Production method of non-oriented silicon steel, non-oriented silicon steel and variable frequency compressor

Abstract

The application discloses a kind of production methods of non-oriented silicon steel, non-oriented silicon steel and variable frequency compressor, it is related to electrical steel technical field, comprising the following steps: the molten steel is continuously cast into the thin slab of thickness 60mm-80mm;Thin slab is hot-rolled, and the hot-rolled plate of thickness 1.8mm-2.0mm is obtained;Hot-rolled plate is sequentially normalized, pickled and cold-rolled, and the cold-rolled plate of thickness 0.20mm-0.35mm is obtained;Cold-rolled plate is annealed and blued, and the non-oriented silicon steel is obtained;The process of bluing includes: under the condition that water vapor and inert gas are simultaneously introduced into annealing furnace, heat treatment is carried out, Fe3O4 insulation layer is generated in situ on the surface of cold-rolled plate after oil removal, the volume fraction of water vapor is controlled to be 20%-30%, the operating temperature is controlled to be 515 DEG C-525 DEG C, and the holding time is 2min-5min.The application keeps excellent magnetic properties while reducing thickness and improving insulation.

Description

Technical Field

[0001] This invention relates to the field of electrical steel technology, and in particular to a method for producing non-oriented silicon steel, non-oriented silicon steel, and a variable frequency compressor. Background Technology

[0002] Non-oriented silicon steel is a soft magnetic alloy containing silicon and based on iron. It belongs to the core type of electrical steel and is mainly used to manufacture the cores of electromagnetic equipment such as motors and transformers. With the development of the electrical industry, variable frequency compressors are gradually replacing traditional fixed frequency compressors, which places higher demands on the performance of silicon steel. The lightweight requirements of variable frequency compressors have driven the development of thinner silicon steel sheets, which effectively reduces energy consumption, minimizes heat generation, and extends the lifespan of the compressor core, aligning with the direction of green and energy-saving development. Currently, the commonly used non-oriented silicon steel grades for compressor motor cores are 50W800 and 50W600, which are relatively thick and have high iron losses. Furthermore, the lamination effect of 0.5mm thick silicon steel is poor, with a low edge quality pass rate. Lamination can also cause the coating material on the silicon steel surface to peel off, seriously affecting insulation.

[0003] Currently, the production process of non-oriented silicon steel used in variable frequency compressors mostly employs coating with insulating materials, resulting in poor insulation at the edges of the stamped laminations after punching. Some existing technologies use a bluing medium for bluing treatment, avoiding the need for an insulating layer and instead using a bluing oxide layer. However, this still requires material spraying, and the use of CO gas during annealing severely affects the surface properties and quality of the silicon steel. Other existing technologies increase the surface roughness of the silicon steel instead of coating, but this results in a thicker finished product, failing to meet the requirements for thinner finished products. Therefore, there is an urgent need to optimize the production process of non-oriented silicon steel to reduce the thickness of the finished product while simultaneously improving its performance. Summary of the Invention

[0004] Based on the deficiencies of the existing technology, the present invention provides a method for producing non-oriented silicon steel, non-oriented silicon steel and a variable frequency compressor, which solves the problems of large thickness and poor performance of finished products in the existing non-oriented silicon steel preparation process.

[0005] The present invention adopts the following technical solution: In a first aspect, the present invention provides a method for producing non-oriented silicon steel, comprising the following steps: Molten steel is continuously cast into thin slabs with a thickness of 60mm-80mm; The thin slab is hot-rolled to obtain a hot-rolled plate with a thickness of 1.8mm-2.0mm; the hot-rolled plate is then subjected to normalizing, pickling, and cold rolling to obtain a cold-rolled plate with a thickness of 0.20mm-0.35mm. The cold-rolled sheet is degreased, annealed, and blued to obtain non-oriented silicon steel. The bluing process includes: heat treatment under conditions of simultaneous introduction of water vapor and inert gas in an annealing furnace to generate an in-situ Fe3O4 insulating layer on the surface of the degreased cold-rolled sheet, wherein the volume fraction of water vapor is controlled at 20%-30%, the operating temperature is controlled at 515℃-525℃, and the holding time is 2min-5min.

[0006] Preferably, during the blueing process, the water vapor flow rate is as follows: ; In the formula, For water vapor flow rate, k For safety reasons, A This represents the surface area of ​​the strip steel that needs to be oxidized per unit time. For the target oxide film density, R max For the maximum film thickness growth rate, The molar mass of Fe3O4 Here is the molar mass of H2O; The inert gas is nitrogen, and the specific flow rate of nitrogen is as follows: ; In the formula, Nitrogen flow rate, The absolute pressure inside the furnace. It represents the volume fraction of water vapor. R is the gas constant, and T is the bluing temperature.

