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

Abstract

The invention discloses high-grade non-oriented silicon steel and a preparation method thereof, and relates to the technical field of non-oriented silicon steel. The high-grade non-oriented silicon steel comprises the following components in percentage by weight: less than or equal to 0.002% of C, 3.0-3.6% of Si, 0.15-0.25% of Mn, 0.05-0.20% of Als, less than or equal to 0.001% of S, less than or equal to 0.015% of P, less than or equal to 0.0015% of N, less than or equal to 0.002% of Ti and the balance of Fe and inevitable impurities. The manufacturing method of the high-grade non-oriented silicon steel in the claim 1 sequentially comprises the following steps of converter smelting, RH refining, continuous casting, heating, hot rolling, coiling, normalizing, acid pickling, cold rolling, annealing and coating. Wherein the heating temperature is controlled to be 1110 DEG C to 1200 DEG C; the hot rolling comprises rough rolling and finish rolling, and the hot rolling temperature is controlled to be 900-1000 DEG C; the coiling temperature ranges from 550 DEG C to 600 DEG C; the normalizing temperature ranges from 850 DEG C to 970 DEG C; the total reduction rate of cold rolling is 80-87%; and the annealing temperature ranges from 840 DEG C to 960 DEG C. According to the invention, through precise control of chemical components and a two-stage annealing process, collaborative improvement of low iron loss and high magnetic induction is realized.

Description

Technical Field

[0001] This invention relates to the field of non-oriented silicon steel technology, specifically to a high-grade non-oriented silicon steel and its preparation method. Background Technology

[0002] High-grade non-oriented silicon steel is a core soft magnetic material for manufacturing high-efficiency motors, drive motors for new energy vehicles, and precision instruments. With its high magnetic induction, low iron loss, and high strength, it has become a product with high technical barriers and high added value in the steel industry.

[0003] High-grade non-oriented silicon steel must simultaneously meet several stringent electromagnetic and mechanical performance indicators, which are often mutually restrictive, thus posing a significant technical challenge. These indicators include high magnetic induction, low iron loss, high strength, and good stamping processability. Achieving these properties involves overcoming numerous technical difficulties: 1. The challenge of balancing performance: Increasing strength often requires introducing dislocations and precipitation phases, which hinders magnetic domain movement and increases iron loss; increasing silicon content can reduce iron loss but increases brittleness, which is detrimental to processing and stamping; 2. Pure steel quality and precise composition control: The content of impurity elements such as C, N, S, and O must be extremely low (usually ≤0.0025%), and elements such as Ti, Nb, and V, which form harmful precipitates, must be precisely controlled; 3. Microstructure and texture control: A coarse and favorable texture can be obtained through normalizing, cold rolling, and annealing processes to improve magnetic induction; or dislocation strengthening can be used to achieve ultra-high strength.

[0004] The core of high-grade non-oriented silicon steel lies in how to synergistically optimize its magnetic and mechanical properties through precise composition design, extreme process control, and innovative strengthening mechanisms to meet the demands of modern high-efficiency energy conversion equipment. The manufacturing challenge of high-grade silicon steel lies in the contradictory requirements for iron loss, magnetic induction, and mechanical properties, necessitating coordinated control of composition design and process development. Existing technologies, including some patents and research, have attempted to improve product quality through optimized composition control, heat treatment processes, and cold rolling processes, but significant room for improvement remains.

[0005] Chinese Patent Publication No. CN120519760A discloses a high-efficiency, low-energy-consumption method for optimizing the magnetic properties and producing non-oriented silicon steel, including: 1) composition design based on mass percentage; 2) process steps: smelting and continuous casting; hot rolling; selective normalizing; cooling control; cold rolling and annealing: total reduction rate 70%-85%, annealing adopts a two-stage process, the first stage at 850±10℃ in a wet atmosphere, and the second stage at 950±10℃ in a dry atmosphere. Through the synergistic optimization of composition design and process, the magnetic properties of high-grade non-oriented silicon steel products are improved while reducing energy consumption in the normalizing process. The implemented results are B50 = 1.72T, P1.5 / 50 = 3.2W / kg, with relatively high iron loss. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a high-grade non-oriented silicon steel, comprising, by weight percentage: C≤0.002%, Si: 3.0~3.6%, Mn: 0.15~0.25%, Als: 0.05~0.20%, S≤0.001%, P≤0.015%, N≤0.0015%, Ti≤0.002%, with the remainder being Fe and unavoidable impurities.

