A conversion solution and process for forming a surface conversion film on non-oriented silicon steel

Abstract

The application discloses a conversion liquid for forming a surface conversion film of non-oriented silicon steel, the conversion liquid is acidic, the solid content of the conversion liquid is 10-30wt%, and the solid content includes: inorganic conversion film components, which are at least one of fluorides of titanium, zirconium, hafnium and silicon, and the mass percentage of the inorganic conversion film components in the conversion liquid is 1-10wt%; and aqueous organic resin, the mass percentage of the aqueous organic resin in the conversion liquid is 0-20wt%. Correspondingly, the application also discloses a process for forming a surface conversion film of non-oriented silicon steel, which is characterized in that: before an insulating coating process, the non-oriented silicon steel substrate is subjected to surface immersion treatment by using the conversion liquid according to the application; the immersion time is 2-15s, the immersion temperature is 5-40 DEG C; and the surface conversion film is formed by drying and curing.

Description

Technical Field

[0001] This invention relates to a coating liquid, a steel plate, and a method for manufacturing the same, and more particularly to a coating liquid for non-oriented silicon steel, a non-oriented silicon steel plate, and a method for manufacturing the same. Background Technology

[0002] Electrical steel is a core material widely used in motors and transformers. To reduce short circuits between layers of electrical steel sheets and thus increase eddy current losses, an insulating coating needs to be applied to its surface.

[0003] For thick coatings with a dry film thickness of more than 2μm, the presence of a considerable amount of inorganic fillers in the coating can easily lead to poor film formation performance of the organic-inorganic mixed amorphous coating formed after baking and curing on polar metal substrates with high surface tension.

[0004] Furthermore, for water-soluble silicon steel insulating thick coatings, these coatings require high surface insulation, heat resistance, and hot-press stability. Their formulations typically contain a significant amount of submicron-sized inorganic fillers, with a typical content of approximately 30–70 wt% in the dry film. Applying such thick coatings to steel plates is difficult to produce, easily leading to coating defects and poor film quality. This manifests as poor coating adhesion, powdering and bright spots, poor scratch resistance, and coating peeling or cracking at edges during stamping and shearing, severely degrading the performance characteristics of the coated product.

[0005] Therefore, in order to improve the corrosion resistance and adhesion of metal surface coatings, appropriate passivation treatment of the metal substrate is performed before coating to form an interface conversion film to enhance coating performance, which is a method already adopted in the prior art. For example, Chinese patent document with publication number CN104250754A, publication date December 31, 2014, entitled "A Passivation Process for Cold-Rolled Steel Sheet Surface", discloses such a process. The passivation solution is composed of the following components by weight percentage: sodium hydroxide 0.8-1.2%, sodium carbonate 1.4-1.8%, sodium tripolyphosphate 1.5-2.5%, anhydrous sodium metasilicate 2-4%, phytic acid 3-5%, sodium bicarbonate 2.5-3.5%, sodium benzoate 4-6%, triethanolamine 5-7%, polyethylene glycol 3.5-4.5%, sodium dodecyl sulfonate 0.5-1.5%, silicone defoamer 0.1-0.3%, and the balance being 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 it in the oiling process position of the cold rolling production line, and spray it onto the surface of the cold-rolled steel plate. The residual heat of the cold-rolled steel plate surface allows the passivation solution to react with the steel plate surface to generate a passivation film.

[0006] Passivation treatment before coating generally includes chromate method, titanium / zirconium method and rare earth conversion method. Among them, titanium / zirconium method is the chromium-free conversion technology that is currently being used in industrial applications. For example, WO2009 / 115504 discloses the composition of conversion agents for various applications.

[0007] However, for conventional chemical treatment of cold-rolled strip steel surfaces, the formation of passivation or conversion films requires a considerable reaction time. The process necessitates heating to promote film formation, and water treatment may be required after film formation. On the other hand, the continuous annealing and coating production lines of mainstream silicon steel manufacturers typically have high throughput speeds of 80–200 meters per minute. The process equipment and space available in the unit layout after annealing and before coating are very limited. This determines that the effective formation time of the conversion film on the strip steel surface is generally only a few seconds to tens of seconds. Furthermore, there are no conditions for rinsing or other water treatments after the conversion film is formed. Therefore, the aforementioned chemical treatment methods for cold-rolled strip steel surfaces cannot be used for passivation or conversion treatment of silicon steel surfaces after annealing and before coating.

