Non-oriented silicon steel for high speed motors and its manufacturing method

Abstract

The present application relates to the technical field of non-oriented silicon steel, and more particularly to a non-oriented silicon steel for high-speed motors and a manufacturing method thereof. The chemical components of the non-oriented silicon steel for high-speed motors are as defined in the specification. The thickness of the final product is 0.20-0.30 mm, and the grain size of the final product is 80-100 μm. The manufacturing method of the non-oriented silicon steel for high-speed motors includes the steps of smelting to cast a continuous casting billet, cooling the continuous casting billet, heating, hot rolling, normalizing, pickling, cold rolling, annealing, and coating. The present application provides a method for improving strength and reducing high-frequency iron loss P by utilizing means such as resistivity control, inclusion control, texture control, and grain size control through the control of chemical components and the design of the entire process of the above flow. 1.0 / 1000 Moreover, the smelting cost is low, the production process is simple, the production cost is low, and the requirements for high speed motors, such as high rotation speed, small size and high efficiency, are met.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to a Chinese patent application bearing application number 202211107301.5 and entitled "Non-oriented silicon steel for high-speed motors and its manufacturing method" filed with the State Intellectual Property Office of the People's Republic of China on September 13, 2022, the entire contents of which are incorporated herein by reference. [Technical field]

[0002] The present application relates to the technical field of non-oriented silicon steel, and more particularly to a non-oriented silicon steel for high speed motors and a method for producing the same. [Background technology]

[0003] High-speed motors usually refer to motors with a rotation speed of more than 10,000 r / min. High-speed motors have prominent advantages such as high rotation speed, small size, high power density and high efficiency, and are widely used in many scenes such as centrifugal compressors in air conditioners and refrigerators, energy storage flywheels, and high-speed grinders, and have broad application prospects in electric vehicles and distributed power generation systems. At present, it has become one of the research hotspots in the field of international electrical engineering.

[0004] The main features of a high-speed motor are high rotor speed, high stator winding current, and high magnetic flux frequency in the iron core. The centrifugal force acting on the rotor of the motor is proportional to the square of the linear speed. Since the rotation speed of a high-speed motor exceeds 10,000 r / min, the non-oriented silicon steel used in the iron core of the rotor has high mechanical strength requirements. In order to meet the technical indicator of high rotation speed, the size of a high-speed motor is much smaller than that of a normal-speed motor with the same output, so the non-oriented silicon steel used in the iron core of the high-speed motor has high magnetic induction requirements. In short, to realize the control requirements of high rotation speed, small size, and high efficiency of a high-speed motor, the non-oriented silicon steel, which is the main material of the iron core, has low strength and high-frequency iron loss P. 1.0 / 1000 It is required that the magnetic flux density is small and the magnetic induction is high.

[0005] Most of the existing technologies for producing non-oriented silicon steel focus only on iron loss under frequency conditions of 50Hz to 400Hz, and there are only a few production technologies that focus on iron loss under frequency conditions of 1000Hz or more. However, the production process is complicated, making it difficult to meet the needs of the rapid development of high-speed motors in the future.

[0006] For example, a patent document with Chinese Patent Publication No. CN111471927A discloses a high magnetic induction non-oriented silicon steel for automobile generators and a manufacturing method thereof, in which the non-oriented silicon steel contains, as chemical components, Si 0.60-1.60% by weight, Mn 0.10-0.65% by weight, P 0.040-0.100% by weight, Als≦0.0080% by weight, and Sn 0.01-0.10% by weight, with C+S+O+N+Ti≦100 ppm, the contents of each element being all 25 ppm or less, and the remaining components being Fe and unavoidable impurity elements. By optimizing the design of the components and process, the magnetic properties of the final product are improved to include iron loss P 1.5 / 50 ≦4.50W / kg, magnetic induction B 5000 ≧ 1.74T, and the mechanical properties satisfy the Vickers microhardness HV1 range of 110 to 120 and the elongation A50 ≧ 40%.

[0007] The patent document with Chinese Patent Publication No. CN107964631B discloses a non-oriented silicon steel for high-speed motor rotors with yield strength ≥ 500MPa, whose chemical composition is Si: 4.12-4.5wt%, Al: 1.62-2.0wt%, Mn: 0.5-2.0wt%, N ≤ 0.005wt%, S ≤ 0.002wt%, C ≤ 0.003wt%, P ≤ 0.05wt%, Cu ≤ 0.05wt%, Ti + Nb + V + Zr ≤ 0.01wt%. The production method is converter smelting, RH vacuum refining, casting billet heating, rough rolling and finish rolling, coiling, pickling, cold rolling, and annealing. The non-oriented silicon steel for high-speed motor rotors disclosed in the present application has a yield strength of 500 MPa or more, and the final product having a thickness of 0.35 mm or less has an iron loss of P 1.0 / 400 ≦18W / kg.

