Non-oriented electrical steel with excellent punching performance and production method

Abstract

The invention relates to the technical field of production of non-oriented electrical steel, in particular to non-oriented electrical steel with excellent punching performance and a production method, and the non-oriented electrical steel comprises the following chemical components in percentage by weight: less than or equal to 0.002% of C, 0.50%-1.50% of Si, 0.5%-1.5% of Mn, 0.005%-0.015% of Te, 0.001%-0.003% of Ca, 0.005%-0.015% of RE, 0.01%-0.05% of S, less than or equal to 0.002% of N, 0.20%-0.60% of Als and the balance of Fe and inevitable residual elements. Wherein RE comprises Ce and La; the method has the beneficial effects that on the premise that the optimized magnetic performance is maintained, the punching burr height is remarkably reduced, the service life of a die is prolonged, the punching sheet section smoothness and the punching sheet qualification rate are improved, and therefore the overall performance of a motor is optimized.

Description

Technical Field

[0001] This invention relates to the field of non-oriented electrical steel production technology, and in particular to a non-oriented electrical steel with excellent stamping properties and its production method. Background Technology

[0002] Non-oriented electrical steel, as the core material for small motors, general-purpose motors, and various electrical equipment cores, has long been considered the primary factor determining overall machine efficiency due to its magnetic properties. However, with the increasing demands for motor energy efficiency, noise reduction, and lifespan in fields such as home appliances, automobiles, and industrial automation, it has become increasingly clear that the lamination performance of the core has an impact on overall machine performance no less significant than the magnetic properties of the raw material itself. Excellent lamination properties not only preserve the "heredity" of magnetic properties during processing but also directly determine the dimensional accuracy of the core, assembly consistency, tool life, and ultimately, the operational reliability of the motor.

[0003] In existing technologies, electrical steel strips are continuously punched using high-speed progressive dies to form stator and rotor laminations. During the punching process, in addition to shear deformation, the steel strip also undergoes localized work hardening, burr formation, and microstructural damage. Excessive burrs lead to a decrease in the lamination coefficient and an increase in inter-laminated short-circuit eddy current losses; rough punched surfaces and excessively large collapse angles reduce the lamination riveting strength and cause dimensional drift in the inner and outer diameters of the core, ultimately resulting in uneven air gaps between the stator and rotor and increased vibration and noise. To mitigate these defects, traditional approaches have focused on optimizing die materials, cutting edge coatings, or lubrication conditions, while the contribution of the steel itself to lamination performance has long been overlooked. In recent years, with the increasing proportion of die costs, the increased frequency of tool replacements, and the increasingly stringent requirements for dimensional stability in automated production lines, the industry has begun to focus on proactively improving lamination performance through steel composition and process innovation, rather than passively relying on die maintenance.

[0004] Current non-oriented electrical steel compositions are predominantly based on solid solution strengthening elements such as Si, Al, and Mn. While this achieves low iron loss, it often results in increased shear strength and deteriorated shear surface quality, creating a trade-off between magnetic properties and punching performance. Furthermore, conventional approaches to controlling sulfides and carbonitrides focus on minimizing their amount or eliminating their harmfulness, failing to leverage their potential for proactively regulating punching behavior based on their morphology and distribution. Therefore, how to systematically reduce shear resistance, improve shear surface quality, reduce die wear, and simultaneously enhance subsequent cutting dimensional accuracy while maintaining or even optimizing magnetic properties has become a critical technical bottleneck that urgently needs to be overcome in the field of non-oriented electrical steel. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a non-oriented electrical steel with excellent stamping properties and a production method thereof. By adding sulfur and its synergistic elements, the stamping performance of the non-oriented electrical steel is improved. While maintaining optimized magnetic properties, the height of the stamping burrs is significantly reduced, the die life is extended, the surface finish of the stamped sections and the stamping qualification rate are improved, thereby optimizing the overall performance of the motor, improving the production efficiency of the motor core, and reducing the processing cost of the core.

[0006] To achieve the above objectives, the present invention employs the following technical solution: A non-oriented electrical steel with excellent stamping properties has the following chemical composition by weight percentage: C: ≤0.002%, Si: 0.50%~1.50%, Mn: 0.5%~1.5%, Te: 0.005%~0.015%, Ca: 0.001%~0.003%, RE: 0.005%~0.015%, S: 0.01%~0.05%, N: ≤0.002%, Als: 0.20%~0.60%, with the remainder being Fe and unavoidable residual elements; wherein, RE includes Ce and La; Mn / S ≥ 25.

