, they belong to impurity elements. 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 of S element is limited to S≤0.005%, and the mass percentage of N element is limited to N≤0.005%.

[0036] V and Ti: In the high magnetic induction oriented silicon steel described in the present invention, V element will form VN after nitriding treatment of the material, which affects secondary recrystallization and is not conducive to the magnetic properties of the material. And Ti element, because it can preferentially precipitate TiN, and MnS will precipitate attached to TiN, and then AlN will precipitate attached to MnS, thus easily forming coarse MnS+AlN complex inclusions, which is also not conducive 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 of Ti element is limited to Ti≤0.005%, and the mass percentage of V element is limited to V≤0.005%.

[0037] Furthermore, in the high magnetic induction oriented silicon steel described in the present invention, it also contains at least one of the following chemical elements:

[0038] 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%.

[0039] In the high magnetic induction oriented silicon steel of the present invention, each of the above chemical elements can further improve the performance of the high magnetic induction oriented silicon steel of the present invention, and its design principle is as follows:

[0040] 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, which can delay the premature oxidation and decomposition of AlN and 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%, not only the nitriding efficiency will be reduced, but also the cold rolling workability will become poor. 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 be preferably set to 0.01 - 0.08%.

[0041] 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 sheet. In order to fully exert the role of the Cr element, the mass percentage content of the Cr element in the steel can be higher than 0.01%, but considering that when the added Cr 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 be preferably set to 0.01 - 0.40%.

[0042] Sn: In the high magnetic induction oriented electrical steel of the present invention, in some preferred embodiments, Sn is a grain boundary segregation element, which has the function of assisting inhibitors. It can effectively compensate for the problem of the decrease in inhibition force caused by the coarsening of AlN inclusions in cases such as an increase in the Si content in the steel or a reduction in the strip thickness, expand the process window, and is beneficial to the stability of the magnetic properties of the product. However, considering that when the mass percentage addition amount of Sn is less than 0.03%, the above effects cannot be effectively obtained; when the mass percentage addition amount 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, resulting in an increase in manufacturing cost. Therefore, in the high magnetic induction oriented electrical steel of the present invention, in some preferred embodiments, the mass percentage addition amount of Sn can preferably be set to 0.03 - 0.30%.

[0043] Cu: In the high magnetic induction oriented electrical steel of the present invention, in some preferred embodiments, Cu is added because: The Cu element is similar to the Mn element, and both can expand the γ-phase region, which helps to obtain fine AlN inclusions. In addition to expanding the γ-phase region, the Cu element can also preferentially combine with the S element to form Cu2S compared with Mn, which is beneficial to inhibiting the change in the primary grain size. Considering that when the mass percentage addition amount of the Cu element in the steel is less than 0.01%, its above functions cannot be exerted; however, if the mass percentage addition amount of the Cu element in the steel is higher than 0.40%, it will increase the manufacturing cost and the magnetic properties will not be improved. Therefore, in the high magnetic induction oriented electrical steel of the present invention, in some preferred embodiments, the mass percentage addition amount of Cu can preferably be set to 0.01 - 0.40%.

[0044] Sb and Bi: In the high magnetic induction oriented electrical steel of the present invention, in some preferred embodiments, Sb and Bi are added because: Sb and Bi are also grain boundary segregation elements, both of which have the function of assisting inhibitors, can improve the grain boundary migration conditions of Goss nuclei, help to expand the process window, and improve the finished product magnetic induction. However, when the mass percentage content of Sb and Bi in the steel is higher than 0.100%, 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 of the present invention, in some preferred embodiments, the mass percentage content of Sb can preferably be set to less than 0.100%, and the mass percentage content of Bi can also preferably be set to less than 0.100%.

[0045] Nb and Mo: In the high magnetic induction oriented electrical steel according to the present invention, in some preferred embodiments, Nb and Mo are added because: both Nb and Mo are effective grain-refining microalloying elements, which can promote the formation of fine and uniform primary grain sizes. At the same time, the formed carbonitrides can also serve as auxiliary inhibitors, reducing the difficulty of adjusting the morphology of primary inhibitors. However, when the mass percentage content of Nb and Mo exceeds 0.100%, there is a strong inhibitory effect on recrystallization and secondary recrystallization is imperfect. Therefore, in the high magnetic induction oriented electrical steel according to the present invention, in some preferred embodiments, the mass percentage content of Nb can preferably be set to be less than 0.100%, and the mass percentage content of Mo can preferably be set to be less than 0.100%.