[0008] A patent document with Chinese Patent Publication No. CN107974620B discloses a non-oriented silicon steel for high-speed rotors with a yield strength of 600 MPa, whose chemical compositions are C0.001-0.003wt%, Si2.6-3.4wt%, Mn0.20-0.60wt%, P≦0.005wt%, S≦0.005wt%, Als0.75-0.95wt%, N0.002-0.006wt%, and Nb0.053-0.20wt%. The production steps include smelting in a converter and casting into billets, heating the continuous cast billets, normal rough rolling and finish rolling, normalizing, pickling, cold rolling, and continuous annealing. In the non-oriented silicon steel disclosed in the present application, the final product having a thickness of 0.35 mm or less has a yield strength of ≥ 600 MPa, a tensile strength of ≥ 700 MPa, and a P 1.0 / 400 ≦35W / kg, B 5000 ≧1.60T.

[0009] The general non-oriented silicon steel for motors provided by the above patents CN111471927A, CN107964631B, and 107974620B can meet the requirements of high-speed motors in terms of mechanical strength and magnetic induction, but they only focus on the iron loss under the condition of a frequency of 50Hz to 400Hz. The iron loss of non-oriented silicon steel includes three types: hysteresis loss, eddy current loss, and anomalous loss. Since the proportion of anomalous loss in iron loss is small, hysteresis loss and eddy current loss are generally focused on. Hysteresis loss P h =k h *f*B 2 , eddy current loss P e =k e *f 2 *B 2 From the formula for hysteresis loss and eddy current loss, the hysteresis loss P h and f are proportional, and the eddy current loss P e and f 2are inversely proportional to each other. Therefore, as the frequency increases, the eddy current loss of the iron loss increases significantly. At low frequencies (50Hz to 400Hz), hysteresis loss accounts for the majority of the iron loss, while at high frequencies (≧1000Hz), eddy current loss accounts for the majority of the iron loss. Obviously, the composition of the iron loss is different between high and low frequency conditions, so it is difficult to ensure that non-oriented silicon steel that has good magnetic properties under low frequency conditions also maintains good magnetic properties under high frequency conditions. That is, with the non-oriented silicon steel and its manufacturing method described in the above patent, the high-frequency iron loss P of non-oriented silicon steel for high-speed motors is 1.0 / 1000 It is difficult to meet the requirements for use in this way, and there is a drawback in that the iron loss at high frequencies is large.

[0010] A patent document with Chinese patent publication number CN104480386B discloses a 0.2 mm thick non-oriented silicon steel for high speed motors, whose components are 0.001-0.025 wt% C, 2.6-3.0 wt% Si, 0.25-0.55 wt% Al, 0.10-0.30 wt% Mn, P≦0.015 wt%, 0.001-0.0025 wt% S, and 0.001-0.0025 wt% N. The production steps include smelting in a vacuum induction furnace and casting into steel ingots, blooming and heating, forging and heating, hot rolling, normalizing, pickling, first cold rolling, intermediate annealing, second cold rolling, annealing the final product, cooling, cutting, sample preparation, and measurement of magnetic and mechanical properties by conventional methods. 1.0 / 1000 ≦40w / kg, B 5000 ≧1.68T, and the yield ratio of the mechanical properties is 0.70~0.73, which meets the requirements for manufacturing iron cores for high-speed motors.

[0011] A patent document with Chinese patent publication number CN112538592B discloses a non-oriented silicon steel for a high-speed motor having a frequency of ≥ 10000Hz, the composition of which is C ≤ 0.003wt%, Si 2.8-3.5wt%, Mn 0.05-1.0wt%, P ≤ 0.0015wt%, N ≤ 0.0008wt%, Al 0.75-1.5wt%, S ≤ 0.0009wt%, Sb 0.001-0.1wt%, Sn 0.001-0.1wt%, and the sum of Sb and Sn is 0.001-0.1%. The steps include a step of smelting and casting into a billet, a step of heating the cast billet, keeping it at a high temperature, hot rolling and coiling it, a step of normalizing, keeping it at a high temperature, pickling and coiling it, a step of a first cold rolling, a step of a first continuous annealing, a step of a second cold rolling, a step of a second continuous annealing, a step of a third cold rolling, a step of continuous annealing of the final product, a step of slow cooling, a step of applying an insulating layer and a step of curling. 0.1 / 10000 is 15.5W / kg or less, P 0.1 / 400 is 9.5W / kg or less, B 5000 is 1.6T or more.

[0012] The patent documents with Chinese patent publication numbers CN104480386B and CN112538592B disclose non-oriented silicon steel for high-speed motors with current frequencies of 1000Hz and 10000Hz, respectively, but the production process is complicated and the cost is high. For example, the patent document with Chinese patent publication number CN104480386B discloses a non-oriented silicon steel with a thickness of 0.2mm for high-speed motors, the production process of which includes two cold rollings and two annealings, and the patent document with Chinese patent publication number CN112538592B discloses a non-oriented silicon steel for high-speed motors with frequencies ≧10000Hz, the production process of which includes three cold rollings and three annealings.

[0013] Most of the existing technologies for producing non-oriented silicon steel focus only on iron loss under conditions of frequencies from 50 Hz to 400 Hz. Although there are only a few production technologies that focus on iron loss under conditions of frequencies above 1000 Hz, the production process is complex and it is difficult to meet the needs of the rapid development of future high-speed motors.

Summary of the Invention

Problems to be Solved by the Invention

[0014] The technical problem to be solved by this application is to provide a non-oriented silicon steel for high-speed motors and a manufacturing method thereof in order to solve the defects of the conventional non-oriented silicon steel for high-speed motors, which have a complex production process or high iron loss at high frequencies.

