Manufacturing method for non-oriented silicon steel sheet

Abstract

A manufacturing method for a non-oriented silicon steel sheet, comprising the working procedures of slab continuous casting, slab heating, intermediate slab manufacturing, surface treatment, slab assembly, heating, hot rolling, no normalizing, acid pickling, cold rolling, annealing, coating and the like, and further comprising a coiling procedure before or after the cold rolling procedure. In the surface treatment procedure, the intermediate slab enters a tunnel furnace to be subjected to high-temperature reduction heat treatment in a reducing atmosphere of 90％H2+10％H2S, the temperature is maintained at 950-1000℃, and the temperature is maintained for15-30 min; and a single-layer non-oriented silicon steel finished product having a thickness of 0.15-0.30 mm is manufactured without normalizing.

Description

Preparation method of non-oriented silicon steel sheet Technical Field

[0001] The invention belongs to the technical field of steel material preparation, and relates to a method for preparing a non-oriented silicon steel sheet. Background Art

[0002] With the rapid development of new energy vehicles, their drive motors are moving towards high speed, high power density, and high efficiency. As motor speed increases, core loss rises dramatically. Drive motor cores primarily utilize non-oriented silicon steel, which requires excellent magnetic properties, including low iron loss and high magnetic induction intensity. Iron loss is primarily divided into three components: hysteresis loss, eddy current loss, and anomalous loss. Eddy current loss, which accounts for the majority, is proportional to the square of the thickness of the finished non-oriented silicon steel.

[0003] Therefore, how to prepare thinner non-oriented silicon steel products to improve magnetic properties while maintaining the same chemical composition is an important research direction in the field of non-oriented silicon steel.

[0004] The preparation method of non-oriented silicon steel generally includes hot rolling and cold rolling. Since the thinner the hot coil is, the more difficult it is to guarantee the rolling temperature and plate shape, and the greater the rolling load, the thickness of the hot coil is generally above 2.0 mm. However, when the cold rolling reduction is too large, on the one hand, the {111} texture orientation, which is detrimental to the magnetic properties, is enhanced in the final product of the non-oriented silicon steel obtained after annealing, resulting in a decrease in magnetic induction intensity. On the other hand, the cold rolling deformation storage is large, and it is difficult for the grains to grow effectively during the annealing process, resulting in an increase in iron loss. Furthermore, when the hot coil is difficult to thin and the cold rolling reduction cannot be too large, it is difficult to effectively reduce the thickness of the finished product of non-oriented silicon steel using conventional preparation. Accordingly, the extent to which the magnetic properties of the finished non-oriented silicon steel can be improved by thinning the finished product is limited.

[0005] There are also existing technologies that attempt to produce thin-gauge non-oriented silicon steel. For example, patent application CN112538592A proposes a multiple-annealing and multiple-cold-rolling method. While this method can produce thin-gauge products, it requires multiple annealing and cold-rolling cycles, resulting in a long process flow and high production costs. Another example is patent application CN107245644A, which proposes a thin strip continuous casting method. However, due to the short solidification time of the twin-roll thin strip casting slab and the high silicon content of non-oriented silicon steel, which reduces thermal conductivity, this method results in unstable casting and is difficult to produce.

[0006] In summary, there is no feasible solution in the art that is low-cost and has low production difficulty in order to obtain thinner non-oriented silicon steel products and thus improve magnetic properties.

[0007] Summary of the Invention

[0008] The object of the present invention is to provide a method for preparing a non-oriented silicon steel sheet, which can reduce the thickness of the non-oriented silicon steel and improve the magnetic properties, and has low production cost and low production difficulty.

[0009] To achieve the above-mentioned purpose of the invention, one embodiment provides a method for preparing a non-oriented silicon steel sheet. The preparation method comprises the following steps:

[0010] Continuous casting process: a slab continuous casting machine is used to produce continuous casting billets, the thickness of the continuous casting billets is t1 = 200-250 mm, and the chemical composition thereof is, by mass percentage, as follows: C ≤ 0.0025%, S ≤ 0.0015%, Si: 2.50-3.40%, Al: 0.30-1.00%, Mn: 0.20-0.80%, P: 0.02-0.04%, Nb ≤ 0.004%, V ≤ 0.004%, Ti ≤ 0.004%, Ni ≤ 0.03%, Cr ≤ 0.03%, Cu ≤ 0.03%, N ≤ 0.002%, and the rest is Fe and unavoidable inclusions;

[0011] Slab heating process: After leaving the slab continuous casting machine, the continuous casting slab is heated in a heating furnace with a soaking temperature of T1 = T 10 ±10℃, in the furnace for 180~200min, T 10 =1100-30×[Si]-20×[Al], where [Si] and [Al] are 100 times the mass percentage of Si and Al in the continuous casting billet;

[0012] Intermediate billet preparation process: After the continuous casting billet leaves the heating furnace, it undergoes multiple rough rolling passes to form an intermediate billet. The intermediate billet thickness is t2 = t1 / N, where N = 2 to 6;

[0013] Surface treatment process: The intermediate billet enters the tunnel furnace for high-temperature reduction heat treatment in a reducing atmosphere of 90% H2+10% H2S, with a holding temperature of 950-1000°C and a holding time of 15-30 minutes;

[0014] Assembly process: Arrange N intermediate billets into a stacked billet, and weld the four sides of the stacked billet to form an integrated composite billet;

[0015] Heating process: heating the composite blank in a heating furnace at a temperature of 1090-1130°C for 180-200 minutes;

[0016] Hot rolling finishing process: After the composite billet leaves the heating furnace, it is hot rolled to produce a composite hot rolled coil with a thickness of 2.20-2.80 mm. The hot rolling finishing temperature is 820-860°C, and the coiling temperature is 600-640°C.

[0017] Afterwards, the obtained composite hot-rolled coil is sequentially subjected to a pickling process, a cold rolling process, an annealing process and a coating process, as well as a coiling process before or after the cold rolling process, to prepare a single-layer non-oriented silicon steel product with a thickness of 0.15 to 0.30 mm without normalization.

[0018] As a further improvement of this embodiment, the reduction ratio of each rough rolling pass is 20-22%, and the outlet temperature of the last rough rolling pass is T2 = 900 ± 25 °C.

[0019] As a further improvement of this embodiment, the composite billet is a cubic billet with parallel upper and lower surfaces and flat side edges;

[0020] The four sides of the stacked blank are arc welded.

[0021] As a further improvement of this embodiment, in the assembly process, high-temperature resistant insulating coating is applied to the upper and lower surfaces of the intermediate blank by electrostatic spraying, and then N intermediate blanks are arranged into stacked blanks. The high-temperature resistant insulating coating uses MgO high-temperature resistant coating.

[0022] As a further improvement of this embodiment, the coiling process is located before the pickling process, and the composite hot-rolled coil is divided into N single-layer hot-rolled coils by a coiling machine. Thereafter, each single-layer hot-rolled coil is prepared into a single-layer non-oriented silicon steel finished product through a pickling process, a cold rolling process, an annealing process and a coating process in sequence.

