High-grade non-oriented silicon steel and production method therefor

Abstract

The present invention discloses a high-grade non-oriented silicon steel and a production method thereof. The non-oriented silicon steel includes the following chemical components in percent by mass: 0.002-0.004% of C, not greater than 0.003% of S, 1.4-1.7% of Si, 0.7-0.95% of Mn, not greater than 0.03% of P, 0.015-0.035% of Sn; and 11×([Si]-1.4%)=14×([Mn]-0.7%). In the production method of the non-oriented silicon steel, the heating temperature of a continuous casting billet is 1,120-1,150°C; the finishing temperature in finish rolling is 890±15°C; the rolling reduction of the last pass of finish rolling is not less than 30%, the total rolling reduction of the last two passes of finish rolling is not less than 50%, and the coiling temperature is 650±20°C; normalizing treatment is avoided before acid continuous rolling; and the obtained non-oriented silicon steel is excellent in magnetic performance, and free of surface corrugated defect, and meets the requirement for low-cost high-grade non-oriented silicon steel.

Description

High-grade non-oriented silicon steel and production method thereof

[0001] This application claims priority to a Chinese patent application filed on December 16, 2020, with application number 202011486898.X, and invention name “High-grade non-oriented silicon steel and its production method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The invention belongs to the technical field of steel material preparation, relates to high-grade non-oriented silicon steel, and also relates to a production method of the high-grade non-oriented silicon steel. Background Art

[0003] Non-oriented silicon steel is the core material for rotors in electric motors and generators operating in a rotating magnetic field. It requires excellent magnetic properties, including lower iron loss and higher magnetic induction intensity. According to national technical standards and protocols, non-oriented silicon steel with an iron loss of P1.5 / 50 ≤ 4.00 W / kg is generally considered high-grade non-oriented silicon steel. High-grade non-oriented silicon steel is primarily classified by thickness into four categories: 0.35mm series, 0.50mm series, special thick series, and special thin series. High-grade non-oriented silicon steel is primarily used in large motors, small and medium-sized high-efficiency motors, motors for energy-saving home appliances and electric vehicles, micro motors, precision instruments, and other equipment.

[0004] In the chemical composition of non-oriented silicon steel, Si is the primary element affecting iron loss. Generally, as the Si content increases, the iron loss value of non-oriented silicon steel decreases. In other words, the chemical composition of high-grade non-oriented silicon steel is generally high-silicon steel. However, an increase in Si content results in a higher austenite-ferrite phase transition temperature, or even no phase transition. Therefore, in the production process of high-grade non-oriented silicon steel, finishing rolling is generally performed in the low-temperature ferrite region. After rolling, the deformed ferrite structure cannot recrystallize, resulting in a deformed fibrous structure. If hot-rolled coils containing this fibrous structure are directly cold-rolled and annealed, the resulting finished product will have fine grains, corrugated defects on the surface, poor magnetic properties, or even substandard performance.

[0005] The current effective solution to this problem is to normalize the hot-rolled coil before cold rolling. This treatment allows the deformed ferrite fibers to recrystallize, improving the magnetic properties of the finished product and eliminating surface corrugation defects, ultimately enhancing the quality of the finished product to meet the production requirements of high-grade non-oriented silicon steel. However, the addition of a normalizing step not only complicates the production process of high-grade non-oriented silicon steel, increasing production difficulty, but also increases equipment investment, significantly increasing production costs. Furthermore, the production line cannot be used universally for different grades of medium, low, and high-grade products, resulting in poor versatility.

[0006] Summary of the Invention

[0007] In order to solve the technical problem that normalization treatment is required in the production process of high-grade non-oriented silicon steel in the prior art, the purpose of the present invention is to provide a production method of high-grade non-oriented silicon steel that does not require normalization treatment, and to provide a high-grade non-oriented silicon steel prepared by using this production method.

[0008] To achieve the above-mentioned purpose of the invention, one embodiment of the present invention provides a high-grade non-oriented silicon steel, whose chemical composition is as follows, by mass percentage: C: 0.002-0.004%, S≤0.003%, Si: 1.4-1.7%, Mn: 0.7-0.95%, P≤0.03%, Sn: 0.015-0.035%, Nb≤0.004%, V≤0.004%, Ti≤0.005%, Mo≤0.004%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, N≤0.003%, the balance being Fe and unavoidable inclusions, and 11×([Si]-1.4%)=14×([Mn]-0.7%).

[0009] Furthermore, the thickness of the obtained non-oriented silicon steel product is 0.500±0.005mm, and its iron loss P 1.5 / 50 ≤3.8W / kg, magnetic induction intensity B 5000 ≥1.71;

[0010] Or, the thickness of the obtained non-oriented silicon steel product is 0.350±0.004mm, and its iron loss P 1.5 / 50 ≤3.3W / kg, magnetic induction intensity B 5000 ≥1.70.

[0011] In order to achieve the above-mentioned object of the invention, an embodiment of the present invention further provides a method for producing the high-grade non-oriented silicon steel, which comprises the following steps:

[0012] 1) steelmaking is carried out in sequence by hot metal desulfurization, converter smelting, and RH refining, wherein the chemical composition of the final molten steel is, in percentage by mass: C: 0.002-0.004%, S≤0.003%, Si: 1.4-1.7%, Mn: 0.7-0.95%, P≤0.03%, Sn: 0.015-0.035%, Nb≤0.004%, V≤0.004%, Ti≤0.005%, Mo≤0.004%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, N≤0.003%, the balance being Fe and unavoidable inclusions, and 11×([Si]-1.4%)=14×([Mn]-0.7%);

[0013] 2) continuously casting the molten steel obtained in step 1 into a continuous casting billet having a thickness of more than 200 mm;

[0014] 3) heating the continuous casting slab obtained in step 2 to 1120-1150° C. and holding the temperature for more than 200 minutes, and then performing multiple rough rolling passes to obtain an intermediate slab with a thickness of 40-45 mm, and then performing multiple finishing rolling passes, cooling, and coiling to obtain a hot rolled coil with a thickness of 2.50±0.1 mm, wherein the final rolling temperature of the finishing rolling is 890±15° C., the reduction of the last finishing rolling pass is ≥30% and the total reduction of the last two finishing rolling passes is ≥50%, and the coiling temperature is 650±20° C.;

[0015] 4) The hot-rolled coil obtained in step 3 is not subjected to normalization treatment but is sequentially uncoiled, pickled, rinsed, dried, cold rolled, and coiled to obtain a chilled coil having a thickness of 0.500±0.005 mm or 0.350±0.004 mm;

[0016] 5) The chilled coil obtained in step 4 is subjected to final annealing in a continuous annealing furnace in a mixed atmosphere of H2+N2, wherein the final annealing temperature is 920-980°C and the annealing time is 60±5s; the annealed steel strip is cooled, coated and finished to obtain a non-oriented silicon steel product.