[0046] Furthermore, the thickness of the high magnetic induction oriented electrical steel according to the present invention is 0.13 - 0.20 mm.

[0047] Furthermore, in the high magnetic induction oriented electrical steel according to the present invention, its typical iron loss P 17 / 50 ≤0.86 + 2 × plate thickness - 16 × Si, the typical magnetic induction intensity B8 ≥ 2.14 - 6.5 × Si, where the plate thickness is taken as the value with the unit parameter of mm, Si is substituted with the mass percentage content of Si element, the unit parameter of P 17 / 50 is W / kg, and the unit parameter of B8 is T.

[0048] Correspondingly, another object of the present invention is to provide a manufacturing method of the above-mentioned high magnetic induction oriented electrical steel. By using this method in combination with the above-mentioned component ratio, it is possible to efficiently produce thin-gauge high magnetic induction oriented electrical steel by the cold tandem rolling method without the hot rolled sheet annealing step, thereby reducing the manufacturing cost while improving the magnetic properties of the product.

[0049] To achieve the above object, the present invention provides a manufacturing method of high magnetic induction oriented electrical steel, which includes the steps of:

[0050] (1) Smelting and casting;

[0051] (2) Slab heating;

[0052] (3) Hot rolling;

[0053] (4) First cold rolling

[0054] (5) Intermediate annealing;

[0055] (6) Second cold rolling;

[0056] (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 a deviation angle of less than 15° is greater than 1.5%;

[0057] (8) High temperature annealing;

[0058] (9) Insulation coating and flat annealing.

[0059] In the manufacturing method of the present invention, since the present invention can adjust the morphology of the inhibitor in the intermediate annealing in step (5) instead of adjusting it in the conventional hot-rolled sheet annealing process, this change can eliminate the hot-rolled sheet annealing process and greatly reduce the difficulty of cold rolling.

[0060] In the existing decarburized plates of high magnetic induction oriented silicon steel, the number of Goss grains with a deviation angle of less than 15° is usually less than 1.5%. The thinning of the strip thickness will lead to the problem of insufficient number of effective Goss 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 control 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.

[0061] Furthermore, in step (2) of the manufacturing method described in the present invention, the slab heating temperature is ≤1250°C.

[0062] Furthermore, in step (4) of the manufacturing method of the present invention, the first cold rolling adopts cold tandem rolling, and the reduction rate thereof is 50 to 75%.

[0063] Furthermore, 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%.

[0064] 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.

[0065] 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.

[0066] Furthermore, in step (5) of the manufacturing method of the present invention, the intermediate annealing temperature is 900-1050°C.

[0067] In step (5) of the manufacturing method of the present invention, the total oxygen content of the sample after annealing can be controlled to be ≤600 ppm, and the C element content ≥300 ppm. This is beneficial to the stable production of tandem cold rolling in step (6), promotes the formation of a strong γ texture, and further facilitates the formation of perfect secondary recrystallization.

[0068] Furthermore, before step (4) and after step (3) of the manufacturing method of the present invention, there is a hot-rolled sheet annealing step, and the hot-rolled sheet annealing temperature is ≤1000 °C.

[0069] As described above, in the manufacturing method of the present invention, after hot rolling, hot-rolled annealing may not be carried out and cold rolling can be directly performed, thereby reducing the process flow, improving production efficiency, and reducing production costs. However, in some embodiments, hot-rolled annealing can also be carried out after the hot-rolling step, but the hot-rolled sheet annealing temperature needs to be ≤1000 °C, because when the maximum annealing temperature is higher than 1000 °C, it will cause the surface grains of the hot-rolled sheet to coarsen, which is not conducive to the stable production of tandem cold rolling in subsequent step (4).