[0007] Preferably, the water vapor is generated using an evaporator, and the evaporation temperature is controlled at 240℃-280℃; During the bluing process, the pressure of the gas inside the annealing furnace is 102 kPa-110 kPa, and the pressure fluctuation is ≤0.5%.

[0008] Preferably, the chemical composition of the molten steel, by mass percentage, includes: Si 2.4%-3.2%, Al 0.30%-0.80%, Mn 0.2%-0.6%, Σ(C+S+Ti+P+N)≤0.02%, with the remainder being Fe and impurities.

[0009] Preferably, during the continuous casting process, the billet pulling speed is controlled at 3.6m / min-4.2m / min; before continuous casting, the superheat of the molten steel is controlled at 10℃-20℃, the cooling intensity of the secondary cooling zone is 1.2L / kg-1.6L / kg, and electromagnetic stirring is used to control the proportion of equiaxed crystal regions inside the billet to be ≥50%.

[0010] Preferably, the hot rolling process includes: holding the thin slab in a soaking furnace at 980℃-1020℃ for 60s-100s before starting rolling, controlling the final rolling temperature at 890℃-910℃, the coiling temperature at ≥790℃, and hot rolling for 4-6 passes to obtain a hot-rolled plate with a thickness of 1.8mm-2.0mm.

[0011] Preferably, during the constant heating process, the operating temperature is controlled at 820℃-860℃, and the temperature is uniformly heated for 2-5 minutes under inert gas protection.

[0012] Preferably, during the annealing process, the annealing temperature is controlled at 850℃-950℃, and the holding time is 2.5min-3.0min; the annealing process is carried out in a mixed gas with a nitrogen-hydrogen volume ratio of 1:(0.8-1.2). The annealing furnace is a continuous long annealing furnace. After annealing, the temperature is lowered to 490℃-510℃ in an inert atmosphere and bluing treatment is carried out in the annealing furnace. After the treatment is completed, it is cooled to 190℃-210℃ in an inert atmosphere and then taken out of the furnace and allowed to cool naturally. The waste gas generated during the annealing and bluing processes is diluted with nitrogen to maintain a hydrogen gas fraction of less than or equal to 2%, and then combusted and purified.

[0013] Secondly, the present invention provides a non-oriented silicon steel, prepared using the aforementioned method for producing non-oriented silicon steel, wherein the interlayer resistivity of the non-oriented silicon steel is 120 Ω·cm. 2 -360Ω·cm 2 Iron loss P 1.5 / 50 ≤4.7W / kg, magnetic induction: 1.68T≤B50≤1.73T, insulation layer thickness is 1μm-3μm.

[0014] Thirdly, the present invention provides a variable frequency compressor, which is prepared using the aforementioned non-oriented silicon steel.

[0015] Compared with the prior art, the above-mentioned at least one technical solution adopted by the present invention can achieve the following beneficial effects: This invention utilizes thin slab continuous casting to stably produce cold-rolled sheets with a thickness of 0.20mm~0.35mm. Based on this, a continuous integrated annealing and bluing process is employed. Under conditions of 515℃-525℃ and a water vapor volume fraction of 20%-30%, a chemically bonded Fe3O4 insulating layer is formed in situ on the surface of the cold-rolled sheet, eliminating the need for any spraying. This significantly improves the insulation performance of the sheet edges. Simultaneously, an inert gas is used instead of CO gas as the protective atmosphere, eliminating the adverse effects of CO gas on the surface properties and quality of silicon steel. Furthermore, energy saving and consumption reduction are achieved by fully utilizing the residual heat from annealing. While reducing thickness and improving edge insulation, excellent magnetic properties are maintained, making it particularly suitable for the mass production of high-efficiency variable frequency compressor motor cores. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of a method for producing non-oriented silicon steel according to the present invention; Figure 2 The Fe3O4 oxide layer prepared according to the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention proposes a method for producing non-oriented silicon steel, optimizing the preparation process. It eliminates the coating step, resulting in a thinner finished product, and also optimizes the product's electrical resistance and magnetic properties. (See reference...) Figure 1 The production method specifically includes the following steps:

[0020] S1: Continuous casting.

[0021] Continuous casting can transform liquid steel into solid billets. In this embodiment of the invention, molten steel is continuously cast into thin slabs with a thickness of 60mm-80mm, specifically 60mm, 65mm, 70mm, 75mm and 80mm.

[0022] In some embodiments, the raw materials for preparing molten steel, by mass percentage, include: Si 2.4%-3.2%, Al 0.30%-0.80%, Mn 0.2%-0.6%, Σ(C+S+Ti+P+N)≤0.02%, with the remainder being Fe and unavoidable impurities. The composition of the raw materials for preparing molten steel is also the composition of the molten steel, and thus the final composition of non-oriented silicon steel. Specifically, by mass percentage, the mass fraction of Si in non-oriented silicon steel can be 2.4%, 2.6%, 2.8%, 3.0%, and 3.2%, etc.; the mass fraction of Al can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, and 0.8%, etc.; the mass fraction of Mn can be 0.2%, 0.3%, 0.4%, 0.5%, and 0.6%, etc.; and the total mass fraction of C, S, Ti, P, and N is less than or equal to 0.02%, such as 0.020%, 0.018%, 0.015%, 0.013%, and 0.010%, etc.

