Non-oriented silicon steel for motor iron core of air conditioner compressor and preparation method of non-oriented silicon steel

Abstract

The invention discloses non-oriented silicon steel for a motor iron core of an air conditioner compressor and a preparation method of the non-oriented silicon steel. The preparation method comprises the following steps: smelting: molten steel comprises the following chemical components in percentage by weight: 0.75-1.35% of Si, 0.23-0.28% of Al, 0.18-0.45% of Mn, 0.0015-0.0035% of rare earth La, less than or equal to 0.0025% of C, less than or equal to 0.003% of S and the balance of Fe and impurities; continuous casting: controlling the isometric crystal proportion of a continuous casting blank to be greater than or equal to 55%; during hot rolling and heating, the soaking temperature ranges from 1130 DEG C to 1140 DEG C, the heating time ranges from 150 min to 200 min, the outlet temperature of rough rolling is controlled to range from 930 DEG C to 940 DEG C, the final rolling temperature ranges from 835 DEG C to 875 DEG C, and the coiling temperature ranges from 650 DEG C to 680 DEG C; cold continuous rolling; annealing is conducted, the annealing temperature ranges from 880 DEG C to 930 DEG C, and the plate passing speed ranges from 150 m / min to 165 m / min; and cooling, coating and finishing.

Description

Technical Field

[0001] The present application belongs to the technical field of steel material preparation, and relates to a medium-low grade non-oriented silicon steel and a preparation method thereof, and in particular to a non-oriented silicon steel for a motor core of an air-conditioning compressor and a preparation method thereof. Background Art

[0002] With the development of science and technology and the advancement of technology, the energy efficiency level standards of household appliances such as air conditioners are constantly improving. In order to meet higher energy efficiency standards, air conditioner compressors use variable frequency drive technology, two-stage compression technology, etc., which puts higher requirements on the silicon steel used in the motor core material. In addition to magnetic properties, the mechanical properties of silicon steel are also higher, requiring not only high strength but also greater hardness.

[0003] By improving the strength of silicon steel, on the one hand, it can provide safety protection for the high-speed design of the motor to ensure that it can withstand the large centrifugal force caused by high speed; on the other hand, it can improve the processing performance of the iron core, such as increasing the riveting strength of the iron core and preventing the warping of the large iron core punching sheets.

[0004] Hardness not only reflects the toughness of the material surface to maintain its shape and structure without being destroyed when subjected to external forces, but is also directly related to whether the material can withstand various external mechanical effects during use, such as wear, scratches, shearing, etc. The motor core material used in air-conditioning compressors requires silicon steel to have a sufficiently high hardness so that the core can maintain its original shape and performance during long-term operation, and the core is not easily damaged or deformed to extend the service life of the motor.

[0005] Air conditioning compressors usually use medium and low grade non-oriented silicon steel, that is, non-oriented silicon steel with Si content below 1.7%. However, due to the lack of normalization, the mechanical properties of silicon steel products are poor, the yield strength along the rolling direction is generally lower than 240MPa, and the Vickers hardness is generally lower than 130, which is difficult to meet the requirements of air conditioning compressors using variable frequency drive technology, two-stage compression technology, etc. Summary of the invention

[0006] In order to solve the technical problems of the prior art, the purpose of the present application is to provide a non-oriented silicon steel for the motor core of an air-conditioning compressor and a preparation method thereof.

[0007] To achieve the above application purpose, an embodiment of the present application provides a method for preparing non-oriented silicon steel. The preparation method comprises the following steps: Smelting, the chemical composition of the molten steel obtained by smelting includes, by mass percentage: Si 0.75~1.35%, Al 0.23~0.28%, Mn 0.18~0.45%, rare earth La 0.0015~0.0035%, C≤0.0025%, S≤0.003%, and the rest is Fe and unavoidable impurities; Continuous casting: control the equiaxed crystal ratio of the continuous casting billet to be ≥55%; Hot rolling: After heating the continuous casting billet, rough rolling, finish rolling and coiling are carried out in sequence to obtain hot rolled coils. The soaking temperature during heating is 1130~1140℃, the heating time is 150~200min, the outlet temperature of rough rolling is controlled to be 930~940℃, the final rolling temperature is 835~875℃, and the coiling temperature is 650~680℃; Cold rolling, rolling hot rolled coil into strip steel; Annealing: annealing the strip in a mixed atmosphere of H2+N2 or a full H2 atmosphere, with an annealing temperature of 880~930℃ and a plate passing speed of 150~165m / min; After cooling, coating and finishing, the non-oriented silicon steel product is obtained.

