High-strength non-oriented electrical steel for new energy vehicle drive rotor and manufacturing method

Abstract

This invention relates to the field of non-oriented electrical steel technology, specifically to a high-strength non-oriented electrical steel for new energy vehicle drive rotors and its manufacturing method. The high-strength non-oriented electrical steel for new energy vehicle drive rotors comprises the following components by weight percentage: C: 0-0.002%, Si: 2.5-3.5%, Mn: 0.25-0.75%, Al: 0.50-1.50%, P: ≤0.01%, S: ≤0.002%, Sn: 0.02-0.20%, with the balance being iron and unavoidable impurities. This invention achieves high structural strength and lower mid-to-high frequency magnetic properties at a lower cost and with lower iron loss.

Description

Technical Field

[0001] This invention relates to the field of non-oriented electrical steel technology, specifically to a high-strength non-oriented electrical steel for new energy vehicle drive rotors and its manufacturing method. Background Technology

[0002] Electric vehicle drive motors, due to their complex operating conditions (such as high and low temperatures, high frequencies, acceleration, frequent vibration, and overload), have significantly different performance requirements from traditional industrial motors. They need to possess high power density, high torque, and a certain level of material strength. Therefore, for the preparation of drive motor core materials, non-oriented silicon steel must possess both good magnetic properties and a certain strength. However, for silicon steel, improving strength inevitably reduces electromagnetic properties, especially iron losses. How to reconcile the contradiction between the material's magnetic properties and strength has become a key focus and challenge in the research and development of silicon steel for drive motors in recent years.

[0003] Traditional high-grade silicon steel, through the design of the main alloying elements such as Si, Al, and Mn combined with appropriate production processes, can achieve a strength of up to 420-450 MPa. However, the strength requirement for high-speed drive motor rotors is over 600 MPa. Microalloying has become an effective way to further improve the strength of silicon steel materials used in drive motor rotors. Chinese invention patent CN111321344B discloses a high-strength cold-rolled non-oriented electrical steel for electric vehicle drive motors and its production method. This method adds strengthening elements such as Cu and Nb, and microalloying elements such as Sn and Sb, and controls the heating rate during annealing to meet the high strength and low loss requirements of electric vehicle drive motor rotors, effectively reconciling the contradiction between the material's magnetic properties and strength indicators. Although this non-oriented electrical steel improves yield strength while maintaining magnetic induction, its iron loss is relatively high, and the addition of Cu, Nb, Sn, and Sb elements increases costs. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a high-strength non-oriented electrical steel for new energy vehicle drive rotors and a manufacturing method thereof, which achieves higher structural strength and lower mid-to-high frequency magnetic properties at a lower cost and with lower iron loss.

[0005] To address the aforementioned technical problems, in a first aspect, the present invention provides a high-strength non-oriented electrical steel for drive rotors of new energy vehicles, comprising the following components by weight percentage: C: 0-0.002%, Si: 2.5-3.5%, Mn: 0.25-0.75%, Al: 0.50-1.50%, P: ≤0.01%, S: ≤0.002%, Sn: 0.02-0.20%, with the balance being iron and unavoidable impurities.

[0006] C: The main purpose of controlling the C content in this invention is to ensure the strength of the hot-rolled plate. However, excessive C content will reduce the toughness of the steel plate. Moreover, C, whether in the form of solid solution or cementite, will impair the magnetic properties of the steel plate. This invention limits the C content to ≤0.002%.

[0007] Si: Increasing the Si content increases the strength of the steel plate, increases resistivity, reduces hysteresis loss, and reduces iron loss. Therefore, the Si content in the steel should be reduced in this invention. The Si content in this invention is 2.5-3.5%.

[0008] Mn: Mn is beneficial for increasing the resistivity of materials and reducing hysteresis loss. It increases the rollability of hot-rolled plates and can also improve strength through solid solution strengthening. Therefore, this invention sets the Mn content to 0.25-0.75%.

[0009] Al: Al has the same effect as Si, which increases the strength of steel plates, reduces magnetic induction, and reduces iron loss. Therefore, the Al content is controlled at 0.50-1.50% in this invention.

