An ultra-high strength non-oriented silicon steel with a yield strength of ≥ 1300 MPa and a method for producing the same

Abstract

The application relates to the technical field of ultrahigh-strength non-oriented silicon steel, in particular to ultrahigh-strength non-oriented silicon steel with a yield strength of greater than or equal to 1300 MPa and a preparation method thereof. The ultrahigh-strength non-oriented silicon steel comprises the following components in percentage by mass: Si 2.8-3.5%, Al 0.7-1.0%, Mn 0.1-0.5% and Cu 0.5-1.5%, and the rest is Fe and inevitable impurities. The preparation method of the ultrahigh-strength non-oriented silicon steel comprises the following steps: smelting, hot rolling, normalizing treatment, cold rolling and annealing treatment, wherein the temperature of the hot rolling is 1000-1050 DEG C; the normalizing treatment is: keeping at 900-950 DEG C for 5-10 min or keeping at 950-1000 DEG C for 3-5 min; and the annealing treatment is: keeping at 400-500 DEG C for 3-5 min or keeping at 500-550 DEG C for 1-3 min. The ultrahigh-strength non-oriented silicon steel prepared by the application has a yield strength of greater than or equal to 1300 MPa, an iron loss value P 1.0 / 400 of 40-60 W / kg and a magnetic induction intensity B 5000 of 1.50-1.55 T, and the performance can meet the strength requirement of driving motor rotor core at ultrahigh speed.

Description

Technical Field

[0001] This invention belongs to the technical field of ultra-high strength non-oriented silicon steel. Specifically, it relates to an ultra-high strength non-oriented silicon steel with a yield strength ≥1300MPa and its preparation method. Background Technology

[0002] To address the needs of global climate change and energy structure transformation, the new energy vehicle industry has experienced rapid development. As the core power component of new energy vehicles, the drive motor's increasing speed and power density have become crucial industry trends. Currently, the maximum speed of commercially available drive motors generally exceeds 20,000 r / min, and some advanced new energy vehicle manufacturers have developed next-generation drive motors with speeds exceeding 30,000 r / min. This means that the operating conditions of the drive motor rotor core are becoming increasingly demanding. With the continuous increase in motor speed, non-oriented silicon steel, the core material of the rotor core, faces enormous centrifugal stress challenges. Under such extreme speeds, if the strength of the non-oriented silicon steel is insufficient, the rotor is prone to deformation or even fatigue fracture during long-term service, seriously threatening the motor's operational safety. Therefore, developing ultra-high-strength non-oriented silicon steel with higher yield strength has significant engineering application value.

[0003] To meet the high-strength design requirements of ultra-high-speed motors, the industry has undertaken extensive development of high-strength non-oriented silicon steel in recent years, primarily focusing on single or dual strengthening mechanisms such as solid solution strengthening, dislocation strengthening, grain refinement strengthening, and precipitation strengthening. However, limited by traditional alloy composition systems and conventional manufacturing processes, the yield strength of silicon steel is typically increased to the 500–800 MPa level. According to publicly available data from 2025, the ultra-high-strength silicon steel used in Xiaomi's V8s super motor has a yield strength of 960 MPa. Even so, facing the extreme design requirements of future higher-speed motors, existing material systems and strengthening strategies face performance bottlenecks. There is an urgent need to explore more rational alloy composition designs and synergistic multi-coupling strengthening mechanisms to maximize the performance potential of silicon steel materials, thereby providing a feasible path for the development of next-generation ultra-high-strength non-oriented silicon steel with a yield strength exceeding 1000 MPa.

[0004] Patent CN10774694A discloses a high-strength cold-rolled non-oriented silicon steel for drive motors and its manufacturing method. This method involves adding appropriate amounts of Cr and Nb to the cold-rolled non-oriented silicon steel, and by controlling the secondary cold rolling reduction and annealing process, achieving a yield strength of 460–510 MPa. However, the strengthening effect achieved by these trace elements cannot significantly improve the mechanical properties of the non-oriented silicon steel, making it difficult to meet the performance requirements of ultra-strong non-oriented silicon steel.

