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 film on a surface of a non-oriented silicon steel, wherein the conversion liquid is acidic and has a content of solid fraction of 10-30 wt%, and the solid fraction comprises an inorganic conversion film component and an aqueous organic resin. Further disclosed in the present invention is a non-oriented silicon steel, comprising a silicon steel substrate and a conversion film on the surface thereof. Further disclosed in the present invention is a method for forming the conversion film on the surface of the silicon steel substrate.

Description

TECHNICAL FIELD

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

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

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

[0004] In addition, for insulating thick coatings of water-soluble silicon steels, the coatings require high performance such as surface insulation, heat resistance, and stability under hot pressing. The coating formula generally contains a large amount of inorganic fillers with submicron particle sizes, and the typical content of which accounts for about 30-70 wt% in the dry film of the coating. It is difficult to produce and prepare such thick coatings on the surface of steel sheets, which is easily lead to coating defects and poor film-forming quality, such as poor coating adhesion, bright stains formed by powder shedding of the coatings, poor scratch resistance of the coatings, and shedding or cracking of the coatings at edges during punching and shearing, which seriously deteriorate the use characteristics of the coating products.

[0005] To improve the corrosion resistance and adhesion of metal surface coatings, appropriate passivation treatment is performed on the metal substrate before coating to form an interface conversion film to improve the coating performance, which is a treatment method that has been adopted in the prior art.

[0006] For example, Chinese patent document with publication number CN104250754A, published on December 31, 2014, and entitled "Cold-rolled Sheet Surface Passivation Process" discloses such a process. The passivation solution used has a composition in weight percentage as below: 0.8-1.2% of sodium hydroxide, 1.4-1.8% of sodium carbonate, 1.5-2.5% of sodium tripolyphosphate, 2-4% of anhydrous sodium metasilicate, 3-5% of phytic acid, 2.5-3.5% of sodium bicarbonate, 4-6% of sodium benzoate, 5-7% of triethanolamine, 3.5-4.5% of polyethylene glycol, 0.5-1.5% of sodium dodecyl sulfonate, 0.1-0.3% of silicone defoamer, and the balance being water. The passivation process is as follows: preparing a passivation solution with the above components, adjusting the pH value to 2.5-3.5, placing the passivation solution at the oiling process position in the cold rolling production line, and spraying the passivation solution on the surface of the cold rolled steel sheet in the form of a spray, and making the passivation solution react with the surface of the steel sheet by the use of the residual temperature of the surface of the cold rolled steel sheet so as to form a passivation film.

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

[0008] However, for the chemical treatment of the surface of the conventional cold-rolled strip steel, the formation of its passivation film or conversion film requires a considerable reaction time, and the process requires heating to promote the formation of the conversion film. Water treatment may also be required after the film is formed. On the other hand, a sheet-passing speed on the continuous annealing and coating production lines of mainstream silicon steel production plants is generally as high as 80 to 200 meters / minute, and the number of equipment and operating space of the unit after annealing and before coating are very limited, resulting in that the effective generation time of the conversion film on the surface of the strip steel generally is a few seconds to a dozen seconds, and there is no condition for rinsing and other water treatment after the conversion film is formed. Therefore, the above-mentioned chemical treatment method for the surface of cold-rolled strip steel cannot be used for passivation or conversion treatment of the surface of the silicon steel after annealing and before coating.

[0009] In addition, the main purpose of applying conversion film on the surface of general cold-rolled strip steel is to enhance rust prevention / corrosion resistance and adhesion. However, for water-soluble environmentally friendly coating on silicon steel, more attention is paid to the performance such as scratch resistance, punching and shearing processability, and heat resistance of the coating.SUMMARY

[0010] One objective of the present invention is to provide a conversion liquid for forming a conversion film on a surface of a non-oriented silicon steel. After the silicon steel substrate undergoes the final 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 relatively thick coating. The conversion film of the present invention can be quickly generated at room temperature, and does not require subsequent water treatment processes such as rinsing, and the production process is simple and fast.

[0011] To achieve the above objective, the present invention proposes a conversion liquid for forming a conversion film on a surface of a non-oriented silicon steel. The conversion liquid is acidic and has a solid fraction of 10-30 wt%, wherein the solid fraction comprises: an inorganic conversion film component, being selected from at least one of fluorides of titanium, zirconium, hafnium, and silicon, and having a mass percentage content of 1-10 wt% in the conversion liquid; an aqueous organic resin, having a mass percentage content of 0-20 wt % in the conversion liquid.

[0012] In the present invention, the control of the conversion film is realized by controlling the components and contents of the solid fraction of the conversion liquid, preferably in combination with the subsequent optimization of the formation method of the specific conversion film.