[0023] In some embodiments, during continuous casting, the billet pulling speed is controlled at 3.6 m / min-4.2 m / min, such as 3.6 m / min, 3.7 m / min, 3.8 m / min, 3.9 m / min, 4.0 m / min, 4.1 m / min, and 4.2 m / min. Before continuous casting, the superheat of the molten steel is controlled at 10℃-20℃, such as 10℃, 15℃, and 20℃. The cooling intensity of the secondary cooling zone is 1.2 L / kg-1.6 L / kg, such as 1.2 L / kg, 1.4 L / kg, and 1.6 L / kg. Simultaneously, electromagnetic stirring (stirrer current 300A) is used to control the proportion of equiaxed crystal zones inside the billet to ≥50%, such as 50%, 55%, 60%, 65%, 70%, 75%, and 80%.

[0024] S2: Hot-rolled.

[0025] The thin slab with a thickness of 60mm-80mm obtained in step S1 is hot-rolled to break up the coarse casting structure of the continuous casting plate and roll it into the required intermediate thickness to obtain a hot-rolled plate with a thickness of 1.8mm-2.0mm. The specific thickness can be 1.8mm, 1.9mm and 2.0mm, etc.

[0026] In some embodiments, the hot rolling process includes: before the initial rolling of the slab (thin slab), the slab is held in a soaking furnace at 980℃-1020℃ for 60s-100s, the final rolling temperature is controlled at 890℃-910℃, the coiling temperature is ≥790℃, and it is hot rolled to 1.8mm-2.0mm in 4-6 passes. Holding the slab at 980℃-1020℃ first ensures uniform temperature at the edges and inside, reduces stress differences within the slab during rolling, prevents cracking, and reduces the average thickness deviation of the hot-rolled plate. Then, the slab is cooled and hot-rolled to obtain a hot-rolled plate with the required thickness.

[0027] Specifically, the temperature at which the billet is held in a soaking furnace before rolling can be 980℃, 990℃, 1000℃, 1010℃, and 1020℃, etc., and the holding time can be 60s, 70s, 80s, 90s, and 100s, etc. The final rolling temperature can be 890℃, 900℃, and 910℃, etc. The coiling temperature is ≥790℃, such as 790℃, 800℃, 830℃, 850℃, and 870℃, etc., and the coiling temperature is slightly lower than the final rolling temperature. The number of hot rolling passes can be 4, 5, or 6. The reduction rate of the first pass is ≥35% (such as 35%, 40%, 45%, and 50%, etc.), and the reduction rate of each single pass is ≥10% (such as 10%, 13%, 15%, 18%, and 20%, etc.); the final hot-rolled plate thickness is 1.8mm-2.0mm.

[0028] S3: Normalization.

[0029] Normalization of hot-rolled plates is used to optimize their microstructure in preparation for cold rolling.

[0030] In some embodiments, during the normalization process, the operating temperature is controlled at 820℃-860℃, such as 820℃, 830℃, 840℃, 850℃, and 860℃; and the homogenization is carried out under inert gas protection for 2-5 minutes, such as 2 minutes, 3 minutes, 4 minutes, and 5 minutes. The type of inert gas is not limited, such as nitrogen and argon.

[0031] S4: Pickling + Cold Rolling.

[0032] After the normalizing process, pickling and cold rolling are performed sequentially. Pickling removes the surface iron oxide scale, and cold rolling yields a cold-rolled sheet with a final thickness of 0.20mm-0.35mm, forming a texture. Specifically, the final thickness after cold rolling can be 0.20mm, 0.25mm, 0.30mm, and 0.35mm, etc.

[0033] The type of acid used for pickling is not limited; it can be hydrochloric acid solution, sulfuric acid solution, etc.

[0034] The specific equipment and principles of hot rolling, normalizing, and cold rolling can be found in existing technologies and will not be elaborated upon here.

[0035] S5: Degreasing + Annealing.

[0036] By removing surface rolling oil, iron powder, and other contaminants through degreasing, followed by annealing, thermal activation energy is provided to drive atomic diffusion and dislocation movement, thereby dominating the recrystallization process. Combined with temperature control, this promotes magnetically favorable processes. Orientation and *Oriented texture growth suppresses magnetically unfavorable conditions. Orientation-based texture development.

[0037] Degreasing can be done using alkaline cleaning solutions, such as sodium carbonate solution or sodium hydroxide solution, and can be achieved through brushing and spraying.

