Non-oriented electrical steel for new energy vehicle drive motor and manufacturing method thereof

Abstract

The application provides a non-oriented electrical steel for a new energy automobile driving motor and a manufacturing method thereof, and the composition is as follows: C: 0.001-0.005%, Si: 3.2-3.5%, Mn: 0.35-0.65%, Al: 0.50-0.80%, P: <=0.02%, S: <=0.005%, 0.010%<=Ce+Sn<=0.020%, and the balance is iron and inevitable impurities. Compared with the prior art, the application can inhibit the generation of an internal oxidation layer and reduce hysteresis loss by adding Ce and Sn, purifying steel, and micro-alloying to improve the strength and magnetic properties of the non-oriented silicon steel, can increase the proportion of beneficial texture by sectional control of annealing temperature process, has smaller grains and beneficial texture, optimizes grain size uniformity, and makes the produced non-oriented electrical steel have favorable medium-high frequency iron loss, higher yield strength and good magnetic induction.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical materials technology, particularly the field of electrical steel, specifically a non-oriented electrical steel for new energy vehicle drive motors and its manufacturing method. This electrical steel has low iron loss and high strength. Background Technology

[0002] With increasing environmental protection requirements, new energy vehicles, as environmentally friendly modes of transportation, are developing rapidly. The drive motor is one of the core components of new energy vehicles, requiring miniaturization, high efficiency, and high torque. The miniaturization and high efficiency of the motor necessitate that the non-oriented electrical steel used to manufacture its core possess low iron loss and high magnetic flux density. As the rotational speed increases, the enormous centrifugal force can easily damage the motor rotor; therefore, the non-oriented electrical steel needs to have high strength to ensure safety at high speeds.

[0003] Traditional non-oriented silicon steel can meet the requirements of low iron loss and high magnetic induction, but its strength is relatively low. Strength and iron loss are contradictory indicators. Increasing the strength will reduce the magnetic properties. Therefore, developing non-oriented electrical steel with low iron loss and high strength for new energy vehicle drive motors is an important research task.

[0004] The patent CN102747291A, published on October 24, 2012, discloses a high-frequency, low-iron-loss, magnetically excellent non-oriented silicon steel strip and its production method. The composition, by weight percent, is: C 0.001-0.005, Si 2.05-3.75, Als 0.150-0.850, N≤0.003, S≤0.005, P≤0.02, Mn 0.15-0.30, Sn 0.01-0.08, Cr 2.5-3.5, Cu 0.05-0.1, Ti≤0.003, with the remainder being Fe and unavoidable impurities. It obtains low-iron-loss, high-strength silicon steel strip by adding elements such as Sn, Cr, and Cu, and by using high-temperature hot rolling and secondary cold rolling methods, but the improvement in magnetic induction is limited, and the magnetic induction of this non-oriented silicon steel is relatively low. Furthermore, the addition of elements such as Cu can improve strength, but the addition of Cu can cause "copper brittleness," which increases the difficulty of rolling. High-temperature annealing is required to temporarily dissolve Cu and delay recrystallization. Higher heating temperatures can cause abnormal grain growth, which is not conducive to improving strength.

[0005] The patent published on March 26, 2014, with publication number CN103667900A, discloses a method for preparing high magnetic silicon steel for automotive motors. By adding elements such as Sn, Bi, Ce, and Er, and using extremely complex production methods such as hot rolling and secondary cold rolling, high magnetic silicon steel products are finally obtained. However, the production method is complex, requires high equipment modification, and seriously reduces the efficiency of industrial production. Moreover, the Sn, Bi, Ce, and Er elements added in this patent will significantly increase the alloy cost of the product, making it unsuitable for industrial production. Summary of the Invention

[0006] The purpose of this invention is to provide a non-oriented electrical steel for drive motors of new energy vehicles and its manufacturing method. By rationally combining rare earth elements and Sn, and by designing smelting, hot rolling, normalizing, cold rolling and annealing processes, a high-strength non-oriented silicon steel with excellent magnetic properties is finally obtained, which has low iron loss and high strength.

[0007] The specific technical solution of this invention is as follows:

[0008] A non-oriented electrical steel for drive motors in new energy vehicles comprises the following components by weight percentage:

[0009] C: 0.001-0.005%, Si: 3.2-3.5%, Mn: 0.35-0.65%, Al: 0.50-0.80%, P: ≤0.02%, S: ≤0.005%, 0.010%≤Ce+Sn≤0.020%, with the balance being iron and unavoidable impurities.

