High-strength non-oriented silicon steel with yield strength of 930 MPa and production method thereof

Abstract

The invention discloses high-strength non-oriented silicon steel with yield strength of 930 MPa and a production method thereof. The non-oriented silicon steel comprises the following chemical components: 3.0 < = Si < = 4.0%, 0.1 < = Al < = 1.2%, 0.1 < = Mn < = 1.0%, 0.0005 < = Nb < = 0.0010%, 0.0018% < = Ti < = 0.0030%, 0.0010% < = V < = 0.0025%, 0.0020% < = C < = 0.0035%, 0.0010% < = N < = 0.0025%, 4.0 < = Si + Al + Mn < = 5.4%, 0.0045% < = Nb + Ti + V < = 0.0055%, and 0.0035% < = C + N < = 0.0050%. According to the production method of the non-oriented silicon steel, the process route of converter smelting, RH refining, continuous casting, hot rolling, acid pickling, cold rolling, annealing and coating is adopted, the heating temperature is larger than or equal to 1200 DEG C and smaller than or equal to 1250 DEG C, the heating time is larger than or equal to 6 h and smaller than or equal to 8 h, the finish rolling temperature is larger than or equal to 750 DEG C and smaller than or equal to 800 DEG C, the coiling temperature is larger than or equal to 700 DEG C and smaller than or equal to 750 DEG C, the annealing target temperature t is-56.8 A2 + 572.9 A-825.7, the annealing actual temperature T is t + / -30, the annealing target speed c is 120 + 1.5 (T-t), and the annealing actual speed C is c + / -5. Three strengthening modes of dislocation strengthening, solution strengthening and precipitation strengthening are comprehensively used, a component-annealing temperature-annealing speed matching relation and a hot rolling process of'high-temperature long-time heating, low-temperature finish rolling and high-temperature coiling 'are designed, the yield strength Rp0.2 of the obtained non-oriented silicon steel is larger than or equal to 930 MPa, the iron loss P1.0 / 400 is smaller than or equal to 57 W / kg, and the magnetic polarization strength J5000 is larger than or equal to 1.52 T.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel metallurgy, and in particular relates to a high-strength non-oriented silicon steel with a yield strength of 930 MPa and a production method thereof. Background Art

[0002] Non-oriented silicon steel is a functional metallic material. Generally speaking, its most important performance indicator is magnetic properties, primarily including iron loss and magnetic polarization. In high-speed or variable-frequency motor applications, iron loss is primarily measured as P1.0 / 400, which is the loss when magnetizing the silicon steel to 1.0 T in a 400 Hz alternating magnetic field. Magnetic polarization is primarily measured as J5000, which is the magnetic polarization strength of the silicon steel at a magnetic field strength of 5000 A / m.

[0003] In recent years, the design speeds of automotive drive motors have been increasing, and variable-speed pumped-storage generators have also developed rapidly. Due to centrifugal force, the silicon steel used in the rotors of automotive drive motors and variable-speed pumped-storage generators requires high mechanical strength. High-strength non-oriented silicon steel is essential for these applications. For high-strength non-oriented silicon steel, its mechanical and magnetic properties are equally important. Mechanical properties affect the mechanical strength of the rotor, while magnetic properties contribute to the power and energy efficiency of the motor or generator.

[0004] The yield strength of conventional, top-grade non-oriented silicon steel is typically only approximately 430 MPa, which cannot meet the mechanical requirements for high-strength non-oriented silicon steel used in high-speed drive motors or variable-speed pumped-storage units. Steel strengthening methods include solid solution strengthening, precipitation strengthening, dislocation strengthening, and grain refinement. These methods are the only ones available to improve the strength of non-oriented silicon steel, making it difficult and challenging to achieve mechanical strength improvements. Some of these methods, such as solid solution strengthening through the addition of nickel, are costly and carry the risk of brittle fracture during cold rolling. Furthermore, the extent of solid solution strengthening is extremely limited. Grain refinement is the only strengthening method that can simultaneously improve both strength and toughness, but for silicon steel, the strength improvement is minimal. Regarding precipitation strengthening, some techniques using Cu precipitates can improve the mechanical strength of the product. However, the precipitation of Cu precipitates requires a specific aging process, which complicates the silicon steel production process and increases manufacturing costs. Furthermore, Cu is an expensive alloying element, and achieving a yield strength greater than 900 MPa using Cu precipitation strengthening alone is difficult. Dislocation strengthening can significantly improve the mechanical properties of silicon steel, but it cannot be relied upon solely because dislocation strengthening can significantly degrade the product's magnetic properties while also strengthening it. Dislocation strengthening is primarily achieved by leaving unrecrystallized structure in the finished product. In an incompletely recrystallized state, different degrees of matrix recovery correspond to different dislocation contents. Therefore, the application of dislocation strengthening is difficult and requires the use of appropriate annealing processes.