Means for Solving the Problems

[0015] Therefore, this application provides a non-oriented silicon steel for high-speed motors, whose chemical composition is C≤0.0020% by mass, S≤0.0010% by mass, N≤0.0030% by mass, Si: 3.0 - 3.4% by mass, Al: 0.80 - 1.0% by mass, Mn: 0.2 - 0.4% by mass, P≤0.01% by mass, Sn + Sb≤0.004% by mass, Nb≤0.005% by mass, V≤0.005% by mass, Ti≤0.005% by mass, Mo≤0.005% by mass, Cr≤0.05% by mass, Ni≤0.05% by mass, Cu≤0.05% by mass, and the rest are Fe and inevitable impurities, 0 < C + S + N≤0.0050%, the thickness of the final product is 0.20 - 0.30 mm, and the grain size of the final product is 80 - 100 μm.

[0016] Furthermore, the non-oriented silicon steel for high-speed motors has a yield strength of ≥550 MPa, magnetic induction B 5000 ≥1.65, and at a thickness of 0.30 mm, the high-frequency iron loss P 1.0 / 1000 ≤45 W / kg, at a thickness of 0.25 mm, the high-frequency iron loss P 1.0 / 1000 ≤40 W / kg, and at a thickness of 0.20 mm, the high-frequency iron loss P 1.0 / 1000 ≤35 W / kg.

[0017] Furthermore, 4.8% ≦ Si + 2Al ≦ 5.2%.

[0018] The main functions of each element and process in this application are as follows.

[0019] C ≦ 0.0020%, S ≦ 0.0010%, N ≦ 0.0030%: C, S, and N are all harmful elements in non-oriented silicon steel. When the C content increases, the iron loss increases and the magnetic induction decreases. When C is high, there may also be problems with magnetic aging, and the lower its content, the better. S and Mn form fine MnS, and N and Al form fine AlN. This not only hinders the growth of crystal grains during annealing but also directly hinders the movement of magnetic walls and increases the hysteresis loss. Non-oriented silicon steel generally adopts vacuum refining, and it is not difficult to control C below 0.002% and N below 0.003%. Generally, the S content of medium and low-grade non-oriented silicon steel is controlled below 0.0030%, but if the S content continues to be reduced, the cost will increase. However, for the high-grade non-oriented silicon steel for high-speed motors in this application, since the Si content is controlled at 3.0 - 3.4% and the Al content is controlled at 0.80 - 1.0%, the O content in the molten steel is significantly reduced. According to the desulfurization reaction CaO + S = CaS + O, when the O content in the molten steel decreases, the difficulty of desulfurization is reduced. Therefore, in this application, C is controlled below 0.0020%, S below 0.0010%, N below 0.0030%, and also 0 < C + S + N ≦ 0.0050%. By controlling the harmful elements C, S, and N, not only is the hysteresis loss during high-frequency operation of the non-oriented silicon steel in this application reduced, but also the magnetic induction is improved and magnetic aging is reduced.

[0020] Si 3.0-3.4%, Al 0.80-1.0%: Both Si and Al are effective additive elements for improving resistivity, reducing iron loss, and improving strength. However, as the Si and Al contents increase, the difficulty of rolling the steel increases, and edge cracks are more likely to occur during hot rolling, and sheet breakage is more likely to occur during cold rolling. In particular, when the Si content exceeds 3.5%, the difficulty of rolling increases significantly. In addition, as the Si and Al contents increase, the magnetic induction of the steel sheet decreases. In the present application, the Si content is controlled to 3.0-3.4% and the Al content to 0.80-1.0%, thereby reducing high-frequency iron loss and improving the strength of the steel sheet, and also significantly reducing the O content in the molten steel, creating conditions for ultra-low S smelting. By controlling the compounded chemical composition (P, Sn+Sb), naturally cooling the cast billet to 400-500°C, heating it to 1080-1100°C at a heating rate of 10°C / min or less, then keeping it at that temperature for 0.5-1.0h before hot rolling, and normalizing it at a low temperature of 830-870°C. Also, by preheating the steel plate to 100-200°C before cold rolling, there is no edge cracking in hot rolling and stable production is possible, and in cold rolling, stable production is possible with a large reduction rate, and the plate breakage rate in cold rolling is less than 0.5%. Furthermore, the above low-temperature normalizing process gives the final product a high magnetic induction.

[0021] Mn 0.2-0.4%: Adding an appropriate amount of Mn is advantageous in improving the magnetic properties of the steel sheet, and can also improve the strength of the steel sheet. Mn suppresses thermal brittleness caused by S, and easily forms coarse MnS precipitates together with S, reducing the iron loss of the steel sheet. Since Mn alloys are relatively expensive, in the present application, the Mn content is controlled to 0.2-0.4% in consideration of costs. In the present application, the S content is ≦0.0010%, so the Mn / S ratio is high, which can promote the precipitation and growth of MnS, and is advantageous for the magnetic properties.