[0008] In addition, the main purpose of the surface conversion coating of general cold-rolled strip steel is to enhance rust / corrosion resistance and adhesion, but for water-soluble environmentally friendly coatings of silicon steel, the focus is more on the coating's scratch resistance, punching and shearing processability and heat resistance. Summary of the Invention

[0009] One objective of this invention is to provide a conversion solution for forming a surface conversion film on non-oriented silicon steel. This solution is applied to silicon steel coils after the final annealing process but before the insulating coating process to form a surface conversion film. Its function is to additionally impart or enhance the scratch resistance, punching and shearing properties, salt spray resistance, and heat resistance of the silicon steel coating, while ensuring the main properties of the insulating coating, thereby significantly improving the performance satisfaction of thicker silicon steel coating products. This surface conversion film can be rapidly formed at room temperature without the need for subsequent rinsing or other water treatment processes, thus simplifying and accelerating the production process.

[0010] To achieve the above objectives, this invention provides a conversion solution for forming a conversion film on the surface of non-oriented silicon steel. This conversion solution is acidic and has a solids content of 10–30 wt%, comprising:

[0011] The inorganic conversion membrane component is selected from at least one of titanium, zirconium, hafnium, and silicon fluorides, and its mass percentage in the conversion solution is 1 to 10 wt%.

[0012] Aqueous organic resin, comprising 0–20 wt% of the conversion solution.

[0013] This invention controls the amount of conversion film by controlling the solid content and composition of the conversion solution, combined with the combination and optimization of subsequent specific conversion processes.

[0014] Within the solid content range defined by this invention, the higher the solid content of the conversion solution, the more conversion films can be formed, and the more continuous and dense they are, which is more conducive to improving the performance of subsequent coatings. However, at the same time, the more conversion solution is consumed, the more difficult it is to control the quality stability of the conversion film, and the narrower the control window of the conversion process.

[0015] In the conversion solution described in this invention, the inorganic conversion film component is selected from at least one of titanium, zirconium, hafnium, and silicon fluorides, such as one or more substances selected from fluorozirconic acid, fluorotitanic acid, fluorohafnium acid, and fluorosilicic acid. While corroding the silicon steel surface, it can rapidly form a relatively continuous conversion film layer. The content of the inorganic conversion film component directly determines the formation rate and quality of the conversion film. If the content exceeds the upper limit of this invention, the uniformity and density of the conversion film will deteriorate, increasing the cost of use, and high-concentration fluoride treatment will make wastewater treatment more difficult.

[0016] Considering that the surface conversion film formed by this invention is mainly an inorganic system and the film formation process is rapid, the conversion film may exhibit local discontinuities, cracks, micropores, etc. Therefore, the conversion solution described in this invention uses a water-based organic resin with excellent compatibility and stability as the film-forming agent, instead of a water-dispersible emulsion. This enhances the interfacial adhesion between the inorganic conversion film and the silicon steel coating, thereby improving the surface quality of the formed conversion film and contributing to the continuity and density of the conversion film formation. However, its content exceeds the upper limit of this invention. The stability of the water-soluble water-based organic resin in the acidic conversion solution deteriorates, and it may also mask and weaken the functionality of the inorganic conversion film.

[0017] The pH value of the conversion solution described in this invention can be between 2 and 4. pH value is a characterization of the composition of the conversion solution. A pH value that is too low indicates a high solid content or concentration in the conversion solution, which can easily cause large fluctuations in the quality of conversion films between different production batches, and also leads to high consumption of the conversion solution and easy corrosion of the tank. A pH value that is too high means insufficient effective content of the conversion solution, resulting in a reduced amount of conversion film formed and faster deterioration of the conversion solution.

[0018] Furthermore, in the conversion solution of the present invention, the inorganic conversion membrane component includes at least titanium fluoride and / or zirconium fluoride.

[0019] In this invention, titanium fluoride exhibits the highest reactivity at the interface with the silicon steel substrate, resulting in the fastest conversion film formation rate, and is therefore a preferred component. Additionally, zirconium fluoride is also preferably used. Furthermore, it is even more preferable to use a combination of titanium fluoride and zirconium fluoride.

