Non-oriented silicon steel and preparation method therefor

Abstract

Disclosed in the present invention are non-oriented silicon steel and a preparation method therefor. The preparation method comprises: 3.3-3.6% of Si and 0.4-0.8% of Al of a continuous casting slab; heating, hot rolling, and coiling the continuous casting slab, carrying out first-stage cold rolling to prepare a 0.50-0.70 mm primary cold-rolled plate, and maintaining the primary cold-rolled plate at a constant temperature of 820-860°C; then carrying out second-stage cold rolling to prepare a 0.15-0.20 mm secondary cold-rolled plate and then maintaining the secondary cold-rolled plate at a constant temperature of 900-1000°C to obtain a secondary annealed plate; and cooling, coating, and finishing the secondary annealed plate to obtain a finished product. The finished product can be used as a material of an iron core of a stator of a new energy driving motor and solves the technical problems of poor magnetic performance, a high level of alloy elements, a long process route, and a complex process in the prior art.

Description

Non-oriented silicon steel and preparation method thereof

[0001] This application claims priority to a Chinese patent application filed on November 27, 2023, with application number 202311588428.8 and invention name “Method for preparing non-oriented silicon steel”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention belongs to the technical field of steel material preparation, and relates to non-oriented silicon steel and a preparation method of non-oriented silicon steel, in particular to ultra-thin non-oriented silicon steel for stator core of new energy drive motor and a production method thereof. Background Art

[0003] New energy electric vehicles are one of the driving forces of the rapidly emerging global new energy economy, bringing historic changes to the global automotive manufacturing industry and significantly impacting other industries. The new energy drive motor is one of the three core components of new energy electric vehicles. Its driving characteristics directly determine key performance indicators such as gradeability, acceleration, and top speed, making it a crucial component of new energy electric vehicles.

[0004] The drive motor primarily consists of a stator, rotor, and housing. Its driving principle is roughly as follows: Based on electromagnetic induction, the stator generates a rotating magnetic field that acts on the rotor, generating magnetic force that drives the vehicle. Therefore, the magnetic properties of the iron core, such as iron loss and magnetic induction intensity, especially the iron loss of the stator core, determine the drive characteristics of the drive motor. Furthermore, the mechanical strength of the iron core, especially the strength of the rotor core, also affects the reliability of the drive motor during high-speed operation.

[0005] However, existing technologies for non-oriented silicon steel used in drive motor stator cores, such as those with application numbers CN201711204222.5, CN202010143200.8, and CN201710670723.6, generally suffer from poor magnetic properties and high production costs due to the high concentration of alloying elements. Another type of existing technology, such as those with application numbers CN201910612755.X and CN202010143200.8, employs a normalizing process to improve magnetic properties, but this introduces the risk of difficulty in cold rolling. Consequently, preheating is required before cold rolling, resulting in a long and complex process, and high equipment and process costs.

[0006] Summary of the Invention

[0007] In order to solve the technical problems of the prior art, the object of the present invention is to provide a non-oriented silicon steel and a preparation method thereof.

[0008] To achieve the above-mentioned object, one embodiment of the present invention provides a non-oriented silicon steel. The chemical composition of the base material of the non-oriented silicon steel is, by mass percentage, as follows: C ≤ 0.0020%, S ≤ 0.0015%, Si: 3.30-3.60%, Al: 0.40-0.80%, Mn: 0.50-1.00%, P ≤ 0.015%, Sn: 0.03-0.06%, Nb ≤ 0.003%, V ≤ 0.003%, Ti ≤ 0.003%, Cr ≤ 0.02%, Ni ≤ 0.02%, Cu ≤ 0.02%, N ≤ 0.0030%, and the balance is Fe and unavoidable inclusions.

[0009] Preferably, the chemical composition of the non-oriented silicon steel is calculated in mass percentage: 4.00%≤Si+Al≤4.20%.

[0010] Preferably, the magnetic induction intensity B of non-oriented silicon steel is 5000 ≥1.64T, medium frequency iron loss P 1.0 / 400 ≤12.0W / kg, high frequency iron loss P 1.0 / 1000 ≤30.0W / kg.

[0011] Preferably, the thickness of the non-oriented silicon steel is 0.15 mm, and the magnetic induction intensity B 5000 ≥1.64T, medium frequency iron loss P 1.0 / 400 ≤11.0W / kg, high frequency iron loss P 1.0 / 1000 ≤27.0W / kg.

[0012] Preferably, the thickness of the non-oriented silicon steel is 0.20 mm, and the magnetic induction intensity B 5000 ≥1.64T, medium frequency iron loss P 1.0 / 400 ≤12.0W / kg, high frequency iron loss P 1.0 / 1000 ≤30.0W / kg.

[0013] Preferably, the average grain size of the non-oriented silicon steel is 60-120 μm.

