Conversion liquid for forming conversion coating on surface of non-oriented silicon steel, and method

Abstract

Disclosed in the present invention is a conversion liquid for forming a conversion coating on the surface of a non-oriented silicon steel. The conversion liquid is acidic, and contains solids having a content of 10-30 wt%. The solids comprise an inorganic conversion coating component and a water-based organic resin. Further disclosed in the present invention is a non-oriented silicon steel, comprising a silicon steel substrate and a conversion coating on the surface of the silicon steel substrate. Further disclosed in the present invention is a method for forming the conversion coating on the surface of a silicon steel substrate.

Description

Conversion liquid and method for forming conversion film on surface of non-oriented silicon steel Technical Field

[0001] The present invention relates to a coating liquid, a steel plate and a manufacturing method thereof, and in particular to a conversion liquid for forming a conversion film on the surface of non-oriented silicon steel, a non-oriented silicon steel plate and a manufacturing method thereof. Background Art

[0002] Electrical steel is a material widely used in the iron cores of motors and transformers. In order to reduce the short circuit between the stacked layers of electrical steel sheets and increase the eddy current loss, an insulating coating needs to be applied to the surface of the steel sheets.

[0003] For thick coatings with a dry film thickness of more than 2μm, because the coating contains a considerable amount of inorganic fillers, the organic-inorganic mixed amorphous coating formed after the coating is baked and cured is likely to have poor film-forming performance on polar metal substrates with high surface tension.

[0004] Furthermore, thick, water-soluble insulating coatings for silicon steel require high surface insulation, heat resistance, and stability under hot pressing. Coating formulations typically contain a high concentration of submicron-sized inorganic fillers, typically accounting for approximately 30-70% by weight of the dry film. Applying such thick coatings to steel surfaces is challenging and can easily lead to coating defects, resulting in poor film quality. These defects manifest as poor adhesion, bright spots due to coating shedding, poor scratch resistance, and shedding or cracking at edges during punching and shearing, severely degrading the coating's performance.

[0005] In order to improve the corrosion resistance and adhesion of metal surface coatings, the metal substrate is appropriately passivated before coating to form an interface conversion film to improve coating performance. This is a treatment method that has been adopted in the existing technology.

[0006] For example, a Chinese patent document entitled "A process for passivating the surface of cold-rolled sheet" with publication number CN104250754A, published on December 31, 2014, discloses such a process. The composition of the passivating solution used is, by weight, 0.8-1.2% sodium hydroxide, 1.4-1.8% sodium carbonate, 1.5-2.5% sodium tripolyphosphate, 2-4% anhydrous sodium metasilicate, 3-5% phytic acid, 2.5-3.5% sodium bicarbonate, 4-6% sodium benzoate, 5-7% triethanolamine, 3.5-4.5% polyethylene glycol, 0.5-1.5% sodium lauryl sulfonate, 0.1-0.3% organosilicon defoamer, and the balance is water. The passivation process is as follows: prepare a passivation solution with the above components, adjust the pH value to 2.5-3.5, place the passivation solution at the oiling process position in the cold rolling production line, and spray it onto the surface of the cold-rolled steel plate in the form of spraying. Use the residual temperature of the cold-rolled steel plate surface to make the passivation solution react with the steel plate surface to form a passivation film.

[0007] The passivation treatments before coating generally include the chromate method, the titanium / zirconium method, and the rare earth conversion method. The titanium / zirconium method is a chromium-free conversion technology that is currently being applied in industry. For example, WO2009 / 115504 discloses the conversion agent composition for various application scenarios.

[0008] However, for conventional chemical treatment of the surface of cold-rolled strip, the formation of its passivation film or conversion film requires a considerable reaction time. The process requires heating to promote the formation of the conversion film, and water treatment may be required after the film is formed. On the other hand, the continuous annealing and coating production lines of mainstream silicon steel production plants generally have a high plate speed of 80 to 200 meters per minute. The number of equipment and operating space of the units after annealing and before coating are very limited, resulting in the effective formation time of the conversion film on the strip surface being generally a few seconds to more than ten seconds. Moreover, there is no condition for rinsing and other water treatment after the conversion film is formed. Therefore, the above-mentioned chemical treatment methods for the surface of cold-rolled strip cannot be used for passivation or conversion treatment of silicon steel surfaces after annealing and before coating.