[0020] Furthermore, in the conversion liquid described in this invention, its solid content comprises the following items:

[0021] The inorganic conversion membrane component is selected from at least one of titanium, zirconium, hafnium, and silicon fluorides, and its mass percentage in the conversion solution is 1 to 10 wt%.

[0022] Aqueous organic resin, comprising 0–20 wt% of the conversion solution.

[0023] Furthermore, in the conversion solution described in this invention, the solid content is 15-20 wt%.

[0024] Furthermore, in the conversion solution described in this invention, the aqueous organic resin is selected from one of water-soluble phenolic resin, polyester resin, and polyurethane resin.

[0025] Furthermore, in the conversion solution described in this invention, the solid component further includes additives, which include phosphates and / or silicon-based additives.

[0026] Furthermore, the additive accounts for 2-15% of the mass percentage of the conversion solution.

[0027] In a preferred embodiment, the additive can promote the formation rate of the surface conversion film, improve the continuity and density of the surface conversion film, and stabilize the composition system of the conversion solution. However, its content should not be too high. Additives exceeding the upper limit of the present invention may cause the conversion film to be loose or locally enriched, which is detrimental to the heat resistance and punching / shearing performance of the coating.

[0028] Furthermore, in some embodiments, the phosphate is selected from at least one of the phosphates of Mn, Fe, and Co.

[0029] In this embodiment, the phosphates of Mn, Fe, and Co play a certain transformation role on the metal surface.

[0030] Furthermore, in the conversion solution described in this invention, the silicon-based additive is selected from nanoscale SiO2 sol and / or silane coupling agents.

[0031] As mentioned above, phosphates of Mn, Fe, and Co themselves play a certain role in the conversion of metal surfaces. When used in conjunction with silane coupling agents, the conversion films formed after hybridization with Ti / Zr materials have higher density and more continuous film layers.

[0032] In some implementations, when nanoscale SiO2 sol is used, the rapid penetration of silica sol into the substrate can be utilized to accelerate film formation.

[0033] The present invention also provides a non-oriented silicon steel, wherein the surface of the non-oriented silicon steel substrate has a surface conversion film formed based on the conversion solution described above.

[0034] Furthermore, the Ti+Zr content in the surface conversion film is controlled to be 1–800 mg / m³. 2 .

[0035] Furthermore, in the non-oriented silicon steel described in this invention:

[0036] When the content of Ti+Zr in the surface conversion film is controlled to be 80–800 mg / m³, and the content of 0.2 wt% ≤ (Si+Al) < 3.0 wt% in the non-oriented silicon steel substrate is 0.2 wt% ≤ (Si+Al) < 3.0 wt%. 2 ;

[0037] When the content of Ti+Zr in the non-oriented silicon steel substrate is 3.0wt%≤(Si+Al)≤4.5wt%, the content of Ti+Zr in the surface conversion film should be controlled to be 1~100mg / m. 2 .

[0038] Furthermore, when the content of Ti+Zr in the non-oriented silicon steel substrate is 0.2wt% ≤ (Si+Al) < 3.0wt%, the content of Ti+Zr in the surface conversion film is controlled to be 100–500 mg / m². 2 .

[0039] Furthermore, when the Si+Al content in the non-oriented silicon steel substrate is 3.0–4.5 wt%, the Ti+Zr content in the surface conversion film is controlled to be 3–50 mg / m. 2 .

[0040] Another objective of this invention is to provide a process for forming a surface conversion film on non-oriented silicon steel. This process is performed after the final annealing step of the silicon steel coil and before the insulating coating step to form the surface conversion film. Its function is to additionally impart or enhance the scratch resistance, punching and shearing properties, salt spray resistance, and heat resistance of the silicon steel coating, while ensuring the main properties of the insulating coating, thereby significantly improving the performance satisfaction of thicker silicon steel coating products. This surface conversion film can be rapidly formed at room temperature without the need for subsequent rinsing or other water treatment processes, thus making the production process simple and quick.

[0041] To achieve the above objectives, the present invention proposes a process for forming a conversion film on the surface of non-oriented silicon steel, comprising the steps of: before the insulating coating process:

[0042] The surface of the non-oriented silicon steel substrate was impregnated using the conversion solution described above; the impregnation time was 2 to 15 seconds and the impregnation temperature was 5 to 40°C.

[0043] Dry and cure to form a surface conversion film.