[0014] To achieve the above-mentioned purpose, one embodiment of the present invention provides a method for preparing non-oriented silicon steel. The preparation method comprises:

[0015] Steelmaking and preparing a continuous casting billet with a thickness of 220-240 mm; the chemical composition of the continuous casting billet is as follows, in percentage by mass: C ≤ 0.0020%, S ≤ 0.0015%, Si: 3.30-3.60%, Al: 0.40-0.80%, Mn: 0.50-1.00%, P ≤ 0.015%, Sn: 0.03-0.06%, Nb ≤ 0.003%, V ≤ 0.003%, Ti ≤ 0.003%, Cr ≤ 0.02%, Ni ≤ 0.02%, Cu ≤ 0.02%, N ≤ 0.0030%, and the balance is Fe and unavoidable inclusions;

[0016] The continuous casting slab is heated to 1080-1120°C and kept at this temperature for 150-200 minutes, and then rolled into an intermediate slab with a thickness of 35-45 mm. The intermediate slab is then finish rolled and coiled to obtain a hot rolled coil with a thickness of 2.00-2.70 mm. The finishing rolling start temperature is 930-970°C, the final rolling temperature is 820-860°C, the coiling temperature is 580-620°C, and the finishing rolling reduction is 93-95%.

[0017] The hot-rolled coil is directly pickled, and then subjected to 3 to 5 passes of first-stage cold rolling to obtain a primary cold-rolled sheet with a thickness of 0.50 to 0.70 mm. The primary cold-rolled sheet is then kept in a mixed atmosphere of 25% H2+75% N2 at 820°C to 860°C for 2 to 5 minutes to obtain a primary annealed sheet. The starting temperature of the first-stage cold rolling is 20 to 40°C, the total reduction is 70 to 80%, and the reduction of each pass is 15 to 30%.

[0018] The primary annealed sheet is subjected to 2-3 passes of two-stage cold rolling to obtain a secondary cold rolled sheet with a thickness of 0.15-0.20 mm. The secondary cold rolled sheet is then kept in a mixed atmosphere of 25% H2+75% N2 at 900°C-1000°C for 2-5 minutes to obtain a secondary annealed sheet. The starting temperature of the second stage cold rolling is 20-40°C, the total reduction is 65-75%, and the reduction of each pass is 25-45%.

[0019] The secondary annealed sheet is cooled, coated and finished to obtain a non-oriented silicon steel product.

[0020] Preferably, the chemical composition of the continuous casting slab is calculated in mass percentage: 4.00%≤Si+Al≤4.20%.

[0021] Preferably, during steelmaking, molten iron and scrap steel are first subjected to converter smelting, and then vacuum smelting and alloying are performed to obtain molten steel for continuous casting; wherein, the end point of converter smelting is, in mass percentage, C: 0.020-0.050%, S≤0.0020%, and P≤0.015%.

[0022] Preferably, the chemical composition of the molten iron is as follows in mass percentage: C ≥ 3.5%, S ≤ 0.0015%, Si: 0.20-0.80%, Al ≤ 0.10%, Mn ≤ 0.60%, P ≤ 0.15%, Nb ≤ 0.003%, V ≤ 0.03%, Ti ≤ 0.10%, Cr ≤ 0.03%, Ni ≤ 0.02%, Cu ≤ 0.02%, and the remainder is Fe and unavoidable inclusions.

[0023] Preferably, the scrap steel is scrap steel that satisfies, in terms of mass percentage, C≤0.0050%, S≤0.0025%, Si:0.50~3.60%, Al≤1.0%, Mn:0.20~1.50%, P≤0.05%, Sn≤0.20%, Nb≤0.003%, V≤0.003%, Ti≤0.003%, Cr≤0.02%, Ni≤0.02%, and Cu≤0.02%.

[0024] Preferably, the weight of the scrap steel accounts for 20-25% of the total weight of the scrap steel and the molten iron.

[0025] Preferably, the roughness Ra of the working rolls of the rolling mill used in the first stage of cold rolling is 3.5 to 3.0 μm.

[0026] Preferably, the roughness Ra of the working rolls of the rolling mill used for the two-stage cold rolling is 0.6 to 0.3 μm.

[0027] Preferably, the average grain size of the primary annealed sheet is 50 to 80 μm.

[0028] Preferably, the average grain size of the secondary annealed sheet is 60-120 μm.

[0029] Preferably, the magnetic induction intensity B of the non-oriented silicon steel product is 5000 ≥1.64T, medium frequency iron loss P 1.0 / 400 ≤12.0W / kg, high frequency iron loss P 1.0 / 1000 ≤30.0W / kg.

[0030] Preferably, the thickness of the non-oriented silicon steel product is 0.15 mm, and the magnetic induction intensity B 5000 ≥1.64T, medium frequency iron loss P 1.0 / 400 ≤11.0W / kg, high frequency iron loss P 1.0 / 1000 ≤27.0W / kg.

[0031] Preferably, the thickness of the non-oriented silicon steel product is 0.20 mm, and the magnetic induction intensity B 5000 ≥1.64T, medium frequency iron loss P 1.0 / 400 ≤12.0W / kg, high frequency iron loss P 1.0 / 1000 ≤30.0W / kg.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) In terms of chemical composition, Nb, V, Ti, Cr, Ni, Cu and other elements are used as impurity elements (not added during alloying during steelmaking), and the design concept of high silicon and high aluminum is combined. Under the condition of low alloy cost, the chemical composition lays the foundation for the excellent magnetic properties of the finished product;

[0034] (2) On the basis of chemical composition, the process routes and specific parameter settings of hot rolling, first-stage cold rolling and annealing, and second-stage cold rolling and annealing are further combined. On the one hand, the control of grain size, inclusions, texture and other aspects is achieved, and ultra-thin steel plates can be obtained. At the same time, the medium-frequency iron loss and high-frequency iron loss of the finished product are reduced, ensuring excellent magnetic properties. On the other hand, compared with the existing technology, the normalization process and preheating before cold rolling are eliminated, solving the problems of the existing technology such as long process routes, complex processes, high equipment costs and high process costs. On the other hand, the problem of high difficulty in cold rolling caused by factors such as high silicon and high aluminum and ultra-thin finished products is avoided, and stable production is achieved with low cold rolling difficulty.

