A method of manufacturing high-strength non-oriented electrical steel

Abstract

The application discloses a high-strength non-oriented electrical steel manufacturing method, and relates to the technical field of electrical steel manufacturing. The high-strength non-oriented electrical steel manufacturing method creatively applies phase transition and water quenching technology, significantly optimizes magnetic performance while reaching or exceeding the existing strengthening technical level in yield strength, and is lower in magnetic performance iron loss and better in magnetic induction compared with a dislocation strengthening scheme, thereby meeting the dual strict requirements of high strength and low iron loss of a high-speed motor. In terms of chemical composition, only appropriate addition of C elements is needed to realize phase transition, without the need of introducing a large amount of precious metals such as Cr, Ni and Cu or rare elements such as Nb and Zr, so that the alloy cost is significantly reduced; in terms of process, a conventional smelting, hot rolling, normalizing, cold rolling and annealing process is adopted, without the need of additional aging treatment, so that the production steps are simplified, and the equipment investment and production cycle cost are reduced.

Description

Technical Field

[0001] This application belongs to the field of electrical steel manufacturing technology, and in particular relates to a method for manufacturing high-strength non-oriented electrical steel. Background Technology

[0002] Non-oriented electrical steel, as a core soft magnetic material in electromagnetic conversion scenarios, has been widely used in the manufacture of various motor cores. With the rapid development of industries such as aerospace, new energy vehicles, and wind power, photovoltaic, and energy storage, equipment is upgrading towards higher speed, higher efficiency, and lighter weight, which places dual stringent requirements on non-oriented electrical steel.

[0003] On the one hand, the rotor core of a high-speed motor needs to withstand a huge moment of inertia, which requires the material to have extremely high strength; on the other hand, the energy-saving requirements of electrical equipment require the material to maintain excellent magnetic properties such as low iron loss and high magnetic induction.

[0004] In existing technologies, the main approaches to improving the strength of non-oriented electrical steel include solid solution strengthening, precipitation strengthening, dislocation strengthening, and composite strengthening, but all have significant drawbacks. Some solutions use high-silicon compositions or add elements such as chromium and tin to achieve solid solution strengthening. While this can improve strength, it leads to easy breakage of the steel coil during cold rolling and a significant increase in hysteresis loss. Some solutions add precipitation strengthening elements such as niobium or use nano-intermetallic compound precipitation strengthening processes, but these suffer from high iron loss in the finished product, increased costs due to high alloy content, long aging treatment times, and difficulties in cold working. Other solutions rely on the principle of dislocation strengthening, retaining some deformed structures by controlling the amount of reduction in secondary cold rolling and two annealing processes. This not only results in complex processes and high manufacturing costs but also leads to poor high-frequency iron loss performance in the product.

[0005] To achieve optimal magnetic properties, conventional high-grade non-oriented electrical steel typically has extremely low carbon content and high silicon and aluminum content. During heat treatment, it forms only a single ferrite structure, making it difficult to meet the strength requirements of high-end equipment. Existing manufacturing methods for high-strength electrical steel either struggle to balance strength and magnetic properties, rely heavily on adding precious metals and rare elements, or require complex processes and specialized equipment, resulting in high costs and limiting industrialization.

[0006] Therefore, the industry urgently needs a manufacturing method for non-oriented electrical steel that is simple in process, cost-controllable, and can simultaneously achieve high yield strength and excellent magnetic properties, in order to solve the technical problems of "contradiction between strength improvement and magnetic property protection" and "imbalance between cost and process complexity" in the existing technology. Summary of the Invention

[0007] To address some or all of the technical problems existing in the prior art, this application provides a method for manufacturing high-strength non-oriented electrical steel.

[0008] This application provides a method for manufacturing high-strength non-oriented electrical steel, comprising the following steps performed sequentially: Step S1: Chemical composition design. The chemical composition of the billet, by mass percentage, meets the following requirements: C: 0.01~0.10%, Si: 2.50~4.00%, Mn: 0.10~0.50%, Al: 0.02~1.2%, P: ≤0.02%, S: ≤0.005%, N: ≤0.005%, Ti: ≤0.005%, with the remainder being Fe and unavoidable impurities. Step S2: Heating the billet, heating the billet with the above composition to a preset temperature range; Step S3: Hot rolling and coiling: The heated billet is hot rolled to the preset thickness, and the final rolling temperature and coiling temperature are controlled. Step S4: Normalizing treatment, the hot-rolled plate is normalized to eliminate the inhomogeneity of the hot-rolled structure; Step S5: Cold rolling, pickling the normalized hot-rolled plate to remove the oxide scale, and then cold rolling it to the finished thickness in one step; Step S6: Finished product annealing and rapid cooling. The cold-rolled sheet is annealed at a temperature above the phase transformation point AC3 and held at that temperature for a preset time. After annealing, it is immediately quenched in water for rapid cooling. Step S7: Coating and curing. Apply a coating liquid to the rapidly cooled steel plate, and then dry and cure it at a preset temperature to obtain high-strength non-oriented electrical steel.