[0007] A method for manufacturing high-grade non-oriented silicon steel includes the following steps: The process includes converter smelting, RH refining, continuous casting, heating, hot rolling, coiling, normalizing, pickling, cold rolling, annealing, and coating; wherein the heating temperature is controlled at 1110~1200℃; the hot rolling includes roughing and finishing rolling, and the hot rolling temperature is controlled at 900~1000℃; the coiling temperature is 550~600℃; the normalizing temperature is 850~970℃; the total reduction rate of cold rolling is 80~87%; and the annealing temperature is 840~960℃.

[0008] Furthermore, the surface temperature of the billet obtained by continuous casting is ≥500℃ before heating.

[0009] Furthermore, the heating adopts a multi-stage heating method, with the first stage heating temperature controlled at 950~1050℃, the second stage heating temperature controlled at 1050~1150℃, and the third stage heating temperature controlled at 1150~1200℃, and the total heating time not less than 180min.

[0010] Furthermore, the roughing rolling temperature is 960~1000℃, and the finishing rolling temperature is 900~930℃.

[0011] Furthermore, the winding process involves heat preservation for ≥24 hours at a temperature ≥500℃.

[0012] Furthermore, the normalization temperature is 890~930℃, and the normalization time is controlled within 1~3 minutes.

[0013] Furthermore, the pickling temperature is 75℃~90℃.

[0014] Furthermore, the final reduction rate of the cold rolling process is ≤20%.

[0015] Furthermore, during the annealing process, the partial pressure of water vapor P(H2O) / partial pressure of hydrogen P(H2) < 0.005, and a mixed gas of H2 and N2 is used for protection in the furnace during annealing, with a ratio of H2 to N2 of 4:6. The annealing process adopts a multi-stage annealing method, with the temperature of the first stage annealing being 850±10℃, the time of the first stage annealing being 120s, and the dew point of the first stage annealing being -15℃. The temperature of the second stage annealing is 950±10℃, the time of the second stage annealing being 60s, and the dew point of the second stage annealing being -30℃.

[0016] The beneficial effects of this invention are as follows: 1. By precisely controlling the chemical composition and employing a two-stage annealing process, a synergistic improvement in both low iron loss and high magnetic induction was achieved. Product iron loss P 1.5 / 50 ≤2.2W / kg, far superior to existing technologies (such as 3.2W / kg for N120519760A), magnetic induction B 5000 With a capacity of ≥1.76T, it can significantly reduce the energy consumption and heat generation of the motor, making it suitable for core scenarios with stringent requirements for magnetic performance, such as high-efficiency motors and drive motors for new energy vehicles.

[0017] 2. By optimizing the proportions of alloying elements such as Mn and Al, and designing a final cold rolling reduction rate of ≤20%, the product achieves a yield strength of 600~640MPa and a tensile strength of 670~700MPa, capable of withstanding the centrifugal force of high-speed motor rotors while maintaining good stamping processability. This resolves the contradiction between the high strength and easy stamping of high-grade silicon steel, meeting the efficiency requirements of large-scale stamping production and reducing processing losses.

[0018] 3. Employing precise process control including multi-stage heating (1110~1200℃), hot rolling in the austenitic single-phase region (finishing temperature 900~930℃), and low-temperature coiling (550~600℃), combined with strict control of impurity elements, effectively avoids problems such as hindered grain growth and uneven texture. The product exhibits a thickness difference of ≤6μm within the same plate, a longitudinal thickness fluctuation within ±2μm, and a flat plate shape. Its quality stability is significantly superior to existing technologies, reducing assembly risks in downstream applications.

[0019] 4. Through process design such as short cycle time (1~3min) and one-time cold rolling (total reduction rate 80~87%), the production process is shortened and energy consumption is reduced while ensuring product performance; and the process parameter control window is clear (such as annealing atmosphere H2:N2=4:6, water-hydrogen partial pressure ratio <0.005), which is compatible with existing industrial production lines and can be industrialized without large-scale equipment modification, combining technological advancement and economic feasibility. Detailed Implementation

[0020] Unless otherwise specified, all raw materials used below are commercially available products, and all methods used are conventional methods in this field.