[0035] (3) Non-oriented silicon steel products can be used as materials for the stator core of new energy drive motors, solving the technical problems of poor magnetic properties, high alloy elements, long process routes and complex procedures in the existing technology. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0037] An embodiment of the present invention provides a method for preparing non-oriented silicon steel, which adopts a process route including steelmaking, continuous casting, heating, hot rolling, pickling, first-stage cold rolling and annealing, second-stage cold rolling and annealing, cooling, coating, and finishing to prepare a non-oriented silicon steel product.

[0038] The resulting non-oriented silicon steel product is an ultra-thin sheet, for example, with a thickness of 0.15 to 0.20 mm, which is the thickness of the secondary cold-rolled sheet obtained during the second-stage cold rolling. It should be noted that, as is well known in the art, given that the secondary cold-rolled sheet undergoes a coating process, the thickness of the non-oriented silicon steel product, strictly speaking, is the sum of the thickness of the secondary cold-rolled sheet and the thickness of the coating. However, because the coating thickness is very thin compared to the secondary cold-rolled sheet, i.e., almost non-existent, the coating thickness is generally not considered when describing the thickness of the non-oriented silicon steel product in the art. Therefore, in the present invention, the thickness of the secondary cold-rolled sheet can be considered as the thickness of the finished product.

[0039] Specifically, this preparation method achieves the advantages of short process route, simple and easy quality control process, low alloy cost and production equipment cost in production through chemical composition design and process design. In terms of product performance, the obtained non-oriented silicon steel product has excellent magnetic properties and is suitable for making iron cores for new energy drive motors, especially when used as a material for stator iron cores, it has significant advantages over existing technologies.

[0040] Specifically, the preparation method includes the following steps 1 to 5.

[0041] Step 1, Steelmaking and Continuous Casting

[0042] In step 1, steelmaking is first performed, and the molten steel obtained by the refining is continuously cast to prepare continuous casting billets with a thickness of 220 to 240 mm.

[0043] During the alloying process of steelmaking, no Nb, V, Ti, Cr, Ni, or Cu is added. The chemical composition of the continuous casting ingot, in percentage by mass, is as follows: C ≤ 0.0020%, S ≤ 0.0015%, Si: 3.30-3.60%, Al: 0.40-0.80%, Mn: 0.50-1.00%, P ≤ 0.015%, Sn: 0.03-0.06%, N ≤ 0.0030%, with the remainder being Fe and unavoidable inclusions. In other words, Nb, V, Ti, Cr, Ni, and Cu are treated as impurity elements in this preparation method. For example, the percentages by mass of these elements in the continuous casting ingot can be: Nb ≤ 0.003%, V ≤ 0.003%, Ti ≤ 0.003%, Cr ≤ 0.02%, Ni ≤ 0.02%, and Cu ≤ 0.02%.

[0044] It is understood that in order to obtain a continuously cast ingot with the above chemical composition, the molten steel must be produced according to the above chemical composition during the steelmaking process. In other words, the chemical composition of the molten steel obtained from the steelmaking process is the same as that of the continuously cast ingot. Furthermore, the chemical composition of the continuously cast ingot is also the chemical composition of the base material of the final non-oriented silicon steel product.

[0045] That is, one embodiment of the present invention provides a non-oriented silicon steel, the chemical composition of which is calculated as follows by mass percentage: C≤0.0020%, S≤0.0015%, Si:3.30~3.60%, Al:0.40~0.80%, Mn:0.50~1.00%, P≤0.015%, Sn:0.03~0.06%, Nb≤0.003%, V≤0.003%, Ti≤0.003%, Cr≤0.02%, Ni≤0.02%, Cu≤0.02%, N≤0.0030%, and the balance is Fe and unavoidable inclusions.

[0046] The following is an introduction to the functions of some chemical elements mentioned in the above chemical composition.

[0047] Si and Al: Si and Al can increase the resistivity of steel sheets, thereby reducing both mid-frequency and high-frequency iron losses in finished products. However, increased Si and Al content reduces magnetic induction and makes cold rolling difficult. In the present invention, through process improvements, low-difficulty cold rolling is achieved on the basis of high silicon and high aluminum, with Si content controlled at 3.30-3.60% and Al content at 0.40-0.80%.

[0048] Mn: can improve the structure and texture of hot-rolled plates and is beneficial to improving magnetic properties;

[0049] Sn: It tends to segregate at grain boundaries and can improve magnetic properties.