[0010] P: P is promoted by Sn to produce segregation, which refines the grains, improves strength and texture. However, Fe3P segregation will make the steel plate embrittled and reduce toughness. Therefore, this invention controls P≤0.010%.

[0011] S: S can form ductile MnS inclusions with Mn in steel, which can reduce hot brittleness, but it can also cause the strip to form a banded structure, which reduces the toughness and formability of the steel plate. In addition, S has a great influence on magnetic properties. This invention controls the S content to be ≤0.002%.

[0012] Sn: During hot rolling, Sn segregates at the original grain boundaries and promotes the segregation of P, hindering grain growth, refining the grains, and increasing the strength of the steel plate. However, grain refinement leads to increased hysteresis loss. Since the segregation of Sn and P improves the texture and reduces the impact of segregation on magnetic induction, this invention controls the Sn content to be 0.02-0.20%.

[0013] Furthermore, the grain size is 15μm to 40μm.

[0014] Further, it includes the following components by weight percentage: C: 0.0018%, Si: 3.35%, Mn: 0.49%, Al: 0.62%, P: ≤0.01%, S: 0.0009%, Sn: 0.12%.

[0015] Secondly, the present invention provides a method for manufacturing high-strength non-oriented electrical steel for drive rotors of new energy vehicles, comprising:

[0016] S1, Smelting;

[0017] S2, continuous casting;

[0018] S3, hot-rolled;

[0019] S4, normalizing, pickling;

[0020] S5, cold-rolled, two-stage annealing;

[0021] S6. Apply a coating.

[0022] Further, step S5 includes:

[0023] S51. Cold roll the target thickness to 60-80% of the target thickness;

[0024] S52. Perform the first annealing at a temperature of 860–1040°C.

[0025] S53. Cold roll the target thickness to the target thickness and perform a second annealing at a temperature of 860–1040°C.

[0026] Furthermore, in step S52, the first annealing adopts a two-stage heating method: the temperature is increased from 0 to 500℃ at a heating rate of 10℃ / s, and the temperature is increased from 500 to 1040℃ at a heating rate of 40℃ / s. After reaching the first annealing temperature, the temperature is held for 5 to 20 seconds.

[0027] Furthermore, in step S53, the temperature is increased to the second annealing temperature at a heating rate of 40℃ / s, and held for 10–30s.

[0028] Furthermore, in step S5, the rolling target is annealed by a protective gas comprising 60% nitrogen and 40% hydrogen.

[0029] Furthermore, in step S3, the initial rolling temperature of hot rolling is 1100-1200℃, the final rolling temperature is 870-890℃, and the coiling temperature is 620-680℃.

[0030] Furthermore, in step S4, the normalization temperature is 920-980℃.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. This invention refines the grain size and reduces the finished strip size by adding Sn element, and adopts a two-stage annealing method. By controlling the temperature and heating rate, the grain size is controlled to 15μm~40μm, and the texture is optimized. As a result, the non-oriented electrical steel of this invention achieves high strength at a lower cost and also has lower medium and high frequency iron loss compared with the prior art.

[0033] 2. The non-oriented electrical steel B of the present invention 50 =1.50-1.70T, W 1.0 / 400≤30.0W / Kg, yield strength R p0.2 ≥600MPa, tensile strength R m ≥650MPa. Attached Figure Description

[0034] Figure 1 This is a microstructure diagram of the non-oriented electrical steel of the present invention. Detailed Implementation

[0035] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0036] Example 1

[0037] The chemical composition (in mass percentage) of this embodiment is as follows:

[0038] Table 1 Chemical composition of continuously cast billets (unit: %)

[0039] C Si Sn Mn P S Al N 0.0018 3.35 0.12 0.49 ≤0.01 0.0009 0.62 0.0011

[0040] Steelmaking is carried out according to the chemical composition ratio in Table 1: After smelting and continuous casting, the billet thickness is 230mm, the hot rolling initial rolling temperature is 1100-1200℃, the final rolling temperature is 870-890℃, the coiling temperature is 620-680℃, and the steel plate thickness is 1.9-2.2mm; normalizing and pickling are carried out, with a normalizing temperature of 920-980℃.