[0009] The high-strength non-oriented electrical steel manufacturing method of this application has the following advantages and positive effects: While achieving or exceeding the level of existing strengthening technologies, the magnetic properties are significantly optimized. Compared with dislocation strengthening schemes, the magnetic properties have lower iron loss and better magnetic induction, meeting the dual stringent requirements of high-speed motors for "high strength and low iron loss".

[0010] In terms of chemical composition, phase transformation is achieved by adding an appropriate amount of C element, without the need to introduce large amounts of precious metals such as Cr, Ni, and Cu or rare elements such as Nb and Zr, which significantly reduces the cost of the alloy. In terms of process, conventional smelting, hot rolling, normalizing, cold rolling and annealing processes are adopted, without the need for additional aging treatment, which simplifies the production steps and reduces equipment investment and production cycle costs. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are only for further understanding of the embodiments of this application and constitute a part of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a metallographic diagram of Embodiment 1 of this application; Figure 2 This is an electron microscope tissue image of Embodiment 1 of this application; Figure 3 This is a metallographic diagram of Comparative Example 1 of this application. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0013] The method for manufacturing high-strength non-oriented electrical steel according to this application includes the following steps performed sequentially: Step S1: Chemical composition design. The chemical composition of the billet, by mass percentage, meets the following requirements: C: 0.01~0.10%, Si: 2.50~4.00%, Mn: 0.10~0.50%, Al: 0.02~1.2%, P: ≤0.02%, S: ≤0.005%, N: ≤0.005%, Ti: ≤0.005%, with the remainder being Fe and unavoidable impurities. Step S2: Heating the billet, heating the billet with the above composition to a preset temperature range; the billet heating temperature is 1100~1200℃ to ensure that the billet structure is fully homogenized; Step S3: Hot rolling and coiling. The heated billet is hot rolled to the preset thickness, and the final rolling temperature and coiling temperature are controlled. The thickness of the steel plate after hot rolling is 1.6~3.0mm, the final rolling temperature is controlled at 900~950℃, and the coiling temperature is 450~600℃. Step S4: Normalizing treatment, the hot-rolled plate is normalized to eliminate the inhomogeneity of the hot-rolled structure; the normalizing treatment temperature is 900~1000℃ to ensure the formability of the subsequent cold rolling process; Step S5: Cold rolling. The normalized hot-rolled plate is pickled to remove the oxide scale, and then cold-rolled to the finished thickness in one step. The finished thickness after cold rolling is 0.15~0.65mm, and the forming is completed in one cold rolling step. Step S6: Finished product annealing and rapid cooling. The cold-rolled sheet is annealed at a temperature above the phase transformation point AC3 and held at that temperature for a preset time. After annealing, it is immediately quenched in water for rapid cooling. The finished product annealing temperature is 850~950℃ and the annealing time is 60~300s to ensure that the steel fully undergoes phase transformation. Step S7: Coating and curing. Apply the coating liquid to the rapidly cooled steel plate, and then dry and cure it at a preset temperature to obtain high-strength non-oriented electrical steel. The drying and curing temperature is 200~300℃, and the curing time is 30~120s to ensure that the coating liquid and the steel plate are firmly bonded.

[0014] This application provides two sets of specific embodiments and two sets of comparative examples.

[0015] Example 1: Chemical composition (in mass percentage): C: 0.07%, Si: 3.45%, Mn: 0.46%, Al: 0.90%, S: 0.0028%, N: 0.0024%, Ti: 0.0022%, P: 0.009%, with the remainder being Fe and unavoidable impurities.

[0016] Billet heating: heating temperature 1160℃, holding time 3h.

[0017] Hot rolling and coiling: hot rolling to a thickness of 2.3 mm, with a final rolling temperature of 940℃ and a coiling temperature of 500℃.

[0018] Normalizing and cold rolling: The hot-rolled plate is normalized at 950℃, pickled, and then cold rolled to a finished thickness of 0.50mm in one step.

[0019] Annealing and cooling of finished products: Annealing temperature 920℃, holding time 3min, annealing atmosphere is 25%H2+75%N2 mixed gas; after annealing, quench in water for rapid cooling.