[0050] On the basis of the above chemical composition, as a further preferred design, the chemical composition of the continuous casting billet also satisfies, in terms of mass percentage: 4.00% ≤ Si + Al ≤ 4.20%. In this implementation, compared with other implementations of Si + Al content that meet the conditions of Si: 3.30-3.60% and Al: 0.40-0.80% (for example, Si + Al < 4.00%, or Si + Al > 4.20%), better magnetic properties can be obtained.

[0051] Step 2, heating and hot rolling

[0052] In step 2, the continuous cast slab is first heated in a heating furnace to 1080-1120°C and held at this temperature for 150-200 minutes. After exiting the heating furnace, the slab enters the hot rolling process, specifically rolling into an intermediate slab with a thickness of 35-45 mm. This intermediate slab is then finish-rolled and coiled to produce a hot-rolled coil with a thickness of 2.00-2.70 mm.

[0053] The start rolling temperature of the finishing rolling is 930-970°C, the final rolling temperature is 820-860°C, the coiling temperature is 580-620°C, and the finishing rolling reduction rate is 93-95%.

[0054] In this way, the technology of low-temperature heating, low-temperature hot rolling and low-temperature coiling is adopted. On the one hand, a lower temperature is adopted in the heating process to avoid the solid solution of coarse precipitates such as MnS and AlN during the heating process, thereby avoiding the formation of fine precipitates in the subsequent hot rolling process and deterioration of magnetic properties; on the other hand, by controlling the hot rolling temperature and coiling temperature, a uniform deformed ferrite structure is obtained in the hot-rolled coil, the rollability of the rolled material is improved, and a smooth foundation is laid for stable cold rolling under high silicon and high aluminum compositions, making it possible to prepare products with excellent magnetic properties under high silicon and high aluminum compositions.

[0055] Step 3: Pickling, first stage cold rolling and annealing

[0056] In step 3, the hot rolled coil is directly pickled after being uncoiled. That is, in the present invention, the hot rolled coil does not need to be normalized before pickling.

[0057] After pickling, the plate undergoes 3-5 passes of primary cold rolling to produce a 0.50-0.70 mm thick sheet. That is, in this primary cold rolling process, the pickled plate undergoes 3-5 passes of cold rolling to produce a 0.50-0.70 mm thick sheet. For ease of understanding, the sheet obtained through the primary cold rolling process is referred to herein as "primary cold rolled sheet."

[0058] Annealing is then performed. Specifically, the resulting cold-rolled sheet is held in a mixed atmosphere of 25% H₂ + 75% N₂ at 820°C to 860°C for 2 to 5 minutes to obtain an annealed sheet. Similar to the previous example, for ease of understanding, this application will refer to the resulting sheet as a primary annealed sheet.

[0059] In step 3, the starting temperature of the first stage cold rolling is 20-40° C. It can be seen that the plate of the present invention does not need to be preheated before cold rolling after pickling and before the first stage cold rolling as in the prior art mentioned in the background art.

[0060] Furthermore, the total reduction ratio of the first stage cold rolling is 70-80%, and the reduction ratio of each pass is 15-30%.

[0061] Thus, after the aforementioned hot rolling, first stage cold rolling and annealing, the average grain size of the primary annealed sheet is made to be 50 to 80 μm.

[0062] Step 4: Second stage cold rolling and annealing

[0063] In step 4, the primary annealed sheet obtained in step 3 is subjected to two to three passes of two-stage cold rolling to produce a secondary cold-rolled sheet with a thickness of 0.15 to 0.20 mm. This second-stage cold rolling process includes three to five passes of cold rolling, resulting in a sheet with a thickness of 0.50 to 0.70 mm. For ease of understanding, the sheet obtained in this two-stage cold rolling process is referred to herein as secondary cold-rolled sheet.

[0064] The secondary cold rolled sheet is then kept in a mixed atmosphere of 25% H2 + 75% N2 at 900°C to 1000°C for 2 to 5 minutes to obtain an annealed sheet. Similar to the above, for ease of understanding, the sheet obtained here is named secondary annealed sheet in this application.

[0065] In step 4, the starting temperature of the second stage cold rolling is 20-40°C. It can be seen that the plate of the present invention does not need to be preheated before cold rolling after the first stage cold rolling and annealing and before the second stage cold rolling as in the prior art mentioned in the background art.

[0066] In addition, the total reduction ratio of the two-stage cold rolling is 65 to 75%, and the reduction ratio of each pass is 25 to 45%.

[0067] Thus, after the aforementioned hot rolling, first-stage cold rolling, and annealing, combined with the second-stage cold rolling and annealing in this step, the average grain size of the double-annealed sheet is 60-120 μm. This not only achieves excellent magnetic properties despite its high silicon and aluminum content, but also reduces rolling difficulty, avoiding the risk of strip breakage caused by the difficulty of cold rolling. It is understood that the average grain size of the double-annealed sheet is the average grain size of the final product.

[0068] Step 5: Cooling, coating and finishing

[0069] The secondary annealed sheet obtained in step 4 is cooled, coated and finished to obtain a non-oriented silicon steel product. In the present invention, cooling, coating and finishing adopt conventional techniques known in the art and will not be described in detail.