[0070] Furthermore, 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 and warming rate is 30 - 150 °C / s.

[0071] Furthermore, 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.

[0072] In the manufacturing method of the present invention, through nitriding treatment, nitrogen combines with the original aluminum in the steel to form secondary inhibitors of fine and dispersed AlN, (Al,Si)N, (Al,Si,Mn)N and other particles. During the subsequent high-temperature annealing process, the secondary inhibitors and the primary inhibitors jointly promote the secondary recrystallization process.

[0073] The high magnetic induction oriented silicon steel of the present invention has the following advantages and beneficial effects compared with the prior art:

[0074] The high magnetic induction oriented silicon steel of the present invention can significantly reduce the hot-rolled sheet annealing temperature or even cancel the hot-rolled sheet annealing 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, and realize the efficient production of thin-gauge high magnetic induction oriented silicon steel with excellent magnetic properties by the tandem cold rolling method.

[0075] Compared with the prior art, the present invention can solve the problems of rapid ripening of the inhibitor and insufficient number of effective Goss crystal nuclei after the strip thickness is thinned, which is beneficial to improving the magnetic properties of the final product. Therefore, thin-gauge high magnetic induction oriented electrical steel can be produced without further thinning the thickness of the hot-rolled sheet, thereby avoiding a series of problems caused by the production of thin-gauge hot-rolled coils on a conventional hot-rolling production line. At the same time, by canceling the annealing of the hot-rolled sheet and realizing the efficient production of thin-gauge high magnetic induction oriented electrical steel by the cold tandem rolling method, the manufacturing cost can be significantly reduced.

[0076] In addition, the manufacturing method described in the present invention also has the above-mentioned advantages and beneficial effects. Specific embodiments

[0077] The following will further explain and illustrate the high magnetic induction oriented electrical steel and its manufacturing method according to the present invention with specific embodiments. However, this explanation and illustration shall not unduly limit the technical solution of the present invention.

[0078] First, the various detection means of the embodiments and comparative examples in this case are described as follows:

[0079] The average primary grain size is obtained by area analysis after obtaining the metallographic photograph of the primary grain size.

[0080] P of the non-scribed product steel 17 / 50 and B8 are obtained by the method of measuring the magnetic properties of electrical steel sheets (strips) with an Epstein square according to the regulations in GB / T 3655.

[0081] P of the scribed product steel 17 / 50 and B8 are obtained by the method of measuring the magnetic properties of electrical steel sheets (strips) with a single-sheet tester according to the regulations in GB / T 13789.

[0082] Examples 1-12 and Comparative Examples 1-8

[0083] The high magnetic induction oriented electrical steel of Examples 1-12 and the comparative steel of Comparative Examples 1-8 are manufactured according to the following steps:

[0084] (1) Smelting and casting: Smelt with a converter or an electric furnace and continuously cast into a slab with a thickness of 230 mm.

[0085] (2) Slab heating: Control the slab heating temperature at 1200 °C and the heating time at 250 min.

[0086] (3) Hot rolling: Hot roll into a hot-rolled sheet with a thickness of 2.3 mm.

[0087] (4) First cold tandem rolling: Obtain a thickness of 0.75 mm by the first cold rolling, and control the reduction ratio of the first cold tandem rolling at 67.4%.

[0088] (5) Intermediate annealing: The continuous annealing method with uncoiling was adopted. The intermediate annealing temperature was controlled at 975 °C, and the intermediate annealing time was 120 s. The total oxygen content of the sample after intermediate annealing was 261 - 594 ppm, and the C element content was 308 - 939 ppm.

[0089] (6) Second cold tandem rolling: The thickness after second cold rolling was 0.19 mm, and the reduction rate of second cold tandem rolling was controlled at 74.7%.

[0090] (7) Decarburizing annealing: The decarburizing annealing temperature was 835 °C, the decarburizing annealing time was 125 s, and the heating rate in the heating section was 115 °C / s. The [C] content in the steel plate was reduced to less than 50 ppm, and the primary grain size and the proportion of Goss grains shown in Table 2 were obtained.