[0041] The steel coil is then cold-rolled to 0.15–0.2 mm (60–80% of the target thickness, with a target thickness of 0.25 mm). After cold rolling, the coil undergoes a first annealing in a high-temperature tubular annealing furnace with a protective gas mixture of 60% nitrogen and 40% hydrogen. The annealing temperature is 860–950 °C, using a two-stage heating method: heating from 0–500 °C at a rate of 10 °C / s, and from 500–1040 °C at a rate of 40 °C / s. After reaching the first annealing temperature of 860–950 °C, the temperature is held for 5–20 seconds. It is then cold-rolled again to the target thickness of 0.25 mm and subjected to a second annealing, with the temperature increased to 860–950 °C at a rate of 40 °C / s.

[0042] After annealing, the steel coil is coated with a semi-organic coating to ensure insulation and interlayer resistance.

[0043] The magnetic induction intensity B of the non-oriented silicon electrical steel obtained by the above process 50 It is 1.547T, W 1.0 / 400 =29.87W / Kg, yield strength R 0.2 The tensile strength is 686.80 MPa, and the tensile strength R is...m It is 722.95 MPa.

[0044] Example 2

[0045] The chemical composition (in mass percentage) of this embodiment is as follows:

[0046] Table 2 Chemical composition of continuously cast billets (unit: %)

[0047] C Si Sn Mn P S Al N 0.0018 3.35 0.12 0.49 ≤0.01 0.0009 0.62 0.0011

[0048] Steelmaking is carried out according to the chemical composition ratio in Table 2: After smelting and continuous casting, the billet thickness is 230mm, the hot rolling initial rolling temperature is 1100-1200℃, the final rolling temperature is 870-890℃, the coiling temperature is 620-680℃, and the steel plate thickness is 1.9-2.2mm; normalizing and pickling are carried out, with a normalizing temperature of 920-980℃.

[0049] The steel coil is then cold-rolled to a thickness of 0.15–0.2 mm. After cold rolling, the coil undergoes a first annealing in a high-temperature tubular annealing furnace with a protective gas mixture of 60% nitrogen and 40% hydrogen. The annealing temperature is 950–1040℃, using a two-stage heating method: heating from 0–500℃ at a rate of 10℃ / s, and from 500–1040℃ at a rate of 40℃ / s. After reaching the first annealing temperature of 950–1040℃, the temperature is held for 5–20 seconds. The coil is then cold-rolled to the target thickness of 0.25 mm and subjected to a second annealing, with the temperature increased to 950–1040℃ at a rate of 40℃ / s.

[0050] After annealing, the steel coil is coated with a semi-organic coating to ensure insulation and interlayer resistance.

[0051] The magnetic induction intensity B of the non-oriented silicon electrical steel obtained by the above process 50 It is 1.655T, W 1.0 / 400 =27.57W / Kg, yield strength R 0.2 The tensile strength is 622.32 MPa, and the tensile strength R is... m It is 702.25 MPa.

[0052] Comparative Example 1

[0053] The chemical composition (in mass percentage) of this comparative example is as follows:

[0054] Table 3 Chemical composition of continuously cast billets (unit: %)

[0055]

[0056]

[0057] Steelmaking is carried out according to the chemical composition ratio in Table 3: After smelting and continuous casting, the billet thickness is 230mm, the hot rolling initial rolling temperature is 1100-1200℃, the final rolling temperature is 870-890℃, the coiling temperature is 620-680℃, and the steel plate thickness is 1.9-2.2mm; normalizing and pickling are carried out, with a normalizing temperature of 920-980℃.

[0058] The steel coil is then cold-rolled to 0.25 mm. The cold-rolled coil is then annealed in a high-temperature tubular annealing furnace with a protective gas mixture of 60% nitrogen and 40% hydrogen at a temperature of 860–950°C. After annealing, the steel coil is coated with a semi-organic coating to ensure insulation and interlayer resistance.