[0009] Furthermore, the main purpose of applying conversion coatings to cold-rolled steel strip is to enhance rust / corrosion resistance and adhesion. However, for water-soluble, environmentally friendly coatings on silicon steel, the focus is on the coating's scratch resistance, punching and shearing properties, and heat resistance.

[0010] Summary of the Invention

[0011] One of the purposes of the present invention is to provide a conversion liquid for forming a conversion film on the surface of non-oriented silicon steel. After the silicon steel substrate has undergone the last annealing process, the conversion liquid is applied to the surface of the silicon steel substrate to form a conversion film on the surface of the silicon steel substrate. Subsequently, an insulating coating is applied to the surface of the conversion film to form a finished non-oriented silicon steel sheet. The function of the conversion film is to additionally impart or enhance the scratch resistance, punching and shearing processability, salt spray corrosion resistance, and heat resistance of the surface coating of the silicon steel sheet, so as to improve the comprehensive performance of the finished non-oriented silicon steel sheet with a thicker coating. The conversion film of the present invention can be quickly generated at room temperature and does not require subsequent water treatment steps such as rinsing, and the production process is simple and fast.

[0012] In order to achieve the above object, the present invention provides a conversion liquid for forming a conversion film on the surface of non-oriented silicon steel. The conversion liquid is acidic and has a solid content of 10 to 30 wt %. The solid content comprises:

[0013] The inorganic conversion film component is selected from at least one of titanium, zirconium, hafnium and silicon fluorides, and its mass percentage in the conversion liquid is 1 to 10 wt%;

[0014] The water-based organic resin has a mass percentage content of 0 to 20 wt % in the conversion liquid.

[0015] The present invention controls the solid content and composition of the conversion liquid, preferably in combination with subsequent optimization of a specific conversion film forming method, to achieve control of the conversion film.

[0016] Within the solids content range defined in this invention, higher solids content in the conversion solution results in a more voluminous, continuous, and dense conversion coating, which is more conducive to improving the subsequent properties of the insulation coating. However, increased conversion solution consumption increases the difficulty in controlling the quality and stability of the conversion coating, narrowing the control window for the conversion process.

[0017] In the present invention, the liquid component in the conversion liquid is water.

[0018] In the conversion solution described herein, the inorganic conversion coating component is selected from at least one of titanium, zirconium, hafnium, and silicon fluorides, for example, one or more of fluorozirconic acid, fluorotitanic acid, fluorohafnic acid, and fluorosilicic acid. The inorganic conversion coating component rapidly forms a relatively continuous conversion coating layer while corroding the silicon steel surface. The content of the inorganic conversion coating component directly determines the speed and quality of the conversion coating. If the content exceeds the upper limit specified herein, the uniformity and density of the conversion coating will be degraded, increasing its cost. Furthermore, high concentrations of fluorides can complicate wastewater treatment.

[0019] Considering that the surface conversion film formed by the present invention is primarily composed of an inorganic component system and the film-forming process is rapid, the conversion film may exhibit local discontinuities, cracks, micropores, and other phenomena. Therefore, the conversion liquid described in the present invention preferably utilizes an aqueous organic resin with excellent compatibility and stability as the film-forming agent, rather than a water-dispersible emulsion, to enhance the interfacial adhesion of the inorganic conversion film, improve the surface quality of the conversion film, and contribute to the continuity and density of the conversion film. However, if the content of the aqueous organic resin exceeds the upper limit specified in the present invention, the stability of the water-soluble aqueous organic resin in the acidic conversion liquid will deteriorate, and the functionality of the inorganic conversion film will also be weakened.

[0020] The pH of the conversion solution described herein is preferably between 2 and 4. A low pH indicates a high solids content or concentration in the conversion solution, which can lead to significant quality fluctuations between conversion film batches, high conversion solution consumption, and container corrosion. A high pH indicates insufficient active ingredient content in the conversion solution, resulting in reduced conversion film production and rapid deterioration of the conversion solution.

[0021] Preferably, in the conversion liquid of the present invention, the inorganic conversion film component contains at least titanium fluoride and / or zirconium fluoride.