[0017] Preferably, in step 3, the continuous casting slab obtained in step 2 is heated to 1130-1150° C. and kept warm for more than 200 minutes.

[0018] Preferably, in step 3, the cooling process is as follows: the steel plate obtained by the final rolling is cooled in two stages, the first stage of cooling is natural slow cooling without water cooling and lasts for 3 to 8 seconds, and the second stage of cooling is rapid cooling with water cooling.

[0019] Preferably, in the molten iron desulfurization process: the temperature of the molten iron after desulfurization is controlled to be ≥1320°C, the sulfur content is ≤0.0015% by mass, and the slag skimming rate is ≥98%;

[0020] In the converter smelting process, desulfurized molten iron is mixed with scrap steel and smelted in a converter, wherein the scrap steel accounts for 20-25% of the total molten steel by mass; during the tapping process, sufficient tin ingots are added to the molten steel according to Sn: 0.015-0.035% in the finished product; after the tapping is completed, a slag surface deoxidizer is added to the molten steel;

[0021] In the RH refining process: in a pre-vacuumed RH refining furnace, the molten steel is decarburized, and then ultra-low titanium ferrosilicon and metallic manganese are added to the molten steel according to the alloying scheme of Si: 1.4-1.7%, Mn: 0.7-0.95% and 11×([Si]-1.4%)=14×([Mn]-0.7%) in the finished product, and the steel is tapped after a net circulation of more than 7 minutes, wherein a desulfurizer is added to the molten steel during the net circulation for deep desulfurization treatment.

[0022] Preferably, in the pickling process: after the hot rolled coil obtained in step 3 is unrolled, HCl is used for three-stage pickling, wherein the concentration of the first-stage acid solution is 50-80 g / L and the Fe content in the acid solution is 0. 2+ Concentration ≤ 130g / L, the concentration of the second-stage acid solution is 90-120g / L and the Fe content in the acid solution is 2+ Concentration ≤90g / L, the concentration of the third-level acid solution is 140-160g / L and the Fe content in the acid solution is 2+ Concentration ≤50g / L;

[0023] During each stage of pickling, the acid solution temperature is 75-85°C, and the acid solution contains a silicon steel pickling accelerator, the weight percentage of the silicon steel pickling accelerator in the acid solution is 0.05-0.10%;

[0024] The rinsing water temperature is 45-55°C, and the pickling and rinsing speeds are controlled at 100-180 mpm.

[0025] Preferably, in step 5, a three-stage cooling method is used to cool the finished annealed steel strip, wherein: the first stage of cooling is slow cooling at a high temperature, and the steel strip is cooled from the annealing temperature to 850°C at a cooling rate of ≤5°C / s; the second stage of cooling is circulating gas jet controlled cooling, and the steel strip is further cooled from 850°C to below 350°C at a cooling rate of ≤15°C / s; the third stage of cooling is circulating water jet cooling, and the steel strip is further cooled from 350°C to below 100°C.

[0026] In order to achieve the above object of the invention, another embodiment of the present invention also provides a method for producing the high-grade non-oriented silicon steel, which comprises the following steps:

[0027] 1) steelmaking is carried out in sequence by hot metal desulfurization, converter smelting, and RH refining, wherein the chemical composition of the final molten steel is, in percentage by mass: C: 0.002-0.004%, S≤0.003%, Si: 1.4-1.7%, Mn: 0.7-0.95%, P≤0.03%, Sn: 0.015-0.035%, Nb≤0.004%, V≤0.004%, Ti≤0.005%, Mo≤0.004%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, N≤0.003%, the balance being Fe and unavoidable inclusions, and 11×([Si]-1.4%)=14×([Mn]-0.7%);

[0028] 2) continuously casting the molten steel obtained in step 1 into a continuous casting billet having a thickness of more than 200 mm;

[0029] 3) The continuous casting slab obtained in step 2 is heated to 1120-1150°C and kept at this temperature for more than 200 minutes, and then subjected to multiple passes of rough rolling to obtain an intermediate slab with a thickness of 40-45 mm, and then subjected to multiple passes of finishing rolling and coiling to obtain a hot rolled coil with a thickness of 2.50±0.1 mm, wherein the final rolling temperature of the finishing rolling is (A r1 -40)±15℃,A r1 The temperature at which austenite transforms to ferrite. The reduction of the last finishing pass is ≥30% and the total reduction of the last two finishing passes is ≥50%. The coiling temperature is 650±20℃. The steel plate obtained by the final finishing is cooled in two stages before coiling. The first stage of cooling is natural slow cooling without water cooling and lasts for 3 to 8 seconds. The second stage of cooling is rapid cooling with water cooling.

[0030] 4) The hot-rolled coil obtained in step 3 is not subjected to normalization treatment but is sequentially uncoiled, pickled, rinsed, dried, cold rolled, and coiled to obtain a chilled coil having a thickness of 0.500±0.005 mm or 0.350±0.004 mm;

[0031] 5) The chilled coil obtained in step 4 is subjected to final annealing in a continuous annealing furnace in a mixed atmosphere of H2+N2, wherein the final annealing temperature is 920-980°C and the annealing time is 60±5s; the annealed steel strip is cooled, coated and finished to obtain a non-oriented silicon steel product.

[0032] Preferably, in step 3, the continuous casting slab obtained in step 2 is heated to 1130-1150° C. and kept warm for more than 200 minutes.

[0033] Preferably, in step 3, A r1 The final rolling temperature is 933℃ and the finishing rolling temperature is 893±15℃.

[0034] Preferably, in the molten iron desulfurization process: the temperature of the molten iron after desulfurization is controlled to be ≥1320°C, the sulfur content is ≤0.0015% by mass, and the slag skimming rate is ≥98%;

[0035] In the converter smelting process, desulfurized molten iron is mixed with scrap steel and smelted in a converter, wherein the scrap steel accounts for 20-25% of the total molten steel by mass; during the tapping process, sufficient tin ingots are added to the molten steel according to Sn: 0.015-0.035% in the finished product; after the tapping is completed, a slag surface deoxidizer is added to the molten steel;

[0036] In the RH refining process: in a pre-vacuumed RH refining furnace, the molten steel is decarburized, and then ultra-low titanium ferrosilicon and metallic manganese are added to the molten steel according to the alloying scheme of Si: 1.4-1.7%, Mn: 0.7-0.95% and 11×([Si]-1.4%)=14×([Mn]-0.7%) in the finished product, and the steel is tapped after a net circulation of more than 7 minutes, wherein a desulfurizer is added to the molten steel during the net circulation for deep desulfurization treatment.