[0007] The rationale for the chemical composition design of this invention is explained in detail below: C: Carbon reacts with iron to form iron carbide (Fe3C). This compound increases the hardness and brittleness of the material, thereby reducing its stamping performance. However, carbon can effectively improve the toughness and stamping performance of the material by controlling the carbon content to ≤0.002%.

[0008] Silicon (Si) is mainly used to increase the resistivity of materials, thereby reducing iron loss and improving electromagnetic properties. The target product of this patent is primarily used in small and medium-sized motors in household appliances; therefore, the silicon content is set within the range of 0.50% to 1.50%.

[0009] Mn: A key element in the formation of MnS inclusions with sulfur. By controlling the manganese content between 0.5% and 1.5% and ensuring that Mn / S ≥ 25, the formation of the brittle FeS phase can be effectively avoided, while optimizing the morphology and distribution of MnS inclusions, reducing stress concentration, and improving stamping performance.

[0010] Te: It can modify MnS inclusions to make them spherical or spindle-shaped, further refine the size of the inclusions, thereby improving the cutting and stamping performance. It can effectively improve the morphology of the inclusions. The amount of tellurium added should be set in the range of 0.005% to 0.015%.

[0011] Ca: CaS nuclei are formed in steel, promoting heterogeneous nucleation of MnS inclusions and improving the uniformity of inclusion distribution. This can effectively optimize the distribution of inclusions, and the calcium content should be controlled within the range of 0.001% to 0.003%.

[0012] RE(Ce+La): It can purify grain boundaries, inhibit the segregation of MnS inclusions at grain boundaries, and prevent intergranular cracking during sheeting. The purpose is to improve grain boundary performance, and the addition amount of rare earth elements is set in the range of 0.005% to 0.015%.

[0013] S is a key element in the formation of MnS inclusions. It can optimize the morphology and distribution of inclusions, ultimately resulting in spherical or spindle-shaped inclusions with an aspect ratio controlled to ≤3. This morphology effectively reduces stress concentration, preventing crack propagation caused by stress concentration during punching. Simultaneously, MnS inclusions can act as a stress buffer phase during punching, reducing localized stress concentration. This stress regulation helps reduce punching burr height and improve punching performance by controlling the sulfur content to 0.01%–0.05%.

[0014] N: It can form iron nitride (Fe4N) with iron, which increases the hardness and brittleness of the material, thereby reducing the stamping performance. It can effectively reduce the formation of nitrides and control the nitrogen content to ≤0.002%.

[0015] Als: Used to assist silicon in improving resistivity, reducing iron loss, effectively reducing the formation of oxide inclusions, and improving the toughness and electromagnetic properties of materials. The aluminum content is controlled within the range of 0.20% to 0.60%.

[0016] Furthermore, under the working conditions of the non-oriented electrical steel stamping with excellent stamping properties, the burr height is ≤0.017mm; the surface roughness Ra of the stamping surface is 0.8~1.2µm; and the automatic riveting qualification rate is 97~99%.

[0017] A method for producing non-oriented electrical steel with excellent stamping properties, wherein the production process of the non-oriented electrical steel with excellent stamping properties is: converter smelting - continuous casting - hot rolling - cold rolling - annealing. The specific method is as follows: Converter smelting: Converter smelting is adopted. The final sulfur content of the converter is 0.010% to 0.020%. During the refining process, sulfur is fed in with a feed rate of 180m / min to 220m / min and an argon flow rate of 40L / min to 60L / min. The sulfur recovery rate is ≥85%. The final deoxidation is carried out using a Ca-Si line. Continuous casting: Electromagnetic stirring in the crystallizer is adopted, combined with light pressure. The secondary cooling section of the continuous casting adopts a weak cooling process with a specific water volume of 0.3L / kg to 0.5L / kg. Hot rolling: furnace temperature in the preheating section of the heating furnace: 850℃~900℃, soaking temperature: 1180℃~1220℃, reduction per pass in rough rolling is controlled at 10%~25%, rolling speed is controlled at 2.2m / s~2.8m / s, rolling temperature: 1120℃~1180℃, and final rolling temperature is set at 880℃~960℃; Cold rolling: 5-stand six-high continuous rolling mill, total reduction rate 70%–90%, first pass reduction rate 30%–35%, last pass reduction rate 10%–15%, emulsion temperature: 42℃–48℃, emulsion concentration: 3.5%–4.5%; Annealing: Segmented annealing was adopted. The first stage soaking temperature was 830℃~870℃, the first stage soaking time was 2min~3min, and the furnace tension was 1.5MPa~2.0MPa. The second stage soaking temperature was 930℃~970℃, the second stage soaking time was 1min~2min, and the furnace tension was 0.8MPa~1.5MPa. After annealing, a semi-organic + chromate insulating coating was applied, with a coating amount of 0.8g / m² on one side. 2 ~1.2g / m 2 The curing temperature is 300℃~350℃.