[0010] The composition of the non-oriented electrical steel for the drive motor of the new energy vehicle also meets the following requirements: C+S+N+Ti≤0.0048%, Nb+V+Ti+Zr≤0.0030%, which are controlled as residual elements.

[0011] The composition of the non-oriented electrical steel used in the drive motor of the new energy vehicle also satisfies: Ce / Sn=0.25-2.0.

[0012] The thickness of the non-oriented electrical steel used in the drive motor of the new energy vehicle is 0.25mm;

[0013] The microstructure of the non-oriented electrical steel used in the drive motor of the new energy vehicle has a grain size of 70-120μm.

[0014] The non-oriented electrical steel used in the drive motor of the new energy vehicle has a product performance of B. 50 =1.69-1.72T, W 1.0 / 400 =11.0-12.2 W / kg, yield strength R el The tensile strength is 450-470 MPa, and the tensile strength R is... mThe strength is 550-600 MPa, and the elongation is A. 50 18-20%.

[0015] The present invention provides a method for manufacturing non-oriented electrical steel for drive motors of new energy vehicles, comprising: smelting, slab heating, hot rolling and coiling, normalizing, pickling, first cold rolling, intermediate annealing, second cold rolling, and annealing;

[0016] The smelting process controls the impurity elements in the steelmaking composition to be C+S+N+Ti≤0.0048% and Nb+V+Ti+Zr≤0.0030%.

[0017] The hot rolling process involves controlling the thickness of the hot plate to 1.8mm-2.4mm, followed by hot rolling and coiling, and then holding at 500℃-700℃ for 0.1h-10h. After holding, the plate is slowly cooled in a protective gas. The protective gas consists of 50-100% N2 and 0-50% H2 by volume.

[0018] Before normalizing and pickling, the steel plate is trimmed, with each side having a trim width of 0.5mm-5mm.

[0019] The normalizing pickling process is carried out at a normalizing temperature of 850-950℃ for 30-500 seconds.

[0020] The reduction rate during the first cold rolling is controlled between 50% and 85%.

[0021] The intermediate annealing is performed at a temperature of 800-950℃.

[0022] The intermediate annealing specifically involves heating the slab after the first cold rolling to the target temperature (800-950℃) at a heating rate ≥100℃ / s, and then holding it at that temperature for 20-60 seconds. This invention uses a high Si composition, with a Si content of 3.2-3.5% and a phase transformation temperature of 800-870℃. In the intermediate annealing of this invention, the temperature is raised from room temperature to 800-950℃ at a heating rate of 200℃ / s. The hydrogen volume content in the annealing furnace atmosphere is controlled to be ≥30%, with the remainder being nitrogen. After this stage of heating and annealing, the grain size of the steel plate is controlled to be 70-90μm.

[0023] The second cold rolling is performed to the target thickness. The second cold rolling is carried out in three passes, with a reduction rate of more than 35% in the first pass, in order to obtain better grain breakage so as to obtain more fibrous structure in the later stage, and provide more nucleation sites for subsequent annealing and growth.

[0024] The annealing is carried out after the second cold rolling, and this annealing is divided into three stages.

[0025] The first step involves raising the temperature from room temperature to 400-600℃. This temperature range is below the phase transformation temperature and will not cause grain growth. It mainly provides the temperature basis for subsequent processes. The hydrogen volume content in the annealing furnace atmosphere is ≥30%, with the remainder being nitrogen. This prevents surface oxidation and oxygen atom adsorption on the steel plate surface from occurring in this range. This can lead to grain boundary oxidation in the subsequent rapid heating area, affecting hysteresis loss and thus iron loss.

[0026] The second stage involves raising the temperature from 400-600℃ to above the phase transition temperature. Considering the typical 30-60℃ difference between the annealing furnace temperature and the plate surface temperature, and the decrease in thermal conductivity with increasing silicon content (tested at 20-30 W / (m·K), the temperature is set from 400-600℃ to 910-950℃). This temperature range is for rapid heating using electric heating, with a heating rate controlled at greater than 200℃ / s, maintaining a high reducing atmosphere, and controlling the hydrogen volume content to ≥35%, with the remainder being nitrogen. This range primarily aims to increase the proportion of {100} and {110} components and decrease the proportion of {111} components. The second stage, with the temperature rising from 400-600℃ to 910-950℃, mainly targets the grain growth range, providing a greater driving force in the effective region and increasing the heating rate. This second-stage annealing process is also designed considering the Sn and silicon content.

[0027] The third stage involves raising the temperature from 910-950℃ to 980-1050℃, with the heating rate controlled below 100℃ / s and the holding time between 5s and 30s, maintaining a hydrogen volume content of ≥30%. The reduced heating rate in this stage primarily prevents the increase of the {111} component, while the higher temperature is mainly to increase the uniformity of the grain size.