[0037] Preferably, in the pickling process: after the hot rolled coil obtained in step 3 is unrolled, HCl is used for three-stage pickling, wherein the concentration of the first-stage acid solution is 50-80 g / L and the Fe content in the acid solution is 0. 2+ Concentration ≤ 130g / L, the concentration of the second-stage acid solution is 90-120g / L and the Fe content in the acid solution is 2+ Concentration ≤90g / L, the concentration of the third-level acid solution is 140-160g / L and the Fe content in the acid solution is 2+ Concentration ≤50g / L;

[0038] During each stage of pickling, the acid solution temperature is 75-85°C, and the acid solution contains a silicon steel pickling accelerator, the weight percentage of the silicon steel pickling accelerator in the acid solution is 0.05-0.10%;

[0039] The rinsing water temperature is 45-55°C, and the pickling and rinsing speeds are controlled at 100-180 mpm.

[0040] Preferably, in step 5, a three-stage cooling method is used to cool the finished annealed steel strip, wherein: the first stage of cooling is slow cooling at a high temperature, and the steel strip is cooled from the annealing temperature to 850°C at a cooling rate of ≤5°C / s; the second stage of cooling is circulating gas jet controlled cooling, and the steel strip is further cooled from 850°C to below 350°C at a cooling rate of ≤15°C / s; the third stage of cooling is circulating water jet cooling, and the steel strip is further cooled from 350°C to below 100°C.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The iron loss P of the non-oriented silicon steel product prepared by the production method is 0.50 mm thick. 1.5 / 50 ≤3.8W / kg, magnetic induction intensity B 5000 ≥1.71, iron loss P of finished product with a thickness of 0.35mm 1.5 / 50 ≤3.3W / kg, magnetic induction intensity B 5000≥1.70, with excellent magnetic properties, which can be achieved by adopting a production line of hot metal desulfurization, converter smelting, RH refining, continuous casting, hot rolling, acid continuous rolling, annealing, cooling, coating and finishing. The production line can be used for different grades of products, and there is no need to add additional processes and equipment specifically for high-grade non-oriented silicon steel. Normalization treatment is not required before cold rolling, which reduces one process flow and has low production costs. It can meet the demand for low-cost, high-grade silicon steel sheets for electrical steel product upgrades and energy efficiency upgrades of electrical products;

[0043] (2) Based on the design of the elements such as Mn, S, and N in the aforementioned chemical composition, combined with the control of the continuous casting billet heating temperature (1120-1150°C) and the holding time, the production efficiency is guaranteed, which is beneficial to the high-temperature final rolling of the subsequent finishing rolling, while reducing the probability of precipitation of fine MnS and preventing the solid solution of MnS and other precipitates in the steel during the heating process; and based on the design of the elements such as Mn, C, and Si in the aforementioned chemical composition, the austenite region is expanded and the temperature A of the austenite to ferrite transformation is reduced compared with the prior art. r1 , and can maintain A r1 The temperature of the intermediate billet is basically constant, and the thickness of the intermediate billet after rough rolling is controlled to be large. The final rolling temperature of the finishing rolling is controlled in the two-phase region or the high-temperature ferrite region, so as to form high-temperature ferrite and avoid the formation of the deformed fiber structure described in the background technology. The high-temperature ferrite constitutes the basic condition for subsequent recrystallization. Furthermore, combined with the large reduction in the last two passes of the finishing rolling, the high-temperature ferrite formed during the final rolling has more internal storage energy, which is conducive to the recrystallization of the high-temperature ferrite and the elimination of the fiber structure. At the same time, by further controlling the low coiling temperature and the large reduction in the last two passes of the finishing rolling, the formation of dense oxide scale can be avoided, so as to avoid increasing the difficulty of removing the oxide scale in the subsequent pickling.

[0044] (3) By controlling the annealing temperature to be relatively high, even if the grain size formed by direct recrystallization of the hot-rolled coil is relatively small, the magnetic properties of the final non-oriented silicon steel product can be guaranteed. In addition, although the normalizing treatment is eliminated in this embodiment, there is no need to add secondary cold rolling or secondary annealing during the acid continuous rolling step and the annealing process. The overall production method is simple to operate and low in cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG1 is a microscopic metallographic photograph of the hot-rolled coil of Example 1 provided by the present invention;

[0046] FIG2 is a microscopic metallographic photograph of the hot-rolled coil of Example 3 provided by the present invention. DETAILED DESCRIPTION

[0047] One embodiment of the present invention provides a method for producing high-grade non-oriented silicon steel, as well as high-grade non-oriented silicon steel produced using the method. The method comprises the following sequential steps: molten iron desulfurization, converter smelting, RH refining, continuous casting, hot rolling, acid continuous rolling, annealing, cooling, coating, and finishing. Normalization treatment is not required before acid continuous rolling. The resulting non-oriented silicon steel exhibits excellent magnetic properties and is free of surface corrugation defects, meeting the demand for low-cost, high-grade non-oriented silicon steel.

[0048] In this embodiment, the chemical composition design scheme of the non-oriented silicon steel is as follows, and its chemical composition is calculated as follows in percentage by mass: C: 0.002-0.004%, S≤0.003%, Si: 1.4-1.7%, Mn: 0.7-0.95%, P≤0.03%, Sn: 0.015-0.035%, Nb≤0.004%, V≤0.004%, Ti≤0.005%, Mo≤0.004%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, N≤0.003%, and the balance is Fe and unavoidable inclusions, and 11×([Si]-1.4%)=14×([Mn]-0.7%).

[0049] The role of each element in the chemical composition design scheme is explained as follows.

[0050] C: In non-oriented silicon steel, C is generally considered a harmful element. An increase in C content will lead to fine grains, high iron loss, low magnetic induction, and magnetic aging problems in the finished product. Therefore, the C content is usually controlled as low as possible. However, in this embodiment, a small amount of C is contained in the chemical composition and the C content is controlled to be 0.002-0.004% (in mass percentage). This can expand the austenite region and avoid the problem of difficult control of alloy addition amount caused by C during production.

[0051] Si: It is an effective additive element to increase resistivity and reduce iron loss. However, as the Si content increases, the austenite region decreases. When Si>1.7%, there is no austenite phase transformation. In order to achieve low iron loss and ensure the acquisition of high-grade non-oriented silicon steel, the Si content (in mass percentage) is controlled at 1.4~1.7%.