[0038] In some embodiments, during the annealing process, the annealing temperature of the annealing furnace is controlled at 850℃-950℃, such as 850℃, 880℃, 900℃, 930℃, and 950℃; the holding time is 2.5min-3.0min, such as 2.5min, 2.8min, and 3.0min. The holding time varies depending on the thickness of the cold-rolled sheet; a 0.25mm thick cold-rolled sheet can be held for 2.5min, and a 0.3mm thick cold-rolled sheet can be held for 3min, and so on. The annealing process is carried out in a mixed gas with a nitrogen-hydrogen volume ratio of 1:(0.8-1.2), and the nitrogen-hydrogen volume ratio can be controlled to be 1:0.8, 1:1.0, 1:1.2, etc.

[0039] S6: Bluish.

[0040] After annealing, the bluing stage is initiated, simplifying the original "coating + sintering" insulation process to "dew point bluing." This allows stress-relief annealing and insulation layer formation to be completed directly within a continuous annealing furnace. Coating processes place high demands on the coating rollers and are prone to wear, resulting in uneven roller marks on the coating. The bluing process effectively avoids these problems. Furthermore, while coating materials are trending towards environmentally friendly and harmless options, their application on non-oriented silicon steel surfaces is not yet mature. Insulating coatings containing chromium or volatile organic solvents still urgently need to be replaced. Therefore, the bluing process is more environmentally friendly.

[0041] In actual operation, heat treatment is carried out under conditions where water vapor and inert gas are simultaneously introduced into the furnace. The volume fraction of water vapor is controlled at 20%-30%, the operating temperature of the bluing process is controlled at 515℃-525℃, and the holding time is 2min-5min. This invention improves the process flow after continuous casting, reduces the thickness of the finished product while ensuring certain magnetic properties, and eliminates the coating process. Through annealing-bluing-stamping process, costs are further reduced, while avoiding the absence of an insulating layer on the edge of the iron chip and improving the stability of the compressor.

[0042] Thin slabs with high-equiaxed crystals are prepared by improving the pulling speed and cooling intensity; increasing the hot rolling process temperature and reducing the hot-rolled plate thickness can effectively reduce the normalizing process temperature; after cold rolling, a continuous annealing-bluing process is adopted, increasing the annealing process temperature and reducing the annealing time, and directly combining the temperature drop to the bluing temperature with a suitable gas flow rate for bluing process treatment.

[0043] It should be noted that the dew point blue coloring is achieved by using high-temperature water vapor at a specific temperature (500±5℃) to undergo an oxidation-reduction reaction with a clean silicon steel surface, generating an Fe3O4 film: 3Fe+4H2O(g)→Fe3O4+4H2(g); the use of an inert gas (such as pure nitrogen) protective atmosphere effectively prevents the formation of Fe2O3, resulting in a denser blue-black Fe3O4 insulating layer.

[0044] Specifically, the total volume fraction of water vapor in the introduced water vapor and inert gas is 20%, 23%, 25%, 28%, and 30%, etc., and the inert gas can be nitrogen, with pure nitrogen as the carrier introduced into the furnace, but is not limited to this; the operating temperature of the bluing process can be 515℃, 518℃, 520℃, 523℃, and 525℃, etc.; the holding time can be 2min, 3min, 4min, and 5min, etc.

[0045] In some embodiments, deionized water can be used as the steam source in the furnace, and water vapor is generated by an evaporator. The evaporation temperature is controlled at 240℃-280℃, such as 240℃, 250℃, 260℃, 270℃, and 280℃. During the bluing process, the pressure of the mixed gas in the furnace is 102KPa-110KPa, and the pressure fluctuation is ≤0.5%.

[0046] To further control the reaction process and improve the performance of the finished product, this invention optimizes the flow rates of water vapor and nitrogen gas: During the blueing process, the flow rate of the introduced water vapor is controlled to be... , Satisfy the following formula: (1); In the formula, This indicates the water vapor flow rate, expressed in kg / h. k This represents the safety factor, which is set to 2.0. A This represents the surface area of ​​the strip steel that needs to be oxidized per unit time, expressed in m². 2 It is related to the production line speed v and width w. A = v × w , v It refers to the distance traveled per unit of time. v and w The units are all in meters (m). The target oxide film density is expressed as 5.18 g / cm³. 3 ; R max This represents the maximum film thickness growth rate, taken as 0.5 μm / min; The molar mass of Fe3O4 is expressed as 231.53 g / mol. The value represents the molar mass of H2O, taken as 18 g / mol.

[0047] The flow rate of nitrogen is , Satisfy the following formula: (2); In the formula, This indicates the nitrogen flow rate, in meters (m). 3 / h; This represents the absolute pressure inside the furnace, taken as 1.08 atm; This indicates the volume fraction of water vapor, expressed in % (%). R This represents the gas constant, taken as 0.0821 L·atm / (mol·K); T This indicates the bluing temperature, measured in Kelvin (K).