[0021] The high-grade non-oriented silicon steel of the present invention comprises, by weight percentage: C≤0.002%, Si: 3.0~3.6%, Mn: 0.15~0.25%, Als: 0.05~0.20%, S≤0.001%, P≤0.015%, N≤0.0015%, Ti≤0.002%, with the remainder being Fe and unavoidable impurities; The roles of each element in the high-grade non-oriented silicon steel of this invention are as follows: C: C is a harmful element that can deteriorate the magnetic properties of silicon steel products. Generally, the C content is required to be no more than 0.005%. Considering that this invention is a high-grade non-oriented silicon steel, in order to minimize the impact of impurity elements on magnetic properties and magnetic aging, this invention requires the C content to be controlled below 0.002%.

[0022] Si: Si can reduce iron loss, but it also reduces magnetic induction. Moreover, as the Si content increases, the brittleness and hardness of the finished silicon steel product also increase, and the cold rolling processability deteriorates, which is not conducive to the smooth flow of cold rolling and the punching of users. This invention belongs to high-grade non-oriented silicon steel. Considering the magnetic properties and processing performance of the product, and in order to minimize iron loss, the upper limit of Si content is controlled at 3.6%. In this invention, the Si content is controlled at 3.0~3.6%.

[0023] Mn: Mn can promote the strengthening of favorable texture components and the weakening of unfavorable texture components, which can further improve the magnetic properties of the product. Mn and S form MnS, which reduces the amount of S dissolved in the slab during heating and can effectively suppress the hot brittleness during heating. However, if the Mn content is too high, fine MnS precipitates will be generated during hot rolling, which will cause the grains to grow and deteriorate the magnetic properties. Therefore, the Mn content in this invention is controlled at 0.15~0.25%.

[0024] P: In silicon steel, P element can increase resistivity ρ, shrink the γ phase region, promote grain growth, increase favorable texture components and reduce unfavorable texture components, and also reduce iron loss and increase magnetic induction. However, P element has a grain boundary segregation effect, which can easily cause embrittlement, especially when the C content is very low. When the P content exceeds 0.05%, the processability will be significantly deteriorated. Therefore, the P content should not be too high. In this invention, the P content is controlled below 0.015%.

[0025] Als: Al can improve the magnetic properties of the product. The influence of Al on the brittleness of electrical steel is smaller than that of Si. In order to reduce the iron loss of the product, the Al content is required to be high. However, if the Al content is too high, it will have a greater impact on the magnetic induction and also affect the processing performance. Considering the magnetic properties and processing performance of the product, the Al content in this invention should be controlled at 0.05~0.20%.

[0026] S, N, Ti: S, N, and Ti are harmful elements. To reduce their impact on the magnetic properties of the product, preferably, the content of S is ≤0.001%, the content of N is ≤0.0015%, and the content of Ti is ≤0.002%.

[0027] The molten steel with the above composition is continuously cast into a 230mm thick billet, which is then directly fed into the heating furnace for heating. To ensure uniform heating temperature and prevent cracking, the surface temperature of the billet before entering the furnace must be above 500℃. The heating furnace operates at a low temperature. Excessive furnace temperature can cause impurities such as sulfur (S) and nitrogen (N) to precipitate and dissolve in the billet. These fine precipitates after hot rolling can hinder grain growth and affect magnetic properties. Therefore, the furnace temperature should be controlled below 1200℃. In this invention, the furnace temperature is controlled between 1110 and 1200℃. Furthermore, the first stage heating temperature is controlled between 950 and 1050℃, the second stage between 1050 and 1150℃, and the third stage between 1150 and 1200℃. The total heating and holding time is no less than 180 minutes.

[0028] The above-mentioned slab is rough-rolled to an intermediate slab with a thickness of 30-35 mm. The lower final rolling temperature and low-temperature coiling are conducive to grain growth after normalization of the hot-rolled plate, which helps to improve the magnetic properties of the product. To further improve the magnetic properties of the product, the hot rolling process adopts high-temperature final rolling and low-temperature coiling. The final rolling temperature of roughing is 960-1000℃. The conveyor rolls between roughing and finishing rolling are equipped with heat insulation covers, and the hot-rolled plate is finished in 7 passes to a thickness of 2.0-2.3 mm. The final rolling temperature is 900-930℃, which makes it roll in the single-phase region of austenite, avoiding the simultaneous deformation of ferrite and austenite in the two-phase region, which would lead to uneven deformation and shear bands that affect the magnetic induction of the product. Cooling water pipes and nozzles are arranged between the finishing mill and the coiler. The hot coil is rapidly cooled to the coiling temperature of 550~600℃ through laminar flow cooling to prevent the formation of coarse precipitation of second phase particles such as AlN and MnS, which would hinder grain growth. After coiling, the coil is kept at a temperature of ≥500℃ for ≥24 hours to promote dynamic recrystallization and grain coarsening.