[0044] The process described in this invention mainly achieves control over the amount of conversion film by controlling and optimizing the solid content and composition of the conversion solution, as well as the impregnation time and temperature. Using the conversion solution of this invention, along with the process parameters of impregnation time and temperature, ensures the formation of a surface conversion film with controllable quality.

[0045] Furthermore, in the process described in this invention, the impregnation time is 3 to 8 seconds; and / or the impregnation temperature is 15 to 30°C.

[0046] Furthermore, in the process described in this invention, the conversion liquid is placed in a conversion tank, at least one pair of squeeze rollers are provided at the inlet of the conversion tank, and at least two pairs of squeeze rollers are provided at the outlet of the conversion tank.

[0047] Two or more pairs of squeeze rollers are installed at the outlet of the conversion tank. In addition to preventing the conversion liquid from being carried out of the conversion tank with the strip and causing pollution, the pressure can also be adjusted to control the thickness of the conversion film and regulate the spots caused by uneven formation of the conversion film.

[0048] Furthermore, in the process described in this invention, the Ti+Zr content in the surface conversion film is controlled to be 1–800 mg / m³. 2 .

[0049] By controlling the Ti+Zr content in the surface conversion film within the above-mentioned range, the quality of the subsequent insulating coating can be guaranteed.

[0050] However, the inventors discovered through research that the Ti+Zr content in the surface conversion film is related to the composition of the substrate, therefore:

[0051] In some embodiments, when the content of Ti+Zr in the non-oriented silicon steel substrate is 0.2wt% ≤ (Si+Al) < 3.0wt%, the content of Ti+Zr in the surface conversion film is controlled to be 80–800 mg / m³. 2 Further preferably, the Ti+Zr content in the surface conversion film can be controlled to be 100–500 mg / m³. 2 .

[0052] In other embodiments, when the content of Ti+Zr in the non-oriented silicon steel substrate is 3.0 wt% ≤ (Si+Al) ≤ 4.5 wt%, the content of Ti+Zr in the surface conversion film is controlled to be 1–100 mg / m. 2 The Ti+Zr content in the surface conversion film can be further preferably controlled to be 3-50 mg / m³. 2 .

[0053] This is because non-oriented silicon steel with a total Si+Al content of 3.0–4.5 wt% in the substrate is generally a high-grade silicon steel. Its interface is enriched with Al and / or Si oxides. Even if the oxide film thickness is relatively low, compared to low-grade substrates with a total Si+Al content of 0.2–3.0 wt%, this inorganic non-metallic oxide film modifies the interface microstructure, significantly reducing the interface surface energy. The bonds in contact with the coating are more covalent than metallic, which is beneficial for improving the coating's related properties. Therefore, the amount of conversion film required is relatively small. In practical applications, it has been found that for non-oriented high-grade silicon steel, even a small amount of conversion film can improve some properties of the final coating. Therefore, this film layer is transitional, its purpose being to ensure the excellent performance of the final coating on top of the conversion film.

[0054] Low-grade silicon steel has little or no interfacial oxide formation, so it must rely on conversion film to play the role of the interfacial layer. Therefore, it is necessary to significantly increase the (Ti+Zr) content in the conversion film in order to achieve better final coating performance.

[0055] Furthermore, in the process described in this invention, a hot air drying oven can be used for drying in the drying and curing step. The peak temperature of the steel plate metal at the outlet of the hot air drying oven is controlled to be 50-85℃, the air dew point (DP) inside the hot air drying oven is <40℃, and the airflow from the drying oven to each surface of each square meter of steel strip is ≥300m³. 3 / h.

[0056] Furthermore, in the process described in this invention, surface cleaning is performed before the surface impregnation treatment step.

[0057] The purpose of surface cleaning is twofold: first, to remove floating dust and other contaminants adhering to the surface of the strip steel inside the annealing furnace; and second, to cool the strip steel that is about to undergo surface transformation treatment.

[0058] The surface of the annealed strip steel is cleaned using one or more methods, including immersion in cooling water, spraying, brushing, and electrolytic cleaning. A pair or more squeeze rollers can be installed at the outlet of the cleaning tank to remove residual water from the strip steel surface. A ventilation drying system can also be installed at the outlet of the cleaning tank.