[0091] (8) Nitriding treatment: The nitrogen content of the decarburized annealing plate was controlled at 190 - 250 ppm.

[0092] (9) Coating with MgO coating: The MgO coating was coated on the steel plate.

[0093] (10) High-temperature annealing: Under the condition of a conventional reducing atmosphere and a high-temperature annealing temperature of 1180 °C, a purification annealing was carried out for 25 hours to reduce the [S] and [N] contents in the steel to less than 50 ppm.

[0094] (11) Insulating coating and skin pass annealing: After coating the insulating coating and performing hot stretch skin pass annealing, the finished product with the chemical composition contents shown in Table 1-1 and Table 1-2 was obtained.

[0095] Table 1-1. (wt%, the balance is Fe and other inevitable impurity elements except N, S, V, and Ti)

[0096]

[0097]

[0098] Table 1-2 (wt%, the balance is Fe and other inevitable impurity elements except N, S, V, and Ti)

[0099] Number P Cr Sn Cu Sb Bi Nb Mo Example 1 0.079 0 0.298 0 0.099 0 0 0.097 Example 2 0 0 0.049 0 0.001 0 0.045 0.003 Example 3 0 0.08 0.083 0 0.084 0 0 0 Example 4 0.021 0 0.032 0.29 0 0.003 0 0.076 Example 5 0.075 0.24 0 0 0.066 0.036 0.029 0.022 Example 6 0 0 0.253 0.21 0.012 0.079 0.069 0 Example 7 0.044 0.14 0.065 0.12 0.024 0.098 0.099 0 Example 8 0.067 0.01 0 0.39 0 0 0 0.018 Example 9 0.037 0.35 0.165 0.02 0 0.019 0 0.034 Example 10 0.012 0.4 0.101 0 0.031 0 0 0.045 Example 11 0 0 0 0 0 0 0 0 Example 12 0.029 0 0 0 0.050 0.063 0.002 0.059 Comparative Example 1 0.031 0.2 0.22 0.23 0.109 0.077 0.097 0 Comparative Example 2 0 0.06 0 0.08 0.027 0.053 0 0.096 Comparative Example 3 0.009 0.42 0.124 0 0.0008 0 0.005 0.043 Comparative Example 4 0 0.37 0.029 0.009 0 0.067 0.0008 0.053 Comparative Example 5 0.013 0 0.038 0.17 0.064 0.101 0.016 0.102 Comparative Example 6 0.056 0.14 0.308 0.34 0 0.0007 0.074 0.007 Comparative Example 7 0 0.24 0.064 0.41 0.003 0.098 0 0.087 Comparative Example 8 0.082 0 0 0 0.081 0.033 0.104 0.016

[0100] Table 2

[0101]

[0102]

[0103] As can be seen from Table 1-1, Table 1-2 and Table 2, the slab composition of the high magnetic induction oriented silicon steel in Examples 1-12 of the present invention, the average primary grain size of the decarburized slab, and the proportion of Goss grains in the decarburized slab all meet the scope defined by the claims of this case. Therefore, its iron loss P 17 / 50 is lower than the reference iron loss calculated based on the formula 0.86 + 2 × plate thickness - 16 × Si, and the magnetic induction intensity B8 is higher than the reference magnetic induction calculated based on the formula 2.14 - 6.5 × Si. On the contrary, the iron loss and / or magnetic induction of Comparative Examples 1-8 are inferior to the reference values obtained from the above calculations.

[0104] Examples 13-18 and Comparative Examples 9-13

[0105] Manufacture the high magnetic induction oriented silicon steel in Examples 13-18 and the comparative steel in Comparative Examples 9-13 according to the following steps:

[0106] (1) Smelting and casting: Use a converter or an electric furnace for smelting and continuously cast into a 230 mm thick slab.

[0107] (2) Slab heating: Control the slab heating temperature at 1140 °C and the heating time at 200 min.

[0108] (3) Hot rolling: Roll into hot rolled sheets with thicknesses of 2.4 mm and 2.6 mm as shown in Table 3-1.