[0029] The hot-rolled strip steel is then passed through a normalizing and pickling line. Normalizing increases beneficial texture components and reduces harmful texture components, improving the magnetic properties of the product. Excessive normalizing temperature can lead to overly large grains, causing edge cracking or even strip breakage during cold rolling. The normalizing temperature should be between 890 and 930°C. To prevent the increase of harmful components, a short normalizing time of 1-3 minutes is recommended. To ensure a defect-free cold-rolled surface and thorough cleaning, the normalized strip steel undergoes shot blasting to remove iron oxide scale, followed by pickling with 55% hydrochloric acid at 75°C-90°C to ensure a clean surface. Furthermore, to ensure smooth cold rolling in subsequent processes, the normalized strip steel undergoes edge trimming, with each side trimmed by 10-15mm.

[0030] The normalized steel plate, after being trimmed and cleaned, is cold-rolled in 6-7 passes with a total cold rolling reduction of 80-87%, resulting in a target thickness of 0.30-0.35 mm. This invention pertains to high-grade, thin-gauge non-oriented silicon steel. The material has high strength, but the large total rolling reduction and high rolling force required lead to poor thickness accuracy during rolling. Poor longitudinal thickness precision increases rolling difficulty, reduces production stability, and makes thickness control inaccurate, with significant longitudinal thickness fluctuations. To ensure product shape control, the rolling force needs to be reduced, and the final pass reduction should be minimized, with the final pass reduction rate controlled below 20%.

[0031] The cold-rolled strip was subjected to continuous annealing. To reduce the impact of oil and impurities on the finished product's surface coating, the strip was treated with an aqueous solution of disodium hydrogen phosphate and sodium hydroxide before annealing. This removed rolling oil and dirt from the strip surface and formed a phosphate film on the silicon steel surface, further improving the adhesion of the finished product's surface coating. Considering that this invention pertains to high-grade steels with high alloy content and easy oxidation, the required water vapor partial pressure P(H2O) / hydrogen partial pressure P(H2) is <0.005, and the atmosphere is a mixture of hydrogen and nitrogen, with an H2 to N2 ratio of 4:6. The process included: a first-stage annealing at 850±10℃ for 120s (dew point -15℃) to eliminate cold rolling stress; a second-stage annealing at 950±10℃ for 60s (dew point -30℃) to promote recrystallization; and finally, an insulating coating was applied via a coating roller and cured at 380~650℃.

[0032] The non-oriented silicon steel obtained by the above-mentioned process meets the requirements of low iron loss and high magnetic induction, while also possessing suitable yield strength and tensile strength, as well as good shape control. Compared with the prior art, it has the following advantages: the high-grade non-oriented silicon steel products produced by this invention have lower iron loss P 1.5 / 50 ≤2.2W / kg, B 5000 ≥1.76, yield strength 600~640MPa, tensile strength 670~700MPa, yield strength and tensile strength are tested according to GB / T228.1 standard. Among them, iron loss P 1.5 / 50 For an alternating magnetic field with a frequency of 50Hz and a maximum magnetic flux density of 1.5T, the core loss and magnetic induction B are given. 5000 The magnetic flux density is given by a magnetic field strength of 5000 A / m.

[0033] The specific embodiments of the present invention will be further described in detail through the description of the optimized embodiments.

[0034] Example 1 This embodiment describes a high-grade non-oriented silicon steel with the following chemical composition by weight percentage: C ≤ 0.0015%, Si: 3.5%, Mn: 0.25%, Als: 0.15%, S ≤ 0.0008%, P: 0.01%, N ≤ 0.001%, Ti ≤ 0.001%, with the remainder being Fe and unavoidable impurities.