[0020] Coating and curing: After applying the coating liquid, dry and cure at 280℃ for 40 seconds.

[0021] Product performance: Magnetic properties, iron loss P 1.5 / 50 It is 7.07W / kg, magnetic induction B 50 The yield strength is 1.61T and the yield strength is 586MPa.

[0022] Example 2: Chemical composition (in mass percentage): C: 0.03%, Si: 3.25%, Mn: 0.23%, Al: 0.06%, S: 0.0040%, N: 0.0028%, Ti: 0.0024%, P: 0.012%, with the remainder being Fe and unavoidable impurities.

[0023] Billet heating: heating temperature 1120℃, holding time 4h.

[0024] Hot rolling and coiling: hot rolling to a thickness of 2.1 mm, with a final rolling temperature of 920℃ and a coiling temperature of 550℃.

[0025] Normalizing and cold rolling: The hot-rolled plate is normalized at 960℃, pickled, and then cold rolled to a finished thickness of 0.35mm in one step.

[0026] Annealing and cooling of finished products: Annealing temperature 880℃, holding time 4min, annealing atmosphere is 25%H2+75%N2 mixed gas; after annealing, quench in water for rapid cooling.

[0027] Coating and curing: After applying the coating liquid, dry and cure at 220℃ for 60 seconds.

[0028] Product performance: Magnetic properties, iron loss P 1.0 / 400 It is 36.42W / kg, magnetic induction B 50 The yield strength is 1.58T and the yield strength is 658MPa.

[0029] Comparative Example 1: Chemical composition (in mass percentage): C: 0.0033%, Si: 3.28%, Mn: 0.36%, Al: 1.05%, S: 0.0012%, N: 0.0024%, Ti: 0.0025%, P: 0.009%, with the remainder being Fe and unavoidable impurities.

[0030] Billet heating: heating temperature 1080℃, holding time 3h.

[0031] Hot rolling and coiling: hot rolling to a thickness of 2.3 mm, with a final rolling temperature of 860℃ and a coiling temperature of 670℃.

[0032] Normalizing and cold rolling: The hot-rolled plate is normalized at 870℃, pickled, and then cold rolled to a finished thickness of 0.50mm in one step.

[0033] Annealing and cooling of finished products: Annealing temperature 700℃, holding time 3min, annealing atmosphere is 25%H2+75%N2 mixed gas; slow cooling after annealing.

[0034] Coating and curing: After applying the coating liquid, dry and cure at 280℃ for 40 seconds.

[0035] Product performance: Magnetic properties, iron loss P 1.5 / 50 It is 7.40W / kg, magnetic induction B 50 The yield strength is 1.59T and the yield strength is 560MPa.

[0036] Comparative Example 2: Chemical composition (in mass percentage): C: 0.0028%, Si: 3.32%, Mn: 0.27%, Al: 0.75%, S: 0.0015%, N: 0.0020%, Ti: 0.0022%, P: 0.010%, with the remainder being Fe and unavoidable impurities.

[0037] Billet heating: heating temperature 1050℃, holding time 4h.

[0038] Hot rolling and coiling: hot rolling to a thickness of 2.1 mm, with a final rolling temperature of 850℃ and a coiling temperature of 650℃.

[0039] Normalizing and cold rolling: The hot-rolled plate is normalized at 840℃, pickled, and then cold rolled to a finished thickness of 0.35mm in one step.

[0040] Annealing and cooling of finished products: Annealing temperature 670℃, holding time 3min, annealing atmosphere is 25%H2+75%N2 mixed gas; slow cooling after annealing.

[0041] Coating and curing: After applying the coating liquid, dry and cure at 220℃ for 60 seconds.

[0042] Product performance: Magnetic properties, iron loss P 1.0 / 400 It is 38.54 W / kg, magnetic induction B 50 The yield strength is 1.57T and the yield strength is 646MPa.

[0043] Summarizing the above Examples 1, 2, 1, and 2, the following tables 1, 2, and 3 are derived: Table 1: ; Table 2: ; Table 3: ; Refer to the instruction manual. Figure 1-3 As shown, the embodiment uses an "annealing above the phase transformation point combined with water quenching" process to form a two-phase structure of fully recrystallized ferrite and martensite with more uniform grain size; the comparative example uses a dislocation strengthening process of "low temperature annealing combined with slow cooling" to form only incomplete recrystallized ferrite and fibrous structure with fine grains and residual deformation.