[0048] It should be noted that appropriate amounts of water vapor and nitrogen can better control the reaction process, which is beneficial for improving the density of the insulation layer and enhancing the performance of the finished product. By controlling the holding time and gas flow rate during the bluing process, the thickness of the insulation layer on the surface of the silicon steel sheet can be adjusted, thereby controlling the magnetic properties of the finished product.

[0049] Principle: The main desired reaction is 3Fe + 4H2O(g) → Fe3O4 + 4H2(g). In order to control the oxidation environment and avoid the formation of a loose Fe2O3 oxide layer, the H2O(g) content is appropriately adjusted according to different oxidation times to avoid the oxide layer being too thick. Mixing nitrogen can also prevent the H2(g) produced in the reaction from reducing and destroying the oxide layer structure, while diluting the hydrogen concentration in the furnace and venting it outside the furnace.

[0050] In some embodiments, a continuous long annealing furnace is used, with a very thick furnace wall at the front end, allowing for rapid heating. After annealing, the furnace is cooled to 490℃-510℃ (e.g., 490℃, 500℃, and 510℃) in an inert atmosphere (such as nitrogen). A bluing treatment is then performed in the rear section of the annealing furnace. After this treatment, the furnace is cooled to 190℃-210℃ (e.g., 190℃, 200℃, and 210℃) in an inert atmosphere before being removed from the furnace and allowed to cool naturally. This staged cooling temperature control, focusing on the silicon steel plate and oxide layer, effectively protects the bluing insulation layer from cracking during gentle cooling, preventing interlayer cracks that could affect insulation performance. Simultaneously, controlling the temperature difference between different locations within the furnace to less than 10℃ also effectively prevents the formation of Fe2O3 spots.

[0051] Furthermore, the waste gas generated during the annealing and bluing processes can be diluted with nitrogen to maintain the hydrogen gas fraction at less than or equal to 2%, and then combusted and purified.

[0052] It should be noted that the production method of non-oriented silicon steel provided by the present invention greatly simplifies the process by adopting a thin slab continuous casting and rolling production process. The thin slab has low internal deformation energy storage after hot rolling, and the internal stress removal after heat treatment is simple, which can ensure that the insulation layer will not crack due to the release of internal stress during bluing heat treatment.

[0053] The production of low-to-medium grade non-oriented silicon steel using a thin slab process is a relatively mature technology. Compared to conventional processes, this invention reduces the rough rolling and slab reheating steps, significantly shortening the production cycle, reducing the burn-off rate to 0.3%~0.5%, increasing the yield by 3%~5%, and saving approximately 200 yuan per ton of steel. The thin slab process reduces the hot rolling reduction rate, retaining more {100} oriented microstructure, which is beneficial for improving magnetic properties. Simultaneously, it reduces the internal deformation energy storage of cold-rolled sheets, allowing for faster recrystallization at lower temperatures during annealing.

[0054] This invention also provides a non-oriented silicon steel, which is prepared by the production method provided in this invention. Its mass percentage is: 2.4~3.2% Si, 0.30~0.8% Al, 0.2~0.6% Mn, Σ(C+S+Ti+P+N)≤0.02%, and the remainder is Fe and unavoidable impurities.

[0055] The non-oriented silicon steel prepared by the production method provided in this invention has a thinner insulating layer, with a thickness of 1μm-3μm, such as 1μm, 2μm, 3μm, etc. The non-oriented silicon steel prepared by the production method provided in this invention also has good resistivity and magnetic properties, with an interlayer resistivity of 120Ω·cm. 2 -360Ω·cm 2 Iron loss: P 1.5 / 50 ≤4.7W / kg, magnetic induction: 1.68T≤B50≤1.73T. 1.5 / 50 indicates that the magnetic field strength applied when measuring iron loss is 1.5T and the alternating magnetic field frequency is 50Hz. B50 is the magnetic induction intensity generated inside the material when a magnetic field strength of 5000A / m is applied to the material.

[0056] This invention also provides a variable frequency compressor, prepared using the non-oriented silicon steel provided by this invention. As an important material for motor cores, the thickness and service life of the surface insulation layer of non-oriented silicon steel are crucial. This invention employs a bluing process, which can reduce the surface oxide layer to below 3 μm. Figure 2As shown, it has good resistance and effectively improves the stacking factor; at the same time, the magnetic properties of the finished product are optimized through process adjustment.

[0057] The production process provided by this invention is continuous casting-hot rolling-normalizing-pickling-cold rolling-degreasing-annealing and bluing, employing a dew point bluing process to form a denser, blue-black Fe3O4 insulating layer. By improving the process flow after continuous casting, the thickness of the finished product is reduced while ensuring certain magnetic properties. The bluing process eliminates the traditional "coating + sintering" steps, saving costs and avoiding the use of highly polluting sintered coatings. The process of this invention also effectively utilizes the residual temperature of recrystallization annealing, greatly saving time and energy consumption for reheating. The improved production process of this invention can produce products with thinner thicknesses while possessing good electrical resistance and magnetic properties.