[0008] Preferably, in the smelting process, molten iron and scrap steel are first used for converter smelting, and then refined to obtain molten steel; The rare earth La is added by adding lanthanum-iron alloy during refining, wherein the mass percentage of rare earth La in the lanthanum-iron alloy is 40-50%; the temperature of the molten steel before and after the addition of the lanthanum-iron alloy is controlled to be 1550-1600°C, and the lanthanum-iron alloy addition process is carried out under inert gas or vacuum protection and stirring.

[0009] Preferably, in the chemical composition of the molten steel, the content of rare earth La is controlled to be 0.0018-0.0035%; and the proportion of equiaxed crystals in the continuous casting billet is controlled to be ≥60%.

[0010] Preferably, in the cold rolling process, a five-stand cold rolling mill is used for cold rolling, the total reduction rate is controlled to be 80.9-81.7%, the reduction rate of the fifth pass is 18-20%, and the rolling exit speed is ≥800m / min.

[0011] Preferably, in the cold rolling process, the reduction ratio of the first pass is controlled to be 32-34%.

[0012] Preferably, in the cold rolling process, the emulsion concentration used by the five-stand cold rolling mill is 2.5-2.8%, and the emulsion temperature is 60±3°C.

[0013] Preferably, the thickness of the continuous casting billet is 200-250 mm; In the hot rolling process, the continuous casting billet is rough-rolled into an intermediate billet with a thickness of 40 mm, and then fine-rolled into a hot-rolled coil with a thickness of 2.65-2.70 mm.

[0014] Preferably, in the cold rolling process, the hot-rolled coil is rolled into a strip steel with a thickness of 0.50±0.005 mm.

[0015] In order to achieve the above application purpose, an embodiment of the present application provides a non-oriented silicon steel, which is prepared by the preparation method as described above.

[0016] Preferably, the finished product thickness of the non-oriented silicon steel is 0.50±0.005 mm, and the iron loss P 1.5 / 50 ≤4.4W / kg, magnetic induction B 50 ≥1.69T, yield strength ≥300MPa, Vickers hardness ≥145.

[0017] Compared with the prior art, the beneficial effects of the present application are as follows: by controlling the content of Si and Al, the non-oriented silicon steel can have excellent electromagnetic properties; by adding Mn and rare earth La and controlling their content, the strength, hardness and low-temperature toughness of the silicon steel can be improved; in particular, the rare earth La can purify the molten steel, increase the proportion of equiaxed crystals in the continuous casting billet, and precipitate in the steel in the form of La2O2S. The precipitate can not only serve as a carrier for the nucleation of AlN inclusions, but also combine with Al2O3 to form larger composite inclusions, changing the morphology of the inclusions. and size, playing the role of dispersion strengthening, and rare earth La can also refine the grains, increase the number of grain boundaries, improve the texture, enhance the magnetic properties, further hinder the dislocation movement, and improve the strength and hardness of the steel; on the basis of the chemical composition design scheme, combined with the process route and specific parameter settings of continuous casting, hot rolling, cold rolling and annealing processes, the control of grain size, inclusions, texture and other aspects is achieved, so that medium and low grade non-oriented silicon steel not only has excellent magnetic properties, strength and hardness, but also has a simple process flow and a short production cycle, which greatly reduces the production cost. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in conjunction with the specific implementation methods of the present application. Obviously, the described implementation methods are only part of the implementation methods of the present application, not all of the implementation methods. Based on the implementation methods in the present application, all other implementation methods obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0019] An embodiment of the present application provides a non-oriented silicon steel and a preparation method thereof. The preparation method adopts a process route including smelting, continuous casting, hot rolling, cold rolling, annealing, cooling, coating, and finishing to prepare a non-oriented silicon steel product.