[0070] Thus, the present invention, through the above-mentioned preparation method, includes a combination of chemical composition and production process, with Nb, V, Ti, Cr, Ni, Cu and other elements as impurity elements (not added during alloying during steelmaking), and combined with the design concept of high silicon and high aluminum, under the condition of low alloy cost, lays the foundation for the excellent magnetic properties of the finished product from the chemical composition aspect; and further combines the process route and specific parameter settings of hot rolling, first stage cold rolling and annealing, second stage cold rolling and annealing, on the one hand, it realizes the control of grain size, inclusions, texture and other aspects, and can obtain ultra-thin steel plates, while reducing the medium frequency iron loss and high frequency iron loss of the finished product, ensuring excellent magnetic properties, on the other hand, compared with the prior art, the normalizing process and preheating before cold rolling are eliminated, solving the problems of the prior art of long process route, complex process, high equipment cost and high process cost, and on the other hand, it avoids the problem of high difficulty of cold rolling caused by factors such as high silicon and high aluminum and ultra-thin finished product, and realizes stable production with low cold rolling difficulty.

[0071] In addition, from the principle aspect, the beneficial effects of the present invention include:

[0072] (1) The high Si and high Al composition design and thin finished product gauge design increase the resistivity of non-oriented silicon steel, while laying the foundation for reducing the medium-frequency iron loss and high-frequency iron loss of the finished product;

[0073] (2) The normalization process before cold rolling is eliminated, which improves the cold rolling performance of the rolled material. The combination of first-stage cold rolling and annealing, and second-stage cold rolling and annealing reduces the risk of strip breakage and achieves stable production.

[0074] (3) By controlling the impurity elements and combining the first stage cold rolling and annealing, the resistance of inclusions to the movement of magnetic domain walls is reduced, the proportion of favorable texture is increased, and the medium-frequency iron loss and high-frequency iron loss are reduced and the magnetic induction is improved; at the same time, through the second stage cold rolling and annealing, the grain control of the secondary annealed plate is achieved to avoid the rapid change of magnetization when the magnetic domain walls move under the high-frequency operation conditions of the motor, which greatly increases the eddy current loss, thereby further reducing the high-frequency iron loss;

[0075] (4) In addition, by combining chemical composition and process methods, the surface quality can be improved while improving the magnetic properties and avoiding corrugated defects.

[0076] In summary, the non-oriented silicon steel product obtained by the present invention has excellent magnetic properties, and the magnetic induction intensity B 5000 ≥1.64T, medium frequency iron loss P 1.0 / 400 ≤12.0W / kg, high frequency iron loss P 1.0 / 1000 ≤30.0W / kg. When used to make the stator core of new energy high-speed drive motors, it can meet the high efficiency of new energy vehicles when driving at medium speeds on urban roads and at high speeds on highways, thereby increasing the cruising range.

[0077] More specifically, in one embodiment, the thickness of the obtained non-oriented silicon steel product is 0.20 mm, and the magnetic induction intensity B 5000 ≥1.64T, medium frequency iron loss P 1.0 / 400 ≤12.0W / kg, high frequency iron loss P 1.0 / 1000 ≤30.0W / kg. In a more preferred embodiment, the obtained non-oriented silicon steel product is thinner and has better magnetic properties. Its thickness is 0.15mm and the magnetic induction intensity B 5000 ≥1.64T, medium frequency iron loss P 1.0 / 400 ≤11.0W / kg, high frequency iron loss P 1.0 / 1000 ≤27.0W / kg.

[0078] Furthermore, in step 1, during steelmaking, molten iron and scrap steel are first used for converter smelting, and then vacuum smelting and alloying are performed to obtain molten steel for continuous casting; wherein, the end point of converter smelting is C: 0.020-0.050%, S≤0.0020%, and P≤0.015% in mass percentage.

[0079] The chemical composition of the molten iron is as follows in percentage by mass: C ≥ 3.5%, S ≤ 0.0015%, Si: 0.20-0.80%, Al ≤ 0.10%, Mn ≤ 0.60%, P ≤ 0.15%, Nb ≤ 0.003%, V ≤ 0.03%, Ti ≤ 0.10%, Cr ≤ 0.03%, Ni ≤ 0.02%, Cu ≤ 0.02%, and the remainder is Fe and unavoidable inclusions.

[0080] The scrap steel is a scrap steel material that satisfies, in terms of mass percentage, C≤0.0050%, S≤0.0025%, Si: 0.50-3.60%, Al≤1.0%, Mn: 0.20-1.50%, P≤0.05%, Sn≤0.20%, Nb≤0.003%, V≤0.003%, Ti≤0.003%, Cr≤0.02%, Ni≤0.02%, and Cu≤0.02%.

[0081] The weight of the scrap steel accounts for 20-25% of the total weight of the scrap steel and the molten iron.

[0082] In this way, by designing the composition and ratio of molten iron and scrap steel during steelmaking, the difficulty of steelmaking can be greatly reduced, making it very easy to achieve precise and excellent control of inclusions, and achieving low impurities and high purity. Of course, the steelmaking process of the present invention is not limited to this preferred low-difficulty steelmaking scheme. Other compositions of molten iron and / or scrap steel, and their ratios, can also be used to achieve the advantages of the finished product magnetic properties and cold rolling difficulty described above.