[0059] In some implementations, the surface temperature of the strip after cleaning can be controlled to be between 10 and 35°C; the surface cleanliness of the strip is not worse than Grade 2 (ISO 8502-3 standard, pressure-sensitive tape method), or the total amount of surface residue is ≤100mg / m². 2 (CN102226767A Method for Determination of Surface Residues of Cold-Rolled Steel Sheets); The surface of the strip steel before entering the impregnation treatment step must not have water stains that are clearly visible to the naked eye.

[0060] Strip steel that meets the above conditions can proceed to the subsequent impregnation process; if the silicon steel production unit has a high degree of cleanliness, the strip steel may not need to undergo a surface cleaning step.

[0061] After the silicon steel sheet and strip undergo the above treatment, a surface conversion film is formed. Subsequently, an insulating coating process is carried out on its surface to obtain non-oriented silicon steel products.

[0062] The surface conversion film generated by this invention; the final silicon steel insulating coating applied thereon can be of type C-5 (ASTM A976) or EC-5 (IEC 60404-1-1), or C-6 (ASTM A976) or EC-6 (IEC 60404-1-1) coating.

[0063] The C-5 or C-6 insulating coating applied to the C-4 type conversion film can have a single-sided dry film thickness of 0.3 to 7 μm, and the peak metal temperature range for baking and curing can be 240 to 300 °C.

[0064] The conversion solution and process for forming a conversion film on the surface of non-oriented silicon steel described in this invention have the following advantages and beneficial effects:

[0065] Although the present invention adds a process after annealing and before coating to form an interface conversion film, it has no impact on the coating application and baking curing process.

[0066] The conversion liquid described in this invention has a controllable environmental impact and is a water-based, rinse-free, short-process, green and environmentally friendly liquid for treating metal surface conversion films.

[0067] Using this invention, a surface conversion film can be rapidly generated on the surface of non-oriented silicon steel at room temperature. The process time is generally less than 10 seconds, and no further water treatment such as cleaning or rinsing is required. The process is simple and convenient.

[0068] The silicon steel insulating coating applied to the surface conversion film generated by this invention not only enhances the properties of rust / corrosion resistance and adhesion, but also improves the coating's scratch resistance, punching and shearing properties, and heat resistance, thus meeting the stringent requirements for coating performance. Detailed Implementation

[0069] The conversion solution and process for forming a conversion film on the surface of non-oriented silicon steel described in this invention will be further explained and described below with reference to specific embodiments. However, this explanation and description do not constitute an undue limitation on the technical solution of this invention.

[0070] Examples 1-11 and Comparative Examples 1-4

[0071] The surface conversion films of Examples 1-11 were obtained using the following steps:

[0072] (1) Silicon steel materials of grades B50A290 (Si+Al content total 3.8wt%) and B50A800 (Si+Al content total 1.3wt%) were selected as substrates respectively.

[0073] (2) After the strip steel completes the final annealing process, the surface of the strip steel is sprayed with industrial pure water and brushed with rollers. A pair of squeeze rollers are installed at the outlet of the cleaning tank. The outlet strip steel temperature is about 25°C, the surface cleanliness is level 1 (ISO 8502-3 standard, pressure-sensitive tape method), and there are no obvious visible water stains on the surface.

[0074] (3) The cleaned strip steel enters the conversion tank containing the conversion solution for surface immersion treatment. A pair of squeeze rollers are installed at the inlet of the conversion tank and two pairs of squeeze rollers are installed at the outlet of the conversion tank. The pressure between the squeeze rollers is 3-4 kg.

[0075] Comparative Examples 1 and 2 employed steps that were essentially similar to those in this embodiment, but the solid content of Comparative Example 1 did not meet the requirements of this invention, and the conversion solution of Comparative Example 2 did not contain inorganic conversion membrane components.

[0076] Comparative Examples 3 and 4 employed completely different processing steps than those of the present invention, involving immersing the substrate in phosphoric acid for phosphating pretreatment.

[0077] Table 1 lists the solids composition and mass percentage of the conversion solutions for each embodiment and comparative example.

[0078] Table 1.

[0079]

[0080]

[0081] Table 2 lists the specific process parameters for the surface impregnation treatment in each embodiment and comparative example.

[0082] Table 2.