[0005] At present, there is no feasible method to achieve the comprehensive performance of non-oriented silicon steel: yield strength Rp0.2≥930MPa, iron loss P1.0 / 400≤57W / kg, magnetic polarization intensity J5000≥1.52T, which has restricted the application of non-oriented silicon steel. Summary of the Invention

[0006] In order to solve some or all of the technical problems existing in the above-mentioned prior art, the present invention provides a high-strength non-oriented silicon steel with a yield strength of 930 MPa and a production method thereof.

[0007] In one aspect of the present invention, the chemical composition of the high-strength non-oriented silicon steel with a yield strength of 930 MPa is designed as follows by mass percentage: the solid solution strengthening element content is 3.0≤Si≤4.0%, 0.1≤Al≤1.2%, 0.1≤Mn≤1.0%, and 4.0%≤Si+Al+Mn≤5.4%, and the precipitation strengthening element content is 0.0005%≤Nb≤0.0010%, 0. 0018%≤Ti≤0.0030%, 0.0010%≤V≤0.0025%, 0.0020%≤C≤0.0035%, 0.0010%≤N≤0.0025%, and 0.0045%≤Nb+Ti+V≤0.0055%, 0.0035%≤C+N≤0.0050%, S≤0.0025%, P≤0.015%, and the rest are iron and unavoidable impurities.

[0008] Furthermore, in the above-mentioned high-strength non-oriented silicon steel with a yield strength of 930 MPa, the yield strength Rp0.2 of the high-strength non-oriented silicon steel with a yield strength of 930 MPa is ≥930 MPa, the iron loss P1.0 / 400 is ≤57 W / kg, and the magnetic polarization intensity J5000 is ≥1.52T.

[0009] In another aspect of the present invention, the provided method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa adopts a process route of converter smelting → RH refining → continuous casting → hot rolling → pickling → cold rolling → annealing → coating, wherein:

[0010] (1) The chemical composition of the molten steel produced by converter smelting and RH refining is controlled to be as follows by mass percentage: 3.0≤Si≤4.0%, 0.1≤Al≤1.2%, 0.1≤Mn≤1.0%, 0.0005%≤Nb≤0.0010%, 0.0018%≤Ti≤0.0030%, 0.0010%≤V≤0.0025%, 0.0020%≤C≤0.0035%, 0.0010%≤N≤0.0025%, S≤0.0025%, P≤0.015%, and 4.0%≤Si+Al+Mn≤5.4%, 0.0045%≤Nb+Ti+V≤0.0055%, 0.0035%≤C+N≤0.0050%, with the remainder being iron and unavoidable impurities;

[0011] (2) In the continuous casting process, the molten steel is prepared into a casting billet;

[0012] (3) In the hot rolling process, the ingot is heated, rolled, and coiled to obtain a hot-rolled coil, wherein the hot rolling process parameters are controlled as follows: 1200° C. ≤ heating temperature ≤ 1250° C., 6 h ≤ heating time ≤ 8 h, 750° C. ≤ finishing rolling temperature ≤ 800° C., and 700° C. ≤ coiling temperature ≤ 750° C.;

[0013] (4) Pickling the hot-rolled coil to remove surface iron oxide scale, and then cold rolling it to the target thickness;

[0014] (5) Anneal the cold rolled coil at target annealing temperature t = -56.8A 2 +572.9A-825.7, actual annealing temperature T=t±30, annealing target speed c=120+1.5(Tt), actual annealing speed C=c±5, where A is the total mass percentage content of Si, Al and Mn in the steel, T and t are in °C, and C and c are in m / min.

[0015] Furthermore, the above-mentioned method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa further comprises coating the annealed cold-rolled coil, wherein the coating has a thickness of 4 to 7 μm.

[0016] Preferably, the coating is a self-bonding coating.

[0017] Furthermore, in the above-mentioned method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa, a process of normalizing the hot-rolled coil is further included after the hot rolling process and before the pickling process.

[0018] Furthermore, in the above-mentioned method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa, the target thickness of the non-oriented silicon steel is 0.15 to 0.65 mm.

[0019] Furthermore, in the above-mentioned method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa, the target thickness of the non-oriented silicon steel includes 0.15 mm, 0.20 mm, 0.25 mm, 0.27 mm, 0.30 mm, 0.35 mm, 0.50 mm, and 0.65 mm.

[0020] Furthermore, in the above-mentioned method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa, in the annealing process, a continuous annealing furnace with an effective heating length of 180 to 200 meters is used to anneal the cold-rolled coil.