[0020] Specifically, this preparation method achieves the advantages of short process route, simple process and easy quality control, low alloy cost and production equipment cost in production through chemical composition design and process design. In terms of product performance, the obtained non-oriented silicon steel product has excellent magnetic properties, high strength and hardness, and is suitable for the production of motor cores for air-conditioning compressors using variable frequency drive technology and two-stage compression technology.

[0021] Specifically, the preparation method includes the following steps.

[0022] (1) Smelting process Molten steel is smelted according to the following chemical composition design scheme, and the chemical composition, in terms of mass percentage, includes: Si 0.75~1.35%, Al 0.23~0.28%, Mn 0.18~0.45%, rare earth La 0.0015~0.0035%, C≤0.0025%, S≤0.0030%, and the rest is Fe and unavoidable impurities.

[0023] That is, the chemical composition of the molten steel obtained by smelting is as described above.

[0024] It can be understood that the chemical composition of the continuous casting billet obtained in the subsequent continuous casting process and the non-oriented silicon steel obtained by rolling are consistent with the above chemical composition design scheme, and the chemical composition of the final non-oriented silicon steel product is also as described above, which will not be repeated in the following text.

[0025] The following is an introduction to the functions of some of the chemical elements mentioned in the above chemical composition.

[0026] After Si is dissolved in α-iron, the resistivity increases, and it helps to separate harmful impurities such as carbon. Si combines with oxygen to transform into stable SiO2, avoiding lattice distortion of iron. Therefore, adding silicon can increase magnetic permeability, reduce coercive force, and reduce iron loss. However, excessive Si content will make the material hard and brittle, resulting in decreased thermal conductivity and toughness. In this application, the Si content is controlled to be 0.75~1.35%.

[0027] Al has a deoxidizing effect in steel. Al is easily combined with N to form dispersed AlN precipitate particles, which are retained in the solid solution, can increase the resistivity and coarsen the grains, improve the magnetic properties of silicon steel, and affect the mechanical properties of steel; however, too much Al content will increase the difficulty of steelmaking. In this application, the Al content is controlled to be 0.23~0.28%.

[0028] Mn has a great strengthening effect on steel within a low content range, which can improve strength, hardness and wear resistance, and improve the low-temperature toughness of steel. However, Mn easily forms MnS compounds with S during solidification, which is pinned at the grain boundary and is not conducive to the growth of grains. In this application, the Mn content is controlled to be 0.18~0.45%.

[0029] Rare earth La is added to steel and mainly precipitates in the form of La2O2S. These precipitates can not only serve as carriers for the nucleation of AlN inclusions, but also combine with Al2O3 to form larger composite inclusions, which play a role in dispersion strengthening, thereby improving the tensile strength and yield strength of steel; in addition, rare earth element La can also refine the grains of steel, increase the number of grain boundaries, improve texture, improve magnetic properties, further hinder dislocation movement, and improve the hardness of steel. The content of rare earth La in this application is controlled to be 0.0015~0.0035%.

[0030] C and S are harmful elements in non-oriented silicon steel. They generally hinder grain growth and magnetic domain movement by forming fine precipitation or grain boundary segregation, affecting the structure of steel and having a great influence on mechanical properties and magnetic properties. Therefore, they must be reasonably controlled. In this application, the C content is controlled to be ≤0.0025% and the S content is ≤0.003%.

[0031] Preferably, the content of rare earth La is 0.0018-0.0035% to increase the equiaxed crystal ratio of the continuous casting billet and improve the tensile strength, yield strength, hardness and magnetic properties.

[0032] In the steelmaking process, molten iron and scrap steel are first smelted in a converter and then refined to obtain molten steel.

[0033] The rare earth La is added by adding lanthanum-iron alloy during refining, wherein the mass percentage of the rare earth La in the lanthanum-iron alloy is 40-50%; the temperature of the molten steel before and after the addition of the lanthanum-iron alloy is controlled to be 1550-1600°C; the lanthanum-iron alloy addition process is carried out under the protection of an inert gas or a vacuum, and stirring is performed to ensure that the rare earth La is fully melted and dissolved, and to prevent the rare earth La from oxidizing and failing.

[0034] Specifically, the refining process includes LF refining and RH vacuum refining performed in sequence, and the lanthanum-iron alloy can be added in the LF refining process or in the RH vacuum refining process.