[0028] After the third stage of heat preservation, cooling is carried out at a cooling rate of ≤10℃ / s.

[0029] In the annealing process, the dew point inside the annealing furnace is controlled at (-40)℃-(-10)℃, and the tension inside the furnace is controlled at 0.1Mpa-9Mpa.

[0030] After annealing, an insulating material is applied.

[0031] In this invention, C: This invention controls the C content. C, whether in solid solution or cementite form, will impair the magnetic properties of the steel plate. This invention limits the C content to below 0.005%.

[0032] Si: Increasing the Si content increases the strength of the steel plate, reduces the magnetic induction, increases the resistivity and reduces magnetic hysteresis loss, and increases the difficulty of surface quality control of hot-rolled coils. The Si content of this invention is 3.20-3.50%.

[0033] Mn: Mn is beneficial for increasing the resistivity of electrical steel and reducing iron loss. It can also improve the rollability of hot-rolled sheets. Therefore, this invention sets the Mn content to 0.35-0.65%.

[0034] Al: Increasing the Al content increases the strength and magnetic induction of the steel plate, but excessive Al content can easily cause the molten steel to become sticky. Therefore, this invention controls the Al content to be 0.50-0.80%.

[0035] 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≤0.020%.

[0036] 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 ≤0.005%.

[0037] Ce + Sn: During steelmaking, Ce readily forms Ce oxysulfides with impurities such as O and S in the steel, purifying the steel and improving its magnetic properties. Sn enhances magnetic induction by forming segregation and optimizing the oxide layer on the steel plate surface, thus optimizing the texture composition. During hot rolling, Sn segregates at the original grain boundaries and promotes P segregation, hindering grain growth, refining the grains, and increasing the strength of the steel plate. However, grain refinement leads to increased hysteresis loss. Since Sn and P segregation improves the texture and reduces the impact of segregation on magnetic induction, this invention controls the Ce + Sn content to 0.010%-0.020%. Furthermore, since Sn segregation reduces grain size, smaller grains will increase hysteresis loss. Therefore, Ce is added and the nucleation rate is increased to coarsen grain size. Ce mainly coarsens sulfides, thereby coarsening grain size. However, larger grain size reduces magnetic induction and mechanical properties. To balance multiple indicators, this invention sets Ce / Sn = 0.25-2.0.

[0038] The inventors utilize the characteristics of Sn element microalloying and Ce oxysulfide to purify steel and refine grains, along with a reasonable composition ratio and process, to improve strength and grain uniformity, reduce iron loss, promote the formation of favorable textures, and enhance magnetic properties. Simultaneously, the distribution of reduction rate in the secondary cold rolling process and the optimization of the intermediate annealing process promote favorable textures and uniform grain distribution; the three-stage annealing method increases grain size uniformity and increases favorable components; and the reduced cooling rate lowers the generation of internal stress.

[0039] Compared with existing technologies, this invention improves the strength and magnetic properties of non-oriented silicon steel by adding Ce and Sn to purify the steel and microalloying it. It can suppress the formation of the inner oxide layer and reduce hysteresis loss. The segmented control of the annealing temperature process can increase the proportion of favorable texture, smaller grains and favorable texture, and optimize grain size uniformity. The resulting product has a grain size of 70-120μm, which enables the produced non-oriented electrical steel to obtain favorable medium and high frequency iron loss while having high yield strength and good magnetic induction. Attached Figure Description

[0040] Figure 1 The grain diagram for Example 1 shows a grain size of 90 μm, which improves the favorable texture and composition, reduces hysteresis loss, and makes the grains more uniform.

[0041] Figure 2 The image shown is a grain diagram of Comparative Example 1, where the grain size is relatively large and uneven. Detailed Implementation

[0042] The present invention will now be described with reference to the embodiments.

[0043] Example 1-Example 2

[0044] A non-oriented electrical steel for drive motors of new energy vehicles comprises the following composition by mass percentage: as shown in Scheme 1 in Table 1, where C+S+N+Ti≤0.0048% and Nb+V+Ti+Zr≤0.0030%; the balance not shown in Table 1 is Fe and unavoidable impurities.

[0045] Table 1. Steel composition (wt%) of each Example 1 and Example 2

[0046]

[0047] Comparative Examples 1-3

[0048] A non-oriented electrical steel for drive motors of new energy vehicles comprises the following composition by mass percentage: as shown in Scheme 1 in Table 1, where C+S+N+Ti≤0.0048% and Nb+V+Ti+Zr≤0.0030%; the balance not shown in Table 1 is Fe and unavoidable impurities.