[0059] The magnetic induction intensity B of the non-oriented silicon electrical steel obtained by the above process 50 It is 1.653T, W 1.0 / 400 =20.15W / Kg, yield strength R 0.2 The tensile strength is 589.32 MPa, and the tensile strength R is... m It is 671.23 MPa.

[0060] Comparative Example 2

[0061] The chemical composition (in mass percentage) of this comparative example is as follows:

[0062] Table 4 Chemical composition of continuously cast billets (unit: %)

[0063] C Si Sn Mn P S Al N 0.0018 3.35 0.12 0.49 ≤0.01 0.0009 0.62 0.0011

[0064] Steelmaking is carried out according to the chemical composition ratio in Table 4: After smelting and continuous casting, the billet thickness is 230mm, the hot rolling initial rolling temperature is 1100-1200℃, the final rolling temperature is 870-890℃, the coiling temperature is 620-680℃, and the steel plate thickness is 1.9-2.2mm; normalizing and pickling are carried out, with a normalizing temperature of 920-980℃.

[0065] The steel coil is then cold-rolled to 0.25 mm. After cold rolling, the coil is annealed in a high-temperature tubular annealing furnace with a protective gas mixture of 60% nitrogen and 40% hydrogen at a temperature of 950–1040 °C. The annealed coil is then coated with a semi-organic coating to ensure insulation and interlayer resistance.

[0066] The magnetic induction intensity B of the non-oriented silicon electrical steel obtained by the above process 50 It is 1.643T, W 1.0 / 400 = 35.42 W / kg, yield strength R 0.2 The tensile strength is 687.13 MPa, and the tensile strength R is... m It is 823.52 MPa.

[0067] A comparison of Examples 1 and 2 with Comparative Examples 1 and 2 shows that the two-stage annealing process can ensure the iron loss W while maintaining almost the same magnetic induction intensity. 1.0 / 400 ≤30.0W / Kg, and yield strength R p0.2 ≥600MPa, tensile strength R m ≥650MPa.

[0068] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention 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 the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A high-strength non-oriented electrical steel for drive rotors of new energy vehicles, characterized in that: The composition comprises the following components by weight percentage: C: 0.0018%, Si: 3.35%, Mn: 0.49%, Al: 0.62%, P: ≤0.01%, S: 0.0009%, Sn: 0.12%, with the balance being iron and unavoidable impurities.

2. The high-strength non-oriented electrical steel for new energy vehicle drive rotors according to claim 1, characterized in that: The grain size is 15μm to 40μm.

3. A method for manufacturing high-strength non-oriented electrical steel for drive rotors of new energy vehicles according to any one of claims 1 or 2, characterized in that: include: S1, Smelting; S2, continuous casting; S3, hot-rolled; S4, normalizing, pickling; S5, cold-rolled, two-stage annealing; S6. Apply a coating.

4. The manufacturing method according to claim 3, characterized in that: Step S5 includes: S51. Cold roll the target thickness to 60-80% of the target thickness; S52. Perform the first annealing at a temperature of 860–1040°C. S53. Cold roll the target thickness to the target thickness and perform a second annealing at a temperature of 860–1040°C.

5. The manufacturing method according to claim 4, characterized in that: In step S52, the first annealing adopts a two-stage heating method: the temperature is increased from 0 to 500℃ at a heating rate of 10℃ / s, and the temperature is increased from 500 to 1040℃ at a heating rate of 40℃ / s. After reaching the first annealing temperature, the temperature is held for 5 to 20 seconds.

6. The manufacturing method according to claim 4, characterized in that: In step S53, the temperature is increased to the second annealing temperature at a heating rate of 40℃ / s.

7. The manufacturing method according to claim 3, characterized in that: In step S5, the rolling target is annealed by a protective gas consisting of 60% nitrogen and 40% hydrogen.

8. The manufacturing method according to claim 3, characterized in that: In step S3, the initial rolling temperature of hot rolling is 1100-1200℃, the final rolling temperature is 870-890℃, and the coiling temperature is 620-680℃.

9. The manufacturing method according to claim 3, characterized in that: In step S4, the normalization temperature is 920-980℃.

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