[0035] When adding the lanthanum-iron alloy in the LF refining process, the lanthanum-iron alloy addition process is controlled to be carried out under the protection of an inert gas, and bottom blowing of argon gas is controlled to perform stirring.

[0036] When added during the RH vacuum refining step, the vacuum degree was controlled to ≤ 2 mbr, and electromagnetic stirring was performed.

[0037] (2) Continuous casting process The molten steel obtained in the smelting process is continuously cast to produce continuous casting billets with a thickness of 200~250mm.

[0038] Samples are cut from the continuous casting billet, cut, grind and polish, and then chemically etched to show the solidification structure morphology. The etched samples are observed using an optical microscope or an electron microscope. According to the distribution characteristics of the solidification structure, the equiaxed crystal area usually has a relatively uniform grain size and morphology. The equiaxed crystal area is identified by manual or image recognition technology. The equiaxed crystal ratio is calculated based on the equiaxed crystal area area and the total surface area. The equiaxed crystal ratio = equiaxed crystal area / total surface area × 100%.

[0039] In the present application, the equiaxed crystal ratio of the continuous casting billet is ≥55%.

[0040] After adding rare earth La, the development of columnar crystals in the continuous casting billet can be significantly inhibited, making the coarse columnar crystals become fine and fragmented. Since the oxides and sulfides of rare earth La have a small lattice mismatch with δ-Fe, their nucleation supercooling is also small, much smaller than Al2O3 and SiO2. Therefore, the oxides and sulfides of rare earth La can serve as non-spontaneous crystal nuclei of steel, expanding the equiaxed crystal zone and increasing the proportion of equiaxed crystals. At the same time, it limits the development of columnar crystals, which is beneficial to improving the mechanical properties and processing properties of non-oriented silicon steel.

[0041] Preferably, in the chemical composition of the molten steel, the content of rare earth La is controlled to be 0.0018-0.0035%; and the equiaxed crystal ratio of the continuous casting billet is controlled to be ≥60%. By controlling the content of rare earth La, the continuous casting billet can have a larger equiaxed crystal ratio, so that the internal structure of the continuous casting billet is more uniform, and the internal defects such as shrinkage cavities and segregation caused by the development of columnar crystals are reduced. The uniform equiaxed crystal structure helps to improve the overall strength and toughness of non-oriented silicon steel, making it more resistant to deformation and fracture when subjected to stress, and improving mechanical properties and processing properties.

[0042] (3) Hot rolling process After heating the continuous casting billet, rough rolling, finish rolling and coiling are carried out in sequence to obtain hot rolled coils. The soaking temperature during heating is 1130~1140℃, the heating time is 150~200min, the outlet temperature of rough rolling is controlled to be 930~940℃, the final rolling temperature is 835~875℃, and the coiling temperature is 650~680℃.

[0043] By heating the continuous casting ingot at a relatively low soaking temperature, the re-solidification of precipitates such as AlN in the continuous casting ingot can be suppressed, thereby preventing the refinement of precipitates during hot rolling and obtaining a uniform and coarse grain structure, thereby affecting the electromagnetic properties and inclusion distribution of silicon steel and improving the electromagnetic properties of silicon steel; further, due to the addition of rare earth La, the coarse columnar crystals will become fine and fragmented, so the coiling temperature is controlled at a relatively high level to coarsen the grain size, increase the favorable textures {100} and {110}, and reduce the unfavorable textures {111} and {112}, while avoiding the aggregation of precipitates in silicon steel caused by excessively high coiling temperature. The aggregation of precipitates will reduce the magnetic permeability and toughness of silicon steel, increase its brittleness, cause grain boundary oxidation, generate an inner oxide layer, and increase the difficulty of pickling. Therefore, the coiling temperature is controlled to be 650~680℃ to ensure the uniformity of the temperature during the hot rolling process and further increase the hot rolling structure.

[0044] The continuous casting billet is subjected to rough rolling to obtain an intermediate billet with a thickness of 40 mm, which is then subjected to finish rolling to obtain a hot-rolled coil with a thickness of 2.65-2.70 mm. By controlling the thickness of the intermediate billet and the hot-rolled coil, the reduction of rough rolling and finish rolling can be reasonably allocated, which is beneficial to the control of the non-oriented structure, strength, toughness and thickness of silicon steel.