[0083] In addition, both the first-stage cold rolling mill and the second-stage cold rolling mill are single-stand cold rolling mills. Preferably, the work roll roughness Ra of the first-stage cold rolling mill is 3.5-3.0 μm, while the work roll roughness Ra of the second-stage cold rolling mill is 0.6-0.3 μm. This not only improves magnetic properties, but also further improves the surface quality of the finished product, avoiding "corrugated" defects on the finished product surface.

[0084] Furthermore, in one embodiment, during the two-stage cold rolling and annealing in step 4, a constant speed production is adopted.

[0085] The detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

[0086] The following six examples and five comparative examples illustrate the beneficial effects of the present invention. Of course, the following six examples are not intended to be all examples of the present invention. They are merely a subset of the numerous examples for the purpose of visually demonstrating one embodiment of the present invention. These examples do not negate the feasibility of other examples within one embodiment of the present invention. Furthermore, the following five comparative examples are intended solely to illustrate the beneficial effects of one embodiment of the present invention and are not prior art.

[0087] Specifically, these embodiments and comparative examples adopt the following methods to prepare non-oriented silicon steel products.

[0088] (1) Steelmaking was first performed, and the molten steel obtained by the refining was continuously cast to prepare continuous casting billets; the thickness and chemical composition of the continuous casting billets of each embodiment and comparative example are shown in Table 1.

[0089] [Table 1]

[0090] (2) The continuous casting billet is first heated and kept warm in a heating furnace; then, after the continuous casting billet comes out of the heating furnace, it is first rolled into an intermediate billet; then the intermediate billet is finish rolled and coiled to obtain a hot rolled coil.

[0091] The heating temperature, holding time, intermediate billet thickness, start and finish rolling temperatures, coiling temperature, and hot rolled coil thickness are shown in Table 2.

[0092] [Table 2]

[0093] (3) In Examples 1 to 6, the hot-rolled coils prepared in step 2 are uncoiled and then directly pickled without normalization. Then, without preheating, the hot-rolled coils are directly cold-rolled for 3 to 5 passes to form primary cold-rolled sheets, with the reduction ratio of each pass controlled at 15 to 30%. The primary cold-rolled sheets are first annealed in a mixed atmosphere of 25% H2 + 75% N2 to obtain primary annealed sheets.

[0094] The primary annealed sheet is subjected to 2-3 passes of two-stage cold rolling without preheating to obtain a secondary cold rolled sheet, with the reduction rate of each pass controlled at 25-45%. Thereafter, the secondary cold rolled sheet is subjected to secondary annealing in a mixed atmosphere of 25% H2+75% N2 to obtain a secondary annealed sheet.

[0095] Among them, in each embodiment, the starting temperature of the first stage cold rolling, the roughness of the rolling mill work roll, the thickness of the first cold rolled plate, the first annealing temperature, and the first annealing time are respectively shown in Table 3; the starting temperature of the second stage cold rolling, the roughness of the rolling mill work roll, the thickness of the second cold rolled plate, the second annealing temperature, and the second annealing time are also respectively shown in Table 3.

[0096] [Table 3]

[0097] In Comparative Examples 1 and 2, after the hot-rolled coil in step 2 was uncoiled, it was first subjected to normalization treatment and then to pickling treatment; and - Comparative Example 1 was preheated before cold rolling at a preheating temperature of 200°C, and after preheating, it was cold rolled to 0.16 mm in 9 passes; the cold-rolled sheet was annealed at 990°C for 3 minutes to obtain an annealed sheet; Comparative Example 2 was not preheated before cold rolling, and multiple strip breaks occurred during the cold rolling process, and ultimately no cold-rolled sheet was obtained.

[0098] In comparative examples 3 to 6, after the hot-rolled coil in step 2 was uncoiled, it was directly pickled without normalization; then, without preheating, it was directly cold-rolled through 3 to 5 passes of first-stage cold rolling to produce a single cold-rolled sheet, with the reduction rate of each pass controlled at 15 to 30%. However, in comparative example 5, multiple strip breaks occurred during the first-stage cold rolling process, and ultimately no single cold rolling was achieved.

[0099] The primary cold-rolled sheets obtained in Comparative Examples 3, 4 and 6 were subjected to a primary annealing in a mixed atmosphere of 25% H2 + 75% N2 to obtain primary annealed sheets; the primary annealed sheets were subjected to 2 to 3 passes of two-stage cold rolling to obtain secondary cold-rolled sheets, with the reduction rate of each pass controlled at 25 to 45%; thereafter, the secondary cold-rolled sheets were subjected to a secondary annealing in a mixed atmosphere of 25% H2 + 75% N2 to obtain secondary annealed sheets.

[0100] (4) The secondary annealed sheets obtained in step 3, Examples 1 to 6 and Comparative Examples 3, 4, and 6, and the annealed sheet obtained in Comparative Example 1, were cooled, coated, and finished to obtain finished non-oriented silicon steel products.

[0101] The metallographic structure, magnetic properties and surface quality of the non-oriented silicon steel products obtained in Examples 1 to 6 and Comparative Examples 1, 3, 4 and 6 were tested, including:

[0102] A. The average grain size of the finished products was measured using the GB / T 6394 standard. The average grain size of the finished products of Examples 1 to 6 and Comparative Examples 3, 4, and 6 was also the average grain size of the double-annealed sheet. The average grain size of the finished product of Comparative Example 1 was also the average grain size of the annealed sheet. In addition, the average grain size of the single-annealed sheet was also measured for Examples 1 to 6 and Comparative Examples 3, 4, and 6.