[0022] In the present invention, titanium fluoride is a preferred component due to its high reactivity at the interface with the silicon steel substrate and rapid conversion film formation. Alternatively, zirconium fluoride can be used. Furthermore, the use of both titanium fluoride and zirconium fluoride is also preferred.

[0023] Preferably, the solid content of the conversion solution of the present invention consists of the following:

[0024] The inorganic conversion film component is selected from at least one of titanium, zirconium, hafnium and silicon fluorides, and its mass percentage in the conversion liquid is 1 to 10 wt%;

[0025] The water-based organic resin has a mass percentage content of 0 to 20 wt % in the conversion liquid.

[0026] Preferably, in the conversion liquid of the present invention, the solid content is 15-20 wt%.

[0027] Preferably, in the conversion liquid of the present invention, the aqueous organic resin is selected from: a water-soluble phenolic resin, a water-soluble polyester resin, and a water-soluble polyurethane resin.

[0028] Preferably, in the conversion liquid of the present invention, the solid content further comprises additives, and the additives comprise phosphates and / or silicon-based additives.

[0029] More preferably, the mass percentage of the additive in the conversion liquid is 2 to 15 wt %.

[0030] In preferred embodiments, the additive can accelerate the formation of the surface conversion film, improve the continuity and density of the surface conversion film, and stabilize the composition of the conversion solution. However, its content should be limited. Additive content exceeding the upper limit of the present invention may cause the conversion film to become loose or locally enriched, which may be detrimental to the heat resistance and punching and shearing performance of the finished non-oriented silicon steel sheet coating.

[0031] More preferably, in some embodiments, the phosphate is selected from at least one of the phosphates of Mn, Fe, and Co. The phosphates of Mn, Fe, and Co have a certain conversion effect on the metal surface.

[0032] Preferably, in the conversion liquid of the present invention, the silicon-based auxiliary agent is selected from nano-scale SiO2 sol and / or silane coupling agent.

[0033] As mentioned above, the phosphates of Mn, Fe, and Co themselves have a certain conversion effect on the metal surface. When used in combination with a silane coupling agent, the conversion film formed after hybridization with the Ti / Zr-containing compound has a higher density and a more continuous film layer.

[0034] In some embodiments, when nano-sized SiO 2 sol is used, the film forming speed can be accelerated by utilizing the characteristic of the silica sol that it quickly penetrates the substrate.

[0035] The present invention further provides a non-oriented silicon steel, comprising a non-oriented silicon steel substrate and a conversion film located on the surface of the silicon steel substrate, wherein the conversion film is formed by the conversion liquid described above.

[0036] Preferably, the content of Ti and Zr elements (Ti+Zr) in the conversion film is controlled to be 1-800 mg / m 2 .

[0037] Preferably, the silicon steel substrate contains, in addition to Fe and unavoidable impurities, the following elements in mass percentage: Si: 1.0-3.3 wt% and Al: 0.2-0.8 wt%.

[0038] Preferably, in the non-oriented silicon steel of the present invention:

[0039] When 0.2wt%≤(Si+Al)<3.0wt% in non-oriented silicon steel substrate, the Ti+Zr content in the conversion film is 80~800mg / m 2 ;

[0040] When 3.0wt%≤(Si+Al)≤4.5wt% in the non-oriented silicon steel substrate, the Ti+Zr content in the conversion film is 1~100mg / m 2 .

[0041] More preferably, when 0.2wt%≤(Si+Al)<3.0wt% in the non-oriented silicon steel substrate, the Ti+Zr content in the conversion film is 100-500mg / m 2 .

[0042] More preferably, when the Si+Al content in the non-oriented silicon steel substrate is 3.0-4.5 wt%, the Ti+Zr content in the conversion film is 3-50 mg / m 2 .

[0043] The element symbols in the above expressions represent the mass percentage of the corresponding elements in the silicon steel substrate or conversion film.

[0044] Another object of the present invention is to provide a method for forming a conversion coating on the surface of non-oriented silicon steel. After the silicon steel substrate undergoes the final annealing step and before the insulation coating step, the aforementioned conversion solution is applied to the surface of the silicon steel substrate to form a conversion coating. This method ensures the primary properties of the silicon steel insulation coating while also enhancing or strengthening the silicon steel coating's scratch resistance, punching and shearing properties, salt spray corrosion resistance, and heat resistance, thereby improving the overall performance of silicon steel products with thicker coatings. This surface conversion coating can be rapidly formed at room temperature and eliminates the need for subsequent water treatment steps such as rinsing, making the production process simple and fast.