[0005] Patent CN106282781A discloses a method for preparing high-strength non-oriented silicon steel using nano-Cu precipitation strengthening. This method uses Cu as the alloying element, with the addition of small amounts of Ni and Cr. After recrystallization, the cold-rolled sheet is cooled to 450–650℃ and held at that temperature for 20–60 minutes for aging treatment. The resulting silicon steel has a yield strength of 640–750 MPa, achieving a balance between mechanical and magnetic properties. Although this method achieves a higher yield strength than ordinary non-oriented silicon steel, it still cannot meet the yield strength requirements of ultra-high-speed motor rotor cores.

[0006] Patent CN114058963A discloses a method for preparing high-strength non-oriented silicon steel based on nano-precipitation strengthening. In addition to the basic alloying elements Si, Mn, and Al, this method also adds 2.5–6.5 wt% Ni and a suitable amount of Cu. By utilizing the nano-B2 type NiAl intermetallic compound generated during low-temperature aging, the yield strength of the non-oriented silicon steel can be significantly increased to 700–1000 MPa. This technology relies on the synergistic strengthening effect of solid solution strengthening and NiAl nano-precipitation to achieve the desired enhancement effect. However, the high Ni content leads to a significant increase in the cost of alloy raw materials; furthermore, the additional aging process reduces production efficiency.

[0007] In summary, the yield strength of high-strength non-oriented silicon steel prepared by existing technologies cannot meet the market demand for ultra-high-speed motor rotor cores. This is the purpose of this invention: to provide a simple, low-cost method for preparing ultra-high-strength non-oriented silicon steel suitable for ultra-high-speed motor rotor cores. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, the present invention provides a method for preparing ultra-high strength non-oriented silicon steel with a yield strength ≥1300MPa. The chemical composition of the ultra-high strength non-oriented silicon steel, by mass percentage, includes: Si 2.8-3.5%, Al 0.7-1.0%, Mn 0.1-0.5% and Cu 0.5-1.5%, with the remainder being Fe and unavoidable impurities. The preparation method of ultra-high strength non-oriented silicon steel is as follows: S1. Smelting: Vacuum melting of the chemical composition raw materials of ultra-high strength non-oriented silicon steel to obtain a casting billet; S2. Hot rolling: The billet obtained in step S1 is hot rolled to obtain a hot-rolled plate. The hot rolling temperature is 1000-1050℃. S3. Normalizing treatment: The hot-rolled plate obtained in step S2 is subjected to normalizing treatment, which is: holding at 900-950℃ for 5-10 min; or holding at 950-1000℃ for 3-5 min; S4. Cold rolling: The normalized plate obtained in step S3 is cold rolled to obtain a cold-rolled plate; S5. Annealing treatment: The cold-rolled sheet obtained in S4 is annealed by holding it at 400-500℃ for 3-5 minutes; or at 500-550℃ for 1-3 minutes. Preferably, in step S5, when the mass percentage of Cu is 0.5% to 1.0%, the annealing treatment is performed in... Keep warm at 500-550℃ for 1-3 minutes.

[0009] Preferably, in step S5, when the mass percentage of Cu is 1.0–1.5%, the annealing treatment is performed at… Keep warm at 400-500℃ for 3-5 minutes.

[0010] The yield strength of ultra-high strength non-oriented silicon steel is not less than 1300 MPa, and the iron loss value P 1.0 / 400 The magnetic induction intensity B is 40-60 W / kg. 5000 It is 1.50 to 1.55T.

[0011] Traditional processes require high-temperature annealing and recrystallization followed by aging to precipitate well-coherent nano-Cu particles; furthermore, the size of Cu particles is difficult to control during aging. This proposed method, however, involves low-temperature annealing after cold rolling. This preserves some of the cold-rolled deformed structure, achieving dislocation strengthening and grain refinement, while also promoting the precipitation of a large amount of Cu-rich nano-phase. Simultaneously, the short annealing holding time maintains a good coherent relationship in the Cu precipitates, maximizing the precipitation strengthening effect. Combined with the solid solution strengthening effects of the alloy's Si, Al, and Mn elements, ultra-high-strength non-oriented silicon steel with a yield strength of not less than 1300 MPa is thus produced.

[0012] Preferably, in step S3, the normalizing treatment is cooled by water quenching. The high-temperature holding process of the normalizing treatment allows Cu to fully dissolve into the ferrite matrix; the rapid cooling process of water quenching can effectively suppress the premature precipitation of coarse Cu precipitates, resulting in a Cu supersaturated solid solution.

