Low iron loss and high strength non-oriented electrical steel for new energy vehicle drive motor and preparation method thereof

Abstract

The invention discloses a low iron loss high strength non-oriented electrical steel for new energy vehicle drive motor and a preparation method thereof. The low iron loss high strength non-oriented electrical steel for new energy vehicle drive motor comprises 0.001-0.005% C, 3.0-3.5% Si, 0.25-0.7% Mn, 0.70-1.50% Al, 1.5-2.5% Cr, 1.5-2.0% Cu, P≤0.02%, S≤0.005%, and 0.015-0.20% Sn by weight percentage. By adding Sn, Cr, and Cu alloy elements, the steel is purified, the grains are refined, the strength and grain uniformity are improved, the iron loss is reduced, the formation of favorable textures is promoted, and the magnetic properties are improved; and the addition of Sn, Cr, and Cu solid solution metal elements does not require high temperature annealing, and the produced non-oriented electrical steel has high strength and excellent magnetic properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrical steel, and specifically relates to a low iron loss and high strength non-oriented electrical steel for a new energy vehicle drive motor and a preparation method thereof. Background Art

[0002] As the country's environmental protection requirements increase, new energy vehicles, as an environmentally friendly means of transportation, are developing more and more rapidly; the drive motor is one of the core components of new energy vehicles and needs to meet the requirements of miniaturization, high efficiency and high torque. The miniaturization and high efficiency of the motor require that the non-oriented electrical steel used to make its core should have low iron loss and high magnetic induction; as the speed increases, the huge centrifugal force can easily damage the motor rotor, so the non-oriented electrical steel needs to have high strength to ensure safety at high speeds. Traditional non-oriented silicon steel can meet the requirements of low iron loss and high magnetic induction, but the strength is low. Strength and iron loss are contradictory indicators. The increase in strength will reduce magnetic properties. Therefore, it is an important research task to develop low iron loss and high strength non-oriented electrical steel for new energy vehicle drive motors.

[0003] The main methods to improve the strength of non-oriented electrical steel include precipitation strengthening, solid solution strengthening, dislocation strengthening and composite strengthening. Precipitation strengthening mainly improves the strength by forming fine carbide particles through microalloy elements and C. These fine carbide particles will hinder the rotation of magnetic domains and reduce magnetic properties. Solid solution strengthening improves the strength through elements such as Si, Mn, Al, and Cu, but too high Si can easily lead to difficulties in cold rolling. The addition of Cu will cause "copper brittleness", which increases the difficulty of rolling. High-temperature annealing is required to temporarily dissolve Cu and delay recrystallization. Higher heating temperatures will cause abnormal grain growth, which is not conducive to improving strength.

[0004] Japan has been researching high-strength non-oriented electrical steel since the 1980s. For example, Nippon Steel & Sumitomo Metal Corporation (formerly Nippon Steel & Sumitomo Metal, referred to as NSSMC) and JFE, patent 201280004130.1 discloses a high-strength non-oriented electrical steel sheet, which is added with 0.5-3.0% Ni and 0.5-3.0% Cu, and annealed at high temperature to make the interaction between Cu precipitates and sulfides, so as to obtain good magnetic properties and excellent strength properties. 1.0 / 400 =20.2~30.5W / kg, yield strength R el Japanese patent 200980113090.2 discloses a high-strength non-oriented electrical steel sheet and its manufacturing method, by adding 0.5-3.0% Cu, Cu precipitates and strengthens the steel sheet after a high-temperature annealing process at 950-1000°C, but the annealing temperature is high, and some grains grow abnormally, which is not conducive to the iron loss P 10 / 400 The reduction and magnetic induction B 50 The improvement of magnetic induction B50 1.60~1.65T, iron loss P 10 / 400 It is 25.0~30.0W / kg, and the iron loss and magnetic induction do not meet the high efficiency requirements of non-oriented electrical steel for new energy vehicles.

[0005] China is also accelerating the pace of research and development of high-strength non-oriented electrical steel. For example, Chinese patent CN106282781A discloses a method for preparing high-strength non-oriented silicon steel based on nano-Cu precipitation strengthening. The nano-Cu precipitation has little hindering effect on the movement of magnetic domain walls, and has almost no effect on the magnetic induction while greatly improving the strength. However, the method of strengthening by Cu precipitation requires high-temperature annealing to temporarily dissolve Cu, delay recrystallization, and control the recrystallization rate. However, high-temperature annealing causes some grains to grow abnormally, and the magnetic induction B 50 1.67~1.74T, iron loss P 10 / 400 It is 22.5~31.5W / kg, and the iron loss is relatively high.