[0013] Within the solid fraction range defined in the present invention, the higher the solid fraction of the conversion liquid, the more conversion film is formed, and the more continuous and dense the conversion film is, which is more conducive to improving the performance of subsequent insulating coating. However, at the same time, the more conversion liquid 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.

[0014] In the present invention, the liquid component in the conversion liquid is water.

[0015] In the conversion liquid described in the present invention, the inorganic conversion film component is selected from at least one of fluorides of titanium, zirconium, hafnium, and silicon, for example, selected from one or more of fluorozirconic acid, fluorotitanic acid, fluorohafnic acid, and fluorosilicic acid. The inorganic conversion film component can quickly form a relatively continuous conversion film layer while corroding the surface of silicon steel. The content of the inorganic conversion film component directly determines the generation speed and quality of the conversion film. If its content is higher than the upper limit specified in the present invention, the uniformity and compactness of the conversion film will be deteriorated, the use cost will be increased, and the high concentration of fluoride will bring difficulties to wastewater treatment.

[0016] Considering that the surface conversion film formed by the present invention is mainly an inorganic component system, and that the film-forming process is rapid, there may be phenomena of local discontinuity, cracks, microholes, or the like in the conversion film. Therefore, preferably, the conversion liquid described in the present invention also uses an aqueous organic resin with excellent compatibility and stability instead of a water-dispersible emulsion as a film-forming material, so as to improve the interfacial adhesion of the inorganic conversion film, improve the surface quality of the conversion film, and contribute to the continuity and compactness of the conversion film. However, if its content is higher than the upper limit defined in the present invention, the stability of the water-soluble aqueous organic resin in the acidic conversion liquid becomes poor, and the functionality of the inorganic conversion film is also weakened.

[0017] The pH value of the conversion liquid described in the present invention is preferably 2 to 4. A too low pH value indicates that the content or concentration of the solid fraction of the conversion liquid is relatively high, which can easily cause large quality fluctuations between conversion films of different production batches, and there are also problems such as high consumption of the conversion liquid and easy corrosion of containers. A too high pH value means that the content of the effective components in the conversion liquid is insufficient, resulting in a reduced amount of conversion film and faster deterioration of the conversion liquid.

[0018] Preferably, in the conversion liquid described in the present invention, the inorganic conversion film component contains at least titanium fluoride and / or zirconium fluoride.

[0019] In the present invention, the titanium fluoride has high reaction activity with the silicon steel substrate interface and a fast conversion film formation speed, and can be used as a preferred component. In addition, a zirconium fluoride can also be preferably used. Furthermore, it is also preferred to use a titanium fluoride and a zirconium fluoride simultaneously.

[0020] Preferably, the solid fraction of the conversion liquid described in the present invention consists of the following: an inorganic conversion film component, being selected from at least one of fluorides of titanium, zirconium, hafnium, and silicon, and having a mass percentage content of 1-10 wt% in the conversion liquid; an aqueous organic resin, having a mass percentage content of 0-20 wt % in the conversion liquid.

[0021] Preferably, in the conversion liquid described in the present invention, the content of the solid fraction is 15-20 wt%.

[0022] Preferably, in the conversion liquid described in the present invention, the aqueous organic resin is selected from one of a water-soluble phenolic resin, a water-soluble polyester resin, and a water-soluble polyurethane resin.

[0023] Preferably, in the conversion liquid described in the present invention, the solid fraction further comprises an additive, and the additive comprises a phosphate and / or a silicon-based auxiliary agent.

[0024] More preferably, the additive has a mass percentage content of 2-15 wt% in the conversion liquid.

[0025] In a preferred embodiment, the additive can promote the formation speed of the surface conversion film, improve the continuity and compactness of the surface conversion film, and stabilize the component system of the conversion liquid. However, its content cannot be too much. An additive content higher than the upper limit of the present invention may cause the conversion film to be loose or the components to be locally enriched, which is not conducive to the heat resistance and punching and shearing processability of the finished non-oriented silicon steel sheet coating.

[0026] 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.

[0027] Preferably, in the conversion liquid described in the present invention, the silicon-based auxiliary agent is selected from nano-scale SiO 2 sol and / or silane coupling agent.

[0028] As mentioned above, phosphates of Mn, Fe, and Co themselves have a certain conversion effect on the metal surface. When they are used in combination with the silane coupling agent, the conversion film formed after hybridized with Ti / Zr-containing compounds has a higher compactness and a more continuous film layer.

[0029] In some embodiments, when the nano-sized SiO 2 sol is used, the film forming speed can be accelerated by utilizing the characteristic of rapid penetration of silica sol into the substrate.

[0030] 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.

[0031] Preferably, the content of Ti and Zr elements (Ti+Zr) in the conversion film is controlled to be 1-800 mg / m 2< .