[0023] As a further improvement of this embodiment, in the cold rolling process, each single-layer hot-rolled coil is cold rolled on a single-stand cold rolling mill to form a single-layer chilled coil, with a cold rolling reduction rate of 74-87% and a plate thickness of 0.15-0.30 mm.

[0024] As a further improvement of this embodiment, the coiling process is located between the cold rolling process and the annealing process. The composite hot-rolled coil is first subjected to a pickling process and a cold rolling process in sequence to form a composite chilled coil. Thereafter, the composite chilled coil is divided into N single-layer chilled coils by a coiling machine. Each single-layer chilled coil is subjected to an annealing process and a coating process in sequence to prepare a single-layer non-oriented silicon steel finished product.

[0025] As a further improvement of this embodiment, in the cold rolling process, the composite hot-rolled coil is cold rolled on a single-stand cold rolling mill to produce a composite chilled coil, with a cold rolling reduction rate of 73-86%, a thickness of the composite chilled coil of 0.30-0.60 mm, and a plate thickness of the single-layer chilled coil of 0.15-0.30 mm.

[0026] As a further improvement of this embodiment, in the annealing process: the single-layer chilled coil is annealed in a continuous annealing furnace to obtain an annealed steel strip;

[0027] During the annealing process, the heating rate is 30-50℃ / s, the soaking temperature is 980-1020℃, the cooling rate is 10-15℃ / s, the protective atmosphere is 20% H2+80% N2, the dew point is 10-20℃, and the unit tension is 2-3N / mm 2 .

[0028] As a further improvement of this embodiment, in the coating process: an insulating coating with a thickness of 0.5 to 0.8 μm is applied to each surface of the annealed steel strip.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) Compared to the existing conventional technology of directly hot-rolling an intermediate billet into a hot-rolled coil, the present invention combines N intermediate billets into an integrated composite billet, and hot-rolls the composite billet in a hot rolling finish rolling process to obtain a composite hot-rolled coil having N single-layer hot-rolled coils. When the thickness of the composite hot-rolled coil is consistent with the thickness of the hot-rolled coil in the existing conventional technology (for example, the thickness is also 2.20 mm), not only can the hot rolling temperature and plate shape, low load and low rolling difficulty be guaranteed (that is, there is no need to excessively hot-roll in pursuit of ultra-thinness, which causes a significant increase in rolling difficulty, deterioration of plate shape, and even deterioration of microstructure), but the thickness of the single-layer hot-rolled coil rolled from each intermediate billet is much smaller than that of the hot-rolled coil in the existing conventional technology. Therefore, when the cold rolling reduction in the subsequent cold rolling process is lower than that of the existing conventional technology, a single-layer chilled coil thinner than that of the existing conventional technology is obtained;

[0031] 2) Based on the above point 1, not only can the magnetic properties of non-oriented silicon steel be improved due to thinner thickness (for example, thinner thickness means lower iron loss); but also the cold rolling reduction is lower, thereby ensuring that the {111} texture that is detrimental to magnetic properties is weakened, while the {100} texture and {110} texture that are beneficial to magnetization are enhanced, thereby avoiding the reduction of magnetic induction intensity due to cold rolling, that is, the magnetic induction intensity can be improved compared with the existing conventional technology; furthermore, the cold rolling reduction is lower, so that the cold rolling deformation storage is reduced, and the grains are easy to grow during annealing, thereby reducing the iron loss compared with the existing conventional technology;

[0032] 3) In addition, the present invention can further improve the microstructure, surface quality and plate shape of the non-oriented silicon steel product by precisely controlling the temperature and time in the slab heating process, as well as the temperature in the heating process and the hot rolling and finishing process, and improve the performance of the non-oriented silicon steel product, especially the magnetic properties;

[0033] 4) Furthermore, the intermediate billet is maintained at a high temperature (for example, a holding temperature of 950-1000°C) during the surface treatment process without the intermediate billet being lowered to room temperature. On the one hand, the generation of surface cracks is avoided, and the surface quality of the non-oriented silicon steel product is further improved. On the other hand, the microstructure of the intermediate billet can be improved at high temperature, which is conducive to further improving the magnetic properties of the final non-oriented silicon steel. Even the normalizing process can be omitted to obtain excellent magnetic properties. As a result, the overall process flow is simple. Compared with the existing conventional technology, there is no additional high-cost and high-difficulty additional process. Compared with the existing conventional technology, the difficulty of hot rolling and cold rolling can be greatly reduced. Overall, it has the advantages of low production cost, low production difficulty, and stronger quality stability, which is conducive to industrial implementation and has huge economic benefits. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further introduced below in conjunction with specific implementation methods.

[0035] The present invention provides a method for producing non-oriented silicon steel sheets. The method includes the following steps: continuous slab casting, slab heating, intermediate slab preparation, surface treatment, assembling, heating, hot rolling, normalization or non-normalization, pickling, cold rolling, annealing, and coating. The method also includes a coiling step before or after the cold rolling step, thereby producing a finished non-oriented silicon steel product.

[0036] Next, various embodiments based on the basic inventive concept of the present invention are described in detail.

[0037] <First embodiment>

[0038] This embodiment provides a method for preparing a non-oriented silicon steel sheet.

[0039] In this embodiment, the production method includes the following sequential steps: slab continuous casting, slab heating, intermediate billet preparation, surface treatment, assembly, heating, hot rolling, normalizing, pickling, cold rolling, coiling, annealing, and coating, thereby producing a non-oriented silicon steel product. These steps are described below.

[0040] Slab continuous casting process

[0041] Molten steel is cast into continuous casting slabs through a slab continuous casting machine. The thickness of the continuous casting slabs is 200-250 mm, preferably 220 mm. Compared to the thin strip continuous casting method mentioned in the background art, the continuous casting process of the present invention is less difficult to produce, has more stable casting, and can easily ensure the quality of the continuous casting slabs.

[0042] The chemical composition of the continuous casting billet meets the chemical composition of non-oriented silicon steel, and can be specifically implemented with the chemical composition of the currently known non-oriented silicon steel.

[0043] In a preferred embodiment, the chemical composition of the continuous casting billet is as follows, by mass percentage: C≤0.0025%, S≤0.0015%, Si: 2.50-3.40%, Al: 0.30-1.00%, Mn: 0.20-0.80%, P: 0.02-0.04%, Nb≤0.004%, V≤0.004%, Ti≤0.004%, Ni≤0.03%, Cr≤0.03%, Cu≤0.03%, N≤0.002%, and the remainder is Fe and unavoidable inclusions. Based on this chemical composition, high-grade non-oriented silicon steel can be produced. On the one hand, compared with the chemical composition of the existing known non-oriented silicon steel, this chemical composition can greatly improve the magnetic properties of the final non-oriented silicon steel product. On the other hand, the higher the Si content in the thin strip continuous casting method mentioned in the background art, the worse the casting stability. However, in the present invention, under the principle of the basic invention, a continuous casting process can be used to ensure the production of high-grade non-oriented silicon steel products.