[0006] Chinese patents CN106435358A and CN105803311A use twin-roller thin strip continuous casting technology, add precipitation strengthening element Nb, and combine composition design, rolling and heat treatment to produce non-oriented electrical steel with excellent magnetic properties and high strength. 50 1.68-1.73T, iron loss P 10 / 400 It is 25.5~37.5W / kg, and the iron loss is relatively high.

[0007] Baosteel patent CN108286014A improves strength through Si solid solution strengthening ability, but the high Si content reduces the toughness of the steel plate, which is not conducive to product processing; China patent CN106435358A adopts ultra-low C steelmaking technology and improves strength by adding precipitation strengthening element Nb, but its finished product iron loss P 10 / 400 The higher one is 28.0~38.2W / kg; Chinese patent CN111235461A adopts a high C (0.03~0.08%) component system to improve the strength of non-oriented silicon steel by adding Nb, Ti and trace rare earth, but C and Ti will reduce the magnetic properties of non-oriented silicon steel.

[0008] Chinese patent CN112030076A adopts a high Si (2.8-3.5%) composition system to improve the strength of non-oriented silicon steel by adding Cr, Sn, and Ce for solid solution strengthening, but Cr significantly increases hysteresis loss and iron loss is high. Although the high Si composition system can greatly improve the strength, when the Si content exceeds 3.0%, rolling is difficult and it is easy to cause the steel coil to break. Summary of the invention

[0009] The purpose of the present invention is to solve the above technical problems and to provide a low iron loss and high strength non-oriented electrical steel for new energy vehicle drive motors and a preparation method thereof, which has lower iron loss and maintains higher strength.

[0010] To achieve the above-mentioned object, the present invention provides a low iron loss and high strength non-oriented electrical steel for a new energy vehicle drive motor, wherein the chemical composition of the non-oriented electrical steel comprises, by weight percentage, 0.001-0.005% C, 3.0-3.5% Si, 0.25-0.7% Mn, 0.70-1.50% Al, 1.5-2.5% Cr, 1.5-2.0% Cu, P≤0.02%, S≤0.005%, 0.015-0.20% Sn, and the remainder is iron and unavoidable impurities.

[0011] Furthermore, when the thickness of the non-oriented electrical steel is 0.2-0.3 mm, B 50 =1.57~1.71T、W 1.0 / 400 =45~80W / Kg, yield strength R el 810~915MPa, tensile strength R m It is 900~1000MPa.

[0012] A method for preparing the non-oriented electrical steel as described above is also provided as follows:

[0013] 1) The steel having the chemical composition as claimed in claim 1 is subjected to molten iron pretreatment, converter steelmaking, vacuum treatment and then continuous casting into slabs;

[0014] 2) After the slab is cooled, it enters the heating furnace for heating;

[0015] 3) The finishing temperature of hot rolling is 1000-1100°C, the final rolling temperature of hot rolling is 780-850°C, and the temperature of the hot rolled plate is reduced to the coiling temperature of 600-680°C after air cooling;

[0016] 4) The hot-rolled plate is subjected to normalizing treatment, pickling, and first cold rolling in sequence;

[0017] 5) The first annealing is performed after the first cold rolling;

[0018] 6) Second cold rolling after the first annealing;

[0019] 7) After the second cold rolling, a second annealing is performed.

[0020] Furthermore, in the step 1), the vacuum deoxidation and continuous casting are maintained for 2 to 4 minutes; and the thickness of the slab is 200 to 300 mm.

[0021] Furthermore, in the step 2), the slab is cooled to 450-550° C., and then heated to 1100-1150° C. at a heating rate of 3-5° C. / s, and the heating and heat preservation time is 210-300 min.

[0022] Furthermore, in the step 3), the thickness of the hot-rolled plate is 1.8 to 2.2 mm.

[0023] Furthermore, in the step 4), the normalizing temperature is 820-980° C. and the insulation time is 1-5 min; the acid used for pickling is HCl with a mass concentration of 5%, and the pickling temperature is 90-95° C.; the first cold rolling is repeated for multiple passes to a target thickness of 0.5-0.8 mm.

[0024] Furthermore, in the step 5), the specific process of performing the first annealing after the first cold rolling is as follows:

[0025] After the hot-rolled plate is pickled, the first annealing is carried out. The atmosphere is produced with H2 and N2 protection, and the H2 content is ≥45%. The dew point in the furnace is controlled at -40~-10℃; the higher H2 content inhibits the formation of the inner oxide layer.