[0021] Furthermore, in the above-mentioned method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa, in the converter smelting process, a slide plate is used to block the slag for tapping, and the tapping slag thickness is controlled to be no more than 40 mm.

[0022] Furthermore, in the above-mentioned method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa, in the continuous casting process, the thickness of the ingot is controlled to be 200-230 mm.

[0023] The high-strength non-oriented silicon steel with a yield strength of 930 MPa and the production method thereof of the present invention have the following advantages and beneficial effects:

[0024] The present invention comprehensively utilizes three strengthening methods, namely dislocation strengthening, solid solution strengthening, and precipitation strengthening, and determines the annealing temperature and annealing rate based on the content of the main alloying elements, thereby inventing a strict composition-annealing temperature-annealing rate matching relationship. Thus, while relying on the unrecrystallized structure to improve mechanical properties, the magnetic properties are not deteriorated. The content design of the solid solution strengthening elements Si, Al, and Mn prevents production problems such as cold-rolled strip breakage in the product while achieving solid solution strengthening. The content design of the precipitation strengthening elements Nb, Ti, V, C, and N, in conjunction with the "high-temperature, long-time heating, low-temperature final rolling, and high-temperature coiling" hot rolling process, achieves strengthening through the effective precipitation of Nb, Ti, and V carbonitrides, while preventing excessive precipitation from deteriorating the magnetic properties. Therefore, by comprehensively using dislocation strengthening, solid solution strengthening, precipitation strengthening and through the coordinated design of composition and process, the non-oriented silicon steel prepared by the present invention has excellent mechanical properties and comprehensive magnetic properties, with a yield strength Rp0.2≥930MPa, an iron loss P1.0 / 400≤57W / kg, and a magnetic polarization intensity J5000≥1.52T. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are only used to further understand the embodiments of the present invention and constitute part of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0026] Figure 1 This is a microstructure metallographic diagram of the finished non-oriented silicon steel plate of Invention Example 1 (0.25 mm product annealing temperature 620° C.) in Example 3 of the present invention;

[0027] Figure 2 This is a metallographic diagram of the non-oriented silicon steel finished plate of Comparative Example 2 (0.25 mm product annealing temperature 650° C.) in Example 3 of the present invention;

[0028] Figure 3 This is a microstructure metallographic diagram of the finished non-oriented silicon steel plate of Invention Example 4 (0.35 mm product annealing temperature 640° C.) in Example 3 of the present invention;

[0029] Figure 4 This is a metallographic diagram of the finished non-oriented silicon steel plate of Comparative Example 5 (0.35 mm product annealing temperature 650° C.) in Example 3 of the present invention;

[0030] Figure 5 This is a microstructure metallographic diagram of the finished non-oriented silicon steel plate of Invention Example 7 (0.65 mm product 590° C. annealing temperature) in Example 3 of the present invention;

[0031] Figure 6 This is a metallographic diagram of the non-oriented silicon steel finished plate of Comparative Example 8 (0.65 mm product annealing temperature 650° C.) in Example 3 of the present invention. DETAILED DESCRIPTION

[0032] 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 specific embodiments of the present invention and corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] As mentioned above, all kinds of steel strengthening methods have advantages and disadvantages when applied to silicon steel, and there are some typical drawbacks in particular, such as dislocation strengthening and precipitation strengthening can seriously deteriorate silicon steel performance, solid solution strengthening can bring production problems such as cold rolling brittle fracture, the strengthening amplitude of fine grain strengthening and solid solution strengthening is relatively small, and the alloy cost of solid solution strengthening and precipitation strengthening is relatively high. Therefore, a single strengthening method is used, and it is impossible to develop a high-strength non-oriented silicon steel with a yield strength greater than 930MPa and excellent magnetic properties. In response to these problems, the present invention comprehensively uses dislocation strengthening, solid solution strengthening, and precipitation strengthening these three strengthening methods to obtain excellent mechanics and magnetic comprehensive properties, and, in the present invention, each strengthening method is all designed in coordination with composition and process, and the beneficial strengthening effects of these strengthening methods are reasonably applied, thereby avoiding the cold rolling easy-to-break band production problem of solid solution strengthening and avoiding the significant deterioration of magnetic properties by dislocation strengthening and precipitation strengthening.

[0034] For solid solution strengthening, the present invention primarily utilizes Si, Al, and Mn, taking into account factors such as product mechanical strength, magnetic properties, and cold rolling processability. The solid solution strengthening alloying element content is 3.0 ≤ Si ≤ 4.0%, 0.1 ≤ Al ≤ 1.2%, 0.1 ≤ Mn ≤ 1.0%, and 4.0% ≤ Si + Al + Mn ≤ 5.4%. The lower limit of the alloying element content ensures the solid solution strengthening effect; too low a content of the alloying element will result in insufficient solid solution strengthening and deviate from the magnetic properties. The upper limit of the alloying element content is to prevent cold rolling breakage.