[0058] Example 1 This embodiment provides a method for producing non-oriented silicon steel, the steps of which are as follows: Continuous casting: The non-oriented silicon steel prepared has the following composition by mass percentage: 3.0% Si, 0.6% Al, 0.4% Mn, Σ(C+S+Ti+P+N)≤0.01%, with the remainder being Fe and unavoidable impurities. The raw materials are batched according to the composition, and molten steel is obtained through smelting. The molten steel is then transformed into a 60mm thin slab using a continuous casting process. The casting speed is controlled at 4.0m / min. Before continuous casting, the superheat of the molten steel is controlled at 15℃, and the cooling intensity in the secondary cooling zone is 1.4L / kg. Simultaneously, electromagnetic stirring (stirrer current 300A) is employed to control the proportion of equiaxed crystal regions within the slab to be ≥50%.

[0059] Hot rolling: Before hot rolling, the billet temperature is raised to 1000℃ and held for 80s; the final rolling temperature is 900℃ and the coiling temperature is 800℃; 1.8mm is rolled in 5 passes.

[0060] Normalization: The normalization temperature is 840℃, and the temperature is uniformly heated for 3 minutes in a N2 protective atmosphere.

[0061] Pickling + Cold Rolling: Pickling is performed using a 5% (by mass) dilute hydrochloric acid (HCl) solution at 50°C, followed by cold rolling. The final dimensions of the cold-rolled plate are 0.25 mm (thickness) and 1.2 m (width).

[0062] Degreasing + Annealing: Degreasing was performed using a mixed alkaline solution of 3.5% NaOH and 5% Na2CO3 by mass, followed by holding at 900℃ for 2.5 min in an atmosphere with a volume ratio of N2:H2=1:1.

[0063] Bluing: A continuous long annealing furnace was used. After annealing, the temperature was lowered to 500℃ in a nitrogen atmosphere, and bluing treatment was performed in the annealing furnace. Deionized water was evaporated at 260℃, mixed with nitrogen gas preheated to 150℃, and then held at 520℃ for 5 minutes in the bluing furnace. The pressure of the mixed gas in the furnace was 106 kPa, with pressure fluctuation ≤0.5%. The steam flow rate was set to 1.86 kg / h, and the nitrogen flow rate was set to 18.65 m³ / h. 3 / h, water vapor volume fraction is 25%. When calculating using Equation 1, the strip surface area A = 12m². 2 The nitrogen flow rate is calculated using Equation 2: T = 520℃ + 273.15 = 793.15 K. After cooling to 200℃ in a nitrogen atmosphere, the furnace is removed and allowed to cool naturally.

[0064] SEM image of the non-oriented silicon steel prepared in Example 1 is shown below. Figure 2 As shown.

[0065] Testing revealed that the 0.25mm thick non-oriented silicon steel insulation layer obtained in this embodiment had a thickness of 2.4μm and an interlayer resistivity of 360Ω·cm. 2 Iron loss P 1.5 / 50 =4.33W / kg, magnetic induction B 50 =1.68T.

[0066] Test method description: (1) Insulation layer thickness, scanning electron microscope (SEM); (2) Interlayer resistivity, four-probe method; (3) Iron loss P 1.5 / 50 Epstein square (16 pieces); (4) Magnetic induction B 50 Epstein Square (16 pieces).

[0067] Example 2 The only difference from Example 1 is that the bluing process is kept at a constant temperature for 2 minutes (strip surface area A = 30m²). 2 The steam flow rate was set to 4.64 kg / h, and the nitrogen flow rate was set to 46.62 m³ / h. 3 / h.

[0068] Testing revealed that the thickness of the non-oriented silicon steel insulation layer obtained in this embodiment was 1.0 μm, and the interlayer resistivity was 315 Ω·cm. 2 Iron loss P 1.5 / 50 =3.97W / kg, magnetic induction B 50 =1.70T.

[0069] Comparing Example 1 and Example 2, it can be seen that shortening the heat preservation time and appropriately increasing the bluing steam flow rate can reduce the insulation layer thickness and improve the magnetic properties of the finished board.

[0070] Example 3 The only difference from Example 1 is that the cold-rolled sheet has a thickness of 0.3 mm and a width of 1.2 m.

[0071] Testing revealed that the thickness of the non-oriented silicon steel insulation layer obtained in this embodiment was 2.5 μm, and the interlayer resistivity was 210 Ω·cm. 2 Iron loss P 1.5 / 50 =4.6W / kg, magnetic induction B 50 =1.73T.