[0045] In order to achieve the above object, the present invention proposes a method for forming a conversion coating on the surface of non-oriented silicon steel, which comprises the following steps performed in sequence:

[0046] Immersing: Immerse the silicon steel substrate in the conversion solution for 2 to 15 seconds at a temperature of 5 to 40°C.

[0047] Drying and curing: Drying and curing the silicon steel substrate to form a conversion film on the surface of the silicon steel substrate;

[0048] Preferably, an insulating coating is applied on the surface of the conversion film to obtain a finished non-oriented silicon steel sheet;

[0049] Preferably, the surface of the silicon steel substrate is cleaned before the immersion step.

[0050] The immersion temperature mentioned in the present invention refers to the temperature of the conversion liquid.

[0051] The method described herein primarily controls and optimizes the composition and content of the solids in the conversion solution, as well as the immersion time and temperature, to achieve controllable conversion coating formation on the surface of finished non-oriented silicon steel sheets. The conversion solution described herein, combined with the immersion time and temperature process parameters, ensures the formation of a quality-controlled conversion coating on silicon steel substrates.

[0052] Preferably, in the above-mentioned immersion step, the immersion time is 3 to 8 seconds; and / or the immersion temperature is 15 to 30°C. Preferably, in the method of the present invention, the conversion liquid is placed in a conversion tank, at least one pair of squeeze rollers is provided at the inlet of the conversion tank to squeeze out residual water on the surface of the silicon steel substrate, and at least two pairs of squeeze rollers are provided at the outlet of the conversion tank to squeeze out the silicon steel substrate immersed in the conversion liquid.

[0053] Two or more pairs of squeezing rollers are set at the outlet of the conversion tank. In addition to preventing the conversion liquid from being carried out of the conversion tank with the silicon steel plate and causing pollution, the thickness of the conversion film on the surface of the silicon steel substrate can be controlled by adjusting the pressure to avoid spots caused by uneven formation of the conversion film.

[0054] Preferably, in the method of the present invention, the content of Ti+Zr in the conversion film is controlled to be 1-800 mg / m 2 .

[0055] Controlling the Ti+Zr content in the conversion film within the above range can ensure the quality of the subsequent insulation coating.

[0056] However, the inventors have found through research that the control of the Ti+Zr content in the conversion film is related to the composition of the substrate. Therefore:

[0057] In some embodiments, when 0.2wt%≤(Si+Al)<3.0wt% in the non-oriented silicon steel substrate, the content of Ti+Zr in the conversion film is controlled to be 80-800mg / m 2 ; Further preferably, the content of Ti+Zr in the conversion film is controlled to be 100-500 mg / m 2 .

[0058] In other embodiments, when the non-oriented silicon steel substrate has a content of 3.0 wt% ≤ (Si + Al) ≤ 4.5 wt%, the content of Ti + Zr in the conversion film is controlled to be 1 to 100 mg / m 2 It is further preferred to control the content of Ti+Zr in the conversion film to 3-50 mg / m 2 .

[0059] This is because non-oriented silicon steel with a total Si+Al content of 3.0-4.5wt% in the substrate is generally high-grade silicon steel, and there is an enrichment of Al and / or Si oxides on its surface. Even if the thickness of the oxide film is relatively small, compared with low-grade silicon steel substrates with a total Si+Al content of 0.2-less than 3.0wt%, the inorganic non-metallic oxide on the substrate surface modifies the microscopic morphology of the substrate surface, significantly reducing the surface energy of the substrate interface. The contact with the coating is more covalent rather than metallic, which is beneficial to improving the overall performance of the coating. Therefore, the amount of Ti+Zr in the conversion film required for this type of substrate is relatively small. In actual applications, it has been found that for non-oriented high-grade silicon steel, even if the amount of conversion film generated is small, some properties of the final coating can be improved. Therefore, the conversion film of the present invention plays a transitional role, the purpose of which is to ensure that the coating subsequently coated on the conversion film has excellent performance.