[0035] For dislocation strengthening, low temperature annealing is performed to keep the finished product structure in an unrecrystallized state to achieve strengthening. The annealing target temperature t (°C) of the present invention is set according to the total content A (%) of Si, Al, and Mn. That is, when the solid solution strengthening effect is large, the annealing temperature is appropriately increased to reduce the dislocation strengthening effect, and when the solid solution strengthening effect is small, the annealing temperature is appropriately lowered to enhance the dislocation strengthening effect. Thus, by matching the annealing temperature with the product composition, an optimal match between solid solution strengthening and dislocation strengthening is achieved. Specifically, the annealing target temperature t = -56.8A 2+572.9A-825.7, based on the actual situation of large-scale production, the actual annealing temperature T (℃) can fluctuate by plus or minus 30℃ based on the annealing target temperature t, that is, T = t±30. If the actual annealing temperature is lower than the lower limit, the dislocation density in the structure is too high. Although the product has a large mechanical margin, the magnetic properties deteriorate significantly and the magnetic properties target of the present invention is not achieved. If the actual annealing temperature is higher than the upper limit, the structure undergoes partial band crystallization, the dislocation density in the structure is low, the dislocation strengthening effect is insufficient, and the product mechanics cannot achieve the mechanical target of the present invention. The dislocation strengthening effect is mainly determined by the annealing temperature. On the premise that the actual annealing temperature meets the requirements of the invention, the present invention formulates the annealing speed according to the annealing temperature, that is, by matching the annealing temperature and annealing speed, it ensures that the steel plate annealing process obtains appropriate energy. When the annealing temperature is high, the annealing speed can be appropriately increased, and when the annealing temperature is low, the annealing speed should be appropriately slowed down. Based on multiple trials, the present invention requires that the annealing target speed c (m / min) be determined by the formula c = 120 + 1.5 (Tt), and the actual annealing speed C (m / min) can fluctuate by plus or minus 5 m / min based on the annealing target speed c, that is, C = c ± 5.

[0036] The present invention strengthens the alloy by precipitating carbonitrides of Nb, Ti, and V. Taking into account both the mechanical strength and magnetic properties of the product, the precipitation strengthening element content is as follows: 0.0005% ≤ Nb ≤ 0.0010%, 0.0018% ≤ Ti ≤ 0.0030%, 0.0010% ≤ V ≤ 0.0025%, 0.0020% ≤ C ≤ 0.0035%, 0.0010% ≤ N ≤ 0.0025%, and 0.0045% ≤ Nb + Ti + V ≤ 0.0055%, and 0.0035% ≤ C + N ≤ 0.0050%. The lower limits for Nb, Ti, V, C, and N are designed to ensure sufficient precipitate-forming elements to achieve the precipitation strengthening effect, while the upper limits for precipitation strengthening elements are designed to prevent excessive precipitates from deteriorating magnetic properties. The principle of precipitation strengthening in this invention is to ensure that the precipitates are fully precipitated during the hot rolling process. Therefore, a hot rolling process combining high-temperature, long-duration heating, low-temperature finish rolling, and high-temperature coiling is designed. The key hot rolling process parameters are: 1200°C ≤ heating temperature ≤ 1250°C, 6h ≤ heating time ≤ 8h, 750°C ≤ finish rolling temperature ≤ 800°C, and 700°C ≤ coiling temperature ≤ 750°C. High-temperature, long-duration heating allows the precipitates in the ingot to completely dissolve, meaning that the constituent elements of the precipitates remain in solution in the heated ingot. This facilitates the fine, dispersed precipitation of the precipitates during hot rolling. Influenced by the precipitation free energy and the element diffusion coefficient, there is an optimal precipitation temperature for the precipitates. With the composition of this invention, the optimal precipitation temperature is between 750 and 800°C. Therefore, the finish rolling temperature is set within this range to facilitate rapid precipitation under the strain induced by hot rolling. After hot rolling, the present invention also utilizes a high-temperature coiling process as close to the final rolling temperature as possible during the coiling process. This serves as a supplement to hot rolling, ensuring more complete precipitation of the precipitate phase during the coiling process. By properly designing both the precipitation strengthening element content and the hot rolling process, the precipitation strengthening effect is maintained while preventing the precipitate from deteriorating the magnetic properties.

[0037] In summary, the present invention, through the comprehensive application of dislocation strengthening, solid solution strengthening, and precipitation strengthening, creatively coordinates the design and matching of component element contents, annealing process parameters, and hot rolling process parameters, and develops a high-strength non-oriented silicon steel with a yield strength of 930 MPa and a production method thereof, thereby obtaining a high-strength non-oriented silicon steel with a yield strength of 930 MPa and excellent comprehensive mechanical and magnetic properties.