[0026] The first annealing is to rapidly heat up to 820-980°C at a heating rate of 50-60°C / s and keep the temperature for 30-250s to ensure the rapid growth of grains. The faster heating rate leads to the initial nucleation of favorable textures, which increases the proportion of favorable textures. Then the temperature is lowered to below 100°C at a cooling rate of 5-10°C / s.

[0027] Furthermore, in the step 6), the specific process of the second cold rolling is: rolling the target thickness to 0.2-0.3 mm through multiple (e.g., 5) passes, controlling the reduction rate of the first pass to ≥35%, and ensuring that the roughness of the roller Ra of the last pass is ≤0.1 μm, mainly to prevent the formation of an inner oxide layer and an inner nitride layer.

[0028] Furthermore, in step 7), the specific process of performing the second annealing after the second cold rolling is as follows:

[0029] The first stage of heating is to raise the temperature to 400-600℃, with a heating rate of less than 20℃ / s to prevent surface oxidation caused by rapid heating; the second stage of heating is to raise the temperature from 400-600℃ to the target temperature t1+30℃, t1=600-850℃, H2 content ≥45%, and the holding time is 20-500s at a heating rate of 5-10℃ / s; then cool to room temperature at a cooling rate of 5-10℃ / s; the dew point in the furnace is controlled at -40--10℃. Rapid heating optimizes the texture, and the target control of the recrystallization ratio of the organization controls the strength of the steel strip by controlling the fiber organization ratio.

[0030] Compared with the prior art, the invention has the following beneficial effects: the invention purifies steel quality, refines grains, improves strength and grain uniformity, reduces iron loss, promotes the formation of favorable textures, and improves magnetic properties by adding Sn, Cr, and Cu alloy elements; and the addition of Sn, Cr, and Cu solid solution metal elements does not require high-temperature annealing, and the produced non-oriented electrical steel has high strength and excellent magnetic properties; the produced non-oriented electrical steel has a thickness of 0.2 to 0.3 mm, and B 50 =1.57~1.71T、W 1.0 / 400 =45~80W / Kg, yield strength R el 810~915MPa, tensile strength R m It is 900~1000MPa. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with specific embodiments.

[0032] The chemical composition (by mass percentage) is as follows:

[0033] Table 1 Main chemical composition of continuous casting slab Unit: %

[0034] plan Cu Si Sn Mn P S Al Cr C 1 1.8 3.4 0.12 0.49 ≤0.01 0.002 0.85 2.0 0.002

[0035] Table 2 Main preparation process information

[0036]

[0037] The final properties of the steel plate products obtained in each embodiment and comparative example are shown in Table 3 below.

[0038] Table 3 Performance information of the products of the embodiments and comparative examples

[0039]

[0040] It can be seen from Table 3 that the comprehensive performance of Examples 1 to 6 of the present invention is better than that of the comparative example.

[0041] Table 4 Main chemical composition of continuous casting slab Unit: %

[0042] plan Cu Si Sn Mn P S Al Cr C 1 2.0 3.3 0.18 0.6 ≤0.01 0.002 1.0 2.2 0.003

[0043] When the Cu content is greater than 1.5%, a large amount of precipitates will be formed during the hot rolling process, pinning the grain boundaries and inhibiting grain growth, thereby significantly increasing the coercive force and hysteresis loss of the silicon steel, and directly leading to a significant deterioration of the iron loss and magnetic induction of the steel. However, with the increase of annealing temperature, the pinning effect of the above-mentioned precipitates on the grain boundaries decreases, the grain size is gradually able to grow, and the iron loss of the finished strip can be gradually reduced, but it has little effect on the magnetic induction of the finished strip. The increase in Sn content mainly increases the proportion of favorable textures, improves the magnetic induction, and reduces low-frequency iron losses. On the one hand, it is due to the solid solution strengthening caused by the addition of Cr, and on the other hand, it is because Cr promotes the further precipitation of Nb, thereby enhancing the precipitation strengthening effect of Nb. Cr also promotes the formation of favorable textures while inhibiting the formation of unfavorable textures, increasing the texture factor, and thus increasing the magnetic induction of high-strength non-oriented silicon steel containing Nb. Under the combined effect of these two factors, the addition of Cr has a significant effect on the iron loss P of high-strength non-oriented silicon steel containing Nb. 1.0 / 400 Almost no impact.

[0044] Table 5 Main preparation process information

[0045]

[0046] The final properties of the steel plate products obtained in each embodiment and comparative example are shown in Table 6 below.

[0047] Table 6 Performance information of examples and comparative examples

[0048]

[0049] It can be seen from Table 6 that the comprehensive performance of Examples 1 to 6 of the present invention is better than that of the comparative example.