[0022] P≦0.01%: P has little effect on magnetism, and increasing its content can improve the strength of the steel sheet. However, in the case of high-grade non-oriented silicon steel, the difficulty of cold rolling increases significantly when the P content is high, and the sheet is more likely to break during rolling. In this application, the idea of ​​control is to adopt high Si and high Al composition design and thin specification design of the final product to obtain high strength by controlling the fine crystal of the final product. Since the thickness of the final product is obtained by one cold rolling, it is necessary to control P≦0.01% in order to improve the rollability of the steel sheet and simplify the manufacturing process.

[0023] Sn+Sb≦0.004%: Sn and Sb are both grain boundary segregation elements. The purpose of adding Sn alone, Sb alone, or a combination of Sn and Sb to non-oriented silicon steel is to reduce the proportion of unfavorable {111} texture by the grain boundary segregation of Sn and Sb, and improve the magnetic induction of the final product. The effect is particularly prominent in production processes without a normalizing process. However, the grain boundary segregation behavior of Sn and Sb embrittles the grain boundaries of the steel sheet, making sheet breakage more likely to occur in cold rolling and making production more difficult. In the present application, the normalizing treatment is performed on the hot rolled coil before cold rolling, which can significantly reduce the proportion of unfavorable texture in the final product {111}, so in order to ensure the rollability of the steel sheet and simplify the manufacturing process, Sn and Sb are not intentionally added when designing the composition, and Sn+Sb is controlled to 0.004% or less.

[0024] Nb≦0.005%, V≦0.005%, Ti≦0.005%, Mo≦0.005%, Cr≦0.05%, Ni≦0.05%, Cu≦0.05%: Nb, V, Ti, Mo, Cr, Ni, and Cu reduce the grain size of the final product of non-oriented silicon steel, which results in a decrease in the magnetic properties of non-oriented silicon steel under low-frequency conditions, such as increased iron loss and decreased magnetic induction strength. In this application, non-oriented silicon steel for high-speed motors is required to have low iron loss under high-frequency operating conditions, and the grain size needs to be appropriately reduced to reduce eddy current loss. Therefore, in this application, the presence of appropriate contents of Nb, V, Ti, Mo, Cr, Ni, and Cu in non-oriented silicon steel for high-speed motors can reduce the grain size of the final product of non-oriented silicon steel. This not only improves the strength, but also helps to reduce high-frequency eddy current loss. However, considering that the alloy prices of these elements are relatively high, this application does not intentionally add them, but appropriately expands the control requirements to reduce the difficulty of steelmaking: Nb≦0.005%, V≦0.005%, Ti≦0.005%, Mo≦0.005%, Cr≦0.05%, Ni≦0.05%, Cu≦0.05%.

[0025] The iron loss of non-oriented silicon steel includes three types of loss: hysteresis loss, eddy current loss, and anomalous loss. Hysteresis loss is the energy loss caused by the hysteresis phenomenon in which the magnetic induction intensity lags behind the change in magnetic field intensity during the magnetization and demagnetization process of a magnetic material, as a result of factors such as inclusions, crystal defects, internal stress, and crystal orientation in the material preventing the movement of the magnetic domain walls and preventing the change in magnetic flux. Eddy current loss is the energy loss caused by the generation of eddy currents due to the local electromotive force induced around the magnetic flux according to Faraday's law of electromagnetic induction when the magnitude and direction of the magnetic flux change during the alternating magnetization process of a magnetic material. In other words, when the magnetic domain walls move, the magnetization changes rapidly, and eddy current loss occurs, which can be calculated according to the classical eddy current loss formula. Anomalous loss is the energy loss caused by differences in the magnetic domain structure when the material is magnetized, and its proportion in iron loss is small.

number

[0026] From the above, it has been found that hysteresis loss, eddy current loss, and anomalous loss are all energy losses that occur in the process of magnetization and demagnetization of magnetic materials. Since anomalous loss accounts for a small proportion of iron loss, hysteresis loss and eddy current loss are generally the focus of attention. Hysteresis loss P h =k h *f*B 2 , eddy current loss P e =k e *f 2 *B 2 At the power supply frequency (50Hz), hysteresis loss accounts for approximately 70% and eddy current loss accounts for approximately 30%. From the formula for hysteresis loss and eddy current loss, P h and f are proportional, and P e and f 2 is proportional to the frequency, and therefore, as the frequency increases, the eddy current loss of the iron loss increases significantly. At low frequencies (50Hz to 400Hz), hysteresis loss accounts for the majority of the iron loss, and at high frequencies (≧1000Hz), eddy current loss accounts for the majority of the iron loss.

[0027] Since the compositions of low-frequency iron loss and high-frequency iron loss are different, the present application employs a design concept that is completely different from that of conventional non-oriented silicon steel.

[0028] Conventional design philosophy of non-oriented silicon steel: Under low frequency conditions, the proportion of hysteresis loss is high for non-oriented silicon steel with the same composition, so the process design generally needs to focus on the large crystal grains of the final product. Since the grain boundaries prevent the movement of the domain walls, the crystal grains increase, the grain boundaries decrease, the hysteresis loss decreases, and the iron loss decreases. If the crystal grains of the final product are designed to be large, it is advantageous for reducing low-frequency iron loss, but the strength of the steel sheet decreases as the crystal grains increase. In other words, under low frequency conditions, low iron loss and high strength are contradictory in controlling the crystal grain size. To reduce iron loss, it is necessary to increase the crystal grain size and improve the strength by strengthening methods such as solid solution strengthening, precipitation strengthening, and dislocation strengthening. For example, in the composition design, alloy elements such as Cu, Cr, Ni, Nb, V, and Ti are added, and in the process design, incomplete recrystallization annealing or secondary cold rolling is performed, or a combination of the above two methods.