[0038] The chemical composition of the yield strength 930MPa grade high-strength non-oriented silicon steel of the present invention is designed as follows by mass percentage: the solid solution strengthening element content is 3.0≤Si≤4.0%, 0.1≤Al≤1.2%, 0.1≤Mn≤1.0%, and 4.0%≤Si+Al+Mn≤5.4%, and the precipitation strengthening element content is 0.0005%≤Nb≤0.0010%, 0.0018%≤Ti≤0 0.0030%, 0.0010%≤V≤0.0025%, 0.0020%≤C≤0.0035%, 0.0010%≤N≤0.0025%, and 0.0045%≤Nb+Ti+V≤0.0055%, 0.0035%≤C+N≤0.0050%, the content of other impurity elements is S≤0.0025%, P≤0.015%, and the rest is iron and unavoidable impurities.

[0039] The method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa adopts a process route of converter smelting → RH refining → continuous casting → hot rolling → pickling → cold rolling → annealing → coating, and specifically includes the following steps:

[0040] (1) In the converter smelting process, a slide plate is used to block the slag for tapping, and the tapping slag thickness is controlled to be no more than 40 mm. In the RH refining process, alloying is performed, and the chemical composition of the molten steel is controlled by mass percentage as follows: 3.0≤Si≤4.0%, 0.1≤Al≤1.2%, 0.1≤Mn≤1.0%, 0.0005%≤Nb≤0.0010%, 0.0018%≤Ti≤0.0030%, 0.001 0%≤V≤0.0025%, 0.0020%≤C≤0.0035%, 0.0010%≤N≤0.0025%, S≤0.0025%, P≤0.015%, and 4.0%≤Si+Al+Mn≤5.4%, 0.0045%≤Nb+Ti+V≤0.0055%, 0.0035%≤C+N≤0.0050%, and the rest are iron and unavoidable impurities.

[0041] (2) In the continuous casting process, the molten steel is prepared into ingots, and the thickness of the ingots is controlled to be 200-230 mm.

[0042] (3) In the hot rolling process, the ingot is heated, rolled, and coiled to produce a hot-rolled coil, wherein the hot rolling process parameters are controlled as follows: 1200°C ≤ heating temperature ≤ 1250°C, 6h ≤ heating time ≤ 8h, 750°C ≤ final rolling temperature ≤ 800°C, and 700°C ≤ coiling temperature ≤ 750°C.

[0043] (4) The hot rolled coil is pickled to remove the surface iron oxide scale, and then cold rolled to the target thickness of 0.15 to 0.65 mm using a 20-high Sendzimir mill.

[0044] (5) Anneal the cold rolled coil, annealing target temperature t = -56.8A 2 +572.9A-825.7, actual annealing temperature T=t±30, annealing target speed c=120+1.5(Tt), actual annealing speed C=c±5, where A is the total mass percentage content of Si, Al and Mn in the steel, T and t are in °C, and C and c are in m / min.

[0045] Furthermore, in the method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa of the present invention, a coating is also applied to the annealed cold-rolled coil. According to actual use requirements, the coating can be any coating, including a self-adhesive coating. Preferably, the coating thickness is 4 to 7 μm.

[0046] Optionally, in the method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa of the present invention, a process of normalizing the hot-rolled coil may be included after the hot rolling process and before the pickling process.

[0047] As a specific embodiment, the method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa of the present invention can produce non-oriented silicon steel with a thickness of 0.15 to 0.65 mm. For example, the finished product specifications of the non-oriented silicon steel can be 0.15 mm, 0.20 mm, 0.25 mm, 0.27 mm, 0.30 mm, 0.35 mm, 0.50 mm, and 0.65 mm.

[0048] Furthermore, in the method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa of the present invention, a continuous annealing furnace with an effective heating length of 180 to 200 meters is used to anneal the cold-rolled coil.

[0049] In accordance with GB / T 3655 and GB / T 228, magnetic and mechanical properties of the non-oriented silicon steel produced by the method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa of the present invention were tested, and the test results were as follows: yield strength Rp0.2 ≥ 930 MPa, iron loss P1.0 / 400 ≤ 57 W / kg, and magnetic polarization intensity J5000 ≥ 1.52 T.

[0050] The following detailed description of the present invention is provided in conjunction with specific examples. The cold-rolled coil annealing process in the following examples is performed using a continuous furnace with an effective heating length of 187.6 m. Unless otherwise specified, conventional process conditions are used.