[0044] Annealing temperature and cooling method are key control factors. In the example, annealing was performed above the phase transformation point AC3 to ensure that the steel undergoes a phase transformation, followed by water quenching to lock in the two-phase microstructure. In the comparative example, the annealing temperature was lower than the phase transformation point. The comparative example had high Si and Al content and low C content, and its microstructure was a single ferrite at any temperature, which could not undergo a phase transformation. Its strength was improved by retaining the deformed microstructure through low-temperature annealing.

[0045] The example shows that by adding an appropriate amount of carbon element (0.03%~0.07%), the steel is endowed with phase transformation ability; the comparative example has an extremely low carbon content (≤0.0033%), and the heat treatment process is a single α phase, which cannot form a martensitic structure, and can only rely on dislocation strengthening to improve strength.

[0046] The dual-phase microstructure of the embodiment enhances mechanical properties by leveraging the high strength of martensite and ensures magnetic properties through fully recrystallized ferrite; while the residual deformation microstructure of the comparative embodiment can improve strength, it increases hysteresis loss, resulting in higher iron loss in magnetic properties.

[0047] This application achieves or exceeds the yield strength of existing strengthening technologies while significantly optimizing magnetic properties. Compared to dislocation strengthening schemes, it exhibits lower iron loss and superior magnetic flux density, meeting the stringent dual requirements of high-speed motors for both high strength and low iron loss.

[0048] In terms of chemical composition, phase transformation is achieved by adding only an appropriate amount of C element, without the need to introduce large amounts of precious metals such as Cr, Ni, and Cu or rare elements such as Nb and Zr, which significantly reduces the cost of the alloy. In terms of process, conventional smelting, hot rolling, normalizing, cold rolling and annealing processes are adopted, without the need for additional aging treatment, which simplifies the production steps and reduces equipment investment and production cycle costs.

[0049] It should be noted that, unless otherwise expressly specified and limited, the term "connection" or its synonyms should be interpreted broadly in this document. For example, "connection" can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal communication of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. Furthermore, expressions such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. At the same time, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. In addition, the terms "front," "rear," "left," "right," "upper," and "lower" in this document refer to the placement states shown in the accompanying drawings.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for manufacturing high-strength non-oriented electrical steel, characterized in that, The steps are as follows, performed sequentially: Step S1: Chemical composition design. The chemical composition of the billet, by mass percentage, meets the following requirements: C: 0.01~0.10%, Si: 2.50~4.00%, Mn: 0.10~0.50%, Al: 0.02~1.2%, P: ≤0.02%, S: ≤0.005%, N: ≤0.005%, Ti: ≤0.005%, with the remainder being Fe and unavoidable impurities. Step S2: Heating the billet, heating the billet with the above composition to a preset temperature range; Step S3: Hot rolling and coiling: The heated billet is hot rolled to the preset thickness, and the final rolling temperature and coiling temperature are controlled. Step S4: Normalizing treatment, the hot-rolled plate is normalized to eliminate the inhomogeneity of the hot-rolled structure; Step S5: Cold rolling, pickling the normalized hot-rolled plate to remove the oxide scale, and then cold rolling it to the finished thickness in one step; Step S6: Finished product annealing and rapid cooling. The cold-rolled sheet is annealed at a temperature above the phase transformation point AC3 and held at that temperature for a preset time. After annealing, it is immediately quenched in water for rapid cooling. Step S7: Coating and curing. Apply a coating liquid to the rapidly cooled steel plate, and then dry and cure it at a preset temperature to obtain high-strength non-oriented electrical steel.

2. The method for manufacturing high-strength non-oriented electrical steel according to claim 1, characterized in that, In step S2, the billet heating temperature is 1100~1200℃.

3. The method for manufacturing high-strength non-oriented electrical steel according to claim 1, characterized in that, In step S3, the thickness of the hot-rolled steel plate is 1.6~3.0mm, the final rolling temperature is controlled at 900~950℃, and the coiling temperature is 450~600℃.

4. The method for manufacturing high-strength non-oriented electrical steel according to claim 1, characterized in that, In step S4, the normalization temperature is 900~1000℃.

5. The method for manufacturing high-strength non-oriented electrical steel according to claim 1, characterized in that, In step S5, the thickness of the finished product after cold rolling is 0.15~0.65mm, and the forming is completed in one cold rolling.

6. The method for manufacturing high-strength non-oriented electrical steel according to claim 1, characterized in that, In step S6, the annealing temperature of the finished product is 850~950℃, and the annealing time is 60~300s.

7. The method for manufacturing high-strength non-oriented electrical steel according to claim 1, characterized in that, In step S7, the drying and curing temperature is 200~300℃, and the curing time is 30~120s.

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