[0029] Design concept of non-oriented silicon steel in this application: Under high frequency conditions, in the case of non-oriented silicon steel with the same composition, the proportion of eddy current loss is high, so large crystal grains in the final product are not pursued during process design. This is because as the crystal grains become larger, the grain boundaries decrease, the magnetic domains move faster, the magnetization changes rapidly, and the eddy current loss increases. In other words, under high frequency conditions, the eddy current loss, which accounts for the largest proportion of high frequency iron loss, can be reduced by reducing the crystal grain size. Hysteresis loss increases, but the overall high frequency iron loss decreases. In addition, the strength of the steel sheet can be improved by fine grains. In other words, under high frequency conditions, low iron loss and high strength are organically integrated in terms of controlling the crystal grain size, and by controlling the crystal grain size, fine grain strengthening and low high frequency iron loss can be achieved simultaneously.

[0030] The present application also provides a method for producing non-oriented electrical steel for high-speed motors, including the steps of smelting to cast a continuous casting billet, cooling the continuous casting billet, and performing heating, hot rolling, normalizing, pickling, cold rolling, annealing, and coating treatments.

[0031] Furthermore, the normalizing temperature is 830 - 870°C, the holding time is 3 - 5 minutes, the cold rolling reduction ratio is controlled to be 89% - 90%, the annealing temperature is 880 - 900°C, and the holding time is 120 - 150 seconds.

[0032] Furthermore, it is smelted using a vacuum induction furnace, controlled to 0 < C + S + N ≤ 0.0050%, and a continuous casting billet with a thickness of 200 - 250 mm is cast.

[0033] Furthermore, in the steps of cooling and heating the casting billet, after the casting billet is naturally cooled to 400 - 500°C, it is heated to 1080 - 1100°C at a heating rate of 10°C / min or less, and then held for 0.5 - 1.0 hour.

[0034] Furthermore, the hot rolling includes six rough rolling steps and seven finish rolling steps, and / or An intermediate billet with a thickness of 30 - 45 mm is obtained by rough rolling, and a hot rolled sheet with a thickness of 2.0 - 3.0 mm is obtained by finish rolling, and / or The final rolling temperature of the finish rolling is 800 - 860°C, the coiling temperature is 600 - 660°C, the variation range of the final rolling temperature and the coiling temperature of the finish rolling is ±15°C, and the total reduction ratio of the finish rolling is 92.5 - 93.5%.

[0035] Furthermore, after normalizing, the steel plate is cooled to 80 - 150°C, and then shot blasting and pickling processes are performed.

[0036] For pickling, existing conventional reagents such as hydrochloric acid can be used. The temperature of the acid solution is 75 - 85°C, and the concentration of hydrochloric acid in the acid solution is 120 - 160 g / L.

[0037] Furthermore, before cold rolling, the steel plate is preheated to 100 - 200°C, and / or the recrystallized grain size after normalizing is 60 - 80 μm, and the volume ratio of the recrystallized structure is 100%.

Advantages of the Invention

[0038] The technical solution of the present application has the following advantages.

[0039] 1. The non-oriented silicon steel for high-speed motors according to the present application has a chemical composition of C ≤ 0.0020% by mass, S ≤ 0.0010% by mass, N ≤ 0.0030% by mass, Si: 3.0 - 3.4% by mass, Al: 0.80 - 1.0% by mass, Mn: 0.2 - 0.4% by mass, P ≤ 0.01% by mass, Sn + Sb ≤ 0.004% by mass, Nb ≤ 0.005% by mass, V ≤ 0.005% by mass, Ti ≤ 0.005% by mass, Mo ≤ 0.005% by mass, Cr ≤ 0.05% by mass, Ni ≤ 0.05% by mass, Cu ≤ 0.05% by mass, and the rest is Fe and inevitable impurities, with 0 < C + S + N ≤ 0.0050%. The thickness of the final product is 0.20 - 0.30 mm, and the grain size of the final product is 80 - 100 μm. By accurately controlling the chemical composition and the thickness and grain size of the final product, the strength is improved, and the high-frequency iron loss P 1.0 / 1000 is reduced. Moreover, the smelting cost is low, the production process is simple, the production cost is low, meeting the requirements for the use of high-speed motors with high rotational speed, small size, and high efficiency. There is no need to additionally add alloy strengthening elements such as Cu, Cr, Ni, Nb, V, and Ti, nor is there a need to add grain structure control elements such as Sn and Sb.

[0040] 2. In the final product of the non-oriented silicon steel for high-speed motors according to the present application, the yield strength is ≥ 550 MPa, the magnetic induction B 5000 is ≥ 1.65, the high-frequency iron loss P 1.0 / 1000 ≤ 45 W / kg at a thickness of 0.30 mm, the high-frequency iron loss P 1.0 / 1000 ≤ 40 W / kg at a thickness of 0.25 mm, and the high-frequency iron loss P 1.0 / 1000 ≤ 35 W / kg at a thickness of 0.20 mm. It can meet the needs of the rapid development of future high-speed motors.