[0051] Example 1

[0052] The chemical composition of the molten steel produced by converter smelting and RH refining is as follows: Nb, Ti, and V total content 0.0051%, C + N total content 0.0046%, S content 0.0022%, P content 0.011%. The main alloying elements Si, Al, and Mn are shown in Table 1 below. The molten steel was continuously cast into ingots with a cross-section of 220 × 1100 mm. The ingots were heated at 1240°C for 7 hours. The ingots were rough-rolled to a thickness of 33 mm and then rolled in a hot rolling mill in seven passes to a thickness of 2.02 mm. The finishing rolling temperature was 780°C and the coiling temperature was 730°C. The hot-rolled coils were not normalized. After pickling, they were cold-rolled to 0.15 mm and 0.50 mm, respectively. The cold-rolled coils were annealed and coated with a self-adhesive coating with a thickness of 5 μm. The annealing parameters are shown in Table 1 below. The performance of the finished non-oriented silicon steel was tested. The magnetic test used Epstein square rings, and the mechanical test was parallel to the rolling direction. The performance of the finished product is shown in Table 1 below.

[0053] As shown in Table 1, those marked with underlines do not conform to the limitations of the present invention and are therefore comparative examples in Example 1. Others that conform to the limitations of the present invention are therefore inventive examples in Example 1.

[0054] In Comparative Example 4, the Si content and the total content of Si+Al+Mn did not reach the lower limit required by the present invention. Although the yield strength of the product met the requirements of the invention, the iron loss and magnetic polarization strengthening of the product were significantly deviated.

[0055] In Comparative Example 6, the total content of Si+Al+Mn did not reach the lower limit required by the present invention, and the iron loss of the product was significantly poor.

[0056] Inventive Examples 1, 2, 3, and 5 all meet the requirements of the present invention and exhibit excellent mechanical and magnetic properties.

[0057] Table 1 Example 1

[0058]

[0059] Example 2

[0060] The chemical composition of the molten steel produced by converter smelting and RH refining is as follows, by mass: 3.45% Si, 0.75% Al, 0.50% Mn, 0.0018% S, 0.007% P, 0.0022% C, and 0.0019% N. The precipitation-strengthening elements Nb, Ti, and V are shown in Table 2 below. The molten steel was cast into ingots with a cross-sectional dimension of 220 × 1180 mm. The ingots were heated for 7 hours and then hot-rolled to a depth of 2.2 mm. The heating, finishing, and coiling temperatures are shown in Table 2 below. The hot-rolled coils were normalized at 870°C for 4 minutes, pickled, and cold-rolled to a depth of 0.30 mm. The cold-rolled coils were annealed at 620°C at 132 m / min and coated with a self-adhesive coating with a thickness of 6 μm. The performance of the finished non-oriented silicon steel was tested. The magnetic test used Epstein square rings, and the mechanical test was parallel to the rolling direction. The performance of the finished product is shown in Table 2 below.

[0061] As shown in Table 2, those marked with underlines do not conform to the limitations of the present invention and are therefore comparative examples in Example 2. Others that conform to the limitations of the present invention are therefore inventive examples in Example 2.

[0062] In Comparative Example 3, the total content of Nb+Ti+V is lower than the lower limit required by the present invention, and the precipitation strengthening effect is insufficient, resulting in a product yield strength Rp0.2 of less than 930 MPa.

[0063] In Comparative Example 4, the total amount of Nb+Ti+V exceeds the upper limit required by the present invention, and too many precipitated phases lead to deterioration of the magnetic properties of the product, and the magnetic properties do not meet the standards.

[0064] The hot rolling process parameters of Comparative Examples 5, 6, and 7 do not meet the requirements of the present invention, the precipitation strengthening effect is weak, and the yield strength Rp0.2 of the product is lower than 930 MPa.

[0065] Inventive Examples 1 and 2, the Nb, Ti, and V contents and hot rolling process parameters are within the design range of the invention, the products achieve good precipitation strengthening effects, and the magnetic properties do not deteriorate, and the comprehensive performance of the products reaches the invention goal.

[0066] Table 2 Example 2

[0067]

[0068] Example 3

[0069] The chemical composition of the molten steel produced by converter smelting and RH refining is as follows: 3.6% Si, 1.0% Al, 0.25% Mn as the main alloying elements; 0.0045-0.0055% Nb, Ti, and V in total; 0.0037-0.0045% C and N in total; 0.0025% S, ≤0.015% P, ≤0.015%; and a Si, Al, and Mn total content (A) of 4.85%. The molten steel is cast into ingots with a cross-sectional dimension of 220 x 1150 mm. The ingots are heated to 1230°C for 7.5 hours. They are rough-rolled to a thickness of 35 mm and then rolled in seven passes in a hot rolling mill to a thickness of 1.8 mm. The final finishing temperature is 760-770°C, and the coiling temperature is 730-740°C. After normalizing at 880°C for 4 minutes, the hot-rolled coils were pickled and cold-rolled to 0.25mm, 0.35mm, and 0.65mm, respectively. The cold-rolled coils were annealed. The annealing rates and temperatures are shown in Table 3 below. The finished non-oriented silicon steel was subjected to performance testing. Magnetic testing was performed using an Epstein square ring, and mechanical testing was performed parallel to the rolling direction. The finished product properties are shown in Table 3 below.