[0044]

Slab heating process

[0045] After leaving the slab continuous casting machine, the continuous casting billet is heated in a heating furnace with a soaking temperature of T1 = T 10 ±10℃, the furnace time is 180~200min. 10 =1100 - 30 × [Si] - 20 × [Al], where [Si] and [Al] are 100 times the mass percentages of Si and Al in the continuous casting ingot. For example, if the mass percentage of Si in the continuous casting ingot is 2.5%, the value of [Si] in the formula is 2.5. By adopting this soaking temperature, the surface quality of the continuous casting ingot and the excellent microstructure obtained in the subsequent intermediate billet preparation can be guaranteed, thereby improving the performance of the final non-oriented silicon steel product.

[0046] Preferably, the continuous casting strands are directly heated in a heating furnace after leaving the slab continuous casting machine, that is, the continuous casting strands are heated with temperature.

[0047]

Intermediate billet preparation process

[0048] After leaving the heating furnace, the continuous casting slab undergoes multiple rough rolling passes to form an intermediate slab, the thickness of which is t2 = t1 / N.

[0049] In a further preferred embodiment, the reduction ratio of each rough rolling pass is 20-22%, and the outlet temperature of the final rough rolling pass is T2 = 900 ± 25°C. Such temperature and reduction ratio control, combined with the previous soaking temperature control, can further improve the intermediate bar preparation effect and ensure the surface quality and microstructure of the intermediate bar.

[0050] Furthermore, in the intermediate bar preparation step, it is preferred to perform three passes of rough rolling to produce the intermediate bar.

[0051]

Surface treatment process

[0052] After the intermediate blank is cooled to room temperature, the oxide scale on the surface of the intermediate blank is mechanically polished and cleaned. After cleaning, the surface roughness of the intermediate blank is Ra=0.8~1.2μm.

[0053]

Assembly process

[0054] N intermediate blanks are arranged into a stacked blank, and four sides of the stacked blank are welded to form an integrated composite blank.

[0055] Here, N is an integer from 2 to 6, meaning that the laminated billet is formed by stacking 2 to 6 intermediate billets. It is understood that the N intermediate billets in this process are all produced through the preceding continuous casting, slab heating, intermediate billet preparation, and surface treatment. Furthermore, the chemical composition of the N intermediate billets can be the same or different.

[0056] Preferably, the four sides of the stacked blank are arc welded. Of course, the present application is not limited thereto, and other welding techniques known in the art may also be used.

[0057] Furthermore, the composite billet is a cubic billet with parallel upper and lower surfaces and flat sides. Specifically, in one embodiment, N intermediate billets of uniform length and width are stacked together and welded to their seams, resulting in a naturally cubic composite billet. In another embodiment, N intermediate billets of varying lengths and / or widths are stacked together and welded to the differing sides using sealing strips or solder to form a cubic composite billet. These are, of course, just some examples, and the present application is not limited thereto.

[0058] Preferably, a high-temperature resistant insulating coating is first applied to the upper and lower surfaces of the intermediate blanks by electrostatic spraying, and then N intermediate blanks are arranged into a stack. Of course, at least in the stack, the upper and lower adjacent intermediate blanks are separated by the high-temperature resistant insulating coating. Specifically, the high-temperature resistant insulating coating can be applied to at least one of the surfaces of the upper and lower adjacent intermediate blanks that are to come into contact, and then the two intermediate blanks are stacked.

[0059] Here, the "surface to be contacted" refers to the surface of an intermediate blank that faces and abuts against another intermediate blank in a stack of intermediate blanks. For example, if intermediate blank A is stacked adjacent to intermediate blank B, and the lower surface P1 of intermediate blank A is in contact with / abuts against the upper surface P2 of intermediate blank B, then lower surface P1 constitutes the surface to be contacted of intermediate blank A, and upper surface P2 constitutes the surface to be contacted of intermediate blank B.

[0060] When applying the high-temperature resistant insulating coating, the high-temperature resistant insulating coating can be applied only to the lower surface P1 of the intermediate blank A, or only to the upper surface P2 of the intermediate blank B, or both the lower surface P1 of the intermediate blank A and the upper surface P2 of the intermediate blank B can be coated with the high-temperature resistant insulating coating. In these three methods, the upper and lower adjacent intermediate blanks A and B in the stacked blanks can be separated by the high-temperature resistant insulating coating.

[0061] Preferably, the applied high temperature resistant insulating coating is MgO high temperature resistant coating.

[0062]

Heating process

[0063] The composite blank is heated in a heating furnace at a temperature of 1090 to 1130° C. for 180 to 200 minutes.

[0064]

Hot rolling and finishing process

[0065] After the composite billet is taken out of the heating furnace, it is hot rolled to form a composite hot-rolled plate with a thickness of 2.20 to 2.80 mm, and then the composite hot-rolled plate is coiled into a composite hot-rolled coil. In this way, the present invention hot-rolls the composite billet, and the prepared composite hot-rolled plate only needs to meet the thickness of 2.20 to 2.80 mm, which can ensure that a non-oriented silicon steel product with a thickness similar to or thinner than that of the existing conventional technology is obtained under a small cold rolling reduction. In this way, not only can the magnetic properties of the non-oriented silicon steel be improved based on the thinner thickness (for example, the thinner thickness means lower iron loss), but also based on the lower cold rolling reduction, the magnetic induction intensity can be improved and the iron loss can be reduced. It can also avoid the difficulty of hot rolling, the hot rolling temperature and plate shape, and the low load and low rolling difficulty (that is, there is no need to carry out excessive hot rolling in pursuit of ultra-thinness, which causes a significant increase in rolling difficulty, deterioration of plate shape, and even deterioration of microstructure).

[0066] In addition, when hot rolling is carried out in the form of a composite billet, the contact surfaces of the upper and lower adjacent intermediate billets are not exposed to the external environment, so it is not easy to generate surface oxide scale, which can improve the surface quality of the final non-oriented silicon steel product and reduce the steel loss rate.

[0067] The hot rolling finishing temperature is 820-860°C, and the coiling temperature is 600-640°C. This can further improve the microstructure, surface quality and plate shape of the non-oriented silicon steel products, and improve the performance of the non-oriented silicon steel products, especially the magnetic properties.

[0068]

Normalization process

[0069] The composite hot rolled coil is subjected to normalizing heat treatment in a continuous normalizing furnace, and the normalizing temperature is T3 = T 30 ±10℃, T 30=980-20×[Si]-10×[Al].

[0070] As mentioned above, [Si] and [Al] are 100 times the mass percentage of Si and Al in the continuous casting billet.

[0071] In this embodiment, the control of the normalizing temperature can further improve the microstructure, surface quality and plate shape of the non-oriented silicon steel product, and improve the performance of the non-oriented silicon steel product, especially the magnetic properties.