[0041] 3. The manufacturing method of non-oriented silicon steel for high-speed motors according to the present invention includes the steps of smelting to cast a continuous casting billet, cooling the continuous casting billet, and carrying out heating, hot rolling, normalizing, pickling, cold rolling, annealing, and coating treatments. The production flow is short and the production efficiency is high. By controlling the chemical components and designing the entire process of the above flow, the contradictions of high-frequency iron loss, magnetic induction, and strength are balanced by using means such as resistivity control, inclusion control, texture control, and grain size control, and high strength, high magnetic properties, and excellent high-frequency magnetic properties are realized.

[0042] 4. The manufacturing method of non-oriented silicon steel for high-speed motors according to the present invention can avoid cracks in the high-silicon steel casting billet and ensure smooth hot rolling by controlling the content of P, Sn, and Sb elements in the composition design, and controlling the natural cooling temperature and heating rate of the casting billet. By controlling the recrystallized grain size after normalizing and performing preheating before cold rolling, it is possible to realize one-time cold rolling of high-silicon steel with a large reduction ratio, and a final product with a thickness of 0.20 to 0.30 mm can be obtained with one annealing, resulting in a short production flow and high production efficiency.

[0043] 5. The manufacturing method of non-oriented silicon steel for high-speed motors according to the present application involves normalizing at 830-870℃ for 3-5min, and then heating at a low temperature for a long time, which not only achieves complete recrystallization of the hot-rolled sheet, but also avoids the grains from being too large, and makes the grain size 60-80μm. The reason for controlling the reduction rate of cold rolling to 89%-90% is to increase the stored energy and nucleation points, increase the annealing nucleation rate, and create conditions for accurate and stable control of the grain size of the final product in the annealing process. Combined with annealing at 880-900℃ for 120-150s, the control of the above three process conditions combined with accurate control of chemical components ensures complete recrystallization and controls the grain size of the final product to 80-100μm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] The following examples are provided to better understand the present application. The present application is not limited to the aforementioned best embodiment, and the following examples do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone's suggestion of the present application or by combining the features of the present application with other prior arts falls within the protection scope of the present application.

[0045] When specific experimental steps or conditions are not specified in the examples, they may be carried out according to the operations or conditions of the normal experimental steps described in the literature in this field. The reagents or instruments used are not specified by the manufacturer, and all are ordinary reagent products that can be obtained commercially.

[0046] Examples 1 to 8 respectively provide non-oriented silicon steel for high-speed motors, and its chemical composition is shown in Table 1 in mass percentage, and the rest are Fe and inevitable impurities. Also, the non-oriented silicon steel for high-speed motors manufactured in each example is specifically a steel plate with the thickness shown in Table 1.

[0047]

Table 1

[0048] The non-oriented silicon steel for high-speed motors in each example of the present application is produced according to the following steps.

[0049] (1) Smelt using a vacuum induction furnace, control 0 < C + S + N ≤ 0.0050%, and cast a continuous casting billet with a thickness of 220 mm. The chemical composition of the continuous casting billet is shown in Table 1. Nb, V, Ti, Mo, Cr, Ni, and Cu are not intentionally added during the smelting process, but the requirements of these controls are appropriately broadened to control Nb ≤ 0.005%, V ≤ 0.005%, Ti ≤ 0.005%, Mo ≤ 0.005%, Cr ≤ 0.05%, Ni ≤ 0.05%, and Cu ≤ 0.05%. This reduces the difficulty of steelmaking.

[0050] (2) The continuous cast billets obtained in step (1) were stacked and naturally cooled to 450°C, and then sent to a heating furnace where they were heated at a heating rate of 5°C / min and kept at that temperature. The heating temperature and the keeping time are shown in Table 2.

[0051] (3) The continuous casting billet heated in step (2) was subjected to rough rolling and finish rolling. In the rough rolling, a 1+5 mode was adopted, and an intermediate billet was obtained after six passes of rolling. Then, seven passes of finish rolling and coiling were performed to obtain a hot-rolled sheet coil. The thickness of the intermediate billet obtained by rough rolling, the final rolling temperature of the finish rolling, the total reduction rate in the finish rolling, the thickness of the obtained hot-rolled sheet, and the coiling temperature are shown in Table 2.

[0052] (4) The hot-rolled sheet coil obtained in step (3) is dried in pure N 2 The normalizing temperature and normalizing time are shown in Table 3. After normalizing, the steel plate was cooled to 100°C, shot blasted, and then pickled in hydrochloric acid. The temperature of the acid solution was 80°C, the concentration of hydrochloric acid in the acid solution was 140g / L, and the Fe content in the pickling solution was 1.2g / L. 2+ The mass concentration of is controlled to 50±20 g / L. As a result of detecting the metal structure of the normalized steel sheet in each example, the volume fraction of the recrystallized structure and the recrystallized grain size measured are shown in Table 3.

[0053] (5) The normalized and pickled steel sheet obtained in step (4) is preheated and then cold rolled. The preheating temperature, thickness before rolling, thickness after rolling, and reduction ratio of cold rolling are shown in Table 4.