[0049] Comparative Example 4

[0050] A non-oriented electrical steel for drive motors of new energy vehicles comprises the following composition by mass percentage: as shown in Scheme 2 in Table 1, where C+S+N+Ti≤0.0048% and Nb+V+Ti+Zr≤0.0030%; the balance not shown in Table 1 is Fe and unavoidable impurities.

[0051] Comparative Example 5

[0052] A non-oriented electrical steel for drive motors of new energy vehicles comprises the following mass percentage composition as shown in Scheme 3 in Table 1, wherein C+S+N+Ti≤0.0048% and Nb+V+Ti+Zr≤0.0030%; the balance not shown in Table 1 is Fe and unavoidable impurities.

[0053] The manufacturing methods of non-oriented electrical steel for new energy vehicle drive motors in the above embodiments and comparative examples include the following steps: smelting, preparing slabs, heating slabs, hot rolling and coiling, normalizing, pickling, first cold rolling, intermediate annealing, second cold rolling, annealing and coating with insulating materials.

[0054] Specifically as follows:

[0055] The impurity elements in the steelmaking composition should be controlled to be C+S+N+Ti≤0.0048% and Nb+V+Ti+Zr≤0.0030%.

[0056] Hot rolling is performed to control the thickness of the hot plate to 2.0 mm. After coiling, it is first held at 650℃ for 0.5 h, and then slowly cooled in N2 with a volume fraction of 60% and H2 with a volume fraction of 40%.

[0057] Then the steel plate is trimmed, with each side having a trim width of 0.5mm-5mm.

[0058] Then perform normal pickling at a temperature of 870℃ for 120 seconds.

[0059] Then, a first cold rolling process is performed, with the reduction rate controlled at 70%, to a thickness of 0.60 mm.

[0060] Then, intermediate annealing is performed: the slab after the first cold rolling is heated to the target temperature of 900℃ at a heating rate of 200℃ / s, and then held for 40s; the hydrogen volume content in the atmosphere of the annealing furnace is controlled at ≥30%, and the remainder is nitrogen. After heating in this section, the grain size is controlled at 70-90μm.

[0061] The second cold rolling process uses three passes, with a reduction rate of 38% in the first pass; after three passes, the thickness is reduced to 0.25 mm.

[0062] Finally, annealing is performed; the process is divided into three stages.

[0063] The first step involves raising the temperature from room temperature to 400-600℃ at a rate of 20℃ / s. The annealing furnace atmosphere contains ≥30% hydrogen by volume, with the remainder being nitrogen. This prevents surface oxidation and oxygen atom adsorption on the steel plate surface from causing grain boundary oxidation in the subsequent rapid heating zone, which would affect hysteresis loss and consequently iron loss.

[0064] The second phase involves raising the temperature from 400-600℃ to above the phase transition temperature. Considering the typical 30-60℃ difference between the furnace temperature and the plate surface temperature, and the decrease in thermal conductivity with increasing silicon content, and based on a thermal conductivity test result of 20-30 W / (m*K), the temperature range is set from 400-600℃ to 910-950℃. This temperature range involves rapid heating using electric heating, with a heating rate controlled at over 200℃ / s, while maintaining a highly reducing atmosphere. The hydrogen content is controlled to be ≥38% by volume, with the remainder being nitrogen. This range primarily aims to increase the proportion of {100} and {110} components and decrease the proportion of {111} components.

[0065] The third stage: The temperature is controlled between 910-950℃ and 980-1050℃, with a heating rate of 20℃ / s and a holding time of 25s, maintaining a hydrogen volume content of ≥38% and the remainder being nitrogen; after holding, cooling is carried out at a cooling rate of 8℃ / s.

[0066] The dew point inside the annealing furnace is controlled at (-40)℃-(-10℃), and the furnace tension is controlled at 0.1Mpa-9Mpa.

[0067] After annealing, the steel coil is coated with a semi-organic coating (insulating material coating) to ensure insulation and interlayer resistance.

[0068] The specific process parameters of the annealing sections for each embodiment and comparative example are shown in Table 2. The thickness of the produced steel is 0.25 mm, and the performance tests are shown in Table 2.

[0069] Table 2. Steel production processes and properties of each embodiment and comparative example.

[0070]

[0071] The underlined data above does not meet the requirements of this invention.