[0072]

Pickling process

[0073] After leaving the continuous normalizing furnace, the composite hot-rolled coil undergoes shot blasting and pickling to remove surface oxide scale. Thus, in this embodiment, the pickling is performed on the composite hot-rolled coil (i.e., before it is split into coils at the time of pickling). This reduces the surface area requiring pickling and reduces the potential for environmental pollution caused by pickling.

[0074]

Cold rolling process

[0075] The composite hot-rolled coil after pickling is cold-rolled on a single-stand cold rolling mill to produce a composite chilled coil.

[0076] Among them, the single-stand cold rolling mill preferably adopts a twenty-high single-stand cold rolling mill.

[0077] Thus, combined with the above description, it can be seen that the present application only requires one cold rolling, and the cold rolling reduction is low, so as to obtain a non-oriented silicon steel product with a thickness comparable to or even thinner than that of the existing conventional technology; from another perspective, even if a smaller cold rolling reduction than that of the existing conventional technology is used, a non-oriented silicon steel product thinner than that of the existing conventional technology can be obtained.

[0078] For example, in one embodiment, the cold rolling reduction ratio is 73 to 86%, and the thickness of the composite chilled coil is 0.30 to 0.60 mm.

[0079]

Volume separation process

[0080] The composite chilled coil obtained in the cold rolling process is divided into N single-layer chilled coils by a coil splitter. The N single-layer chilled coils correspond to the N intermediate billets, that is, each intermediate billet is converted into a corresponding single-layer chilled coil.

[0081] In one embodiment, the thickness of N intermediate billets is the same, and correspondingly, the thickness of N single-layer chilled coils is the same. The thickness of each single-layer chilled coil is one-Nth of the thickness of the composite chilled coil. For example, N is 2, and the coiling process obtains two single-layer chilled coils and the thickness of each single-layer chilled coil is half the thickness of the composite chilled coil (for example, the thickness of the composite chilled coil mentioned above is 0.30-0.60 mm, and correspondingly, the thickness of the single-layer chilled coil is 0.15-0.30 mm).

[0082]

Annealing process

[0083] The single-layer chilled coil is annealed in a continuous annealing furnace to obtain annealed strip steel.

[0084] During the annealing process, the heating rate is 30-50℃ / s, the soaking temperature is 980-1020℃, the cooling rate is 10-15℃ / s, the protective atmosphere is 20% H2+80% N2, the dew point is 10-20℃, and the unit tension is 2-3N / mm 2 .

[0085]

Coating process

[0086] An insulating coating with a thickness of 0.5 to 0.8 μm is coated on each surface of the annealed steel strip, thereby obtaining a finished non-oriented silicon steel product.

[0087] It can be understood that the actual thickness of the resulting non-oriented silicon steel product is the sum of the thickness of the corresponding single-layer chilled coil and the thickness of the upper surface insulation coating and the thickness of the lower surface insulation coating of the corresponding annealed steel strip. For example, if the thickness of a single-layer chilled coil is 0.15 mm, and the thickness of the upper surface insulation coating and the thickness of the lower surface insulation coating of the corresponding annealed steel strip are both 0.5 μm, then the actual thickness of the corresponding non-oriented silicon steel product is 0.15 mm + 0.5 μm + 0.5 μm = 0.1510 mm. However, since the thickness of the coating is very small relative to the thickness of the single-layer chilled coil, the thickness of the non-oriented silicon steel product is basically the same as the thickness of the single-layer chilled coil. Therefore, in this application, the thickness of the non-oriented silicon steel product is taken as the thickness of the single-layer chilled coil.

[0088] The above describes the preparation method of this embodiment in detail. Next, this embodiment also provides a non-oriented silicon steel sheet produced using the preparation method. Even when using the same chemical composition and thickness as conventional technology, the magnetic properties of the sheet are significantly improved compared to conventional technology, and the production difficulty and cost are reduced.

[0089] The thickness of the non-oriented silicon steel sheet is 0.15-0.30 mm, and the iron loss P 1.5 / 50 ≤2.40W / kg, P 1.0 / 400 ≤16.0W / kg, magnetic induction intensity B 5000 ≥1.65T.

[0090] In terms of chemical composition, the non-oriented silicon steel sheet has the following chemical composition by mass percentage: C ≤ 0.0025%, S ≤ 0.0015%, Si: 2.50-3.40%, Al: 0.30-1.00%, Mn: 0.20-0.80%, P: 0.02-0.04%, Nb ≤ 0.004%, V ≤ 0.004%, Ti ≤ 0.004%, Ni ≤ 0.03%, Cr ≤ 0.03%, Cu ≤ 0.03%, N ≤ 0.002%, and the remainder is Fe and unavoidable inclusions. Based on this chemical composition, the non-oriented silicon steel sheet is a high-grade non-oriented silicon steel with excellent magnetic properties.

[0091] It can be understood that the chemical composition of the non-oriented silicon steel sheet is the same as the chemical composition of the continuous casting billet prepared by the preparation method.

[0092] The following provides three specific examples based on this embodiment. Specifically, the implementation process of these examples is as follows:

[0093] (1) Casting molten steel into continuous casting billets with a thickness of 220 mm through a slab continuous casting machine;

[0094] (2) After leaving the slab continuous caster, the continuous casting slab is heated in a heating furnace. The soaking temperature and the time in the furnace are shown in Table 1.

[0095] (3) After leaving the heating furnace, the continuous casting slab is subjected to multiple rough rolling passes to produce an intermediate slab with a thickness of 110 mm. The reduction ratio of each rough rolling pass is 20-22%. The outlet temperature of the last rough rolling pass is shown in Table 1.

[0096] (4) After the intermediate blank is cooled to room temperature, the oxide scale on the surface of the intermediate blank is mechanically polished and cleaned. After cleaning, the surface roughness of the intermediate blank is Ra = 0.8 to 1.2 μm; then, the surface of the intermediate blank is coated with MgO high-temperature resistant insulating coating, and then two intermediate blanks are arranged into a stacked blank. After that, the four sides of the stacked blank are welded to form an integrated composite blank;

[0097] (5) heating the composite blank in a heating furnace, the heating temperature and heating time are shown in Table 1;

[0098] [Table 1]

[0099] (6) After the composite billet leaves the heating furnace, it is hot rolled to form a composite hot-rolled plate, which is then coiled into a composite hot-rolled coil. The thickness H1, final rolling temperature, and coiling temperature of the composite hot-rolled plate are shown in Table 2.

[0100] (7) The composite hot-rolled coil is subjected to normalizing heat treatment in a continuous normalizing furnace, and the normalizing temperature is shown in Table 2; after the composite hot-rolled coil leaves the continuous normalizing furnace, it is subjected to shot blasting and pickling to remove the surface oxide scale;

[0101] (8) After pickling, the composite hot-rolled coil is cold-rolled on a single-stand cold rolling mill to produce a composite chilled coil. The thickness H2 of the composite chilled coil is shown in Table 2.