[0054] (6) The full hardened steel plate obtained in step (5) is 2 and N 2 The samples were subjected to continuous annealing in a mixed gas atmosphere. 2 The content is 15%. The annealing temperature and incubation time are shown in Table 4.

[0055] (7) The steel plate obtained in step (6) was coated and finished in the usual manner.

[0056] [Table 2]

[0057] [Table 3]

[0058] [Table 4]

[0059] Comparative Example Comparative Examples 1 to 8 each provide a non-oriented silicon steel, and the chemical components (mass%) thereof are shown in Table 5. The non-oriented silicon steel produced in each Comparative Example is specifically a steel sheet having a thickness shown in Table 5.

[0060] [Table 5]

[0061] The non-oriented silicon steels of Comparative Examples 1 to 8 were all produced according to the design concept of low-frequency non-oriented silicon steel.

[0062] In Comparative Examples 1 to 3, the recrystallized grain size after normalizing is increased by controlling the normalizing temperature and the warm-holding time, and the large grain size of the final product can be obtained by combining the control of the cold rolling reduction, the annealing temperature and the warm-holding time. The specific process parameters are shown in Tables 6 to 8.

[0063] In Comparative Examples 4 to 6, based on Comparative Examples 1 to 3, the Nb and Ti contents are increased in the component design, and the strength of the steel sheet is improved by the solid solution strengthening by the minute alloying elements Nb and Ti and the strengthening effect by fine grains.

[0064] In Comparative Example 7, the increase in the Si content in the component design exceeds the range of the present application, making the plate prone to breakage during cold rolling. Therefore, in Comparative Example 8, based on Comparative Example 7, the thickness of the final product is increased to 0.35 mm to reduce the risk of plate breakage.

[0065] The steps for producing the non-oriented silicon steels of Comparative Examples 1 to 8 are as follows.

[0066] (1) The steel was smelted in a vacuum induction furnace and cast into a continuous casting billet with a thickness of 220 mm. The chemical composition of the continuous casting billet is shown in Table 5.

[0067] (2) The continuous cast billets obtained in step (1) were stacked and naturally cooled to 450°C, then sent to a heating furnace, where they were heated at a heating rate of 5°C / min and kept at that temperature. The heating temperature and the keeping time are shown in Table 6.

[0068] (3) The continuous casting billet heated in step (2) was subjected to rough rolling and finish rolling, and the rough rolling employed a 1+5 mode, and an intermediate billet was obtained after six passes of rolling. Then, seven passes of finish rolling and coiling were performed to obtain a hot-rolled sheet coil. The thickness of the intermediate billet obtained by rough rolling, the final rolling temperature of the finish rolling, the total reduction in the finish rolling, the thickness of the obtained hot-rolled sheet, and the coiling temperature are shown in Table 6.

[0069] (4) The hot-rolled sheet coil obtained in step (3) is dried in pure N 2 The normalizing temperature and normalizing time are shown in Table 7. The normalized steel sheet was cooled to 100°C, shot blasted, and then pickled in hydrochloric acid. The temperature of the acid solution was 80°C, the concentration of hydrochloric acid in the acid solution was 140g / L, and Fe 2+ The mass concentration of is controlled to 50±20 g / L. As a result of detecting the metal structure of the normalized steel sheet in each comparative example, the volume ratio of the recrystallized structure and the recrystallized grain size measured are shown in Table 7.

[0070] (5) The normalized and pickled steel sheet obtained in step (4) was preheated and then cold rolled. The preheating temperature, thickness before rolling, thickness after rolling, and reduction ratio of cold rolling are shown in Table 8. Among them, in Comparative Example 7, sheet fracture occurred during cold rolling, and rolling was not completed.

[0071] (6) The rolled hard steel plate obtained in step (5) is 2 and N 2 The samples were subjected to continuous annealing in a mixed gas atmosphere. 2 The content is ≧15%. The annealing temperature and incubation time are shown in Table 8.

[0072] (7) The steel plate from step (6) was coated and finished in the usual manner.

[0073] [Table 6]

[0074] [Table 7]

[0075] [Table 8]

[0076] The recrystallized grain size, volume fraction (%) of the recrystallized structure, yield strength, tensile strength, and iron loss P of the non-oriented silicon steels produced in Examples 1 to 8, Comparative Examples 1 to 6, and Comparative Example 8. 1.0 / 1000 The magnetic induction strength B of the non-oriented silicon steels produced in Examples 1 to 8 and Comparative Examples 4 to 6 was measured. 5000 The results are shown in the table below.

[0077] [Table 9]

[0078] As can be seen from the above Examples 1 to 8, when the non-oriented silicon steel for high-speed motors according to the embodiments of the present application is used, not only does it have high strength and high magnetic induction, but also the high-frequency iron loss P 1.0 / 1000 The powder is small, the smelting cost is low, the production process is simple, the production cost is low, and it meets the application requirements of high-speed motors.

[0079] In Comparative Examples 1 to 3, chemical compositions similar to those in Examples 1 to 3 were used, and large crystal grains were obtained in the final product by controlling the normalizing temperature, heat-holding time, cold rolling reduction, annealing temperature, and heat-holding time. However, the strength of the final product was much lower than that of Examples 1 to 3, and the high-frequency core loss P 1.0 / 1000 was much larger than in Examples 1 to 3.