[0060] However, low-grade silicon steel has little or no oxide formed on the surface of the silicon steel substrate, so it must rely on the conversion film to play its role as an interface layer. Therefore, the Ti+Zr content in the conversion film must be significantly increased so that the subsequent coating applied on the conversion film can have better performance.

[0061] Preferably, in the method of the present invention, in the drying and curing step, a hot air drying oven can be used for drying. The peak metal temperature (PMT, indicating the peak surface temperature of the steel plate) at the outlet of the hot air drying oven is controlled to be 50-85°C, and the dew point DP of the air in the hot air drying oven is less than 40°C. The lower limit of the air volume per square meter of each surface of the substrate is 300m 3 / h, the upper limit of the preferred air volume is 500m 3 / h.

[0062] Preferably, in the method of the present invention, the surface of the silicon steel substrate is cleaned before the immersion step.

[0063] One of the purposes of surface cleaning is to clean away pollutants such as dust adhering to the surface of the silicon steel substrate in the annealing furnace. Another purpose is to cool the silicon steel substrate in preparation for subsequent surface conversion treatment.

[0064] The surface cleaning method can be one or more of cooling water immersion, spraying, brushing with a brush roller, and electrolytic cleaning. Preferably, at least one pair of squeeze rollers are provided at the outlet of the cleaning tank to squeeze out any residual water from the surface of the cleaned silicon steel substrate. More preferably, a ventilation and drying device is also provided at the outlet of the cleaning tank.

[0065] In some embodiments, the surface temperature of the silicon steel substrate after cleaning is preferably controlled to be 10-35°C. More preferably, the surface cleanliness of the silicon steel substrate is level 2 or better (referring to ISO 8502-3 standard, pressure-sensitive tape method), or the total amount of residue on the surface of the silicon steel substrate is ≤100 mg / m2 (Refer to the method for determining the residue on the surface of cold-rolled sheet disclosed in CN102226767A.) Before the immersion step, there is no water stain on the surface of the silicon steel substrate that is clearly visible to the naked eye.

[0066] If the silicon steel substrate meets the above conditions, the impregnation step can be performed. If the silicon steel substrate production unit has a high degree of cleanliness, the surface cleaning step of the obtained silicon steel substrate can also be omitted.

[0067] After the above treatment, a conversion film is formed on the surface of the silicon steel substrate, and then an insulating coating is coated on the conversion film to obtain a finished non-oriented silicon steel sheet.

[0068] The insulating coating formed on the surface of the conversion film of the present invention may be a C-5 (referring to ASTM A976) or EC-5 (referring to IEC 60404-1-1), or a C-6 (referring to ASTM A976) or EC-6 (referring to IEC 60404-1-1) coating.

[0069] The C-5 or C-6 insulating coating formed on the conversion coating of the C-4 category (refer to C-4 of ASTM A976 or EC-4 of IEC 60404-1-1) can have a single-sided dry film thickness of 0.3 to 7 μm, and the metal peak temperature range for baking and curing is preferably 240 to 300°C.

[0070] The conversion liquid and method for forming a conversion film on the surface of non-oriented silicon steel according to the present invention have the following advantages and beneficial effects:

[0071] Although the present invention adds a process to form a conversion film on the surface of the silicon steel substrate after annealing and before applying the insulating coating, it has no effect on the coating process and the baking and curing process of the insulating coating.

[0072] The conversion liquid of the present invention is environmentally friendly and is a water-based, wash-free, short-process, green and environmentally friendly liquid for forming a conversion film on a metal surface.

[0073] By adopting the solution of the present invention, a conversion film can be quickly formed on the surface of a non-oriented silicon steel substrate at room temperature. The film formation time is usually less than 10 seconds, and no additional water treatment processes such as cleaning or rinsing are required. The production process is simple and convenient.

[0074] The insulating coating formed on the conversion film of the present invention has enhanced rust / corrosion resistance, adhesion and other properties, and the overall scratch resistance, punching and shearing processability and heat resistance of the substrate surface coating are also improved, showing improved comprehensive performance. DETAILED DESCRIPTION

[0075] The conversion solution and method for forming a conversion film on the surface of non-oriented silicon steel according to the present invention will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an undue limitation to the technical solution of the present invention.