[0102] (9) The composite chilled coil obtained in the cold rolling process is divided into two single-layer chilled coils by a coil splitter;

[0103] (10) The single-layer chilled coil is annealed in a continuous annealing furnace to obtain an annealed strip. During the annealing process, the heating rate and the soaking temperature are shown in Table 2, the cooling rate is 10°C / s, the protective atmosphere is 20% H2+80% N2, the dew point is 15°C, and the unit tension is shown in Table 2.

[0104] [Table 2]

[0105] (11) coating each surface of the annealed steel strip with an insulating coating having a thickness of 0.8 μm, thereby obtaining a finished non-oriented silicon steel product;

[0106] The chemical composition of one of the non-oriented silicon steel products obtained in each embodiment is shown in Table 3. In addition to the elements shown in Table 3, the remaining chemical components are Fe and unavoidable inclusions. Furthermore, the thickness, iron loss and magnetic induction intensity of the non-oriented silicon steel product are shown in Table 4.

[0107] [Table 3]

[0108] [Table 4]

[0109] <Second embodiment>

[0110] This embodiment provides a method for preparing a non-oriented silicon steel sheet.

[0111] In this embodiment, the preparation method includes the following steps: continuous casting, slab heating, intermediate slab preparation, surface treatment, assembling, heating, hot rolling, pickling, cold rolling, coiling, annealing and coating, thereby preparing a non-oriented silicon steel product.

[0112] This embodiment differs from the first embodiment described above in that the surface treatment step is omitted and the normalization step is omitted. Furthermore, the continuous casting step, slab heating step, intermediate billet preparation step, assembly step, heating step, hot rolling and finishing step, pickling step, cold rolling step, coiling step, annealing step, and coating step of this embodiment are identical to those of the first embodiment described above. The differences between this embodiment and the first embodiment are described below.

[0113]

Surface treatment process

[0114] In this embodiment, the intermediate billet obtained in the intermediate billet preparation process enters a tunnel furnace and undergoes high-temperature reduction heat treatment in a reducing atmosphere of 90% H2+10% H2S, with a holding temperature of 950-1000°C and a holding time of 15-30 minutes. In this way, the surface treatment process of this embodiment can not only achieve the treatment of surface oxide scale, thereby facilitating the surface quality of the subsequently obtained non-oriented silicon steel product; moreover, compared with the mechanical polishing method adopted in the surface treatment process in the first embodiment, the intermediate billet of this embodiment maintains a high temperature (for example, a holding temperature of 950-1000°C) during the surface treatment process without the intermediate billet being lowered to room temperature. On the one hand, the generation of surface cracks is avoided, thereby further improving the surface quality of the non-oriented silicon steel product. On the other hand, the microstructure of the intermediate billet can be improved at high temperature, thereby further improving the magnetic properties of the final non-oriented silicon steel, and even the normalizing process can be omitted to obtain excellent magnetic properties, thereby shortening the process flow and reducing production costs. On the other hand, the use of a reducing atmosphere of 90% H2+10% H2S to treat the surface oxide scale can improve the yield rate and further reduce production costs.

[0115] It is to be supplemented here that the normalizing step is omitted in this embodiment. Accordingly, in the pickling step, the composite hot-rolled coil obtained in the hot-rolling and finishing rolling step is directly subjected to shot blasting and pickling to remove surface oxide scale.

[0116] Furthermore, the non-oriented silicon steel sheet provided in this embodiment is produced using the above-described production method. Even with the same chemical composition and thickness as conventional technology, its magnetic properties are greatly improved, and its production difficulty and cost are low.

[0117] The thickness of the non-oriented silicon steel sheet is 0.15-0.30 mm, and the iron loss P 1.5 / 50 ≤2.35W / kg, P 1.0 / 400 ≤14.5W / kg, magnetic induction intensity B 5000 ≥1.66T.

[0118] In terms of chemical composition, the non-oriented silicon steel sheet has the following chemical composition by mass percentage: C ≤ 0.0025%, S ≤ 0.0015%, Si: 2.50-3.40%, Al: 0.30-1.00%, Mn: 0.20-0.80%, P: 0.02-0.04%, Nb ≤ 0.004%, V ≤ 0.004%, Ti ≤ 0.004%, Ni ≤ 0.03%, Cr ≤ 0.03%, Cu ≤ 0.03%, N ≤ 0.002%, and the remainder is Fe and unavoidable inclusions. Based on this chemical composition, the non-oriented silicon steel sheet is a high-grade non-oriented silicon steel with excellent magnetic properties.

[0119] The following provides three specific examples based on this embodiment. Specifically, the implementation process of these examples is as follows:

[0120] (1) Casting molten steel into continuous casting billets with a thickness of 200 mm through a slab continuous casting machine;

[0121] (2) After leaving the slab continuous caster, the continuous casting slab is heated in a heating furnace. The soaking temperature and the time in the furnace are shown in Table 5.

[0122] (3) After leaving the heating furnace, the continuous casting slab is subjected to multiple rough rolling passes to produce an intermediate slab with a thickness of 100 mm. The reduction ratio of each rough rolling pass is 20-22%. The outlet temperature of the last rough rolling pass is shown in Table 5.

[0123] (4) The intermediate billet enters a tunnel furnace and undergoes high-temperature reduction heat treatment in a reducing atmosphere of 90% H2+10% H2S. The holding temperature and holding time are shown in Table 5. Then, the surface of the intermediate billet is coated with MgO high-temperature resistant insulating coating. Two intermediate billets are then arranged into a stacked billet, and the four sides of the stacked billet are welded to form an integrated composite billet.

[0124] (5) The composite blank is heated in a heating furnace. The heating temperature and heating time are shown in Table 5.

[0125] [Table 5]

[0126] (6) After the composite billet leaves the heating furnace, it is hot rolled to produce a composite hot-rolled plate, which is then coiled into a composite hot-rolled coil. The thickness H1, final rolling temperature, and coiling temperature of the composite hot-rolled plate are shown in Table 6.

[0127] (7) The composite hot-rolled coil is directly shot blasted and pickled without normalization to remove the surface oxide scale;

[0128] (8) After pickling, the composite hot-rolled coil is cold-rolled on a single-stand cold rolling mill to produce a composite chilled coil. The thickness H2 of the composite chilled coil is shown in Table 6.

[0129] (9) The composite chilled coil obtained in the cold rolling process is divided into two single-layer chilled coils by a coil splitter;

[0130] (10) The single-layer chilled coil is annealed in a continuous annealing furnace to obtain an annealed strip. During the annealing process, the heating rate and the soaking temperature are shown in Table 6. The cooling rate is 10°C / s. The protective atmosphere is 20% H2+80% N2 with a dew point of 15°C. The unit tension is shown in Table 6.

[0131] [Table 6]

[0132] (11) coating each surface of the annealed steel strip with an insulating coating having a thickness of 0.8 μm, thereby obtaining a finished non-oriented silicon steel product;

[0133] The chemical composition of one of the non-oriented silicon steel products obtained in each embodiment is shown in Table 7. In addition to the elements shown in Table 7, the remaining chemical components are Fe and unavoidable inclusions. Furthermore, the thickness, iron loss and magnetic induction intensity of the non-oriented silicon steel product are shown in Table 8.