[0013] Preferably, in step S4, the cold rolling temperature is room temperature, and the thickness of the cold-rolled sheet is 0.1–0.3 mm. Throughout the entire preparation process, the total cold rolling reduction rate of the silicon steel does not exceed 80%.

[0014] Preferably, in step S1, the smelting temperature is 1400–1500°C.

[0015] In addition, the present invention also provides an ultra-high strength non-oriented silicon steel, which is prepared according to the above-mentioned method for preparing ultra-high strength non-oriented silicon steel.

[0016] This invention, based on Si, Al, and Mn, adds a small amount of Cu element and prepares ultra-high strength non-oriented silicon steel with a yield strength ≥1300MPa through smelting, hot rolling, normalizing, cold rolling, and annealing processes. The chemical composition system of this preparation process is simple, the alloy cost is low, and the smelting process is easy to control, making it suitable for industrial production applications.

[0017] This invention employs multiple enhanced coupling methods to maximize the mechanical properties of non-oriented silicon steel while maintaining its magnetic properties within a reasonable range, thereby obtaining ultra-high strength non-oriented silicon steel with a yield strength ≥1300MPa.

[0018] The ultra-high strength non-oriented silicon steel prepared by this invention has the following mechanical and magnetic properties as tested: yield strength not less than 1300 MPa, and iron loss value P 1.0 / 400 The magnetic induction intensity B is 40-60 W / kg. 5000 With a strength of 1.50 to 1.55T, this performance can meet the strength requirements of the rotor core of the drive motor at ultra-high speeds. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The image shows the microstructure of the ultra-high strength non-oriented silicon steel prepared in Example 1. Figure 2 The image shows the morphology of the Cu precipitate in the ultra-high strength non-oriented silicon steel prepared in Example 1. Figure 3 The stress-strain curve of the ultra-high strength non-oriented silicon steel prepared in Example 1 is shown. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0023] Examples 1-4 and Comparative Examples 1-4 The chemical composition of Examples 1-4 and Comparative Examples 1-4 is shown in Table 1, with the remainder being Fe and unavoidable impurities, in mass percentage.

[0024] The preparation methods of Examples 1-4 and Comparative Examples 1-4 are as follows: The ultra-high strength non-oriented silicon steel was vacuum melted according to its chemical composition and cast into slabs at 1450℃. The slabs were then hot-rolled at 1000℃ to obtain hot-rolled plates with a thickness of 1.0±0.5mm. The hot-rolled plates were then normalized at 950℃ for 3 minutes. The normalized hot-rolled plates were then cold-rolled at room temperature to obtain cold-rolled plates with a thickness of 0.2±0.1mm. The cold-rolled plates were then annealed at 550℃ for 3 minutes.

[0025] The ultra-high strength non-oriented silicon steels prepared in Examples 1-4 and Comparative Examples 1-4 were tested to detect their performance, and the test data are shown in Table 1.

[0026] Table 1 Example 2 and Comparative Example 1 had the same Si, Mn, and Cu content, with the only difference being the Al content. Comparative Example 1 reduced the Al content, resulting in a decrease in the yield strength of the ultra-high strength non-oriented silicon steel. Example 2 and Example 4 maintained the same Si, Al, and Mn content. Compared to Example 2, Example 4 increased the Cu content, resulting in ultra-high strength non-oriented silicon steel with a higher yield strength.

[0027] The comparative experimental results above show that adjusting the content of Si, Mn, Al, and Cu elements will cause a corresponding change in the yield strength of the resulting ultra-high strength non-oriented silicon steel. Therefore, the suitable mass percentage content of each element in this ultra-high strength non-oriented silicon steel is: Si 2.8–3.5%, Al 0.7–1.0%, Mn 0.1–0.5%, and Cu 0.5–1.5%.

[0028] Examples 5-6 and Comparative Examples 5-6 Referring to Example 1, the hot rolling temperature in the preparation method of ultra-high strength non-oriented silicon steel was changed, and Examples 5-6 and Comparative Examples 5-6 were set. The specific parameters and performance test results are shown in Table 2.