[0083]

[0084]

[0085] After the surface impregnation treatment is completed, the conversion liquid in the conversion tank can be recovered and centrally treated as wastewater. The wastewater can be diluted with water 20 to 50 times, and then calcium hydroxide can be added to make the pH value of the diluted solution ≥12. After thorough mixing and settling, the precipitate can be centrally treated and the remaining wastewater discharged. The environmental protection requirements for the discharged wastewater are: fluoride ion concentration <20mg / L, phosphorus ion concentration <10mg / L, and chemical oxygen demand (COD) <500mg / L.

[0086] (4) After the silicon steel strip passes through the conversion tank to form a wet conversion film layer, it enters a hot air drying oven for drying and curing to form a surface conversion film. In a specific example, the air dew point DP inside the drying oven can be 20℃, and the airflow per square meter of strip per surface can be 450 m³ / h. 3 / h, the peak temperature PMT of the exported steel plate is 70~75℃.

[0087] Table 2 also lists the Ti and Zr contents in the surface conversion films formed in each example and comparative example. The Ti and Zr contents were determined by X-ray fluorescence analysis (XRF).

[0088] After the surface conversion film is formed, a silicon steel insulating coating process can be carried out, that is, a C-6 insulating coating (ASTM A976 standard) is coated on the chemical conversion film. The single-sided dry film thickness can be 4.5±1.2μm, and the peak temperature of the metal for baking and curing is 260~280℃ to obtain non-oriented silicon steel products.

[0089] To verify the implementation effects of each embodiment and comparative example, samples were taken from Examples 1-11 and Comparative Examples 1-4, and the coating performance was tested as follows. The test results are listed in Table 3.

[0090] (1) Bending adhesion: According to GB / T 2522 standard, the four grades of bending adhesion are: "Excellent" (Grade A), "Good" (Grade B), "Medium" (Grade C) and "Poor" (Grade D).

[0091] (2) Scratch resistance: Using a one-yuan coin with no edge wear, hold the coin at a 45° angle to the test plate, apply a force of 1 kg, and move the coin parallel to the rolling direction perpendicular to the steel plate at a speed of 1 cm / s for a distance of 2 cm. Scratch the same area 5 times in parallel. The scratch resistance of the coin is evaluated according to the number of scratches visible on the metal substrate. The four levels are: "Excellent" (0 scratches), "Good" (1-2 scratches), "Medium" (3 scratches), and "Poor" (4-5 scratches).

[0092] (3) Punching and shearing workability: The coated steel sheet is punched or sheared, and the coating peeling within 1 mm of the edge is observed under the same conditions to evaluate the coating punching and shearing workability. The four levels of punching and shearing workability are: "Excellent" (cumulative peeling area within 1 mm of the edge <25%), "Good" (25% ≤ cumulative peeling area within 1 mm of the edge <50%), "Medium" (50% ≤ cumulative peeling area within 1 mm of the edge <75%), and "Poor" (cumulative peeling area within 1 mm of the edge ≥75%).

[0093] (4) Salt spray corrosion resistance: Salt spray corrosion resistance is tested by maintaining a neutral salt spray (NSS) for 7 hours. The four levels of corrosion resistance are: "Excellent" (rust area <10%), "Good" (10% ≤ rust area <20%), "Medium" (20% ≤ rust area <40%) and "Poor" (rust area ≥40%).

[0094] (5) Heat resistance: The coated silicon steel sample was first heated to 180℃ and held for 48 hours. After cooling, it was immersed in pure water for 24 hours. The changes such as blistering, wrinkling, and corrosion on the coating surface were observed to evaluate the density of the coating after heat resistance. The four levels of heat resistance evaluation are: "Excellent" (no change), "Good" (total change area <5%), "Medium" (5% ≤ total change area <10%), and "Poor" (total change area ≥10%).

[0095] Table 3 lists the coating properties of the non-oriented silicon steel sheets of Examples 1-11 and Comparative Examples 1-4.

[0096] Table 3.

[0097]

[0098]

[0099] Note: In Table 3, ◎ represents “Excellent”; 〇 represents “Good”; △ represents “Average”; × represents “Poor”.

[0100] As can be seen from Table 3, the coatings of the non-oriented silicon steel sheets of Examples 1-11 of the present invention have excellent bending adhesion, scratch resistance, punching and shearing properties, heat resistance and corrosion resistance.

[0101] In contrast, Comparative Example 1 had poor coating performance because the solid content of the conversion solution was lower than the lower limit of the present invention.