[0070] As shown in Table 3, those marked with underlines do not conform to the limitations of the present invention and are therefore comparative examples in Example 3. Others that conform to the limitations of the present invention are therefore inventive examples in Example 3.

[0071] Inventive Examples 1, 4, and 7 all meet the requirements of the present invention for the matching relationship between product composition, annealing temperature, and annealing speed. The mechanical properties and magnetic properties of products with different thickness specifications all achieve the goals of the present invention.

[0072] In comparative examples 3, 6, and 9, the actual annealing temperature T is lower than the lower limit of the annealing target temperature t±30°C required by the present invention. Although the mechanical properties reach the target of the invention, the magnetic properties are significantly deteriorated and the magnetic properties do not meet the standards.

[0073] In Comparative Examples 2, 5, and 8, the actual annealing temperature T is higher than the upper limit of the annealing target temperature t±30°C required by the present invention. Although the magnetic properties reach the invention target, the yield strength Rp0.2 of the product does not reach the invention target of ≥930 MPa.

[0074] The metallographic organization diagrams of the non-oriented silicon steel finished plates corresponding to Inventive Example 1, Comparative Example 2, Inventive Example 4, Comparative Example 5, Inventive Example 7 and Comparative Example 8 are shown as follows: Figure 1-6As shown. It can be seen that the finished product structures of Inventive Examples 1, 4, and 7 are not recrystallized, and the dislocation density of the unrecrystallized structure is high, so the products obtain higher mechanical properties and achieve the invention goals. The annealing temperatures of Comparative Examples 2, 5, and 8 are relatively high, and the finished product structures have undergone partial recrystallization. Recrystallization leads to a decrease in dislocation density, a weakening of the dislocation strengthening effect, and a low mechanical strength of the product. In addition, the annealing temperatures of Comparative Examples 3, 6, and 9 are relatively low, and the product structures are not completely recrystallized. There is no obvious difference between the tissue images and Inventive Examples 1, 4, and 7, so the metallographic tissue photos of Comparative Examples 3, 6, and 9 are not listed. However, due to the low annealing temperature, the degree of recovery of the product structure of Comparative Examples 3, 6, and 9 is less than that of the Inventive Examples, so the dislocation density of the structure is higher, resulting in a significant deterioration of the magnetic properties despite the product achieving higher mechanical strength.

[0075] Table 3 Example 3

[0076]

[0077] In summary, since a single strengthening method is difficult to achieve a balance between the mechanical properties, magnetic properties, cost and production feasibility of the product, the present invention comprehensively uses three strengthening methods: dislocation strengthening, solid solution strengthening and precipitation strengthening, thereby obtaining excellent comprehensive mechanical and magnetic properties. Among them, the annealing temperature and annealing rate are determined according to the content of the main alloying elements, and a strict composition-annealing temperature-annealing rate matching relationship is invented, so that while relying on the unrecrystallized structure to improve the mechanical properties, the magnetic properties are guaranteed not to deteriorate; the content design of the solid solution strengthening elements Si, Al, and Mn prevents the product from experiencing production problems such as cold rolling breakage while achieving solid solution strengthening; the content design of the precipitation strengthening elements Nb, Ti, V, C, and N, in conjunction with the hot rolling process of "high temperature and long time heating, low temperature final rolling, and high temperature coiling", achieves strengthening by effectively precipitating Nb, Ti, and V carbonitrides, and prevents excessive precipitation from deteriorating the magnetic properties. Therefore, by comprehensively using dislocation strengthening, solid solution strengthening, and precipitation strengthening and through the coordinated design of composition and process, the non-oriented silicon steel prepared by the present invention has excellent mechanical properties and comprehensive magnetic properties, with a yield strength Rp0.2≥930MPa, an iron loss P1.0 / 400≤57W / kg, and a magnetic polarization intensity J5000≥1.52T. Compared with the existing conventional highest-grade non-oriented silicon steel (yield strength of approximately 430MPa), the yield strength is increased by more than 500MPa, filling the market gap of the current lack of 930MPa-grade high-strength non-oriented silicon steel with excellent comprehensive performance, and does not add expensive alloy elements such as Ni, Cu, Sn, and Sb, and has excellent economy.