[0052] Mn: Adding an appropriate amount of Mn can suppress the hot brittleness caused by S. The solid solubility of MnS in austenite is lower than that in the ferrite phase, which can promote the coarsening of MnS and is beneficial to grain growth. In this embodiment, adding Mn to the chemical composition and controlling the Mn content (in mass percentage) to 0.7-0.95% can help expand the austenite region and reduce the austenite-ferrite transition temperature. In addition, Mn and Si increase and decrease synchronously, and the contents of the two satisfy the relationship 11×([Si]-1.4%)=14×([Mn]-0.7%), where [Mn] and [Si] represent the contents of Mn and Si (in mass percentage), respectively. By controlling the content relationship of Mn and Si, this embodiment can make the austenite-ferrite transition temperature (i.e., the temperature A at which austenite transforms to ferrite according to the present invention) r1 ) basically remains constant and does not fluctuate significantly with changes in Si or Mn.

[0053] S: is a harmful element. The increase of S will lead to a decrease in magnetic induction intensity and an increase in iron loss. In this embodiment, in order to avoid the precipitation of fine MnS during hot rolling, the S content (in mass percentage) is controlled to not exceed 0.003%.

[0054] P: has little effect on magnetism. The increase of P content can effectively improve the strength of the steel plate and enhance the punching performance. In this embodiment, due to the high Si and Mn contents, the strength is already high enough, so there is no need to add P intentionally. At the same time, in order to avoid affecting the realization of deep S removal in the RH smelting process, the upper limit of P content does not need to be controlled too low, and can be controlled at no more than 0.03%.

[0055] Sn: is a grain boundary segregation element. In this embodiment, Sn is added to the chemical composition and the Sn content (in mass percentage) is controlled to be 0.015-0.035%. This can significantly reduce the proportion of unfavorable {111} texture, which is beneficial to improving the magnetic induction intensity of the finished product without normalizing treatment.

[0056] Nb, V, Ti, Mo, Cr, Ni, Cu, N: The more of these elements, the less favorable the grain growth during annealing, which in turn worsens the magnetic properties of non-oriented silicon steel, leading to increased iron loss and reduced magnetic induction intensity. Therefore, the lower the content within a controllable range, the better, for example, Nb≤0.004%, V≤0.004%, Ti≤0.005%, Mo≤0.004%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, N≤0.003%.

[0057] Generally speaking, in terms of chemical composition design, this embodiment designs the contents of C, Si, and Mn. On the basis of increasing the Si content to reduce iron loss, C and Mn are added to expand the austenite region, thereby avoiding an increase in the austenite-ferrite transition temperature due to an increase in the Si content. By controlling the relationship between the Mn and Si contents, the austenite-ferrite transition temperature is kept basically constant, creating conditions for eliminating the deformed fibrous structure of ferrite through hot rolling process control, thereby realizing a production process that eliminates the normalizing process. In addition, while designing the contents of C, Si, and Mn, the control of elements such as S and P is coordinated to reduce the probability of precipitation of fine MnS in the hot rolling process, and to control Nb, V, Ti, Mo, Cr, Ni, Cu, N, and Sn to ensure magnetic properties and achieve low iron loss and high magnetic induction intensity.

[0058] The method for producing the high-grade non-oriented silicon steel of this embodiment includes the following steps.

[0059] 1) Steelmaking steps

[0060] This step includes the molten iron desulfurization process, the converter smelting process and the RH refining process. Specifically, the molten iron desulfurization, converter smelting and RH refining are sequentially adopted to smelt steel according to the aforementioned chemical composition. That is, the chemical composition of the molten steel finally obtained in this step is, in percentage by mass: C: 0.002-0.004%, S≤0.003%, Si: 1.4-1.7%, Mn: 0.7-0.95%, P≤0.03%, Sn: 0.015-0.035%, Nb≤0.004%, V≤0.004%, Ti≤0.005%, Mo≤0.004%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, N≤0.003%, and the balance is Fe and unavoidable inclusions, and 11×([Si]-1.4%)=14×([Mn]-0.7%).

[0061] Preferably, in the molten iron desulfurization process: KR desulfurization technology can be used to desulfurize the molten iron, and the temperature of the molten iron after desulfurization is controlled to be ≥1320°C and the S content in the molten iron is ≤0.0015% by mass, that is, after the molten iron desulfurization process, the S content in the molten iron is made to be ≤0.0015% by mass; the slag skimming rate of the molten iron after desulfurization is controlled to be ≥98%.

[0062] Preferably, in the converter smelting process: the steel tapped in the aforementioned molten iron desulfurization process (i.e., the desulfurized molten iron) is moved into the converter, and scrap steel is mixed in the converter, and the desulfurized molten iron mixed with the scrap steel are smelted together in the converter, wherein the scrap steel can be clean scrap steel, and the mass ratio of scrap steel to the total molten steel is 20-25% (i.e., the amount of scrap steel added accounts for 20-25% of the sum of scrap steel and molten iron); during the tapping process, lime can be added to the molten steel first, and then sufficient tin ingots can be added to the molten steel according to Sn: 0.015-0.035% in the finished product; after the tapping is completed, a slag surface deoxidizer is added to the molten steel.

[0063] Preferably, in the RH refining process: it is implemented in an RH refining furnace, adopts a decarburization treatment mode, and is treated in the order of pre-vacuuming, decarburization, alloying, clean circulation, and breaking vacuum; specifically, in the pre-vacuumed RH refining furnace, the molten steel is decarburized to control the mass percentage of C contained, and then alloyed according to Si: 1.4~1.7%, Mn: 0.7~0.95% and 11×([Si]-1.4%)=14×([Mn]-0.7%) in the finished product, ultra-low titanium ferrosilicon and metallic manganese are added to the molten steel, the net circulation is more than 7 minutes, and then the steel is tapped, wherein a desulfurizer is added to the molten steel during the clean circulation to perform deep desulfurization treatment.

[0064] The tapping of the RH refining process is the final tapping of the steelmaking step, and the chemical composition of the molten steel is as follows, by mass percentage: C: 0.002-0.004%, S≤0.003%, Si: 1.4-1.7%, Mn: 0.7-0.95%, P≤0.03%, Sn: 0.015-0.035%, Nb≤0.004%, V≤0.004%, Ti≤0.005%, Mo≤0.004%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, N≤0.003%, the balance being Fe and unavoidable inclusions, and 11×([Si]-1.4%)=14×([Mn]-0.7%).

[0065] 2) Continuous casting steps

[0066] This step is the continuous casting process. Specifically, the steel produced in the RH refining process is prepared into a continuous casting billet with a thickness of more than 200 mm using continuous casting equipment, preferably with a thickness of 200 mm to 230 mm. The specific operations of the continuous casting process can be achieved using existing feasible continuous casting technologies and will not be elaborated on.