[0102] Comparative Example 2 also suffers from poor coating performance due to the absence of inorganic conversion film components.

[0103] Comparative Examples 3 and 4 both employed a pre-treatment method of immersing the substrate in phosphoric acid before coating, which is completely different from the technical solution of this invention. Therefore, the coating has poor scratch resistance, punching and shearing properties, heat resistance and corrosion resistance.

[0104] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0105] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A non-oriented silicon steel, characterized in that, The surface of the non-oriented silicon steel substrate has a surface conversion film formed based on a conversion solution, wherein the Ti+Zr content in the surface conversion film is controlled to be 1~800 mg / m³. 2 ,in: When the content of Ti+Zr in the surface conversion film is controlled to be 80~800 mg / m when 0.2wt%≤(Si+Al)<3.0wt% in the non-oriented silicon steel substrate. 2 ; When the content of (Si+Al) in the non-oriented silicon steel substrate is 3.0wt%≤(Si+Al)≤4.5wt%, the Ti+Zr content in the surface conversion film is controlled to be 1~100 mg / m. 2 ; The conversion solution is acidic and has a solids content of 10-30 wt%, comprising: The inorganic conversion membrane component is selected from at least one of the fluorides of titanium, zirconium, hafnium, and silicon, and its mass percentage in the conversion solution is 1-10 wt%. Aqueous organic resin, comprising 0-20 wt% of the conversion solution.

2. The non-oriented silicon steel as described in claim 1, characterized in that, When the content of Ti+Zr in the surface conversion film is controlled to be 100~500 mg / m when the content of 0.2wt%≤(Si+Al)<3.0wt% in the non-oriented silicon steel substrate is 0.2wt%≤(Si+Al)<3.0wt%, the content of Ti+Zr in the surface conversion film is controlled to be 100~500 mg / m. 2 .

3. The non-oriented silicon steel as described in claim 1, characterized in that, When the Si+Al content in the non-oriented silicon steel substrate is 3.0~4.5 wt%, the Ti+Zr content in the surface conversion film is controlled to be 3~50 mg / m. 2 .

4. The non-oriented silicon steel as described in claim 1, characterized in that, The solids component of the conversion solution consists of the following: The inorganic conversion membrane component is selected from at least one of the fluorides of titanium, zirconium, hafnium, and silicon, and its mass percentage in the conversion solution is 1-10 wt%. Aqueous organic resin, comprising 0-20 wt% of the conversion solution.

5. The non-oriented silicon steel as described in claim 1 or 4, characterized in that, The inorganic conversion membrane composition includes at least: titanium fluoride and / or zirconium fluoride.

6. The non-oriented silicon steel as described in claim 1 or 4, characterized in that, The solid content of the conversion liquid is 15-20 wt%.

7. The non-oriented silicon steel as described in claim 1 or 4, characterized in that, The water-based organic resin is selected from one of the following: water-soluble phenolic resin, polyester resin, and polyurethane resin.

8. The non-oriented silicon steel as described in claim 1, characterized in that, The solids also include additives, including phosphates and / or silicone-based additives.

9. The non-oriented silicon steel as described in claim 8, characterized in that, The phosphate is selected from at least one of the phosphates of Mn, Fe, and Co.

10. The non-oriented silicon steel as described in claim 8, characterized in that, The silicon-based additives are selected from nanoscale SiO2 sol and / or silane coupling agents.

11. The non-oriented silicon steel as described in claim 8, characterized in that, The additive accounts for 2-15% of the mass of the conversion solution.

12. A process for forming a surface conversion film on non-oriented silicon steel as described in any one of claims 1-11, characterized in that, Including the following steps: Before the insulating coating process: The conversion solution is used to perform surface impregnation treatment on the non-oriented silicon steel substrate; The immersion time is 2~15s, and the immersion temperature is 5~40℃; Dry and cure to form a surface conversion film.

13. The process as described in claim 12, characterized in that, The immersion time is 3-8 seconds; and / or the immersion temperature is 15-30°C.

14. The process as described in claim 12, characterized in that, The conversion liquid is placed in a conversion tank, and at least one pair of squeeze rollers are provided at the inlet of the conversion tank and at least two pairs of squeeze rollers are provided at the outlet of the conversion tank.

15. The process as described in claim 12, characterized in that, Surface cleaning is performed before the surface impregnation treatment step.

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