[0035] The above-mentioned molten steel was continuously cast into slabs with a thickness of 230mm, and the slabs were directly loaded into the heating furnace for heating.

[0036] The heating furnace adopts low-temperature heating, with the furnace temperature controlled at 1150℃ and the heating and holding time at 210min.

[0037] In this embodiment, the roughing rolling temperature is 940℃, and the hot-rolled plate is finished to a thickness of 2.0mm in 7 passes. The finishing rolling temperature is 880℃, and the coiling temperature is 580℃.

[0038] The hot-rolled strip steel is passed through a normalizing and pickling line. Specifically, the normalizing temperature is 920℃, the normalizing time is 2.5min, the pickling temperature is 80℃, and the edges are trimmed by 10mm after normalizing.

[0039] The normalized steel plate, after being trimmed and cleaned, is cold rolled to 0.35mm in six passes using a single cold rolling method, with a total reduction rate of 82.5%. The reduction rate of the final pass is 19%, and the specific reduction rates of the other passes are as follows: 35.5% for the first pass, 35% for the second pass, 35.5% for the third pass, 30% for the fourth pass, and 25% for the fifth pass.

[0040] The cold-rolled strip is subjected to alkaline washing in an alkaline bath at 70-80℃ to remove rolling oil and dirt from the surface. It then enters a continuous annealing furnace. The first annealing stage is at 860℃ for 120 seconds (dew point -15℃) to relieve cold rolling stress. The second annealing stage is at 960℃ for 60 seconds (dew point -30℃). After annealing, the high-temperature cooling rate is 30℃ / s, and the strip exits the high-temperature cooling zone at 600℃. The medium-temperature cooling rate is 20℃ / s, and the strip exits the medium-temperature cooling zone at 180℃. After annealing, an insulating coating is applied using coating rollers and cured at 380-650℃.

[0041] The 0.35mm thick high-grade non-oriented silicon steel manufactured using the above process has a finished product with low iron loss P. 1.5 / 50 It is 2.15W / Kg, magnetic induction B 5000 It has a strength of 1.77T, a yield strength of 610MPa, and a tensile strength of 690MPa. It meets the magnetic performance requirements of high-grade non-oriented silicon steel, namely low iron loss and high magnetic induction, while also having suitable yield strength and tensile strength.

[0042] Example 2 The production process of this embodiment of a high-grade non-oriented silicon steel is basically the same as that of Embodiment 1. The difference is that its chemical composition by weight percentage is: C≤0.0018%, Si: 3.6%, Mn: 0.25%, Als: 0.15%, S≤0.0008%, P: 0.01%, N≤0.001%, Ti≤0.001%, with the remainder being Fe and unavoidable impurities.

[0043] The molten steel was cast into a slab with a thickness of 230 mm. The temperature of the heating furnace was 1100℃, and the heating and holding time was 240 min.

[0044] The roughing rolling temperature is 980℃, and it is finished rolling to a thickness of 2.1mm in 7 passes. The finishing rolling temperature is 910℃, and the coiling temperature is 590℃. The normalizing temperature was controlled at 900℃, the normalizing time was 2.5 min, and the material was rolled to 0.30 mm in 7 passes. The reduction rate of the last pass was 18%, and the reduction rates of the other passes were as follows: 35% for the first pass, 35% for the second pass, 30% for the third pass, 30% for the fourth pass, 25% for the fifth pass, and 20% for the sixth pass.

[0045] After the above-mentioned cold-rolled sheet is alkali washed, it undergoes a first-stage annealing process: 860℃×120s (dew point -15℃), a second-stage annealing process: 960℃×60s (dew point -30℃), and continuous annealing is carried out in a protective atmosphere of H2 and N2 in a 4:6 ratio; after annealing, an insulating coating is applied by a coating roller.

[0046] The 0.30mm ultra-high efficiency air conditioner inverter compressor non-oriented silicon steel manufactured using the above process has a finished product with low iron loss P. 1.0 / 50 It is 2.05W / Kg, magnetic induction B 5000 It has a strength of 1.76T, a yield strength of 625MPa, and a tensile strength of 690MPa.

[0047] Example 3 The production process of this embodiment of a high-grade non-oriented silicon steel is basically the same as that of Embodiment 1. The difference is that its chemical composition by weight percentage is: C≤0.0018%, Si: 3.2%, Mn: 0.25%, Als: 0.15%, S≤0.0008%, P: 0.01%, N≤0.001%, Ti≤0.001%, with the remainder being Fe and unavoidable impurities.