[0109] (4) Prepare cold rolled sheets with a finished thickness of 0.18 mm according to the process shown in Table 3-1. Among them, Examples 13-18 and Comparative Examples 11-13 adopt the two-pass cold rolling process described in the present invention, without annealing the hot rolled sheet, and perform intermediate annealing between the first cold rolling and the second cold rolling. The intermediate annealing adopts an open-coil continuous annealing method, and control the intermediate annealing and its maximum temperature according to the process shown in Table 3-1, with an annealing time of 220 s; Comparative Examples 9-10 adopt the conventional one-pass cold rolling process, control the maximum temperature of the hot rolled sheet annealing at 1150 °C, and control the annealing time at 250 s.

[0110] (5) Decarburizing annealing: The decarburizing annealing temperature is 835 °C, the decarburizing annealing time is 125 s, and the heating rate in the heating section is 115 °C / s, reducing the [C] content in the steel sheet to below 30 ppm.

[0111] (6) Nitriding treatment: Control the nitrogen content of the decarburized annealed sheet at 180 - 250 ppm.

[0112] (7) Coating with MgO coating: Coat the MgO coating on the steel sheet.

[0113] (8) High-temperature annealing: Under the condition of a conventional reducing atmosphere and a high-temperature annealing temperature of 1200 °C, purification annealing is carried out for 20 hours to reduce the [S] and [N] contents in the steel to below 40 ppm.

[0114] (9) Insulating coating and leveling annealing: After applying the insulating coating and hot-stretching leveling annealing, the finished product is obtained. The chemical composition of the obtained finished product is: Si 3.22%, C 0.0016%, Als 0.0334%, N 0.0012%, Mn 0.088%, S 0.0013%, Ce 0.0243%, La 0.0202%, V 0.0025%, Ti 0.0015%.

[0115] Table 3-1

[0116]

[0117] Table 3-2

[0118]

[0119]

[0120] It can be seen from Table 3-1 and Table 3-2 that in Examples 13-18, the two-pass cold rolling method described in the present invention is used to prepare 0.17 mm grain-oriented silicon steel, which can obtain a suitable primary grain size and a higher proportion of Goss grains in the decarburized slab, and the magnetic properties of the obtained product 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 × plate thickness - 16 × Si, and the magnetic induction intensity B8 is all higher than the reference magnetic induction of 1.931 T calculated based on the formula 2.14 - 6.5 × Si. In Comparative Examples 9-10, the conventional one-pass cold rolling method is used to prepare 0.17 mm grain-oriented silicon steel, or in Comparative Examples 11-13, the two-pass cold rolling method is used, but the average primary grain size of the decarburized slab or the proportion of Goss grains in the decarburized slab does not meet the requirements of this case, and the obtained iron loss and / or magnetic induction are inferior to the reference values calculated above.

[0121] Examples 19-22 and Comparative Examples 14-21

[0122] The high magnetic induction grain-oriented silicon steel of Examples 19-22 and the comparative steel of Comparative Examples 14-21 are manufactured according to the following steps:

[0123] (1) Smelting and casting: Smelt using a converter or an electric furnace and continuously cast into a slab with a thickness of 230 mm.

[0124] (2) Slab heating: Control the slab heating temperature to 1190 °C and the heating time to 160 min.

[0125] (3) Hot rolling: The hot-rolled sheet is rolled to a thickness of 2.6 mm.

[0126] (4) First tandem cold rolling: Cold roll to the thickness shown in Table 4-1 for the first time.

[0127] (5) Intermediate annealing: Anneal for 180 s by the method of uncoiling continuous annealing, control the maximum temperature of intermediate annealing according to Table 4-1, and obtain the total oxygen content and C element content of the intermediate annealed sheet shown in Table 4-1.

[0128] (6) Second tandem cold rolling: Cold roll to a thickness of 0.15 mm for the second time.

[0129] (7) Decarburizing annealing: Control the decarburizing annealing temperature according to Table 4-1, 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 plate to less than 30 ppm, and obtain the primary grain size shown in Table 2.

[0130] (8) Nitriding treatment: Control the nitrogen content of the decarburized annealed sheet according to Table 4-1.

[0131] (9) Coating with MgO coating: Coat the MgO coating on the steel plate.