[0078] It should be noted that, unless otherwise specified, the noun terms herein have the meanings commonly understood by those skilled in the art. Moreover, when a numerical range is disclosed herein, the above range is deemed to be continuous and includes the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple range description features are provided, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0079] It should also be noted that, in this article, the term "comprise" or any other variation thereof is intended to cover non-exclusive inclusion, so that an article or device that includes a series of elements includes not only those elements, but also includes other elements that are not explicitly listed, or also includes elements that are inherent to such article or device.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A high-strength non-oriented silicon steel with a yield strength of 930 MPa, characterized in that: The chemical composition of the high-strength non-oriented silicon steel with a yield strength of 930 MPa is designed as follows by mass percentage: the contents of solid solution strengthening elements are 3.0≤Si≤4.0%, 0.1≤Al≤1.2%, 0.1≤Mn≤1.0%, and 4.0%≤Si+Al+Mn≤5.4%; the contents of precipitation strengthening elements are 0.0005%≤Nb≤0.0010%, 0.0018%≤Ti≤0.0030%, 0.0010%≤V≤0.0025%, 0.0020%≤C≤0.0035%, 0.0010%≤N≤0.0025%, and 0.0045%≤Nb+Ti+V≤0.0055%, 0.0035%≤C+N≤0.0050%, S≤0.0025%, P≤0.015%, and the rest are iron and unavoidable impurities.

2. The high-strength non-oriented silicon steel with a yield strength of 930 MPa according to claim 1, characterized in that: The yield strength of the 930 MPa grade high-strength non-oriented silicon steel is Rp0.2≥930 MPa, iron loss P1.0 / 400≤57 W / kg, and magnetic polarization intensity J5000≥1.52 T.

3. A method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa, adopting a process route of converter smelting → RH refining → continuous casting → hot rolling → pickling → cold rolling → annealing → coating, characterized in that: (1) The chemical composition of the molten steel produced by converter smelting and RH refining is controlled to be as follows by mass percentage: 3.0≤Si≤4.0%, 0.1≤Al≤1.2%, 0.1≤Mn≤1.0%, 0.0005%≤Nb≤0.0010%, 0.0018%≤Ti≤0.0030%, 0.0010%≤V≤0.0025%, 0.0020%≤C≤0.0035%, 0.0010%≤N≤0.0025%, S≤0.0025%, P≤0.015%, and 4.0%≤Si+Al+Mn≤5.4%, 0.0045%≤Nb+Ti+V≤0.0055%, 0.0035%≤C+N≤0.0050%, with the remainder being iron and unavoidable impurities; (2) In the continuous casting process, the molten steel is prepared into a casting billet; (3) In the hot rolling process, the ingot is heated, rolled, and coiled to obtain a hot-rolled coil, wherein the hot rolling process parameters are controlled as follows: 1200° C. ≤ heating temperature ≤ 1250° C., 6 h ≤ heating time ≤ 8 h, 750° C. ≤ finishing rolling temperature ≤ 800° C., and 700° C. ≤ coiling temperature ≤ 750° C.; (4) Pickling the hot-rolled coil to remove surface iron oxide scale, and then cold rolling it to the target thickness; (5) Anneal the cold rolled coil at target annealing temperature t = -56.8A 2 +572.9A-825.7, actual annealing temperature T=t±30, annealing target speed c=120+1.5(Tt), actual annealing speed C=c±5, where A is the total mass percentage content of Si, Al and Mn in the steel, T and t are in °C, and C and c are in m / min.

4. The method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa according to claim 3, characterized in that: The method further comprises applying a coating to the annealed cold-rolled coil, wherein the coating has a thickness of 4 to 7 μm.

5. The method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa according to claim 4, characterized in that: The coating is a self-bonding coating.

6. The method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa according to claim 3, characterized in that: After the hot rolling process and before the pickling process, the process of normalizing the hot-rolled coil is also included.

7. The method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa according to claim 3, characterized in that: The target thickness of the non-oriented silicon steel is 0.15-0.65 mm.

8. The method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa according to claim 7, characterized in that: The target thicknesses of the non-oriented silicon steel include 0.15 mm, 0.20 mm, 0.25 mm, 0.27 mm, 0.30 mm, 0.35 mm, 0.50 mm, and 0.65 mm.

9. The method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa according to claim 3, characterized in that: In the annealing process, a continuous annealing furnace with an effective heating length of 180 to 200 meters is used to anneal the cold-rolled coils.

10. The method for producing high-strength non-oriented silicon steel with a yield strength of 930 MPa according to claim 3, characterized in that: In the converter smelting process, a slide plate is used to block the slag during steel tapping, and the slag thickness is controlled to be no more than 40mm.

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