[0045] After coiling, the hot rolled coil is naturally cooled to room temperature.

[0046] (4) Cold rolling process The hot rolled coil is unrolled and rolled into a strip steel with a thickness of 0.50±0.005 mm to meet the specification requirements of non-oriented silicon steel for motor core. In the present application, the hot rolled coil does not need to be normalized.

[0047] Specifically, a five-stand cold rolling mill is used for cold rolling, preferably a UCM five-stand cold rolling mill is used, the total reduction ratio is controlled to be 80.9-81.7%, the fifth pass reduction ratio is 18-20%, and the rolling exit speed is ≥800m / min.

[0048] Preferably, the reduction rate of the first pass is controlled to be 32-34%, and the reduction rate of the fifth pass is controlled to be 18-19% to give full play to the advantages of the cold rolling mill; the rolling force of the first stand is controlled to be appropriately larger, and the first stand is allocated with large deformation reduction to ensure that the grains are fully broken in the first pass, while the fifth pass is allocated with small reduction to ensure the plate shape quality and thickness accuracy of the silicon steel product.

[0049] Among them, the emulsion concentration used in the five-stand cold rolling mill is 2.5~2.8%, that is, the mass fraction of the emulsion is 2.5~2.8%, and the emulsion temperature is 60±3℃. By using emulsions with higher concentrations and higher temperatures, process lubrication can be effectively improved, deformation heat can be reduced, and rolling stability can be improved.

[0050] (5) Annealing process In a continuous annealing furnace, the strip is annealed in a mixed atmosphere of H2+N2 or a full H2 atmosphere, the annealing temperature is 880~930℃, and the plate passing speed is 150~165m / min.

[0051] By annealing and controlling the annealing temperature and plate passing speed, the magnetic properties and mechanical properties of non-oriented silicon steel can be significantly improved. Specifically, on the one hand, during the cold rolling and hot rolling process, the grains in the silicon steel will be stretched and deformed, forming certain internal stresses, resulting in a decrease in magnetic permeability; annealing can eliminate these internal stresses, restore the normal shape and orientation of the grains, thereby improving the magnetic permeability and magnetic saturation magnetic induction intensity; annealing can also improve the grain structure. During the annealing process, the grains in the silicon steel will be fully grown and recrystallized to form a more uniform and fine grain structure, which helps to improve the magnetic properties of silicon steel and reduce iron loss. On the other hand, the internal stress in the silicon steel is released by annealing, and the toughness and plasticity of the material are improved, thereby enhancing the silicon steel's ability to resist deformation and fracture.

[0052] Further, by controlling the protective atmosphere in the continuous annealing furnace, the formation of an inner oxide layer and an inner nitride layer in the strip can be prevented, the surface quality can be improved, and the iron loss can be further reduced.

[0053] (6) Cooling, coating and finishing processes The annealed steel strip is cooled, coated and finished to obtain a non-oriented silicon steel product. In the present invention, cooling, coating and finishing adopt conventional techniques known in the art, which will not be described in detail.

[0054] Thus, the present application adopts the above-mentioned preparation method, including the combination of chemical composition and production process, and can make the non-oriented silicon steel have excellent electromagnetic properties by controlling the content of Si and Al. The strength, hardness and low-temperature toughness of silicon steel can be improved by adding Mn and rare earth La and controlling the content. In particular, rare earth La can purify molten steel and increase the proportion of equiaxed crystals in continuous casting billets. It precipitates in the steel in the form of La2O2S. The precipitates can not only serve as carriers for the nucleation of AlN inclusions, but also combine with Al2O3 to form larger composite inclusions, thereby improving the quality of the steel. The morphology and size of inclusions can be changed, which plays a role of dispersion strengthening. In addition, rare earth La can also refine grains, increase the number of grain boundaries, improve texture, enhance magnetic properties, further hinder dislocation movement, and improve the strength and hardness of steel. On the basis of the chemical composition design scheme, combined with the process route and specific parameter settings of continuous casting, hot rolling, cold rolling and annealing processes, the control of grain size, inclusions, texture and other aspects is achieved, so that medium and low grade non-oriented silicon steel not only has excellent magnetic properties, strength and hardness, but also has a simple process flow and a short production cycle, which greatly reduces the production cost.