[0132] (10) High-temperature annealing: Carry out purification annealing for 18 hours under the condition of a conventional reducing atmosphere and a high-temperature annealing temperature of 1170 °C, and reduce the [S] and [N] contents in the steel to less than 50 ppm.

[0133] (11) Insulating coating and skin pass annealing: Obtain the finished product after coating the insulating coating and hot stretch skin pass annealing. The chemical composition of the obtained finished product is: Si 3.39%, C 0.0007%, Als 0.0275%, N 0.0017%, Mn 0.183%, S 0.0008%, Ce 0.1957%, V 0.0031%, Ti 0.0010%.

[0134] Table 4-1

[0135]

[0136] Table 4-2

[0137]

[0138] As can be seen from Table 4-1 and Table 4-2, although the two-roll cold rolling method described in the present invention is adopted for preparing 0.15 mm grain-oriented silicon steel in Examples 19-22 and Comparative Examples 14-21, the reduction ratio of the first cold rolling, the reduction ratio of the second cold rolling, the highest temperature of the 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, and the proportion of the number of Goss grains in the decarburized sheet in Examples 19-22 all meet the requirements of this case. Therefore, the iron loss P 17 / 50 is lower than the reference iron loss of 0.618 W / kg calculated based on the formula 0.86 + 2 × sheet thickness - 16 × Si, and the magnetic induction intensity B8 is 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 14-21 are inferior to the reference values obtained by the above calculations.

[0139] Examples 23-29 and Comparative Examples 22-28

[0140] The high magnetic induction grain-oriented silicon steel of Examples 23-29 and the comparative steel of Comparative Examples 22-28 are manufactured according to the following steps:

[0141] (1) Smelting and casting: Smelt using a converter or an electric furnace and continuously cast into a slab with a thickness of 230 mm.

[0142] (2) Slab heating: Control the slab heating temperature at 1250 °C and the heating time at 120 min.

[0143] (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.

[0144] (4) First tandem cold rolling: Obtain a thickness of 0.75 mm by the first cold rolling, and control the reduction ratio of the first tandem cold rolling at 70.0%.

[0145] (5) Intermediate annealing: Perform intermediate annealing according to the intermediate annealing method, intermediate annealing temperature, and intermediate annealing time shown in Table 5, where the uncoiling continuous annealing time is 220 s and the batch 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 intermediate annealed sample plate.

[0146] (6) Second tandem cold rolling: Obtain a thickness of 0.13 mm by the second cold rolling, and control the reduction ratio of the second tandem cold rolling at 82.7%.

[0147] (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 plate to below 30 ppm, and obtain the primary grain size and the proportion of the number of Goss grains shown in Table 5-2.

[0148] (8) Nitriding treatment: Control the nitrogen content of the decarburized annealing sheet to be 200 - 230 ppm.

[0149] (9) Coating with MgO coating: Coat the MgO coating on the steel sheet.

[0150] (10) High - temperature annealing: Conduct a 20 - hour purification annealing under the condition of a conventional reducing atmosphere with a high - temperature annealing temperature of 1200 °C to reduce the [S] and [N] contents in the steel to below 30 ppm.

[0151] (11) Insulating coating and skin - pass annealing: Apply an insulating coating and then perform hot - stretch skin - pass annealing to obtain the finished product. The chemical composition of the obtained finished product is: Si 3.17%, C 0.0009%, Als 0.0254%, N 0.0019%, Mn 0.144%, S 0.0027%, La 0.0030%, V 0.0025%, Ti 0.0015%, Sn 0.065%, Cu 0.12%.

[0152] Table 5 - 1

[0153]

[0154] Table 5 - 2

[0155]

[0156] 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 - stage cold rolling method described in the present invention to prepare 0.13 mm grain - oriented silicon steel, the hot - rolled sheet annealing and the highest annealing temperature, intermediate annealing and the highest annealing temperature, the heating - up rate in the decarburizing annealing heating section, the decarburizing annealing temperature, the decarburizing annealing time, as well as the average primary grain size of the decarburized sheet and the proportion of Goss grains in the decarburized sheet 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×sheet 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 calculated above, and even rolling difficulties lead to strip breakage.