[0134] [Table 7]

[0135] [Table 8]

[0136] <Third embodiment>

[0137] This embodiment provides a method for preparing a non-oriented silicon steel sheet.

[0138] In this embodiment, the production method includes the following sequential steps: continuous casting, slab heating, intermediate billet preparation, surface treatment, assembly, heating, hot rolling, coiling, normalizing, pickling, cold rolling, annealing, and coating, thereby producing a non-oriented silicon steel product. These steps are described below.

[0139] First, the slab continuous casting process, slab heating process, intermediate billet preparation process, surface treatment process, slab assembly process, heating process, and hot finishing rolling process of this embodiment are the same as those of the first embodiment, and will not be described in detail. Next, the remaining processes of this embodiment will be described.

[0140]

Volume separation process

[0141] The composite hot-rolled coil obtained in the hot-rolling and finishing process is divided into N single-layer hot-rolled coils by a coil splitter. The N single-layer hot-rolled coils correspond to the N intermediate billets, that is, each intermediate billet is converted into a corresponding single-layer hot-rolled coil.

[0142] In one embodiment, the thickness of N intermediate billets is the same, and accordingly, the thickness of N single-layer hot-rolled coils is the same. The thickness of each single-layer hot-rolled coil is one-Nth of the thickness of the composite hot-rolled coil. For example, N is 2. The coil splitting process obtains two single-layer hot-rolled coils, and the thickness of each single-layer hot-rolled coil is half the thickness of the composite hot-rolled coil (for example, the thickness of the composite hot-rolled coil mentioned above is 2.20-2.80 mm, and correspondingly, the thickness of the single-layer hot-rolled coil is 1.10-1.40 mm).

[0143]

Normalization process

[0144] The single-layer hot-rolled coil is subjected to normalizing heat treatment in a continuous normalizing furnace, and the normalizing temperature is T3 = T 30 ±10℃, T 30 =980-20×[Si]-10×[Al].

[0145] As mentioned above, [Si] and [Al] are 100 times the mass percentage of Si and Al in the continuous casting billet.

[0146] In this embodiment, the control of the normalizing temperature can further improve the microstructure, surface quality and plate shape of the non-oriented silicon steel product, and improve the performance of the non-oriented silicon steel product, especially the magnetic properties.

[0147]

Pickling process

[0148] After leaving the continuous normalizing furnace, the single-layer hot-rolled coil is shot blasted and pickled to remove the surface oxide scale.

[0149]

Cold rolling process

[0150] The single-layer hot-rolled coil after pickling is cold-rolled on a single-stand cold rolling mill to produce a single-layer chilled coil.

[0151] Among them, the single-stand cold rolling mill preferably adopts a twenty-high single-stand cold rolling mill.

[0152] Thus, combined with the above description, it can be seen that the present application only requires one cold rolling, and the cold rolling reduction is low, so as to obtain a non-oriented silicon steel product with a thickness comparable to or even thinner than that of the existing conventional technology; from another perspective, even if a smaller cold rolling reduction than that of the existing conventional technology is used, a non-oriented silicon steel product thinner than that of the existing conventional technology can be obtained.

[0153] For example, in one embodiment, the cold rolling reduction ratio is 74 to 87%, and the thickness of the single-layer chilled coil is 0.15 to 0.30 mm.

[0154]

Annealing process

[0155] The single-layer chilled coil is annealed in a continuous annealing furnace to obtain annealed strip steel.

[0156] During the annealing process, the heating rate is 30-50℃ / s, the soaking temperature is 980-1020℃, the cooling rate is 10-15℃ / s, the protective atmosphere is 20% H2+80% N2, the dew point is 10-20℃, and the unit tension is 2-3N / mm 2 .

[0157]

Coating process

[0158] An insulating coating with a thickness of 0.5 to 0.8 μm is coated on each surface of the annealed steel strip, thereby obtaining a finished non-oriented silicon steel product.

[0159] It can be understood that the actual thickness of the resulting non-oriented silicon steel product is the sum of the thickness of the corresponding single-layer chilled coil and the thickness of the upper surface insulation coating and the thickness of the lower surface insulation coating of the corresponding annealed steel strip. For example, if the thickness of a single-layer chilled coil is 0.15 mm, and the thickness of the upper surface insulation coating and the thickness of the lower surface insulation coating of the corresponding annealed steel strip are both 0.5 μm, then the actual thickness of the corresponding non-oriented silicon steel product is 0.15 mm + 0.5 μm + 0.5 μm = 0.1510 mm. However, since the thickness of the coating is very small relative to the thickness of the single-layer chilled coil, the thickness of the non-oriented silicon steel product is basically the same as the thickness of the single-layer chilled coil. Therefore, in this application, the thickness of the non-oriented silicon steel product is taken as the thickness of the single-layer chilled coil.

[0160] The above describes the preparation method of this embodiment in detail. Next, this embodiment also provides a non-oriented silicon steel sheet produced using the preparation method. Even when using the same chemical composition and thickness as conventional technology, the magnetic properties of the sheet are significantly improved compared to conventional technology, and the production difficulty and cost are reduced.

[0161] The thickness of the non-oriented silicon steel sheet is 0.15-0.30 mm, and the iron loss P 1.5 / 50 ≤2.50W / kg, P 1.0 / 400 ≤16.0W / kg, magnetic induction intensity B 5000 ≥1.65T.

[0162] In terms of chemical composition, the non-oriented silicon steel sheet has the following chemical composition by mass percentage: C ≤ 0.0025%, S ≤ 0.0015%, Si: 2.50-3.40%, Al: 0.30-1.00%, Mn: 0.20-0.80%, P: 0.02-0.04%, Nb ≤ 0.004%, V ≤ 0.004%, Ti ≤ 0.004%, Ni ≤ 0.03%, Cr ≤ 0.03%, Cu ≤ 0.03%, N ≤ 0.002%, and the remainder is Fe and unavoidable inclusions. Based on this chemical composition, the non-oriented silicon steel sheet is a high-grade non-oriented silicon steel with excellent magnetic properties.

[0163] It can be understood that the chemical composition of the non-oriented silicon steel sheet is the same as the chemical composition of the continuous casting billet prepared by the preparation method.

[0164] The following provides three specific examples based on this embodiment. Specifically, the implementation process of these examples is as follows:

[0165] (1) Casting molten steel into continuous casting billets with a thickness of 220 mm through a slab continuous casting machine;

[0166] (2) After leaving the slab continuous caster, the continuous casting slab is heated in a heating furnace. The soaking temperature and the time in the furnace are shown in Table 9.

[0167] (3) After leaving the heating furnace, the continuous casting slab is subjected to multiple rough rolling passes to produce an intermediate slab with a thickness of 110 mm. The reduction ratio of each rough rolling pass is 20-22%. The outlet temperature of the last rough rolling pass is shown in Table 9.