[0048] The molten steel with the above composition was cast into a slab with a thickness of 230 mm. The temperature of the heating furnace was 1150℃, and the heating and holding time was 230 min.

[0049] The roughing rolling temperature is 970℃, and it is finished rolling to a thickness of 2.2mm in 7 passes. The finishing rolling temperature is 890℃, and the coiling temperature is 580℃. The normalizing temperature was controlled at 930℃, the normalizing time was 2.5 min, and the material was rolled to 0.35 mm in 6 passes, with a reduction rate of 20% in the last pass.

[0050] After the above-mentioned cold-rolled sheet is alkali washed, it undergoes a first-stage annealing process: 860℃×120s (dew point -15℃), a second-stage annealing process: 940℃×60s (dew point -30℃), and continuous annealing is carried out in a protective atmosphere of H2 and N2 in a 4:6 ratio; after annealing, an insulating coating is applied by a coating roller.

[0051] The 0.35mm ultra-high efficiency air conditioner inverter compressor non-oriented silicon steel manufactured using the above process has a finished product with low iron loss P. 1.0 / 50 It is 2.2W / Kg, magnetic induction B 5000 It has a strength of 1.78T, a yield strength of 600MPa, and a tensile strength of 670MPa.

[0052] Comparative Example 1 The chemical composition of this comparative example of a high-grade non-oriented silicon steel, by weight percentage, is as follows: C: 0.003%, Si: 2.6%, Mn: 0.30%, Als: 0.45%, Sn: 0.01%, S: 0.003%, P: 0.02%, N: 0.003%, Ti: 0.003%, with the remainder being Fe and unavoidable impurities.

[0053] The molten steel with the above composition was cast into a slab with a thickness of 230 mm. The temperature of the heating furnace was 1150℃, and the heating and holding time was 230 min.

[0054] The above slab is rough-rolled to a thickness of 35 mm to form an intermediate slab, with a final rolling temperature of 870°C, and then finished rolled in 7 passes to a thickness of 2.2 mm, with a final rolling temperature of 850°C and a coiling temperature of 580°C. The normalizing temperature was controlled at 880℃, the normalizing time was 2.5 min, and the material was rolled to 0.35 mm in 6 passes, with a reduction rate of 25% in the last pass.

[0055] The cold-rolled sheet was alkali washed and then annealed at 940℃ for 240s. The annealing was carried out continuously in a protective atmosphere of H2 and N2 in a 3:7 ratio. After annealing, an insulating coating was applied by a coating roller.

[0056] The 0.35mm ultra-high efficiency air conditioner inverter compressor non-oriented silicon steel manufactured using the above process has a finished product with low iron loss P. 1.0 / 50 It is 2.40W / Kg, magnetic induction B 5000 It has a strength of 1.68T, a yield strength of 516MPa, a tensile strength of 590MPa, and a relatively high iron loss.

[0057] Comparative Example 2 The chemical composition of this comparative example of a high-grade non-oriented silicon steel, by weight percentage, is as follows: C: 0.003%, Si: 1.8%, Mn: 0.25%, Als: 0.50%, Sn: 0.01%, S: 0.003%, P: 0.02%, N: 0.003%, Ti: 0.003%, with the remainder being Fe and unavoidable impurities.

[0058] The molten steel with the above composition was cast into a slab with a thickness of 230 mm. The temperature of the heating furnace was 1100℃, and the heating and holding time was 240 min.

[0059] The above slab is rough-rolled to a thickness of 35 mm to form an intermediate slab, with a final rolling temperature of 870°C, and then finished rolled in 7 passes to a thickness of 2.2 mm, with a final rolling temperature of 860°C and a coiling temperature of 640°C. The normalizing temperature was controlled at 900℃, the normalizing time was 2.5 min, and the material was rolled to 0.35 mm in 6 passes, with a reduction rate of 25% in the last pass.

[0060] The cold-rolled sheet was alkali washed and then annealed at 940℃ for 240s. The annealing was carried out continuously in a protective atmosphere of H2 and N2 in a 3:7 ratio. After annealing, an insulating coating was applied by a coating roller.