[0157] In addition, the present invention also uses the method of laser scribing to refine the magnetic domains of the 0.15 mm finished product samples in Examples 23 - 29 in Table 5 - 2, and lists the comparison results of the iron loss before and after scribing in Table 6.

[0158] Table 6

[0159] Number <![CDATA[Iron loss P before notching 17 / 50 (W / kg)]]> <![CDATA[Iron loss P after notching 17 / 50 (W / kg)]]> Example 23 0.596 0.543 Example 24 0.563 0.498 Example 25 0.602 0.536 Example 26 0.592 0.524 Example 27 0.575 0.505 Example 28 0.579 0.499 Example 29 0.609 0.533

[0160] It can be seen from Table 6 that the iron loss of each embodiment after notching is reduced compared with its original iron loss.

[0161] In summary, it can be seen that the high magnetic induction oriented silicon steel and the manufacturing method thereof 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.

[0162] 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 of 0.13-0.20 mm, but also to oriented silicon steel of conventional thickness, such as oriented silicon steel of 0.23-0.30 mm. For oriented silicon steel of conventional thickness, the prominence of the problem 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 of conventional thickness.

[0163] 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.

[0164] 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. A high magnetic induction oriented silicon steel, which contains Fe and other inevitable impurities, is characterized in that, It 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%; At least one of Ce and La, and Ce + La: 0.003 - 0.3%; Among other inevitable impurity elements, N ≤ 0.005%, S ≤ 0.005%, V ≤ 0.005%, Ti ≤ 0.005%.

2. The high magnetic induction oriented silicon steel according to claim 1, wherein The mass percentages of its chemical elements are: C≤0.005％； Si: 3.0 - 3.8%; Als: 0.010 - 0.035%; Mn: 0.05 - 0.20%; At least one of Ce and La, and Ce + La: 0.003 - 0.3%; 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 high magnetic induction oriented silicon steel according to claim 1 or 2, characterized in that, 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%.

4. The high magnetic induction oriented silicon steel according to claim 1 or 2, characterized in that, Its thickness is 0.13 - 0.20 mm.

5. The high magnetic induction oriented silicon steel according to claim 1 or 2, characterized in that, Its typical iron loss P 17 / 50 ≤0.86 + 2×plate thickness - 16×Si, typical magnetic induction intensity B8 ≥ 2.14 - 6.5×Si, where the plate thickness is taken as the value with the unit parameter of mm, and Si is substituted with the mass percentage content of Si element, P 17 / 50 The unit parameter of is W / kg, and the unit parameter of B8 is T.

6. The manufacturing method of the high magnetic induction oriented silicon steel according to any one of claims 1-5, characterized in that, It includes the steps: (1) Smelting and casting; (2) Slab heating; (3) Hot rolling; (4) First cold rolling (5) Intermediate annealing; (6) Second cold rolling; (7) Decarburizing annealing, nitriding treatment, coating with an isolation agent coating, and the average primary grain size of the obtained decarburized annealed sheet is 6 - 18 μm, and the proportion of Goss grains with a deviation angle less than 15° is greater than 1.5%; (8) High - temperature annealing; (9) Insulating coating and skin pass annealing.

7. The manufacturing method according to claim 6, characterized in that, In step (2), the slab heating temperature ≤ 1250°C.

8. The manufacturing method according to claim 6, characterized in that, In step (4), the first cold rolling uses tandem cold rolling, and its reduction ratio is 50 - 75%.

9. The manufacturing method according to claim 6, characterized in that, In step (5), the intermediate annealing temperature is 900 - 1050°C, and the total oxygen content of the sample after annealing is controlled ≤ 600 ppm, and the C element content ≥ 300 ppm.

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

11. The manufacturing method according to claim 6, characterized in that, Before step (4) and after step (3), there is a hot - rolled sheet annealing step, and the hot - rolled sheet annealing temperature ≤ 1000°C.

12. The manufacturing method according to claim 6, 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 of temperature rise is 30 - 150°C / s.

13. The manufacturing method according to claim 6, 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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