[0055] The performance of the non-oriented silicon steel product was tested and the iron loss P 1.5 / 50 ≤4.4W / kg, magnetic induction B 50 ≥1.69T, yield strength ≥300MPa, Vickers hardness ≥145. When used to prepare the motor core of the air-conditioning compressor of the variable frequency drive technology, two-stage compression technology, etc., it can not only meet the requirements of magnetic properties, but also its strength and hardness can ensure that it can withstand the large centrifugal force generated when the motor rotates at high speed, so that the core can maintain its original shape and performance during long-term operation, and the core is not easily damaged or deformed, thereby extending the service life of the motor. It can also improve the processing performance of the core, improve the riveting strength of the core, and prevent the warping of the large core punching sheets.

[0056] The detailed descriptions listed above are merely specific descriptions of feasible implementation methods of the present application. They are not intended to limit the scope of protection of the present application. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present application should be included in the scope of protection of the present application.

[0057] The technical scheme and beneficial effects of the present application are demonstrated below through two embodiments and two comparative examples. Of course, the following two embodiments are not all embodiments under the technical purpose of the present application. They are only a part of the numerous embodiments listed for intuitively demonstrating an implementation mode of the present application, and the feasibility of other embodiments in an implementation mode of the present application cannot be denied based on these embodiments. Moreover, the following two comparative examples are only for illustrating the beneficial effects of an implementation mode of the present application, and these comparative examples are not prior art.

[0058] Specifically, these embodiments and comparative examples adopt the following method to prepare non-oriented silicon steel products.

[0059] (1) Smelting process Molten steel is smelted according to the chemical composition design scheme shown in Table 1. In addition to the elements in the table, the rest are Fe and unavoidable impurities.

[0060] First, steelmaking is carried out, and the molten steel obtained by refining is used to prepare continuous casting billets through continuous casting. The thickness and chemical composition of the continuous casting billets of various embodiments and comparative examples are shown in Table 1.

[0061] (2) Continuous casting process The molten steel obtained from the smelting process is continuously cast to prepare continuous casting billets. The thickness and equiaxed crystal ratio of the continuous casting billets are shown in Table 1.

[0062] Table 1

[0063] (3) Hot rolling process After heating the continuous casting slab, rough rolling, finish rolling and coiling are carried out in sequence to obtain hot rolled coils, and then the hot rolled coils are naturally cooled to room temperature. Among them, the soaking temperature during heating, the heating time, the outlet temperature of rough rolling, the thickness of the intermediate slab, the final rolling temperature, the coiling temperature, and the thickness of the hot rolled coils are shown in Table 2.

[0064] Table 2

[0065] (4) Cold rolling process Normalization is not required. After the hot rolled coil is unrolled, it is rolled into a strip with a thickness of 0.50±0.005mm using a UCM five-stand cold rolling mill, and the rolling exit speed is controlled to be ≥800m / min. Among them, the first pass reduction rate, the fifth pass reduction rate, the total reduction rate, the emulsion concentration used by the cold rolling mill, and the emulsion temperature are shown in Table 3.

[0066] (5) Annealing process In a continuous annealing furnace, the strip is annealed in a mixed atmosphere of H2+N2 or a full H2 atmosphere. The annealing temperature and the plate passing speed are shown in Table 3.

[0067] Table 3

[0068] (5) Cooling, coating and finishing processes The annealed strip is cooled, coated and finished to obtain a non-oriented silicon steel product.

[0069] The magnetic and mechanical properties of the non-oriented silicon steel products obtained in Examples 1-2 and Comparative Examples 1-2 were tested, including: A. Use GB / T 3655 standard to test iron loss P 1.5 / 50 and magnetic induction intensity B 50 ; B. Use GB / T 3076 standard to test yield strength; C. Use GB / T 4340-2009 "Metallic materials Vickers hardness test Part 1: Test method" to measure Vickers hardness; The test results are shown in Table 4.