[0029] Table 2 Example 1 and Comparative Example 5 had the same preparation process conditions, with the only difference being the hot rolling temperature; Comparative Example 5 reduced the hot rolling temperature, resulting in a significant decrease in the yield strength of the ultra-high strength non-oriented silicon steel. Example 1 and Comparative Example 6 had the same preparation process conditions, with the only difference being the hot rolling temperature; Comparative Example 6 increased the hot rolling temperature, resulting in a significant decrease in the yield strength of the ultra-high strength non-oriented silicon steel.

[0030] The results of the comparative experiments above show that adjusting the hot rolling temperature will cause a corresponding change in the yield strength of the resulting ultra-high strength non-oriented silicon steel. Therefore, the suitable hot rolling temperature range for this ultra-high strength non-oriented silicon steel is 1000–1050℃.

[0031] Examples 7-10 and Comparative Examples 7-10 Referring to Example 1, the normalizing temperature and normalizing holding time in the preparation method of ultra-high strength non-oriented silicon steel were changed, and Examples 7-10 and Comparative Examples 7-10 were set up. The specific parameters and performance test results are shown in Table 3.

[0032] Table 3 Examples 1, 8, and 10 were prepared under the same conditions, differing only in the normalizing holding time, which was 3 min, 6 min, and 10 min, respectively. The ultra-high strength non-oriented silicon steel obtained in Example 10 exhibited better yield strength. Examples 10 and Comparative Example 9 were prepared under the same conditions, differing only in the normalizing holding time; the increased normalizing holding time in Comparative Example 9 resulted in a significant decrease in the yield strength of the ultra-high strength non-oriented silicon steel obtained in Comparative Example 9. Examples 1, 9, and Comparative Example 8 were prepared under the same conditions, differing only in the normalizing temperature, which was 950℃, 1000℃, and 1010℃, respectively. The yield strength of the ultra-high strength non-oriented silicon steel obtained in Example 1 was essentially the same as that obtained in Example 9, while the yield strength of the ultra-high strength non-oriented silicon steel obtained in Comparative Example 8 decreased significantly.

[0033] The comparative experimental results above show that adjusting the normalizing temperature and holding time will cause a corresponding change in the yield strength of the ultra-high strength non-oriented silicon steel. Therefore, the suitable normalizing treatment for this ultra-high strength non-oriented silicon steel is: holding at 900–950℃ for 5–10 min; or holding at 950–1000℃ for 3–5 min.

[0034] Examples 11-13 and Comparative Examples 11-14 Referring to Example 1, the annealing temperature and annealing holding time in the preparation method of ultra-high strength non-oriented silicon steel were changed, and Examples 11-13 and Comparative Examples 11-14 were set up. The specific parameters and performance test results are shown in Table 4.

[0035] Table 4 The preparation conditions for Examples 1, 12, and Comparative Example 12 were the same, with the only difference being the annealing temperature, which was 550℃, 500℃, and 560℃, respectively. In Example 12, the annealing temperature decreased, resulting in a decrease in the yield strength of the ultra-high strength non-oriented silicon steel. In Comparative Example 12, the annealing temperature increased, leading to a significant decrease in the yield strength of the ultra-high strength non-oriented silicon steel. The preparation conditions for Examples 1 and 13 were the same, with the only difference being the annealing holding time. In Example 13, the annealing holding time was reduced, resulting in an increase in the yield strength of the ultra-high strength non-oriented silicon steel.

[0036] The results of the comparative experiments above show that adjusting the annealing temperature and holding time will cause a corresponding change in the yield strength of the ultra-high strength non-oriented silicon steel. Therefore, the suitable annealing treatment for this ultra-high strength non-oriented silicon steel is: holding at 400–500℃ for 3–5 minutes; or holding at 500–550℃ for 1–3 minutes. By comparing experiments similar to Examples 1-13 and Comparative Examples 1-14, and through similar analysis and testing, it can be seen that the ultra-high strength non-oriented silicon steel prepared under the process conditions of Cu mass percentage of 0.5-1.0%, annealing temperature of 500-550℃, and annealing holding time of 1-3 min has better performance, with a yield strength of not less than 1380 MPa; the ultra-high strength non-oriented silicon steel prepared under the process conditions of Cu mass percentage of 1.0-1.5%, annealing temperature of 400-500℃, and annealing holding time of 3-5 min also has better performance, with a yield strength of not less than 1430 MPa.