[0103] B. Use GB / T 3655 standard to test iron loss and magnetic induction intensity;

[0104] C. Use GB / T 3076 standard to test tensile strength and yield strength;

[0105] D. The surface quality was measured using the Cognex surface quality online monitoring system. The results are shown in Table 4.

[0106] [Table 4]

[0107] As can be seen from the above, although the chemical compositions of Comparative Examples 1 and 2 match those of an embodiment of the present invention, they employ a traditional production process flow, namely, steelmaking, continuous casting, hot rolling, normalizing, pickling, cold rolling, and annealing, requiring normalizing before pickling. Furthermore, Comparative Example 1 underwent a 200°C preheat treatment before cold rolling, and while no strip breakage occurred during the cold rolling process, nine cold rolling passes were still required to reduce the thickness to 0.16 mm, resulting in low rolling efficiency and increased cold rolling difficulty. Comparative Example 2, on the other hand, did not undergo a preheat treatment before cold rolling, resulting in multiple strip breakages during the cold rolling process, and ultimately, no finished product was obtained.

[0108] Comparative Examples 3 to 6 were produced using the process of primary cold rolling and annealing, secondary cold rolling and finished product annealing according to the present invention; however:

[0109] In comparative example 3, the Si content is 3.23%, the Al content is 0.28%, and the finished product medium frequency iron loss is P 1.0 / 400 is 15.7W / kg, and the high-frequency iron loss is P 1.0 / 1000 It is 36.8W / kg, and the medium-frequency iron loss and high-frequency iron loss do not meet the requirements;

[0110] In comparative example 4, the Si content is 3.67%, the Al content is 0.84%, and the magnetic induction intensity of the finished product is B 5000 The magnetic induction intensity is 1.636T, which does not meet the requirements. In addition, due to the high Si and Al content, corrugated defects appear on the surface of the finished product, and the surface quality does not meet the requirements.

[0111] In Comparative Example 5, the Si content was 3.85% and the Al content was 1.03%. Due to the excessively high Si and Al contents, the brittleness of the hot-rolled coil increased, and multiple strip breaks occurred during the first stage of cold rolling, and no finished product was obtained.

[0112] In Comparative Example 6, the C content is 0.0037%, the S content is 0.0028, and the N content is 0.0033%. The C, S, and N content do not meet the composition requirements of the non-oriented silicon steel of the present invention. The magnetic properties of the finished product are poor, and the medium frequency iron loss P is 1.0 / 400 17.4W / kg, high frequency iron loss P 1.0 / 1000 is 38.3W / kg, magnetic induction intensity B 5000 The magnetic property requirement of the non-oriented silicon steel of the present invention is not met.

[0113] Examples 1 to 6 are produced using the method for preparing non-oriented silicon steel of the present invention, wherein:

[0114] The control of the composition, process, organization and other aspects of Examples 1 to 6 all meet the design of the present invention, the finished product has good surface quality and excellent magnetic properties, and meets the magnetic induction intensity B of the non-oriented silicon steel finished product of the present invention. 5000 ≥1.64T, medium frequency iron loss P 1.0 / 400 ≤12.0W / kg, high frequency iron loss P 1.0 / 1000 ≤30.0W / kg, no surface corrugated defects, short production process, simple technology, easy to produce smoothly;

[0115] Among them, Examples 1 to 4 adopt the optimal implementation method of 4.00%≤Si+Al≤4.20%, while in Example 5, Si+Al<4.0%. Compared with Examples 1 to 4, the medium frequency iron loss P 1.0 / 400 11.9W / kg and high frequency iron loss P 1.0 / 1000 The medium-frequency iron loss and high-frequency iron loss are higher than those in Example 3 with the same specifications. Similarly, in Example 6, Si+Al>4.2%, and compared with Examples 1 to 4, the magnetic induction intensity B 5000 It is 1.641T, and the magnetic induction intensity is relatively low.

Claims

1. A method for preparing non-oriented silicon steel, characterized in that: The preparation method comprises: Steelmaking, and preparing a continuous casting billet with a thickness of 220-240 mm; the chemical composition of the continuous casting billet is as follows by mass percentage: C≤0.0020%, S≤0.0015%, Si: 3.30-3.60%, Al: 0.40-0.80%, Mn: 0.50-1.00%, P≤0.015%, Sn: 0.03-0.06%, Nb≤0.003%, V≤0.003%, Ti≤0.003%, Cr≤0.02%, Ni≤0.02%, Cu≤0.02%, N≤0.0030%, and the balance is Fe and unavoidable inclusions; The continuous casting billet is heated to 1080-1120°C and kept warm for 150-200 minutes, and then rolled into an intermediate billet with a thickness of 35-45 mm, and then the intermediate billet is subjected to finish rolling and coiling to obtain a hot rolled coil with a thickness of 2.00-2.70 mm; wherein the finish rolling start temperature is 930-970°C, the final rolling temperature is 820-860°C, the coiling temperature is 580-620°C, and the finish rolling reduction rate is 93-95%; The hot-rolled coil is directly pickled, and then 3 to 5 passes of first-stage cold rolling are performed to form a primary cold-rolled plate with a thickness of 0.50 to 0.70 mm, and then the primary cold-rolled plate is kept in a mixed atmosphere of 25% H2+75% N2 at 820°C to 860°C for 2 to 5 minutes to obtain a primary annealed plate; wherein the starting temperature of the first-stage cold rolling is 20 to 40°C, the total reduction rate is 70 to 80%, and the reduction rate of each pass is 15 to 30%; The primary annealed sheet is subjected to 2-3 passes of two-stage cold rolling to obtain a secondary cold rolled sheet of 0.15-0.20 mm, and then the secondary cold rolled sheet is kept in a mixed atmosphere of 25% H2+75% N2 at 900°C-1000°C for 2-5 minutes to obtain a secondary annealed sheet; wherein the starting temperature of the two-stage cold rolling is 20-40°C, the total reduction rate is 65-75%, and the reduction rate of each pass is 25-45%; The secondary annealed sheet is cooled, coated and finished to obtain a non-oriented silicon steel product.