[0070] Table 4

[0071] It can be seen from the above that the hardness of comparative example 1 is lower, while the iron loss of comparative example 2 is higher; compared with the comparative example, the iron loss P of the non-oriented silicon steel product of the embodiment of the present application is 1.5 / 50 ≤4.4W / kg, magnetic induction B 50≥1.69T, yield strength ≥300MPa, Vickers hardness ≥145. When used to prepare the motor core of the air-conditioning compressor of the variable frequency drive technology, two-stage compression technology, etc., it can not only meet the requirements of magnetic properties, but also its strength and hardness can ensure that it can withstand the large centrifugal force generated when the motor rotates at high speed, so that the core can maintain its original shape and performance during long-term operation, and the core is not easily damaged or deformed, thereby extending the service life of the motor. It can also improve the processing performance of the core, improve the riveting strength of the core, and prevent the warping of the large core punching sheets.

[0072] It should be understood that although this specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation mode may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0073] The detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing non-oriented silicon steel, characterized in that: The preparation method comprises the following steps: Smelting, the chemical composition of the molten steel obtained by smelting includes, by mass percentage: Si 0.75~1.35%, Al 0.23~0.28%, Mn 0.18~0.45%, rare earth La 0.0015~0.0035%, C≤0.0025%, S≤0.003%, and the rest is Fe and unavoidable impurities; Continuous casting: control the equiaxed crystal ratio of the continuous casting billet to be ≥55%; Hot rolling: After heating the continuous casting billet, rough rolling, finish rolling and coiling are carried out in sequence to obtain hot rolled coils. The soaking temperature during heating is 1130~1140℃, the heating time is 150~200min, the outlet temperature of rough rolling is controlled to be 930~940℃, the final rolling temperature is 835~875℃, and the coiling temperature is 650~680℃; Cold rolling, rolling hot rolled coil into strip steel; Annealing: annealing the strip in a mixed atmosphere of H2+N2 or a full H2 atmosphere, with an annealing temperature of 880~930℃ and a plate passing speed of 150~165m / min; After cooling, coating and finishing, the non-oriented silicon steel product is obtained.

2. The method for preparing non-oriented silicon steel according to claim 1, characterized in that: In the smelting process, molten iron and scrap steel are firstly used for converter smelting, and then refined to obtain molten steel; The rare earth La is added by adding lanthanum-iron alloy during refining, wherein the mass percentage of rare earth La in the lanthanum-iron alloy is 40-50%; the temperature of the molten steel before and after the addition of the lanthanum-iron alloy is controlled to be 1550-1600°C, and the lanthanum-iron alloy addition process is carried out under inert gas or vacuum protection and stirring.

3. The method for preparing non-oriented silicon steel according to claim 1, characterized in that: In the chemical composition of the molten steel, the content of rare earth La is controlled to be 0.0018-0.0035%; and the proportion of equiaxed crystals in the continuous casting billet is controlled to be ≥60%.

4. The method for preparing non-oriented silicon steel according to claim 1, characterized in that: In the cold rolling process, a five-stand cold rolling mill is used for cold rolling, the total reduction rate is controlled to be 80.9-81.7%, the reduction rate of the fifth pass is 18-20%, and the rolling exit speed is ≥800m / min.

5. The method for preparing non-oriented silicon steel according to claim 4, characterized in that: In the cold rolling process, the reduction ratio of the first pass is controlled to be 32-34%.

6. The method for preparing non-oriented silicon steel according to claim 4, characterized in that: In the cold rolling process, the emulsion concentration used by the five-stand cold rolling mill is 2.5-2.8%, and the emulsion temperature is 60±3°C.

7. The method for preparing non-oriented silicon steel according to claim 1, characterized in that: The thickness of the continuous casting billet is 200~250mm; In the hot rolling process, the continuous casting billet is rough-rolled into an intermediate billet with a thickness of 40 mm, and then fine-rolled into a hot-rolled coil with a thickness of 2.65-2.70 mm.

8. The method for preparing non-oriented silicon steel according to claim 7, characterized in that: In the cold rolling process, the hot rolled coil is rolled into a strip steel with a thickness of 0.50±0.005 mm.

9. A non-oriented silicon steel, characterized in that: The non-oriented silicon steel is prepared by the preparation method according to any one of claims 1 to 8.

10. The non-oriented silicon steel according to claim 9, characterized in that: The finished product thickness of the non-oriented silicon steel is 0.50±0.005mm, and the iron loss P 1.5 / 50 ≤4.4W / kg, magnetic induction B 50 ≥1.69T, yield strength ≥300MPa, Vickers hardness ≥145.

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