[0072] Example 4 This embodiment provides a method for producing non-oriented silicon steel, the steps of which are as follows: Continuous casting: The non-oriented silicon steel produced has the following composition by mass percentage: 2.4% Si; 0.30% Al; 0.2% Mn; Σ(C+S+Ti+P+N)≤0.015%, with the remainder being Fe and unavoidable impurities. The raw materials are batched according to the composition, and molten steel is obtained through smelting. The molten steel is then transformed into 80mm thin slabs using a continuous casting process. The casting speed is controlled at 3.6m / min, and the proportion of equiaxed crystal regions within the slab is 50%.

[0073] Hot rolling: Before hot rolling, the billet temperature is raised to 1000℃ and held for 100s; the final rolling temperature is 890℃ and the coiling temperature is 790℃; 2.0mm is rolled in 5 passes.

[0074] Normalization: The normalization temperature is 840℃, and the temperature is uniformly heated for 3 minutes in a N2 protective atmosphere.

[0075] Pickling + Cold Rolling: Pickling is performed using a 5% (by mass) dilute hydrochloric acid (HCl) solution at 50°C, followed by cold rolling. The final dimensions of the cold-rolled plate are 0.25 mm (thickness) and 1.2 m (width).

[0076] Degreasing + Annealing: Degreasing was performed using a mixed alkaline solution of 3.5% NaOH and 5% Na2CO3 by mass, followed by holding at 900℃ for 2.5 min in an atmosphere with a volume ratio of N2:H2=1:1.

[0077] Bluing: A continuous long annealing furnace was used. After annealing, the temperature was lowered to 500℃ in a nitrogen atmosphere, and bluing treatment was performed in the annealing furnace. Deionized water was evaporated at 240℃, mixed with nitrogen, and then held at 520℃ for 5 minutes in the bluing furnace. The pressure of the mixed gas in the furnace was 103 kPa, with pressure fluctuation ≤0.5%. The steam flow rate was set to 1.85 kg / h, and the nitrogen flow rate was set to 18.88 m³ / h. 3 / h, water vapor volume fraction is 25%. When calculating using Equation 1, the strip surface area A = 12m². 2The nitrogen flow rate is calculated using Equation 2: T = 520℃ + 273.15 = 793.15 K. After cooling to 200℃ in a nitrogen atmosphere, the furnace is removed and allowed to cool naturally.

[0078] Testing revealed that the 0.3mm thick non-oriented silicon steel insulation layer obtained in this embodiment had a thickness of 2.6μm and an interlayer resistivity of 130Ω·cm. 2 Iron loss P 1.5 / 50 =4.7W / kg, magnetic induction B 50 =1.69T.

[0079] Example 5 The only difference from Example 1 is that the water vapor flow rate is set to 5.5 kg / h and the nitrogen flow rate is set to 12.28 m³ / h. 3 / h.

[0080] Testing revealed that the thickness of the non-oriented silicon steel insulation layer obtained in this embodiment was 3 μm, and the interlayer resistivity was 200 Ω·cm. 2 Iron loss P 1.5 / 50 =4.9W / kg, magnetic induction B 50 =1.69T.

[0081] Example 6 The only difference from Example 1 is that the water vapor flow rate is set to 1.5 kg / h and the nitrogen flow rate is set to 3.35 m³ / h. 3 / h.

[0082] Testing revealed that the non-oriented silicon steel insulation layer obtained in this embodiment had a thickness of 1.4 μm, but exhibited low coverage and uneven thickness, with an interlayer resistivity of 160 Ω·cm. 2 Iron loss P 1.5 / 50 =4.81W / kg, magnetic induction B 50 =1.67T.

[0083] Example 7 The only difference from Example 1 is that the temperature was maintained at 500°C for 5 minutes in the bluing furnace.

[0084] Testing revealed that the thickness of the non-oriented silicon steel insulation layer obtained in this embodiment was 2.0 μm, and the interlayer resistivity was 170 Ω·cm. 2 Iron loss P 1.5 / 50 =4.47W / kg, magnetic induction B 50 =1.67T.

[0085] Example 8 The only difference from Example 1 is that the temperature was maintained at 530°C for 10 minutes in the bluing furnace.

[0086] Testing revealed that the thickness of the non-oriented silicon steel insulation layer obtained in this embodiment was 6 μm, and the interlayer resistivity was 470 Ω·cm. 2Iron loss P 1.5 / 50 =5.85W / kg, magnetic induction B 50 =1.66T.

[0087] Comparative Example 1 The only difference between this comparative example and Example 1 is that a cooling coating process is performed after annealing, and the coating thickness is 5μm. The specific steps are as follows: After annealing, the surface of the non-oriented silicon steel is cleaned (removing oil and rust spots), and a semi-inorganic composite coating is applied to the surface by dip coating. Then, it is baked in an oven at 300°C for 40 seconds.

[0088] Tests showed that the loss P of the non-oriented silicon steel in this comparative example was... 1.5 / 50 ≤4.96W / kg, magnetic induction B 50 =1.67T, interlayer resistivity 68Ω·cm 2 .