2. The method for preparing non-oriented silicon steel according to claim 1, characterized in that: The chemical composition of the continuous casting slab is calculated in mass percentage: 4.00%≤Si+Al≤4.20%.

3. The method for preparing non-oriented silicon steel according to claim 1, characterized in that: During steelmaking, molten iron and scrap steel are first used for converter smelting, and then vacuum smelting and alloying are performed to obtain molten steel for continuous casting. The end point of converter smelting is calculated by mass percentage as C: 0.020-0.050%, S≤0.0020%, and P≤0.015%.

4. The method for preparing non-oriented silicon steel according to claim 3, characterized in that: The chemical composition of the molten iron is calculated by mass percentage as follows: C≥3.5%, S≤0.0015%, Si: 0.20-0.80%, Al≤0.10%, Mn≤0.60%, P≤0.15%, Nb≤0.003%, V≤0.03%, Ti≤0.10%, Cr≤0.03%, Ni≤0.02%, Cu≤0.02%, and the remainder is Fe and unavoidable inclusions.

5. The method for preparing non-oriented silicon steel according to claim 3, characterized in that: The scrap steel comprises scrap steel materials satisfying, by mass percentage, C≤0.0050%, S≤0.0025%, Si: 0.50-3.60%, Al≤1.0%, Mn: 0.20-1.50%, P≤0.05%, Sn≤0.20%, Nb≤0.003%, V≤0.003%, Ti≤0.003%, Cr≤0.02%, Ni≤0.02%, and Cu≤0.02%.

6. The method for preparing non-oriented silicon steel according to claim 3, characterized in that: The weight of the scrap steel accounts for 20-25% of the total weight of the scrap steel and the molten iron.

7. The method for preparing non-oriented silicon steel according to claim 1, characterized in that: The roughness Ra of the working roll of the rolling mill used in the first stage of cold rolling is 3.5-3.0 μm; the roughness Ra of the working roll of the rolling mill used in the second stage of cold rolling is 0.6-0.3 μm.

8. The method for preparing non-oriented silicon steel according to claim 1, characterized in that: The average grain size of the once annealed sheet is 50 to 80 μm.

9. The method for preparing non-oriented silicon steel according to claim 1, characterized in that: The average grain size of the secondary annealed sheet is 60 to 120 μm.

10. A non-oriented silicon steel, characterized in that: The chemical composition of the substrate of the non-oriented silicon steel is calculated by mass percentage as follows: C≤0.0020%, S≤0.0015%, Si: 3.30-3.60%, Al: 0.40-0.80%, Mn: 0.50-1.00%, P≤0.015%, Sn: 0.03-0.06%, Nb≤0.003%, V≤0.003%, Ti≤0.003%, Cr≤0.02%, Ni≤0.02%, Cu≤0.02%, N≤0.0030%, and the balance is Fe and unavoidable inclusions.

11. The non-oriented silicon steel according to claim 10, characterized in that: Magnetic induction intensity B of non-oriented silicon steel 5000 ≥1.64T, medium frequency iron loss P 1.0 / 400 ≤12.0W / kg, high frequency iron loss P 1.0 / 1000 ≤30.0W / kg.

12. The non-oriented silicon steel according to claim 10, characterized in that: The thickness of non-oriented silicon steel is 0.15mm, and the magnetic induction intensity is B 5000 ≥1.64T, medium frequency iron loss P 1.0 / 400 ≤11.0W / kg, high frequency iron loss P 1.0 / 1000 ≤27.0W / kg.

13. The non-oriented silicon steel according to claim 10, characterized in that: The thickness of non-oriented silicon steel is 0.20mm, and the magnetic induction intensity is B 5000 ≥1.64T, medium frequency iron loss P 1.0 / 400 ≤12.0W / kg, high frequency iron loss P 1.0 / 1000 ≤30.0W / kg.

14. The non-oriented silicon steel according to claim 10, characterized in that: The average grain size of non-oriented silicon steel is 60-120 μm.

15. The non-oriented silicon steel according to claim 10, characterized in that: The chemical composition of the base material of the non-oriented silicon steel is calculated in mass percentage: 4.00%≤Si+Al≤4.20%.