[0067] 3) Hot rolling step

[0068] This step is also the hot rolling process, which sequentially subjects the continuous casting slab obtained in step 2 to heating, multiple rough rolling passes, multiple finish rolling passes, cooling and coiling to prepare a hot-rolled coil.

[0069] Specifically, the continuous casting slab obtained in step 2 is first heated to 1120-1150°C and kept warm for more than 200 minutes, and then subjected to multiple passes of rough rolling to obtain an intermediate slab with a thickness of 40-45 mm, and then subjected to multiple passes of finish rolling, cooling and coiling to obtain a hot-rolled coil with a thickness of 2.50±0.1 mm.

[0070] Among them, the final rolling temperature of the finishing rolling is (A r1 -40)±15℃,A r1 Indicates the temperature at which austenite transforms to ferrite. The reduction in the last finishing pass is ≥30% and the total reduction in the last two finishing passes is ≥50%. The coiling temperature is 650±20℃.

[0071] Thus, based on the design of the elements such as Mn, S, and N in the aforementioned chemical composition, combined with the control of the continuous casting billet heating temperature (1120-1150°C) and the holding time, the production efficiency is ensured, which is beneficial to the high-temperature final rolling of the subsequent finishing rolling, while reducing the probability of precipitation of fine MnS and preventing the solid solution of precipitates such as MnS in the steel during the heating process; and, based on the design of the elements such as Mn, C, and Si in the aforementioned chemical composition, compared with the prior art, the austenite region is expanded and the temperature A at which austenite transforms to ferrite is reduced. r1 , and can maintain A r1 The temperature of the intermediate billet is basically constant. Combined with the control of the thickness of the intermediate billet after rough rolling, the final rolling temperature of the finishing rolling is controlled in the two-phase region or the high-temperature ferrite region to facilitate the formation of high-temperature ferrite and avoid the formation of the deformed fibrous structure described in the background art. The high-temperature ferrite constitutes the basic condition for subsequent recrystallization. Furthermore, combined with the large reduction in the last two passes of finishing rolling, the high-temperature ferrite formed during the final rolling has more internal storage energy, which is conducive to the recrystallization of the high-temperature ferrite and the elimination of the fibrous structure. At the same time, by further controlling the low coiling temperature and the large reduction in the last two passes of finishing rolling, the formation of dense oxide scale can be avoided, so as to avoid increasing the difficulty of removing the oxide scale in the subsequent pickling. In general, through the above series of controls, the purpose of eliminating the need for normalization treatment before subsequent cold rolling is achieved, and hot-rolled coils without fibrous structure and without difficulty in pickling are obtained, thereby obtaining high-grade non-oriented silicon steel with excellent magnetic properties and no corrugated defects on the surface.

[0072] Preferably, the continuous casting billet heating temperature may be preferably 1130-1150° C., that is, the continuous casting billet obtained in step 2 is first heated to 1130-1150° C. and kept warm for more than 200 minutes.

[0073] Preferably, based on the design of the elements such as Mn, C, Si in the above chemical composition, the temperature A at which austenite transforms to ferrite is r1 Basically maintain at about 930 ℃, for example: in an optional embodiment, the temperature A of the transformation from austenite to ferriter1 is 933°C, that is, the final rolling temperature of the finishing rolling is 893±15°C; in another optional embodiment, the temperature A at which austenite transforms to ferrite r1 The final rolling temperature is 930°C, that is, the final rolling temperature of the finishing rolling is 890±15°C. In this way, while facilitating the feasibility of equipment operation, the final rolling temperature of the finishing rolling is ensured to be controlled in the two-phase region or high-temperature ferrite region, so as to facilitate the formation of high-temperature ferrite and the formation of large grains.

[0074] Further preferably, in this step, in the cooling process, the steel plate obtained by the final rolling of the finishing rolling is cooled in two stages, the first stage of cooling is natural slow cooling without water cooling and lasts for 3 to 8 seconds, and the second stage of cooling is water-cooled rapid cooling. Specifically, between the final rolling and coiling, the steel plate just leaving the final rolling mill is not water-cooled but is naturally cooled for about 3 to 8 seconds, and then water cooling is turned on to rapidly cool the steel plate to the coiling temperature of 650±20°C. For example, on the approximately 100m conveyor roller between the final rolling mill and the coiler, the steel plate is air-cooled and conveyed backward on the approximately 30 to 80m roller near the final rolling mill without water cooling, and is rapidly cooled using a large amount of cooling water on the remaining 70 to 20m roller near the coiler. In this way, the steel plate obtained by final rolling can be kept at a high temperature for at least 3 to 8 seconds to ensure sufficient recrystallization, and then quickly cooled to the coiling temperature to reduce or avoid the formation of dense oxide scale, thereby avoiding increasing the difficulty of oxide scale removal in subsequent pickling.

[0075] 4) Acid rolling step

[0076] This step, also known as the continuous casting process, does not normalize the hot-rolled coil obtained in step 3. Instead, it undergoes uncoiling, pickling, rinsing, drying, cold rolling, and coiling in sequence, yielding chilled coils with a thickness of 0.500±0.005mm or 0.350±0.004mm. This embodiment can be used to produce either 0.50mm or 0.35mm high-grade non-oriented silicon steel.

[0077] Specifically, after the hot-rolled coil obtained in step 3 is unrolled, it is pickled with HCl, rinsed and dried, and then cold rolled and coiled to obtain a chilled coil.

[0078] Preferably, HCl is used for three-stage pickling. Wherein: the concentration of the first-stage acid solution is 50-80 g / L and the Fe 2+ Concentration ≤ 130g / L, the concentration of the second-stage acid solution is 90-120g / L and the Fe content in the acid solution is 2+ Concentration ≤90g / L, the concentration of the third-level acid solution is 140-160g / L and the Fe content in the acid solution is 2+Concentration ≤50g / L; during each stage of pickling, the acid solution temperature is 75-85℃, the acid solution contains silicon steel pickling accelerator, and the weight percentage of silicon steel pickling accelerator in the acid solution is 0.05-0.10%; the rinsing water temperature is 45-55℃, and the pickling and rinsing speeds are controlled at 100-180mpm.

[0079] 5) Post-annealing steps

[0080] This step includes the annealing process, the cooling process, the coating process and the finishing process.

[0081] Specifically, the cold-hardened coil obtained in step 4 is subjected to finished product annealing in a mixed atmosphere of H2+N2 using a continuous annealing furnace, wherein the finished product annealing temperature is 920-980°C and the annealing time is 60±5s; the annealed steel strip is cooled, coated and finished to obtain a high-grade non-oriented silicon steel finished product.