[0018] Furthermore, the sulfur feed line for converter smelting is made of FeS cored wire.

[0019] Furthermore, the cold rolling mill employs positive and negative bending of the work rolls and intermediate rolls, as well as CVC shape control, with a plate difference of ≤7μm.

[0020] Furthermore, the adhesion of the insulating coating reaches Grade A, and the interlayer resistance is ≥150Ω·cm² / piece.

[0021] Furthermore, the thickness of the finished strip is 0.35mm, 0.50mm or 0.65mm.

[0022] Compared with the prior art, the beneficial effects of the present invention are: 1) This invention breaks through the traditional thinking of low-sulfur clean steel in the field of non-oriented electrical steel for the first time: with 0.01-0.05wt% fine-grained sulfur as the core, the surface activity of Te is used to induce MnS to form spherical / spindle-shaped inclusions with an aspect ratio ≤3; through CaS heterogeneous nucleation and RE grain boundary purification, the average size of the inclusions is stabilized at 0.4-1.2µm and the distribution density is increased to 120-150 inclusions / mm²; at the same time, a quantitative window of Mn / S≥25, S / Ca≥0.8, and RE / Te≈1 is established to transform the sulfide from a harmful phase into a dual-functional phase with "stress buffer-solid lubrication", realizing the synergistic innovation of composition and process; a two-stage annealing of "low temperature pre-precipitation + high temperature recrystallization" is adopted to significantly soften the matrix while maintaining excellent magnetic properties, and complete the integrated design of microstructure and performance, so that the sulfide becomes a small sphere, which reduces the resistance of the stamping without sacrificing too much magnetism, and achieves half the burrs and improved die life.

[0023] 2) Non-oriented electrical steel has excellent stamping performance: Under the same mold and working conditions (stamping speed and mold clearance), the burr height is reduced from 0.035-0.05mm to ≤0.017mm, a reduction of more than 50%; the surface roughness Ra of the punching surface is reduced from 1.6-2.0µm to 0.8-1.2µm; the cutting edge life of the high-speed punch is increased from 900,000-1,000,000 cycles to ≥1,200,000-1,300,000 cycles; the peak load of the punch press is reduced by 10-15%; the coaxiality error of the stator and rotor is reduced from ±25µm to ±12µm; and the automatic riveting qualification rate is increased from 93-95% to 97-99%, achieving a quantitative leap in stamping performance.

[0024] 3) Significant comprehensive benefits of the processing chain: Eliminating the deburring process saves equipment and labor costs; due to the reduction of burrs, the stacking coefficient increases by 0.8 to 1.0%, the effective iron length increases at the same height, and the motor efficiency increases by 0.5 to 1.2%; the vibration of the motor operation decreases, significantly reducing the cost of subsequent processing and assembly.

[0025] 4) While maintaining optimized magnetic properties, it significantly reduces the height of punching burrs, extends the die life, improves the surface finish of the punched laminations and the pass rate of the punched laminations, thereby optimizing the overall performance of the motor, improving the production efficiency of the motor core, reducing the core processing cost, and the process is simple and has good market application prospects. Detailed Implementation

[0026] The specific embodiments of the present invention will be further described below: The steel production process in this embodiment of the invention is as follows: converter smelting - continuous casting - hot rolling - cold rolling - finished product annealing; Converter smelting: Converter smelting is employed, with the final sulfur content strictly controlled between 0.010% and 0.020% to ensure the sulfur content in the molten steel reaches the target value. During refining, sulfur wire (FeS cored wire) is fed in at a speed of 180–220 m / min, and the argon flow rate is controlled at 40–60 L / min to ensure a sulfur recovery rate ≥85%, further precisely increasing the sulfur content to the target value. This precise sulfur content control is crucial for the subsequent formation and distribution of MnS inclusions. Final deoxidation is performed using Ca-Si wire, ensuring an S / Ca ratio ≥0.8 to form CaS nuclei. The formation of CaS nuclei helps to spherize MnS inclusions, thereby optimizing the morphology and distribution of inclusions and reducing stress concentration during the punching process.