[0076] Examples 1-11 and Comparative Examples 1-4

[0077] The conversion coatings of Examples 1-11 were obtained using the following steps:

[0078] (1) Silicon steel materials of grades B50A290 (the sum of Si+Al element content is 3.8 wt%) and B50A800 (the sum of Si+Al element content is 1.3 wt%) were selected as substrates.

[0079] (2) After the final annealing process, the substrate surface is sprayed with industrial pure water and scrubbed with a brush roller. A pair of squeeze rollers are set at the outlet of the cleaning tank. The substrate temperature at the outlet is about 25°C, and the surface cleanliness is level 1 (referring to ISO 8502-3 standard, pressure-sensitive tape method), with no obvious visible water stains on the surface.

[0080] (3) The cleaned substrate enters a conversion tank containing conversion liquid for surface immersion treatment. A pair of squeeze rollers are set at the entrance of the conversion tank, and two pairs of squeeze rollers are set at the exit of the conversion tank. The pressure between each pair of squeeze rollers is 3 to 4 kg.

[0081] Comparative Examples 1 and 2 employed steps substantially similar to those of the above embodiment, except that the solid content in the conversion liquid of Comparative Example 1 did not meet the requirements of the present invention, and the conversion liquid of Comparative Example 2 did not contain an inorganic conversion film component.

[0082] Comparative Examples 3 and 4 used treatment steps completely different from those of the embodiment of the present invention, wherein the silicon steel substrate was not immersed in the conversion solution of the present invention, but was immersed in phosphoric acid for phosphating pretreatment.

[0083] Table 1 lists the solid components of the conversion liquid of each embodiment and comparative example and the mass percentage of the corresponding components.

[0084] Table 1.

[0085] Table 2 lists the specific process parameters of the surface impregnation treatment of each embodiment and comparative example.

[0086] Table 2.

[0087] After the surface impregnation treatment is completed, the conversion liquid in the conversion tank can be recovered and centrally treated for wastewater. The wastewater can be diluted 20-50 times with water, and then calcium hydroxide is added to achieve a pH of ≥12. After thorough mixing and standing, the precipitate is centrally treated and the remaining wastewater is discharged. The discharged wastewater meets the following requirements: fluoride ion concentration <20mg / L, phosphorus ion concentration <10mg / L, and chemical oxygen demand (COD) <500mg / L.

[0088] (4) After the silicon steel substrate is immersed in the conversion tank to form a wet conversion film layer on its surface, it enters the hot air drying oven for drying and curing to form a conversion film on the substrate surface. In a specific example, the air dew point DP in the drying oven is 20°C, and the drying oven air volume per square meter of each surface of the substrate is 450m 3 / h, the peak temperature PMT of the steel plate surface at the outlet is 70~75℃.

[0089] Table 2 also lists the contents of Ti and Zr elements in the conversion films formed in various examples and comparative examples. The contents of Ti and Zr elements were measured using X-ray fluorescence analysis (XRF).

[0090] In some embodiments of the present invention, after forming a conversion coating on the surface of a silicon steel substrate, an insulating coating, such as a C-6 insulating coating (referring to ASTM A976), is preferably applied to the surface of the conversion coating. The insulating coating may have a dry film thickness of 4.5 ± 1.2 μm on a single side, and the peak temperature of the steel plate surface during baking and curing is 260-280°C to obtain a finished non-oriented silicon steel plate.

[0091] The finished non-oriented silicon steel sheets (including the substrate and the coating on its surface) of Examples 1-11 and Comparative Examples 1-4 were sampled and the following coating performance tests were performed on the samples. The test results are listed in Table 3.

[0092] (1) Bending adhesion: According to GB / T 2522 standard, the bending adhesion is evaluated using four grades: "excellent" (grade A), "good" (grade B), "medium" (grade C) and "poor" (grade D).

[0093] (2) Scratch resistance: Use a one-yuan coin with no edge wear, hold the coin at an angle of about 45 degrees to the sample, apply a force of 1 kg, move the coin at a speed of 1 cm / s perpendicular to the rolling direction of the steel plate, and move a distance of 2 cm. Scratch the coin five times in parallel within the selected test area. The scratch resistance of the finished non-oriented silicon steel sheet is evaluated based on the number of scratches on the visible substrate. The evaluation adopts four grades: "excellent" (number of scratches is 0), "good" (number of scratches is 1-2), "fair" (number of scratches is 3), and "poor" (number of scratches is 4-5).