[0061] The 0.35mm ultra-high efficiency air conditioner inverter compressor non-oriented silicon steel manufactured using the above process has a finished product with low iron loss P. 1.0 / 50 It is 2.51W / Kg, magnetic induction B 5000 The yield strength is 1.71T, the yield strength is 474MPa, the tensile strength is 534MPa, the iron loss is relatively high, and the yield strength and tensile strength are relatively low.

[0062] Comparative Example 3 The chemical composition of this comparative example of a high-grade non-oriented silicon steel, by weight percentage, is as follows: C: 0.003%, Si: 3.8%, Mn: 0.25%, Als: 0.15%, Sn: 0.01%, S: 0.003%, P: 0.02%, N: 0.003%, Ti: 0.003%, with the remainder being Fe and unavoidable impurities.

[0063] The molten steel with the above composition was cast into a slab with a thickness of 230 mm. The temperature of the heating furnace was 1100℃, and the heating and holding time was 240 min.

[0064] The above slab is rough-rolled to a thickness of 35 mm to form an intermediate slab, with a final rolling temperature of 870°C, and then finished rolled in 7 passes to a thickness of 2.2 mm, with a final rolling temperature of 860°C and a coiling temperature of 640°C. The normalizing temperature was controlled at 900℃, the normalizing time was 2.5 min, and the material was rolled to 0.35 mm in 6 passes, with a reduction rate of 25% in the last pass.

[0065] The cold-rolled sheet was alkali washed and then annealed at 940℃ for 240s. The annealing was carried out continuously in a protective atmosphere of H2 and N2 in a 3:7 ratio. After annealing, an insulating coating was applied by a coating roller.

[0066] The 0.35mm ultra-high efficiency air conditioner inverter compressor non-oriented silicon steel manufactured using the above process has a finished product with low iron loss P. 1.0 / 50 It is 2.05W / Kg, magnetic induction B 5000 It has a strength of 1.64T, a yield strength of 554MPa, a tensile strength of 674MPa, and a low magnetic induction.

[0067] The different contents of impurity elements (C, S, N, Ti) in the above embodiments and comparative examples are to verify that "strictly controlling the content of harmful impurities" is the key to reducing iron loss and improving magnetic induction. Impurity elements can form fine precipitates, which hinder magnetic domain movement and grain growth, resulting in significantly higher iron loss and lower magnetic induction in the comparative examples.

[0068] The different Si content in each embodiment and comparative example is to verify the balance range of Si content. Too low Si (1.8-2.6%) leads to increased iron loss; too high Si (3.8%) leads to decreased magnetic induction and increased brittleness. The range of Si content in this invention (3.0-3.6%) can simultaneously achieve low iron loss and high magnetic induction.

[0069] The different Al content in each embodiment and comparative example is to verify that the Al content needs to be appropriately controlled. Excessive Al content will worsen the magnetic induction (magnetic induction of 1.68T and 1.71T in comparative examples 1 and 2, respectively) and increase brittleness, which is not conducive to processing.

[0070] The alloying element P is different in each embodiment and comparative example in order to verify the control of P content. Although P can increase resistivity and reduce iron loss, excessive amount (0.02%) will lead to embrittlement, and the mechanical properties of the comparative examples are insufficient (the yield strength of the comparative examples is 474-516 MPa < the yield strength of the examples is 600-640 MPa).

[0071] The different Mn content in each embodiment and comparative example is to verify the appropriate range of Mn content. Excessive Mn content will form fine MnS precipitates, which will hinder grain growth and result in a higher iron loss (2.40 W / kg) in Comparative Example 1.

[0072] The finishing rolling temperatures in each embodiment were 900~930℃, which is within the austenite single-phase region, while Comparative Example 1 was 850℃ and Comparative Example 2 was 860℃, which are close to the two-phase region. This verifies the necessity of finishing rolling in the austenite single-phase region. Finishing rolling temperatures below the range of this invention will cause ferrite and austenite to deform simultaneously, generating shear bands and affecting the uniformity of magnetic induction. The magnetic induction of the comparative examples is generally lower than that of the embodiments.

[0073] The normalization temperatures of the various embodiments were 890~930℃, while those of Comparative Example 1 were 880℃. This verifies the effect of a suitable normalization temperature on texture optimization. If the normalization temperature is too low, it cannot fully improve the beneficial texture and reduce the harmful texture, resulting in insufficient magnetic properties in Comparative Example 1.