[0027] Continuous casting: Electromagnetic stirring in the crystallizer, combined with light reduction technology, promotes the uniform distribution of MnS inclusions in the steel. This technology effectively reduces inclusion aggregation and improves material uniformity and stamping performance. The secondary cooling section of continuous casting employs a weak cooling process, with the water content controlled at 0.3–0.5 L / kg to avoid the precipitation of excessively large MnS during cooling. A reasonable cooling rate helps maintain the small size of inclusions and reduces burr formation during stamping.

[0028] (3) Hot rolling: The preheating temperature of the heating furnace is 850-900℃, and the soaking temperature is strictly controlled at 1180-1220℃ to avoid exceeding 1250℃, which would cause MnS inclusions to coarsen. A reasonable heating temperature can ensure that the inclusions maintain a good morphology and distribution during subsequent rolling. The reduction per pass of rough rolling is controlled at 10%-25%, the rolling speed is controlled at 2.2m / s-2.8m / s, and the rolling temperature range is 1120℃-1180℃. The reasonable control of these parameters can ensure that the billet has good deformation uniformity and structural stability during rolling, while avoiding rolling defects caused by excessive reduction or excessive rolling speed. The final rolling temperature is set at 880-960℃ to promote complete recrystallization of the billet during rolling and eliminate banded structure. The recrystallization process is crucial for improving the toughness and stamping performance of the material.

[0029] (4) Cold rolling: A 5-stand six-roll mill is used for continuous rolling. The finished strip thickness is 0.35mm, 0.50mm or 0.65mm, with a total reduction rate of 70-90%, a first-pass reduction rate of 30-35%, and a last-pass reduction rate of 10-15%. A combination of work rolls and intermediate rolls with positive and negative bending and CVC shape control is employed to ensure that the strip shape difference is ≤7μm. A good strip shape is beneficial for subsequent sheeting performance. The emulsion temperature is 42-48℃, and the concentration is 3.5-4.5%, providing a clean interface for subsequent normalizing.

[0030] (5) Annealing: Segmented annealing is adopted. The first stage is heated at 830-870℃ for 2-3 minutes with a furnace tension of 1.5-2.0 MPa to promote the full precipitation and spheroidization of MnS. The second stage is heated at 930-970℃ for 1-2 minutes with a tension of 0.8-1.5 MPa to complete recrystallization and uniform grain growth. After annealing, a semi-organic + chromate insulating coating is applied with a coating amount of 0.8-1.2 g / m² on one side and a curing temperature of 300-350℃. The coating adhesion reaches Grade A and the interlayer resistance is ≥150 Ω·cm² / piece, taking into account both the lubrication of the stamping and the heat resistance of welding.

[0031] Example: The finished product thicknesses in the examples of this invention are 0.35mm, 0.50mm, and 0.65mm respectively. The comparative examples are traditional low-sulfur grades from the same production line and with the same specifications, but with S≤0.003% and without Te-Ca-RE treatment. The specific process and results are as follows: The chemical composition of the steel in the embodiments of the present invention is shown in Table 1; the process parameters of the smelting and continuous casting processes in the embodiments of the present invention are shown in Table 2; the process parameters of the hot rolling process in the embodiments of the present invention are shown in Table 3; the process parameters of the cold rolling process in the embodiments of the present invention are shown in Table 4; the process parameters of the steel annealing process in the embodiments of the present invention are shown in Table 5; and the measured results of the magnetic properties and stamping properties in the embodiments of the present invention are shown in Table 6.