[0094] (3) Punching and shearing processability: Punch or shear the finished non-oriented silicon steel sheet, and observe the shedding of the coating on the steel sheet surface within 1 mm of the edge under the same conditions to evaluate the punching and shearing processability of the coating. The punching and shearing processability is evaluated using four levels: "Excellent" (cumulative shedding area within 1 mm of the edge <25%), "Good" (25% ≤ cumulative shedding area within 1 mm of the edge <50%), "Fair" (50% ≤ cumulative shedding area within 1 mm of the edge <75%), and "Poor" (cumulative shedding area within 1 mm of the edge ≥75%).

[0095] (4) Salt spray corrosion resistance: Salt spray corrosion resistance is tested using the 7-hour neutral salt spray (NSS) test method (refer to GB / T 6458-1986). Four grades are used to evaluate salt spray corrosion resistance: "Excellent" (sample corrosion area <10%), "Good" (10% ≤ sample corrosion area <20%), "Fair" (20% ≤ sample corrosion area <40%), and "Poor" (sample corrosion area ≥40%).

[0096] (5) Heat resistance: The sample was heated to 180°C for 48 hours, then cooled and immersed in pure water for 24 hours. Changes such as blistering, wrinkling, and substrate rust on the coating surface were observed to evaluate the density of the coating after heat resistance. The heat resistance was evaluated on a four-grade scale: "Excellent" (no change in the coating on the steel plate surface), "Good" (the area of ​​the coating on the steel plate surface with changes accounts for <5% of the total area), "Medium" (5% ≤ the area of ​​the coating on the steel plate surface with changes accounts for <10% of the total area), and "Poor" (the area of ​​the coating on the steel plate surface with changes accounts for ≥10% of the total area).

[0097] Table 3 lists the coating properties of the finished non-oriented silicon steel sheets of Examples 1-11 and Comparative Examples 1-4.

[0098] Table 3. Note: In Table 3, ◎ represents “excellent”; ○ represents “good”; △ represents “fair”; and × represents “poor”.

[0099] It can be seen from Table 3 that the coatings of the finished non-oriented silicon steel sheets of Examples 1-11 of the present invention have excellent bending adhesion, scratch resistance, punching and shearing workability, heat resistance and corrosion resistance.

[0100] However, in Comparative Example 1, since the solid content of the conversion liquid is lower than the lower limit defined in the present invention, the coating performance is poor.

[0101] Comparative Example 2 does not contain an inorganic conversion film component, which also results in poor coating performance.

[0102] In Comparative Examples 3 and 4, no conversion film and insulating coating are formed on the surface of the silicon steel substrate, and phosphoric acid is used to pre-treat the substrate for phosphating, which is completely different from the technical solution of the present invention. Therefore, the scratch resistance, punching and shearing processability, heat resistance and corrosion resistance of the coating are not good.

[0103] It should be noted that the combination of the various technical features in this case is not limited to the combination described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0104] It should also be noted that the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with by those skilled in the art from the contents disclosed in the present invention, and should all fall within the scope of protection of the present invention.

Claims

1. A conversion liquid for forming a conversion film on the surface of non-oriented silicon steel, characterized in that: The conversion liquid is acidic and has a solid content of 10 to 30 wt %. The solid content comprises: The inorganic conversion film component is selected from at least one of titanium, zirconium, hafnium and silicon fluorides, and its mass percentage in the conversion liquid is 1 to 10 wt%; The water-based organic resin has a mass percentage of 0 to 20 wt % in the conversion liquid.

2. The conversion solution according to claim 1, characterized in that The solid content of the conversion solution consists of the following: The inorganic conversion film component is selected from at least one of titanium, zirconium, hafnium and silicon fluorides, and its mass percentage in the conversion liquid is 1 to 10 wt%; The water-based organic resin has a mass percentage of 0 to 20 wt % in the conversion liquid.

3. The conversion solution according to claim 1 or 2, characterized in that: The inorganic conversion film component at least includes: titanium fluoride and / or zirconium fluoride.