[0168] (4) After the intermediate billet is cooled to room temperature, the surface oxide scale of the intermediate billet is mechanically polished and cleaned. After cleaning, the surface roughness of the casting billet is Ra = 0.8-1.2 μm. Then, the surface of the intermediate billet is coated with MgO high-temperature resistant insulating coating. Then, two intermediate billets are arranged into a stacked billet, and the four sides of the stacked billet are welded to form an integrated composite billet.

[0169] (5) The composite blank is heated in a heating furnace. The heating temperature and heating time are shown in Table 9.

[0170] [Table 9]

[0171] (6) After the composite billet leaves the heating furnace, it is hot rolled to produce a composite hot-rolled plate, which is then coiled into a composite hot-rolled coil. The thickness H1, final rolling temperature, and coiling temperature of the composite hot-rolled plate are shown in Table 10.

[0172] (7) The composite hot-rolled coil obtained in the hot-rolling finishing process is divided into two single-layer hot-rolled coils by a coil splitter;

[0173] (8) The single-layer hot-rolled coil is subjected to normalizing heat treatment in a continuous normalizing furnace. The normalizing temperature is shown in Table 10. After leaving the continuous normalizing furnace, the single-layer hot-rolled coil is subjected to shot blasting and pickling to remove the surface oxide scale.

[0174] (9) After pickling, the single-layer hot-rolled coil is cold-rolled on a single-stand cold rolling mill to produce a single-layer chilled coil. The thickness H3 of the single-layer chilled coil is shown in Table 10.

[0175] (10) The single-layer chilled coil is annealed in a continuous annealing furnace to obtain an annealed strip. During the annealing process, the heating rate and the soaking temperature are shown in Table 10, the cooling rate is 10°C / s, the protective atmosphere is 20% H2+80% N2, the dew point is 15°C, and the unit tension is shown in Table 10.

[0176] [Table 10]

[0177] (11) Applying an insulating coating as shown in Table 12 to each surface of the annealed steel strip, thereby obtaining a finished non-oriented silicon steel product;

[0178] The chemical composition of one of the non-oriented silicon steel products obtained in each embodiment is shown in Table 11. In addition to the elements shown in Table 11, the remaining chemical components are Fe and unavoidable inclusions. Furthermore, the thickness, iron loss, and magnetic induction intensity of the non-oriented silicon steel product are shown in Table 12.

[0179] [Table 11]

[0180] [Table 12]

[0181] <Fourth embodiment>

[0182] This embodiment provides a method for preparing a non-oriented silicon steel sheet.

[0183] In this embodiment, the preparation method includes the following steps: continuous casting, slab heating, intermediate slab preparation, surface treatment, assembling, heating, hot rolling, coiling, pickling, cold rolling, annealing and coating, thereby preparing a non-oriented silicon steel product.

[0184] This embodiment differs from the third embodiment described above in that the surface treatment step is omitted and the normalization step is omitted. Furthermore, the slab continuous casting step, slab heating step, intermediate billet preparation step, assembly step, heating step, hot rolling and finishing step, pickling step, cold rolling step, coiling step, annealing step, and coating step of this embodiment are identical to those of the third embodiment described above. The differences between this embodiment and the third embodiment are described below.

[0185]

Intermediate billet surface treatment process

[0186] In this embodiment, the intermediate billet obtained in the intermediate billet preparation process enters a tunnel furnace and undergoes a high-temperature reduction heat treatment in a reducing atmosphere of 90% H2+10% H2S, with a holding temperature of 950-1000°C and a holding time of 15-30 minutes. Thus, the surface treatment process of this embodiment not only treats the surface oxide scale, thereby improving the surface quality of the subsequent non-oriented silicon steel product; moreover, compared to the mechanical polishing method used in the surface treatment process of the third embodiment, the intermediate billet of this embodiment maintains a high temperature (e.g., a holding temperature of 950-1000°C) during the surface treatment process without cooling the intermediate billet to room temperature. This, on the one hand, avoids the generation of surface cracks and further improves the surface quality of the non-oriented silicon steel product. On the other hand, the high temperature can improve the microstructure of the intermediate billet, which is conducive to further improving the magnetic properties of the final non-oriented silicon steel. It can even be possible to obtain excellent magnetic properties without the normalization process, thereby shortening the process flow and reducing production costs. Furthermore, the use of a hydrogen atmosphere to treat the surface oxide scale can improve the yield rate and further reduce production costs.

[0187] It is to be supplemented here that the normalizing step is omitted in this embodiment. Accordingly, in the pickling step, the single-layer hot-rolled coil obtained in the coiling step is directly subjected to shot blasting and pickling to remove the surface oxide scale.

[0188] Furthermore, the non-oriented silicon steel sheet provided in this embodiment is produced using the above-described production method. Even with the same chemical composition and thickness as conventional technology, its magnetic properties are greatly improved, and its production difficulty and cost are low.

[0189] The thickness of the non-oriented silicon steel sheet is 0.15-0.30 mm, and the iron loss P 1.5 / 50 ≤2.30W / kg, P 1.0 / 400 ≤13.0W / kg, magnetic induction intensity B 5000 ≥1.64T.

[0190] In terms of chemical composition, the non-oriented silicon steel sheet has the following chemical composition by mass percentage: C ≤ 0.0025%, S ≤ 0.0015%, Si: 2.50-3.40%, Al: 0.30-1.00%, Mn: 0.20-0.80%, P: 0.02-0.04%, Nb ≤ 0.004%, V ≤ 0.004%, Ti ≤ 0.004%, Ni ≤ 0.03%, Cr ≤ 0.03%, Cu ≤ 0.03%, N ≤ 0.002%, and the remainder is Fe and unavoidable inclusions. Based on this chemical composition, the non-oriented silicon steel sheet is a high-grade non-oriented silicon steel with excellent magnetic properties.

[0191] The following provides three specific examples based on this embodiment. Specifically, the implementation process of these examples is as follows:

[0192] (1) Casting molten steel into continuous casting billets with a thickness of 250 mm through a slab continuous casting machine;

[0193] (2) After leaving the slab continuous caster, the continuous casting slab is heated in a heating furnace. The soaking temperature and the time in the furnace are shown in Table 13.

[0194] (3) After leaving the heating furnace, the continuous casting slab is subjected to multiple rough rolling passes to produce an intermediate slab with a thickness of 125 mm. The reduction ratio of each rough rolling pass is 20-22%. The outlet temperature of the last rough rolling pass is shown in Table 13.

[0195] (4) The intermediate billet enters a tunnel furnace and undergoes high-temperature reduction heat treatment in a reducing atmosphere of 90% H2+10% H2S. The holding temperature and holding time are shown in Table 13. Then, the surface of the intermediate billet is coated with MgO high-temperature insulating coating. Two intermediate billets are then arranged into a stacked billet, and the four sides of the stacked billet are welded to form an integrated composite billet.

[0196] (5) The composite blank is heated in a heating furnace. The heating temperature and heating time are shown in Table 13.