[0072] As can be seen from the examples and comparative examples, by controlling the composition and production parameters according to this application, the product has a small and uniform grain size, and the performance of the produced product meets the requirements of B. 50 =1.69-1.72T, W 1.0 / 400 = 11.0-12.2 W / Kg, yield strength R el The tensile strength is 450-470 MPa, and the tensile strength R is... m The strength is 550-600 MPa, and the elongation is A. 5018-20%. While Comparative Examples 1 and 2 had the same composition as the examples, the annealing after the second cold rolling was carried out conventionally, with the temperature directly rising from room temperature to 980℃. Comparative Example 1 had a faster temperature rise, while Comparative Example 2 had a slower rise, but both resulted in coarser, larger, and less uniform grains in the product, leading to higher iron loss and higher strength. Comparative Example 3, although having the same composition as the examples and also undergoing three-stage annealing, had a slower heating rate in the second stage, failing to effectively reduce the proportion of unfavorable microstructures, resulting in higher iron loss and lower magnetic induction. Comparative Example 4, although produced according to the process of this invention, did not contain Sn, resulting in lower magnetic induction; Comparative Example 5, although containing Sn, did not contain Ce, failing to properly coarsen the grains, leading to a significant increase in iron loss.

Claims

1. A non-oriented electrical steel for a drive motor of a new energy vehicle, characterized in that, The non-oriented electrical steel for new energy vehicle drive motors comprises the following components by weight percentage: C: 0.001-0.005%, Si: 3.2-3.5%, Mn: 0.35-0.65%, Al: 0.50-0.80%, P: ≤0.02%, S: ≤0.005%, 0.010%≤Ce+Sn≤0.020%, balance being iron and unavoidable impurities; The manufacturing method of the non-oriented electrical steel for the drive motor of the new energy vehicle includes: smelting, slab heating, hot rolling and coiling, normalizing, pickling, first cold rolling, intermediate annealing, second cold rolling, and annealing. The annealing process is performed in three stages. First section: Raise the temperature from room temperature to 400-600℃; The second stage: raise the temperature from 400-600℃ to 910-950℃, and control the heating rate to be greater than 200℃ / s; The third step: The temperature is raised from 910-950℃ to 980-1050℃, and the heating rate is controlled below 100℃ / s, with a holding time of 5s-30s; the composition of the non-oriented electrical steel used in the new energy vehicle drive motor meets the following requirements: Ce / Sn=0.25-2.

0.

2. The non-oriented electrical steel for new energy vehicle drive motors according to claim 1, characterized in that, The new energy automobile drive motor non-oriented electrical steel has a structure with grain size of 70-120 μm, and product performance B 50 =1.69-1.72T, W 1.0 / 400 = 11.0-12.2W / Kg, yield strength R el = 550-600MPa, elongation A m = 550-600MPa, elongation A 50 18-20%.

3. A method for manufacturing non-oriented electrical steel for a new energy vehicle drive motor as described in claim 1 or 2, characterized in that, The manufacturing method includes: smelting, slab heating, hot rolling and coiling, normalizing, pickling, first cold rolling, intermediate annealing, second cold rolling, and annealing; The annealing process is performed in three stages. First section: Raise the temperature from room temperature to 400-600℃; The second stage: raise the temperature from 400-600℃ to 910-950℃, and control the heating rate to be greater than 200℃ / s; The third stage: raise the temperature from 910-950℃ to 980-1050℃, with the temperature rise rate controlled below 100℃ / s and the holding time 5s-30s.

4. The manufacturing method according to claim 3, characterized in that, The hot rolling and coiling process involves controlling the thickness of the hot plate to 1.8mm-2.4mm, hot rolling, coiling, and then holding at 500℃-700℃ for 0.1h-10h. After holding, the plate is cooled in a protective gas. The protective gas consists of 50-100% N2 and 0-50% H2 by volume.

5. The manufacturing method according to claim 4, characterized in that, The first cold rolling process involves a reduction rate controlled between 50% and 85%.

6. The manufacturing method according to claim 4, characterized in that, The intermediate annealing is performed at a temperature of 800-950℃.

7. The manufacturing method according to claim 4 or 6, characterized in that, The intermediate annealing process specifically involves heating the slab after the first cold rolling to 800-950℃ at a heating rate of ≥100℃ / s, and then holding it at that temperature for 20-60s. The hydrogen volume content in the annealing furnace atmosphere is controlled to be ≥30%, with the remainder being nitrogen. After annealing, the grain size is controlled to be 70-90μm.

8. The manufacturing method according to claim 4, characterized in that, The second cold rolling: rolling to the target thickness; the second cold rolling: using three passes, with the first pass having a reduction rate of more than 35%.

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