[0082] In the present embodiment, the hot-rolled coil has no fibrous structure and does not require normalizing treatment. By controlling the annealing temperature to be relatively high, even if the grain size formed by direct recrystallization of the hot-rolled coil is relatively small, the magnetic properties of the final non-oriented silicon steel product can be guaranteed. In addition, although the normalizing treatment is eliminated in the present embodiment, there is no need to add additional secondary cold rolling or secondary annealing during the acid continuous rolling step and the annealing process. The overall production method is simple to operate and low in cost.

[0083] Preferably, in the cooling process of this step, a three-stage cooling method is used to cool the finished annealed steel strip. The first stage is slow cooling at a high temperature, cooling the steel strip from the annealing temperature to 850°C at a cooling rate of ≤5°C / s; the second stage is controlled cooling using circulating gas jets, cooling the steel strip from 850°C to below 350°C at a cooling rate of ≤15°C / s; and the third stage is controlled cooling using circulating water jets, cooling the steel strip from 350°C to below 100°C. In this manner, slower cooling rates are more beneficial for reducing internal stresses in the steel plate. However, excessively long cooling stages can significantly increase production costs. Temperature-controlled cooling using this three-stage method can effectively and cost-effectively control residual stress in the steel plate to ≤50 MPa, facilitating optimal plate shape.

[0084] The steel plate cooled to below 100°C during annealing is coated and finished. The specific operations can be achieved using existing feasible coating and finishing technologies and will not be described in detail. Finally, a non-oriented silicon steel product with a thickness of 0.500±0.005mm or 0.350±0.004mm is obtained.

[0085] In this embodiment, when the thickness of the non-oriented silicon steel product is 0.500±0.005 mm, the iron loss P 1.5 / 50 ≤3.8W / kg, magnetic induction intensity B 5000≥1.71; When the thickness of the non-oriented silicon steel product is 0.350±0.004mm, its iron loss P 1.5 / 50 ≤3.3W / kg, magnetic induction intensity B 5000 ≥1.70, both specifications of non-oriented silicon steel meet the standard requirements of high-grade non-oriented silicon steel.

[0086] Compared with the prior art, the present invention has the following beneficial effects:

[0087] (1) The non-oriented silicon steel product prepared by the production method has excellent magnetic properties, low iron loss and high magnetic induction intensity, and is suitable for the demand for high-grade non-oriented silicon steel of two specifications of 0.50 mm and 0.35 mm. In addition, no normalization treatment is required before cold rolling, which reduces one process flow and has low production cost. It can meet the demand for low-cost high-grade silicon steel sheets for upgrading electrical steel products and energy efficiency upgrading of electrical products;

[0088] (2) Based on the design of the elements such as Mn, S, and N in the aforementioned chemical composition, combined with the control of the continuous casting billet heating temperature (1120-1150°C) and the holding time, the production efficiency is guaranteed, which is beneficial to the high-temperature final rolling of the subsequent finishing rolling, while reducing the probability of precipitation of fine MnS and preventing the solid solution of MnS and other precipitates in the steel during the heating process; and based on the design of the elements such as Mn, C, and Si in the aforementioned chemical composition, the austenite region is expanded and the temperature A of the austenite to ferrite transformation is reduced compared with the prior art. r1 , and can maintain A r1 Basically constant, combined with controlling the thickness of the intermediate billet after rough rolling, the final rolling temperature of the finishing rolling is controlled in the two-phase region or the high-temperature ferrite region, so as to form high-temperature ferrite and avoid the formation of the deformed fiber structure described in the background technology. The high-temperature ferrite constitutes the basic condition for subsequent recrystallization; further, combined with the large reduction in the last two passes of finishing rolling, the high-temperature ferrite formed during the final rolling has more internal storage energy, which is conducive to the recrystallization of the high-temperature ferrite and the elimination of the fiber structure; at the same time, by further controlling the low coiling temperature and the large reduction in the last two passes of finishing rolling, the formation of dense oxide scale can be avoided, so as to avoid increasing the difficulty of removing the oxide scale in the subsequent pickling. In general, through the above series of controls, the purpose of not requiring normalization treatment before subsequent cold rolling is achieved, and it is ensured that a hot-rolled coil without fiber structure and without difficulty in pickling is obtained, thereby obtaining a high-grade non-oriented silicon steel with good magnetic properties and no corrugated defects on the surface;

[0089] (3) By controlling the annealing temperature to be relatively high, even if the grain size formed by direct recrystallization of the hot-rolled coil is relatively small, the magnetic properties of the final non-oriented silicon steel product can be guaranteed. In addition, although the normalizing treatment is eliminated in this embodiment, there is no need to add a secondary cold rolling or secondary annealing during the acid continuous rolling step and the annealing process. The overall production method is simple to operate and low in cost. The difficulty of cold rolling is reduced, and the risk of strip breakage during cold rolling and subsequent annealing is reduced.

[0090] (4) It can be achieved by adopting a production line of hot metal desulfurization, converter smelting, RH refining, continuous casting, hot rolling, acid continuous rolling, annealing, cooling, coating and finishing. There is no need to add additional processes and equipment specifically for high-grade non-oriented silicon steel. The production line can be used for different grades of products, medium, low and high.

[0091] 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. Any 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.

[0092] The following four examples further illustrate the beneficial effects of this embodiment. Of course, these four examples are only a part of the many variations of the present invention, not all of them. The four examples each provide a non-oriented silicon steel, and the production method thereof is as follows:

[0093] (1) Steelmaking steps

[0094] Examples 1 to 4 are all based on the aforementioned embodiment of the present invention, and sequentially adopt molten iron desulfurization, converter smelting, and RH refining. The chemical composition of the obtained molten steel is shown in Table 1 in mass percentage.

[0095] [Table 1]

[0096]

[0097] As can be seen from Table 1, the chemical compositions of Examples 1 to 4, in terms of mass percentage, satisfy the following: C: 0.002 to 0.004%, S ≤ 0.003%, Si: 1.4 to 1.7%, Mn: 0.7 to 0.95%, P ≤ 0.03%, Sn: 0.015 to 0.035%, Nb ≤ 0.004%, V ≤ 0.004%, Ti ≤ 0.005%, Mo ≤ 0.004%, Cr ≤ 0.03%, Ni ≤ 0.03%, Cu ≤ 0.03%, N ≤ 0.003%, the remainder being Fe and unavoidable inclusions, and 11×([Si] − 1.4%) = 14×([Mn] − 0.7%).

[0098] (2) Continuous casting steps

[0099] In Examples 1 to 4, the steel produced in step 1 is prepared into continuous casting billets with a thickness of 220 mm using continuous casting equipment.