[0197] [Table 13]

[0198] (6) After the composite billet leaves the heating furnace, it is hot rolled to produce a composite hot-rolled plate, which is then coiled into a composite hot-rolled coil. The thickness H1, final rolling temperature, and coiling temperature of the composite hot-rolled plate are shown in Table 14.

[0199] (7) The composite hot-rolled coil obtained in the hot-rolling finishing process is divided into two single-layer hot-rolled coils by a coil splitter;

[0200] (8) The single-layer hot-rolled coil is directly shot blasted and pickled without normalization to remove the surface oxide scale;

[0201] (9) After pickling, the single-layer hot-rolled coil is cold-rolled on a single-stand cold rolling mill to produce a single-layer chilled coil. The thickness H3 of the single-layer chilled coil is shown in Table 14.

[0202] (10) The single-layer chilled coil is annealed in a continuous annealing furnace to obtain an annealed strip. During the annealing process, the heating rate and the soaking temperature are shown in Table 14, the cooling rate is 10°C / s, the protective atmosphere is 20% H2+80% N2, the dew point is 15°C, and the unit tension is shown in Table 14.

[0203] [Table 14]

[0204] (11) Applying an insulating coating as shown in Table 16 to each surface of the annealed steel strip, thereby obtaining a finished non-oriented silicon steel product;

[0205] The chemical composition of one of the non-oriented silicon steel products obtained in each embodiment is shown in Table 15. In addition to the elements shown in Table 15, the remaining chemical components are Fe and unavoidable inclusions. Furthermore, the thickness, iron loss and magnetic induction intensity of the non-oriented silicon steel product are shown in Table 16.

[0206] [Table 15]

[0207] [Table 16]

Claims

1. A method for preparing a non-oriented silicon steel sheet, characterized in that: Including the following processes, Continuous casting process: a slab continuous casting machine is used to produce continuous casting billets, the thickness of the continuous casting billets is t1 = 200-250 mm, and the chemical composition thereof is calculated by mass percentage: C ≤ 0.0025%, S ≤ 0.0015%, Si: 2.50-3.40%, Al: 0.30-1.00%, Mn: 0.20-0.80%, P: 0.02-0.04%, Nb ≤ 0.004%, V ≤ 0.004%, Ti ≤ 0.004%, Ni ≤ 0.03%, Cr ≤ 0.03%, Cu ≤ 0.03%, N ≤ 0.002%, and the rest is Fe and unavoidable inclusions; Slab heating process: After leaving the slab continuous casting machine, the continuous casting slab is heated in a heating furnace, and the soaking temperature is T1 = T 10 ±10℃, in the furnace for 180~200min, T 10 =1100-30×[Si]-20×[Al], where [Si] and [Al] are 100 times the mass percentage of Si and Al in the continuous casting billet; Intermediate billet preparation process: After the continuous casting billet leaves the heating furnace, it is subjected to multiple rough rolling to form an intermediate billet, and the intermediate billet thickness is t2 = t1 / N, where N = 2 to 6; Surface treatment process: The intermediate billet enters the tunnel furnace for high-temperature reduction heat treatment in a reducing atmosphere of 90% H2+10% H2S, with a holding temperature of 950-1000°C and a holding time of 15-30 minutes; Assembly process: Arrange N intermediate billets into a stacked billet, and weld the four sides of the stacked billet to form an integrated composite billet; Heating process: heating the composite blank in a heating furnace at a temperature of 1090-1130°C for a heating time of 180-200 minutes; Hot rolling finishing process: After the composite billet comes out of the heating furnace, it is hot rolled to form a composite hot rolled coil with a thickness of 2.20-2.80 mm; wherein the hot rolling finishing temperature is 820-860°C, and the coiling temperature is 600-640°C; Afterwards, the obtained composite hot-rolled coil is sequentially subjected to a pickling process, a cold rolling process, an annealing process and a coating process, as well as a coiling process before or after the cold rolling process, and is prepared into a single-layer non-oriented silicon steel product with a thickness of 0.15 to 0.30 mm without normalization.

2. The method for preparing a non-oriented silicon steel sheet according to claim 1, characterized in that: The reduction rate of each rough rolling pass is 20-22%, and the outlet temperature of the last rough rolling pass is T2=900±25℃.

3. The method for preparing a non-oriented silicon steel sheet according to claim 1, characterized in that: The composite blank is a cubic blank with parallel upper and lower surfaces and flat sides; The four sides of the stacked blank are arc welded.

4. The method for preparing a non-oriented silicon steel sheet according to claim 1, characterized in that: In the billet assembly process, high temperature resistant insulating coating is applied on the upper and lower surfaces of the intermediate billet by electrostatic spraying, and then N intermediate billets are arranged into stacked billets. The high temperature resistant insulating coating uses MgO high temperature resistant coating.

5. The method for preparing a non-oriented silicon steel sheet according to claim 1, characterized in that: The coiling process is located before the pickling process. The composite hot-rolled coil is divided into N single-layer hot-rolled coils by a coiling machine. After that, each single-layer hot-rolled coil is sequentially subjected to a pickling process, a cold rolling process, an annealing process and a coating process to prepare a single-layer non-oriented silicon steel product.

6. The method for preparing a non-oriented silicon steel sheet according to claim 5, characterized in that: In the cold rolling process, each single-layer hot-rolled coil is cold-rolled on a single-stand cold rolling mill to form a single-layer chilled coil, the cold rolling reduction rate is 74-87%, and the thickness of the single-layer chilled coil is 0.15-0.30 mm.

7. The method for preparing a non-oriented silicon steel sheet according to claim 1, characterized in that: The coiling process is located between the cold rolling process and the annealing process. The composite hot-rolled coil is firstly subjected to a pickling process and a cold rolling process in sequence to form a composite chilled coil. Then, the composite chilled coil is divided into N single-layer chilled coils by a coiling machine. Each single-layer chilled coil is subjected to an annealing process and a coating process in sequence to prepare a single-layer non-oriented silicon steel finished product.

8. The method for preparing a non-oriented silicon steel sheet according to claim 7, characterized in that: In the cold rolling process, the composite hot rolled coil is cold rolled on a single-stand cold rolling mill to form a composite chilled coil, the cold rolling reduction rate is 73-86%, the thickness of the composite chilled coil is 0.30-0.60 mm, and the thickness of the single-layer chilled coil is 0.15-0.30 mm.

9. The method for preparing a non-oriented silicon steel sheet according to claim 6 or 7, characterized in that: In the annealing process: the single-layer chilled coil is annealed in a continuous annealing furnace to obtain an annealed steel strip; During the annealing process, the heating rate is 30-50℃ / s, the soaking temperature is 980-1020℃, the cooling rate is 10-15℃ / s, the protective atmosphere is 20% H2+80% N2, the dew point is 10-20℃, and the unit tension is 2-3N / mm 2 .

10. The method for preparing a non-oriented silicon steel sheet according to claim 1, characterized in that: In the coating process: an insulating coating with a thickness of 0.5 to 0.8 μm is coated on each surface of the annealed steel strip.

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