[0074] In each embodiment, the final cold rolling reduction rate was ≤20%, while in each comparative example it was 25%. This verifies the impact of reducing the final reduction rate on the sheet shape. High-grade silicon steel has high strength, and an excessively high final reduction rate will lead to excessive rolling force. The comparative examples did not control this parameter, resulting in excessive thickness fluctuation and sheet-to-sheet difference, and deterioration of the stamping processability.

[0075] Each embodiment underwent two-stage annealing, while each comparative example underwent single-stage annealing. This verifies the effect of two-stage annealing and optimized atmosphere ratio: the first stage of annealing eliminates cold rolling stress, and the second stage of annealing promotes recrystallization and improves magnetic properties; a 40% H2 content reduces oxidation and protects magnetic properties; the comparative examples underwent single-stage annealing with a low H2 content, resulting in insufficient recrystallization, and both mechanical and magnetic properties were inferior to those of the embodiments.

[0076] The winding temperature in each embodiment was 550~600℃, while in Comparative Example 2 it was 640℃. This verifies the necessity of low-temperature winding. Excessive winding temperature will cause coarse precipitation of second-phase particles such as AlN and MnS, which will hinder grain growth. As a result, the magnetic and mechanical properties of Comparative Example 2 are both low.

[0077] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A high-grade non-oriented silicon steel, characterized in that, Included by weight percentage: C≤0.002%, Si: 3.0~3.6%, Mn: 0.15~0.25%, Als: 0.05~0.20%, S≤0.001%, P≤0.015%, N≤0.0015%, Ti≤0.002%, with the remainder being Fe and unavoidable impurities.

2. A method for manufacturing high-grade non-oriented silicon steel according to claim 1, characterized in that, The steps are as follows: Converter smelting, RH refining, continuous casting, heating, hot rolling, coiling, normalizing, pickling, cold rolling, annealing, coating; The heating temperature is controlled at 1110~1200℃; The hot rolling includes roughing and finishing rolling, and the hot rolling temperature is controlled at 900~1000℃; The winding temperature is 550~600℃; The normalization temperature is 850~970℃; The total reduction rate of cold rolling is 80-87%; The annealing temperature is 840~960℃.

3. The method for manufacturing high-grade non-oriented silicon steel according to claim 2, characterized in that: The surface temperature of the billet obtained by continuous casting is ≥500℃ before heating.

4. The method for manufacturing high-grade non-oriented silicon steel according to claim 2, characterized in that: The heating process employs a multi-stage heating method. The first stage heating temperature is controlled at 950~1050℃, the second stage heating temperature is controlled at 1050~1150℃, and the third stage heating temperature is controlled at 1150~1200℃. The total heating time is not less than 180 minutes.

5. The method for manufacturing high-grade non-oriented silicon steel according to claim 2, characterized in that: The roughing rolling temperature is 960~1000℃, and the finishing rolling temperature is 900~930℃.

6. The method for manufacturing high-grade non-oriented silicon steel according to claim 2, characterized in that: The winding process involves heat preservation for ≥24 hours at a temperature ≥500℃.

7. The method for manufacturing high-grade non-oriented silicon steel according to claim 2, characterized in that: The normalization temperature is 890~930℃, and the normalization time is controlled within 1~3 minutes.

8. The method for manufacturing high-grade non-oriented silicon steel according to claim 2, characterized in that: The pickling temperature is 75℃~90℃.

9. The method for manufacturing high-grade non-oriented silicon steel according to claim 2, characterized in that: The final reduction rate of the cold rolling process is ≤20%.

10. The method for manufacturing high-grade non-oriented silicon steel according to claim 2, characterized in that: During annealing, the partial pressure of water vapor P(H2O) / partial pressure of hydrogen P(H2) < 0.

005. A mixed gas of H2 and N2 is used for protection in the furnace during annealing, with a ratio of H2 to N2 of 4:

6. The annealing adopts a multi-stage annealing method. The temperature of the first stage annealing is 850±10℃, the time of the first stage annealing is 120s, and the dew point of the first stage annealing is -15℃. The temperature of the second stage annealing is 950±10℃, the time of the second stage annealing is 60s, and the dew point of the second stage annealing is -30℃.