[0089] The above examples and comparative examples show that, compared with the coating process, the bluing process results in a thinner non-oriented silicon steel insulating layer, has less impact on magnetic properties, can effectively improve the stacking rate, and has a wider range of applications.

[0090] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0091] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for producing non-oriented silicon steel, characterized in that, Includes the following steps: Molten steel is continuously cast into thin slabs with a thickness of 60mm-80mm; The thin slab is hot-rolled to obtain a hot-rolled plate with a thickness of 1.8mm-2.0mm; the hot-rolled plate is then subjected to normalizing, pickling, and cold rolling to obtain a cold-rolled plate with a thickness of 0.20mm-0.35mm. The cold-rolled sheet is degreased, annealed, and blued to obtain non-oriented silicon steel. The bluing process includes: heat treatment under conditions of simultaneous introduction of water vapor and inert gas in an annealing furnace to generate an in-situ Fe3O4 insulating layer on the surface of the degreased cold-rolled sheet, wherein the volume fraction of water vapor is controlled at 20%-30%, the operating temperature is controlled at 515℃-525℃, and the holding time is 2min-5min.

2. The method for producing non-oriented silicon steel as described in claim 1, characterized in that, During the blueing process, the water vapor flow rate is as follows: ； In the formula, For water vapor flow rate, k For safety reasons, A This represents the surface area of ​​the strip steel that needs to be oxidized per unit time. For the target oxide film density, R max For the maximum film thickness growth rate, The molar mass of Fe3O4 Here is the molar mass of H2O; The inert gas is nitrogen, and the specific flow rate of nitrogen is as follows: ； In the formula, Nitrogen flow rate, The absolute pressure inside the furnace. It represents the volume fraction of water vapor. R is the gas constant, and T is the bluing temperature.

3. The method for producing non-oriented silicon steel as described in claim 1, characterized in that, The water vapor is generated using an evaporator, and the evaporation temperature is controlled at 240℃-280℃. During the bluing process, the pressure of the gas inside the annealing furnace is 102 kPa-110 kPa, and the pressure fluctuation is ≤0.5%.

4. The method for producing non-oriented silicon steel as described in claim 1, characterized in that, The chemical composition of the molten steel, by mass percentage, includes: Si 2.4%-3.2%, Al 0.30%-0.80%, Mn 0.2%-0.6%, Σ(C+S+Ti+P+N)≤0.02%, with the remainder being Fe and impurities.

5. The method for producing non-oriented silicon steel as described in claim 1, characterized in that, During the continuous casting process, the billet pulling speed is controlled at 3.6m / min-4.2m / min; before continuous casting, the superheat of the molten steel is controlled at 10℃-20℃, the cooling intensity of the secondary cooling zone is 1.2L / kg-1.6L / kg, and electromagnetic stirring is used to control the proportion of equiaxed crystal regions inside the billet to ≥50%.

6. The method for producing non-oriented silicon steel as described in claim 1, characterized in that, The hot rolling process includes: before starting rolling, the thin slab is held in a soaking furnace at 980℃-1020℃ for 60s-100s, the final rolling temperature is controlled at 890℃-910℃, the coiling temperature is ≥790℃, and after 4-6 passes of hot rolling, a hot-rolled plate with a thickness of 1.8mm-2.0mm is obtained.

7. The method for producing non-oriented silicon steel as described in claim 1, characterized in that, During the constant heating process, the operating temperature is controlled at 820℃-860℃, and the temperature is uniformly heated for 2-5 minutes under inert gas protection.

8. The method for producing non-oriented silicon steel as described in claim 1, characterized in that, During the annealing process, the annealing temperature is controlled at 850℃-950℃, and the holding time is 2.5min-3.0min; the annealing process is carried out in a mixed gas with a nitrogen-hydrogen volume ratio of 1:(0.8-1.2); The annealing furnace is a continuous long annealing furnace. After annealing, the temperature is lowered to 490℃-510℃ in an inert atmosphere and bluing treatment is carried out in the annealing furnace. After the treatment is completed, it is cooled to 190℃-210℃ in an inert atmosphere and then taken out of the furnace and allowed to cool naturally. The waste gas generated during the annealing and bluing processes is diluted with nitrogen to maintain a hydrogen gas fraction of less than or equal to 2%, and then combusted and purified.

9. A non-oriented silicon steel, characterized in that, The non-oriented silicon steel is prepared by the production method of any one of claims 1-8, wherein the interlayer resistivity of the non-oriented silicon steel is 120 Ω·cm. 2 -360Ω·cm 2 Iron loss P 1.5 / 50 ≤4.7W / kg, magnetic induction: 1.68T≤B50≤1.73T, insulation layer thickness is 1μm-3μm.

10. A variable frequency compressor, characterized in that, It is prepared using the non-oriented silicon steel as described in claim 9.

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