[0080] In Comparative Examples 4 to 6, the contents of Nb and Ti were increased in the component design based on Comparative Examples 1 to 3, and the strength was slightly improved compared to the steel sheets of Comparative Examples 1 to 3 due to the solid solution strengthening by the micro-alloy elements Nb and Ti and the strengthening effect by fine grains. As a result of the measurement, the crystal grain size was smaller than that of Comparative Examples 1 to 3, and the strength was higher than that of Comparative Examples 1 to 3. Compared with Examples 1 to 3, in Comparative Examples 4 to 6, when the final product thickness is the same, the strength is lower, the core loss is larger, the magnetic induction is lower, and the alloy cost is higher.

[0081] In Comparative Example 7, the Nb and Ti contents were not increased, and the Si content was increased to 3.5% or more in the composition design. As a result, when rolling a steel sheet with a desired thickness of 0.30 mm, sheet fracture occurred during cold rolling even when the preheating temperature before rolling was increased to 180°C.

[0082] In Comparative Example 8, based on Comparative Example 7, the thickness of the final product was increased to 0.35 mm. Due to the increase in the thickness of the steel sheet, its resistivity decreased. As a result, the high-frequency iron loss of the final product was significantly larger than that of Examples 1 to 8.

[0083] Obviously, the above examples are merely examples for clear explanation, and do not limit the embodiments. Those skilled in the art may make various other changes or modifications based on the above description. It is not necessary or possible to cover all the embodiments here. And, obvious changes or variations derived therefrom still fall within the protection scope of the present invention.

Claims

1. A non-oriented silicon steel for high-speed motors, %. A non-oriented silicon steel for high-speed motors having chemical compositions of C≦0.0020% by mass, S≦0.0010% by mass, N≦0.0030% by mass, Si: 3.0 to 3.4% by mass, Al: 0.80 to 1.0% by mass, Mn: 0.2 to 0.4% by mass, P≦0.01% by mass, Sn+Sb≦0.004% by mass, Nb≦0.005% by mass, V≦0.005% by mass, Ti≦0.005% by mass, Mo≦0.005% by mass, Cr≦0.05% by mass, Ni≦0.05% by mass, Cu≦0.05% by mass, and the balance being Fe and unavoidable impurities, wherein 0<C+S+N≦0.0050%, the thickness of the final product is 0.20 to 0.30 mm, and the grain size of the final product is 80 to 100 μm.

2. Yield strength ≧550MPa, magnetic induction B ５０００ ≧1.65, and high-frequency iron loss P １．０／１０００ ≦45W / kg, high frequency iron loss P at 0.25mm thickness １．０／１０００ ≦40W / kg, high frequency iron loss P at 0.20mm thickness １．０／１０００ 2. The non-oriented silicon steel for high speed motors according to claim 1, characterized in that the strength is ≦35 W / kg.

3. 3. The non-oriented silicon steel for high-speed motors according to claim 1, wherein 4.8%≦Si+2Al≦5.2%.

4. A method for producing a non-oriented silicon steel for high-speed motors according to any one of claims 1 to 3, A method for producing a continuous cast billet, comprising the steps of smelting the billet, cooling the billet, and subjecting the billet to heating, hot rolling, normalizing, pickling, cold rolling, annealing, and coating treatments.

5. The method for producing non-oriented silicon steel for high-speed motors according to claim 4, characterized in that the normalizing temperature is 830-870°C, the warming time is 3-5 min, the cold rolling reduction is controlled at 89%-90%, the annealing temperature is 880-900°C, and the warming time is 120-150 s.

6. 6. The method for producing non-oriented silicon steel for high speed motors according to claim 4, characterized in that the steel is smelted using a vacuum induction furnace, controlled to 0<C+S+N≦0.0050%, and cast into a continuous casting billet having a thickness of 200 to 250 mm.

7. The method for producing non-oriented silicon steel for high-speed motors according to claim 4 or 5, characterized in that the steps of cooling and heating the cast billet include naturally cooling the cast billet to 400-500°C, heating it to 1080-1100°C at a heating rate of 10°C / min or less, and then keeping it at that temperature for 0.5-1.0 h.

8. The hot rolling includes six rough rolling steps and seven finish rolling steps; and / or Rough rolling produces an intermediate billet having a thickness of 30 to 45 mm, and finish rolling produces a hot-rolled plate having a thickness of 2.0 to 3.0 mm, and / or 6. The method for producing non-oriented silicon steel for high-speed motors according to claim 4 or 5, characterized in that a final rolling temperature in the finish rolling is 800 to 860°C, a coiling temperature is 600 to 660°C, the fluctuation ranges of the final rolling temperature and the coiling temperature in the finish rolling are ±15°C, and a total reduction rate in the finish rolling is 92.5 to 93.5%.

9. 6. The method for producing a non-oriented silicon steel for high-speed motors according to claim 4, wherein after normalizing, the steel sheet is cooled to 80 to 150° C., and then the steps of shot blasting and pickling are carried out.

10. The method for producing non-oriented silicon steel for high-speed motors according to claim 4 or 5, characterized in that before cold rolling, the steel sheet is preheated to 100 to 200 ° C. and / or the recrystallized grain size after normalizing is 60 to 80 μm and the volume fraction of the recrystallized structure is 100%.

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