[0100] (3) Hot rolling step

[0101] In Examples 1 to 4, the continuous casting slab obtained in step 2 is subjected to heating, multiple rough rolling passes, multiple finish rolling passes, cooling and coiling in sequence to prepare hot-rolled coils.

[0102] Among them, in the multi-pass finishing rolling, the reduction of the last finishing pass is ≥30% and the total reduction of the last two finishing passes is ≥50%; and the steel plate obtained by the final finishing rolling is subjected to two-stage cooling, the first stage of cooling is natural slow cooling without water cooling and lasts for 3 to 8 seconds, and the second stage of cooling is rapid cooling with water cooling; in addition, the heating temperature and holding time of the continuous casting slab before rough rolling, the thickness of the intermediate slab obtained after multiple passes of rough rolling, the final rolling temperature of finishing rolling, the coiling temperature, and the thickness of the hot-rolled coil are shown in Table 2.

[0103] [Table 2]

[0104]

[0105] The hot-rolled coils obtained in Examples 1 to 4 were subjected to microstructure testing. Figures 1 and 2 show the microstructure photographs of Examples 1 and 3, respectively. Testing revealed that in Examples 1 to 4, high-temperature ferrite formed after final finishing rolling can further yield a recrystallized structure without forming a deformed fibrous structure, thereby eliminating the need for normalizing treatment before subsequent cold rolling.

[0106] (4) Acid rolling step

[0107] In Examples 1-4, the hot-rolled coils obtained in Step 3 were not subjected to normalizing treatment. Instead, they were sequentially uncoiled, pickled, rinsed, dried, cold rolled, and coiled, yielding chilled coils with thicknesses of 0.503 mm, 0.350 mm, 0.501 mm, and 0.349 mm, respectively. Furthermore, the pickling process for the hot-rolled coils in Examples 1-4 was both easy and effective in removing scale, with no apparent difficulty or difficulty in removing the scale.

[0108] (5) Post-annealing steps

[0109] In Examples 1-4, the chilled coil obtained in Step 4 was subjected to final annealing in a continuous annealing furnace in a mixed atmosphere of H₂ + N₂. The annealed steel strip was then cooled, coated, and finished to obtain the final non-oriented silicon steel product. The final annealing temperature and annealing time are shown in Table 3.

[0110] [Table 3]

[0111] Annealing temperature (°C) Annealing time (s) Example 1 93561 Example 2 94563 Example 3 93560 Example 4 94562

[0112] The non-oriented silicon steel products obtained in Examples 1 to 4 all had no corrugated defects on their surfaces, and samples were taken for testing, and the magnetic properties were measured as shown in Table 4.

[0113] [Table 4]

[0114]

[0115] It can be seen from the above Examples 1 to 4 that, when non-oriented silicon steel is produced by one embodiment of the present invention, normalization treatment is not required before cold rolling, and secondary cold rolling or secondary annealing is not required during the acid continuous rolling step and the annealing process. The oxide scale on the surface of the hot-rolled coil is easily removed during the pickling process. The overall production method is simple to operate, has low difficulty, low risk of production abnormalities, and low cost. Moreover, the surface of the obtained non-oriented silicon steel product has no corrugated defects and excellent magnetic properties. As in Examples 1 and 3, when the thickness of the obtained finished product is 0.500±0.005mm, the iron loss P 1.5 / 50 ≤3.8W / kg, magnetic induction intensity B 5000 ≥1.71; As in Examples 2 and 4, when the thickness of the finished product is 0.350±0.004mm, the iron loss P 1.5 / 50 ≤3.3W / kg, magnetic induction intensity B 5000 ≥1.70, two specifications (i.e. 0.50mm and 0.35mm) of non-oriented silicon steel both meet the standard requirements of high-grade non-oriented silicon steel.

[0116] It should be noted again that Experimental Example 1-4 is only an example in this embodiment, and this embodiment is not limited to being implemented in accordance with Experimental Examples 1-4. Without departing from the technical purpose of this embodiment, other implementations different from the Experimental Examples should be included in the scope of protection of the present invention.

Claims

1. A production method of high-grade non-oriented silicon steel, characterized in that, it includes the following steps, 1) Successively carry out steelmaking by hot metal desulfurization, converter smelting, and RH refining. The chemical composition of the finally obtained molten steel is by mass percentage: C: 0.002 - 0.004%, S ≤ 0.003%, Si: 1.4 - 1.7%, Mn: 0.7 - 0.95%, P ≤ 0.03%, Sn: 0.015 - 0.035%, Nb ≤ 0.004%, V ≤ 0.004%, Ti ≤ 0.005%, Mo ≤ 0.004%, Cr ≤ 0.03%, Ni ≤ 0.03%, Cu ≤ 0.03%, N ≤ 0.003%, the balance is Fe and unavoidable inclusions, and 11×([Si] - 1.4%) = 14×([Mn] - 0.7%); 2) Continuously cast the molten steel obtained in step 1 into a continuous casting billet with a thickness of more than 200 mm; 3) Heat the continuous casting billet obtained in step 2 to 1120 - 1150°C and hold for more than 200 min, then obtain an intermediate billet with a thickness of 40 - 45 mm through multiple passes of rough rolling, and then obtain a hot-rolled coil with a thickness of 2.50 ± 0.1 mm through multiple passes of finish rolling, cooling, and coiling. The finishing rolling temperature of the finish rolling is 890 ± 15°C, the reduction of the last pass of finish rolling ≥ 30% and the total reduction of the last two passes of finish rolling ≥ 50%, and the coiling temperature is 650 ± 20°C; 4) Without normalizing treatment, the hot-rolled coil obtained in step 3 is successively uncoiled, pickled, rinsed, dried, cold-rolled, and coiled to obtain a cold-rolled hard coil with a thickness of 0.500 ± 0.005 mm or 0.350 ± 0.004 mm; 5) The cold-rolled coil obtained in step 4 is subjected to finish annealing in a continuous annealing furnace in a mixed atmosphere of H 2 +N 2 , where the finish annealing temperature is 920 - 980 °C and the annealing time is 60 ± 5 s; the annealed steel strip is cooled, coated, and finished to obtain an non-oriented electrical steel product.

2. The production method of high-grade non-oriented silicon steel according to claim 1, characterized in that, The thickness of the obtained non-oriented electrical steel finished product is 0.500 ± 0.005 mm, and its iron loss P 1.5 / 50 ≤ 3.8 W / kg, and the magnetic induction intensity B 5000 ≥ 1.71; Or, the thickness of the obtained non-oriented electrical steel finished product is 0.350 ± 0.004 mm, and its iron loss P 1.5 / 50 ≤ 3.3 W / kg, and the magnetic induction intensity B 5000 ≥ 1.

70.