[0050] Table 7 Main chemical composition of continuous casting slab Unit: %

[0051] plan Cu Si Sn Mn P S Al Cr C 1 1.5 3.4 0.10 0.49 ≤0.01 0.002 0.85 1.5 0.002

[0052] Table 8 Main preparation process information

[0053]

[0054] The final properties of the steel plate products obtained in each embodiment and comparative example are shown in Table 3 below.

[0055] Table 9 Performance information of examples and comparative examples

[0056]

[0057] It can be seen from Table 9 that the comprehensive performance of Examples 1 to 5 of the present invention is better than that of the comparative example.

Claims

1. A low iron loss and high strength non-oriented electrical steel for new energy vehicle drive motor, characterized in that: The chemical composition of the non-oriented electrical steel includes, by weight percentage, 0.001-0.005% C, 3.0-3.5% Si, 0.25-0.7% Mn, 0.70-1.50% Al, 1.5-2.5% Cr, 1.5-2.0% Cu, P≤0.02%, S≤0.005%, 0.015-0.20% Sn, and the remainder is iron and inevitable impurities.

2. The low iron loss and high strength non-oriented electrical steel for new energy vehicle drive motor according to claim 1, characterized in that: When the thickness of the non-oriented electrical steel is 0.2-0.3 mm, B 50 =1.57~1.71T、W 1.0 / 400 =45~80W / Kg, yield strength R el 810~915MPa, tensile strength R m It is 900~1000MPa.

3. A method for preparing non-oriented electrical steel as claimed in claim 1, characterized in that: The preparation method is as follows: 1) The steel having the chemical composition as claimed in claim 1 is subjected to molten iron pretreatment, converter steelmaking, vacuum treatment and then continuous casting into slabs; 2) After the slab is cooled, it enters the heating furnace for heating; 3) The finishing temperature of hot rolling is 1000-1100°C, the final rolling temperature of hot rolling is 780-850°C, and the temperature of the hot rolled plate is reduced to the coiling temperature of 600-680°C after air cooling; 4) The hot-rolled plate is subjected to normalizing treatment, pickling, and first cold rolling in sequence; 5) The first annealing is performed after the first cold rolling; 6) Second cold rolling after the first annealing; 7) After the second cold rolling, a second annealing is performed.

4. The preparation method according to claim 3, characterized in that: In the step 1), the vacuum deoxidation and continuous casting are maintained for 2 to 4 minutes; the thickness of the slab is 200 to 300 mm.

5. The preparation method according to claim 3, characterized in that: In the step 2), the slab is cooled to 450-550° C., and then heated to 1100-1150° C. at a heating rate of 3-5° C. / s, and the heating and heat preservation time is 210-300 min.

6. The preparation method according to claim 3, characterized in that: In the step 3), the thickness of the hot-rolled plate is 1.8 to 2.2 mm.

7. The preparation method according to claim 3, characterized in that: In the step 4), the normalizing temperature is 820-980° C. and the insulation time is 1-5 min; the acid used for pickling is 5% HCl and the pickling temperature is 90-95° C.; the first cold rolling is performed through multiple passes to a target thickness of 0.5-0.8 mm.

8. The preparation method according to claim 3, characterized in that: In the step 5), the specific process of performing the first annealing after the first cold rolling is as follows: After the hot-rolled plate is pickled, the first annealing is carried out. The atmosphere is produced with H2 and N2 protection, and the H2 content is ≥45%. The dew point in the furnace is controlled at -40~-10℃; The first annealing is to rapidly heat up to 820-980°C at a heating rate of 50-60°C / s and keep the temperature for 30-250s, and then cool down to below 100°C at a cooling rate of 5-10°C / s.

9. The preparation method according to claim 3, characterized in that: In step 6), the specific process of the second cold rolling is: rolling through multiple passes to a target thickness of 0.2-0.3 mm, the first pass reduction rate is controlled at ≥35%, and the last pass roll roughness Ra is ensured to be ≤0.1 μm.

10. The preparation method according to claim 3, characterized in that: In the step 7), the specific process of performing the second annealing after the second cold rolling is as follows: The first stage of heating raises the temperature to 400-600°C with a heating rate of less than 20°C / s; the second stage of heating raises the temperature from 400-600°C to the target temperature t1+30°C at a heating rate of 50-60°C / s, t1=600-850°C, H2 content ≥45%, and the insulation time is 20-500s; then the temperature is lowered to room temperature at a cooling rate of 5-10°C / s; the dew point in the furnace is controlled at -40--10°C.

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