4. The conversion solution according to claim 1 or 2, characterized in that: The solid content of the conversion liquid is 15-20wt%; and / or the pH value of the conversion liquid is 2-4.

5. The conversion solution according to claim 1 or 2, characterized in that: The water-based organic resin is selected from one of water-soluble phenolic resin, water-soluble polyester resin and water-soluble polyurethane resin.

6. The conversion solution according to claim 1 or 2, characterized in that: The solid content further comprises additives, and the additives include: phosphate and / or silicon-based additives.

7. The conversion solution according to claim 6, characterized in that The phosphate is selected from at least one of the phosphates of Mn, Fe and Co.

8. The conversion solution according to claim 6, characterized in that The silicon-based auxiliary agent is selected from nano-scale SiO2 sol and / or silane coupling agent.

9. The conversion solution according to claim 6, characterized in that The mass percentage of the additive in the conversion liquid is 2-15wt%.

10. A non-oriented silicon steel, comprising a silicon steel substrate and a conversion film located on the surface of the silicon steel substrate, characterized in that: The conversion film is formed by the conversion liquid according to any one of claims 1 to 9.

11. The non-oriented silicon steel according to claim 10, characterized in that: The content of Ti+Zr in the conversion film is 1-800 mg / m 2 ; and / or the silicon steel substrate contains, in addition to Fe and inevitable impurities, the following elements in mass percentage: Si: 1.0 to 3.3 wt% and Al: 0.2 to 0.8 wt%.

12. The non-oriented silicon steel according to claim 11, characterized in that: When 0.2wt%≤(Si+Al)<3.0wt% in the silicon steel substrate, the content of Ti+Zr in the conversion film is 80-800mg / m 2 ; When 3.0wt%≤(Si+Al)≤4.5wt% in the silicon steel substrate, the content of Ti+Zr in the conversion film is 1-100mg / m 2 .

13. The non-oriented silicon steel according to claim 12, characterized in that: When 0.2wt%≤(Si+Al)<3.0wt% in the silicon steel substrate, the content of Ti+Zr in the conversion film is 100-500mg / m 2 .

14. The non-oriented silicon steel according to claim 12, characterized in that: When the content of Si+Al in the silicon steel substrate is 3.0-4.5wt%, the content of Ti+Zr in the conversion film is 3-50mg / m 2 .

15. A method for forming a conversion film on the surface of a silicon steel substrate, characterized in that: The method comprises the following steps performed in sequence: Immersing: Immersing the silicon steel substrate in the conversion solution according to any one of claims 1 to 9, wherein the immersion time is 2 to 15 seconds and the immersion temperature is 5 to 40° C.; Drying and curing: drying and curing the silicon steel substrate to form a conversion film on the surface of the silicon steel substrate; Preferably, an insulating coating is coated on the surface of the conversion film to obtain a finished non-oriented silicon steel sheet; preferably, the surface of the silicon steel substrate is cleaned before the immersion step.

16. The method according to claim 15, characterized in that The immersion time is 3 to 8 seconds; and / or the immersion temperature is 15 to 30°C.

17. The method according to claim 15, characterized in that In the impregnation step, the conversion liquid is placed in a conversion tank, at least one pair of squeezing rollers is arranged at the inlet of the conversion tank to squeeze out residual water on the surface of the silicon steel substrate, and at least two pairs of squeezing rollers are arranged at the outlet of the conversion tank to squeeze out the silicon steel substrate impregnated with the conversion liquid.

18. The method according to any one of claims 15 to 17, characterized in that The content of Ti+Zr in the conversion film is 1-800 mg / m 2 ; and / or the silicon steel substrate contains, in addition to Fe and inevitable impurities, the following elements in mass percentage: Si: 1.0 to 3.3 wt% and Al: 0.2 to 0.8 wt%.

19. The method of claim 18, wherein: When 0.2wt%≤(Si+Al)<3.0wt% in the silicon steel substrate, the content of Ti+Zr in the conversion film is 80-800mg / m 2 , preferably 100 to 500 mg / m 2 ; When 3.0wt%≤(Si+Al)≤4.5wt% in the silicon steel substrate, the content of Ti+Zr in the conversion film is 1-100mg / m 2 , preferably 3 to 50 mg / m 2 .

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