[0032] Table 1 - Chemical composition of steel in the embodiments of the present invention: Table 2 - Process parameters for smelting and continuous casting in embodiments of the present invention: Table 3 - Process parameters for hot rolling in embodiments of the present invention: Table 4 - Process parameters for cold rolling in embodiments of the present invention: Table 5 - Process parameters for steel annealing in embodiments of the present invention: Table 6 - Measured results of magnetic properties and punching performance of embodiments of the present invention: The above embodiments show that, while maintaining magnetic properties superior to or equivalent to those of the comparative steel, the burr height is reduced by ≥62%, the roughness of the punched surface is reduced by ≥40%, the punch life is increased by ≥26%, the stacking coefficient is increased by 0.6–1.1%, and the coaxiality error is reduced by more than 50%. This fully verifies the replicability and significant punching advantages of the technical solution of the present invention on an industrial scale.

[0033] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A non-oriented electrical steel with excellent stamping properties, characterized in that, Its chemical composition by weight percentage is as follows: C: ≤0.002%, Si: 0.50%~1.50%, Mn: 0.5%~1.5%, Te: 0.005%~0.015%, Ca: 0.001%~0.003%, RE: 0.005%~0.015%, S: 0.01%~0.05%, N: ≤0.002%, Als: 0.20%~0.60%, with the remainder being Fe and unavoidable residual elements; among which, RE includes Ce and La; Mn / S≥25.

2. The non-oriented electrical steel with excellent stamping properties according to claim 1, characterized in that, Under the working conditions of the non-oriented electrical steel stamping with excellent stamping properties, the burr height is ≤0.017mm; the surface roughness Ra of the stamping surface is 0.8~1.2µm; and the automatic stacking and riveting qualification rate is 97~99%.

3. A method for producing non-oriented electrical steel with excellent stamping properties as described in any one of claims 1 to 2, characterized in that, The production process of the non-oriented electrical steel with excellent stamping properties is as follows: converter smelting - continuous casting - hot rolling - cold rolling - annealing; The specific method is as follows: Converter smelting: Converter smelting is adopted. The final sulfur content of the converter is 0.010% to 0.020%. During the refining process, sulfur is fed in with a feed rate of 180m / min to 220m / min and an argon flow rate of 40L / min to 60L / min. The sulfur recovery rate is ≥85%. The final deoxidation is carried out using a Ca-Si line. Continuous casting: Electromagnetic stirring in the crystallizer is adopted, combined with light pressure. The secondary cooling section of the continuous casting adopts a weak cooling process with a specific water volume of 0.3L / kg to 0.5L / kg. Hot rolling: furnace temperature in the preheating section of the heating furnace: 850℃~900℃, soaking temperature: 1180℃~1220℃, reduction per pass in rough rolling is controlled at 10%~25%, rolling speed is controlled at 2.2m / s~2.8m / s, rolling temperature: 1120℃~1180℃, and final rolling temperature is set at 880℃~960℃; Cold rolling: 5-stand six-high continuous rolling mill, total reduction rate 70%–90%, first pass reduction rate 30%–35%, last pass reduction rate 10%–15%, emulsion temperature: 42℃–48℃, emulsion concentration: 3.5%–4.5%; Annealing: Segmented annealing was adopted. The first stage soaking temperature was 830℃~870℃, the first stage soaking time was 2min~3min, and the furnace tension was 1.5MPa~2.0MPa. The second stage soaking temperature was 930℃~970℃, the second stage soaking time was 1min~2min, and the furnace tension was 0.8MPa~1.5MPa. After annealing, a "semi-organic + chromate" insulating coating was applied, with a coating amount of 0.8g / m² on one side. 2 ~1.2g / m 2 The curing temperature is 300℃~350℃.

4. The method for producing high-efficiency, high-strength, thin-gauge non-oriented electrical steel according to claim 3, characterized in that, The sulfur feed line for converter smelting is made of FeS cored wire.

5. The method for producing high-efficiency, high-strength, thin-gauge non-oriented electrical steel according to claim 3, characterized in that, The cold rolling mill uses positive and negative bending rolls of the work rolls and intermediate rolls and CVC shape control, with a plate difference of ≤7μm.

6. The method for producing high-efficiency, high-strength, thin-gauge non-oriented electrical steel according to claim 3, characterized in that, The insulation coating exhibits Class A adhesion and has an interlayer resistance ≥150Ω·cm² / piece.

7. The method for producing high-efficiency, high-strength, thin-gauge non-oriented electrical steel according to claim 3, characterized in that, The finished steel strip has a thickness of 0.35mm, 0.50mm, or 0.65mm.

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