[0037] The microstructure of the ultra-high strength non-oriented silicon steel prepared in Example 1 was characterized by scanning electron microscopy, and the results are as follows: Figure 1 , Figure 2 As shown, where, Figure 1 Its microstructure morphology diagram, Figure 2 The image shows the microstructure of the Cu precipitate.

[0038] Depend on Figure 1 It can be seen that the microstructure of the ultra-high strength non-oriented silicon steel obtained in Example 1 has not yet undergone complete recrystallization, with fine grains and retaining some cold-rolled texture; combined with Figure 2 It is known that the grains contain dislocations and a large number of fine Cu precipitates are distributed in the matrix. The fine grain structure, Cu precipitates and dislocations can achieve the coupled strengthening effect of fine grain strengthening, precipitation strengthening and dislocation strengthening, effectively improving the yield strength of the material. Thus, ultra-high strength non-oriented silicon steel with a yield strength of not less than 1300 MPa is obtained.

[0039] Figure 3 This is the stress-strain curve of the ultra-high strength non-oriented silicon steel obtained in Example 1. Figure 3 It can be seen that the ultra-high strength non-oriented silicon steel prepared in Example 1 has a high yield strength.

[0040] The specific implementation method of this application is simple and has low production cost. The ultra-high strength non-oriented silicon steel obtained has a yield strength ≥1300MPa and suitable magnetic induction intensity, which is suitable for the rotor core of ultra-high speed motor.

[0041] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing ultra-high strength non-oriented silicon steel, characterized in that, The chemical composition of the ultra-high strength non-oriented silicon steel, by mass percentage, includes: Si 2.8-3.5%, Al 0.7-1.0%, Mn 0.1-0.5% and Cu 0.5-1.5%, with the remainder being Fe and unavoidable impurities; The preparation method of the ultra-high strength non-oriented silicon steel is as follows: S1. Smelting: The chemical composition raw materials of the ultra-high strength non-oriented silicon steel are vacuum smelted to obtain a casting billet; S2. Hot rolling: The billet obtained in step S1 is hot rolled to obtain a hot-rolled plate. The hot rolling temperature is 1000-1050℃. S3. Normalizing treatment: The hot-rolled plate obtained in step S2 is subjected to normalizing treatment, which is: holding at 900-950℃ for 5-10 minutes; or holding at 950-1000℃ for 3-5 minutes; S4. Cold rolling: The normalized plate obtained in step S3 is cold rolled to obtain a cold-rolled plate; S5. Annealing treatment: The cold-rolled sheet obtained in S4 is subjected to annealing treatment, wherein the annealing treatment is: holding at 400-500℃ for 3-5 minutes; or holding at 500-550℃ for 1-3 minutes; The yield strength of the ultra-high strength non-oriented silicon steel is not less than 1300 MPa, and the iron loss value P 1.0 / 400 The magnetic induction intensity B is 40-60 W / kg. 5000 It is 1.50 to 1.55T.

2. The method for preparing ultra-high strength non-oriented silicon steel as described in claim 1, characterized in that, step In S5, when the mass percentage of Cu is 0.5-1.0%, the annealing process is to hold at 500-550°C for 1-3 minutes.

3. The method for preparing ultra-high strength non-oriented silicon steel as described in claim 1, characterized in that, step In S5, when the mass percentage of Cu is 1.0 to 1.5%, the annealing process is to hold at 400 to 500°C for 3 to 5 minutes.

4. The method for preparing ultra-high strength non-oriented silicon steel as described in claim 1, characterized in that, step In S3, the normalization process is cooled by water quenching.

5. The method for preparing ultra-high strength non-oriented silicon steel as described in claim 1, characterized in that, In step S4, the cold rolling temperature is room temperature, and the thickness of the cold-rolled sheet is 0.1 to 0.3 mm.

6. The method for preparing ultra-high strength non-oriented silicon steel as described in claim 1, characterized in that, In step S1, the smelting temperature is 1400–1500°C.

7. An ultra-high strength non-oriented silicon steel prepared by the method for preparing ultra-high strength non-oriented silicon steel according to any one of claims 1-6.

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