3. The production method of high-grade non-oriented silicon steel according to claim 1, characterized in that, In step 3, heat the continuous casting billet obtained in step 2 to 1130 - 1150°C and hold for more than 200 min.

4. The production method of high-grade non-oriented silicon steel according to claim 1, characterized in that, In step 3, in the cooling process: the steel plate obtained after the finishing rolling is cooled in two stages. The first-stage cooling is natural slow cooling without water cooling and lasts for 3 - 8 s, and the second-stage cooling is rapid water cooling.

5. The production method of high-grade non-oriented silicon steel according to claim 1, characterized in that, In the hot metal desulfurization process: control the temperature of the desulfurized hot metal ≥ 1320°C and the S content by mass percentage ≤ 0.0015%, and the slag skimming rate ≥ 98%; In the converter smelting process: smelt the desulfurized hot metal mixed with scrap steel in the converter, where the mass ratio of scrap steel to the total molten steel is 20 - 25%; during the tapping process, add sufficient tin ingots to the molten steel according to Sn: 0.015 - 0.035% in the finished product; after the tapping is completed, add a slag surface deoxidizer to the molten steel; In the RH refining process: In an RH refining furnace with preliminary vacuum pumping, decarburization treatment is carried out on the molten steel. Then, according to the alloying scheme of Si: 1.4 - 1.7% and Mn: 0.7 - 0.95% in the finished product and 11×([Si] - 1.4%) = 14×([Mn] - 0.7%), ultra-low titanium ferrosilicon and metallic manganese are added to the molten steel. After a net circulation of more than 7 minutes, tapping is carried out. During the net circulation period, a desulfurizing agent is added to the molten steel for deep desulfurization treatment.

6. The production method of high-grade non-oriented electrical steel according to claim 1, characterized in that, In the pickling process: after uncoiling the hot-rolled coil obtained in step 3, three-stage pickling is carried out with HCl. Among them, the concentration of the first-stage acid solution is 50 - 80 g / L and the Fe concentration in the acid solution ≤ 130 g / L, the concentration of the second-stage acid solution is 90 - 120 g / L and the Fe concentration in the acid solution ≤ 90 g / L, and the concentration of the third-stage acid solution is 140 - 160 g / L and the Fe concentration in the acid solution ≤ 50 g / L; 2+ The concentration of the second-stage acid solution is 90 - 120 g / L and the Fe concentration in the acid solution ≤ 90 g / L, 2+ The concentration of the third-stage acid solution is 140 - 160 g / L and the Fe concentration in the acid solution ≤ 50 g / L; 2+ The concentration of the third-stage acid solution is 140 - 160 g / L and the Fe concentration in the acid solution ≤ 50 g / L; During each stage of pickling, the acid solution temperature is 75 - 85°C, and the acid solution contains a pickling accelerator for electrical steel. The weight percentage of the pickling accelerator for electrical steel in the acid solution is 0.05 - 0.10%; The rinsing water temperature is 45 - 55°C, and the pickling and rinsing speeds are controlled at 100 - 180 mpm.

7. The production method of high-grade non-oriented electrical steel according to claim 1, characterized in that, In step 5, the strip after finish annealing is cooled by a three-stage cooling method, where: the first-stage cooling is slow cooling in the high-temperature section, and the strip is cooled from the annealing temperature to 850°C at a cooling rate ≤ 5°C / s; the second-stage cooling is controlled cooling by cyclic gas injection, and the strip continues to be cooled from 850°C to below 350°C at a cooling rate ≤ 15°C / s; the third-stage cooling is cooling by cyclic water injection, and the strip continues to be cooled from 350°C to below 100°C.

8. A production method of high-grade non-oriented electrical steel, characterized in that, including the following steps, 1) Steelmaking is carried out successively by hot metal desulfurization, converter smelting, and RH refining. The chemical composition of the finally obtained molten steel is, by mass percentage: C: 0.002 - 0.004%, S ≤ 0.003%, Si: 1.4 - 1.7%, Mn: 0.7 - 0.95%, P ≤ 0.03%, Sn: 0.015 - 0.035%, Nb ≤ 0.004%, V ≤ 0.004%, Ti ≤ 0.005%, Mo ≤ 0.004%, Cr ≤ 0.03%, Ni ≤ 0.03%, Cu ≤ 0.03%, N ≤ 0.003%, and the balance is Fe and unavoidable inclusions, and 11×([Si] - 1.4%) = 14×([Mn] - 0.7%); 2) The molten steel obtained in step 1 is continuously cast into a continuous casting billet with a thickness of more than 200 mm; 3) Heat the continuous casting billet obtained in step 2 to 1120 - 1150 °C and hold for more than 200 min, then obtain an intermediate billet with a thickness of 40 - 45 mm through multi-pass rough rolling, and then obtain a hot-rolled coil with a thickness of 2.50 ± 0.1 mm through multi-pass finish rolling and coiling. The finishing rolling temperature of the finish rolling is (A r1 - 40) ± 15 °C, where A r1 represents the temperature of austenite to ferrite transformation. The reduction of the last pass of finish rolling is ≥ 30% and the total reduction of the last two passes of finish rolling is ≥ 50%. The coiling temperature is 650 ± 20 °C. The steel plate obtained from the finishing rolling of the finish rolling is cooled in two stages before coiling. The first-stage cooling is natural slow cooling without water cooling and lasts for 3 - 8 s, and the second-stage cooling is rapid water cooling; 4) The hot-rolled coil obtained in step 3 is not normalized and is successively uncoiled, pickled, rinsed, dried, cold-rolled, and coiled to obtain a cold-rolled hard coil with a thickness of 0.500 ± 0.005 mm or 0.350 ± 0.004 mm; 5) The cold-rolled coil obtained in step 4 is subjected to finish annealing in a continuous annealing furnace in an atmosphere of H 2 +N 2 . The finish annealing temperature is 920 to 980 °C, and the annealing time is 60 ± 5 s. The annealed steel strip is cooled, coated, and finished to obtain an non-oriented electrical steel product.

9. A high-grade non-oriented electrical steel, characterized in that, it is prepared by using the production method described in claim 1.

10. The high-grade non-oriented electrical steel according to claim 9, characterized in that, The thickness of the obtained non-oriented electrical steel finished product is 0.500 ± 0.005 mm, and its iron loss P 1.5 / 50 ≤ 3.8 W / kg, and the magnetic induction intensity B 5000 ≥ 1.71; Or, the thickness of the obtained non-oriented electrical steel finished product is 0.350 ± 0.004 mm, and its iron loss P 1.5 / 50 ≤ 3.3 W / kg, and the magnetic induction intensity B 5000 ≥ 1.70.