[0032] Preferably, the silicon steel substrate contains, in addition to Fe and inevitable impurities, the following elements in mass percentage: Si: 1.0-3.3 wt% and Al: 0.2-0.8 wt%.

[0033] Preferably, in the non-oriented silicon steel described in the present invention: when 0.2 wt% ≤ (Si+Al) < 3.0 wt% in the silicon steel substrate, the Ti+Zr content in the conversion film is 80-800 mg / m 2< ; when 3.0 wt% ≤ (Si+Al) ≤ 4.5wt% in the non-oriented silicon steel substrate, the Ti+Zr content in the conversion film is 1-100 mg / m 2< .

[0034] More preferably, when 0.2 wt% ≤ (Si+Al) < 3.0 wt% in the non-oriented silicon steel substrate, the Ti+Zr content in the conversion film is 100-500 mg / m 2< .

[0035] 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< .

[0036] In the above expressions, the element symbols represent the mass percentage of the corresponding elements in the silicon steel substrate or conversion film.

[0037] Another objective of the present invention is to provide a method for forming a conversion film on the surface of a non-oriented silicon steel. After the silicon steel substrate undergoes the final annealing process and before an insulation coating process is performed, the above-mentioned 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. Its function is to provide or strengthen the scratch resistance, punching and shearing processability, salt spray corrosion resistance, and heat resistance of the silicon steel coating on the basis of ensuring the main performance of the silicon steel insulation coating, so as to improve the comprehensive performance of silicon steel products with relatively thick coatings. The surface conversion film can be quickly generated at room temperature, and no subsequent water treatment processes such as rinsing are required, and the production process is simple and fast.

[0038] To achieve the above objective, the present invention proposes a method for forming a conversion film on the surface of a non-oriented silicon steel, comprising the following steps performed in sequence: immersing: immersing the silicon steel substrate into the conversion liquid, wherein the immersing time is 2 to 15 seconds and the immersing 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;

[0039] Preferably, an insulating coating is applied on the surface of the conversion film to obtain a finished non-oriented silicon steel sheet;

[0040] Preferably, the surface of the silicon steel substrate is cleaned before performing the immersing step.

[0041] The immersing temperature described in the present invention refers to the temperature of the conversion liquid.

[0042] In the method described in the present invention, the control of the conversion film on the surface of the finished non-oriented silicon steel sheet is mainly achieved by controlling and optimizing the composition and content of the solid fraction of the conversion liquid, as well as the immersing time and temperature. By using the conversion liquid of the present invention in combination with the process parameter of the immersing time and temperature, it can be ensured that a quality-controllable conversion film is formed on the surface of the silicon steel substrate.

[0043] Preferably, in the above-mentioned immersing step, the immersing time is 3 to 8 seconds; and / or the immersing temperature is 15-30 °C. Preferably, in the method described in the present invention, the conversion liquid is placed in a conversion tank, wherein at least one pair of wringing rollers is arranged at the inlet of the conversion tank to wring out the residual water on the surface of the silicon steel substrate, and at least two pairs of wringing rollers are arranged at the outlet of the conversion tank to wring out the silicon steel substrate immersed by the conversion liquid.

[0044] Two or more pairs of wringing rollers are arranged at the outlet of the conversion tank. Therefore, in addition to preventing contamination caused by taking the conversion liquid out of the conversion tank with the silicon steel sheet, a thickness of the surface conversion film on the silicon steel substrate can be controlled by adjusting the pressure, so as to avoid spots caused by uneven formation of the conversion film.

[0045] Preferably, in the method described in the present invention, the Ti+Zr content in the conversion film is controlled to be 1-800 mg / m 2< .

[0046] By controlling the Ti+Zr content in the conversion film within the above-mentioned range, the quality of the subsequent insulating coating can be guaranteed.

[0047] 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: In some embodiments, when 0.2 wt% ≤ (Si+Al) < 3.0 wt% in the non-oriented silicon steel substrate, the Ti+Zr content in the conversion film is controlled to be 80-800 mg / m 2< ; and more preferably, the Ti+Zr content in the conversion film is controlled to be 100-500 mg / m 2< .

[0048] In other embodiments, when 3.0 wt% ≤ (Si+Al) ≤ 4.5 wt% in the non-oriented silicon steel substrate, the Ti+Zr content in the conversion film is controlled to be 1-100 mg / m 2< , and more preferably, the Ti+Zr content in the conversion film is controlled to be 3-50 mg / m 2< .

[0049] This is because there is oxide enrichment of Al and / or Si on the surface of the substrate (in which the non-oriented silicon steel with a sum of contents of Si+Al elements of 3.0-4.5 wt% generally belongs to a high-grade silicon steel). As compared with a low-grade silicon steel substrate with a sum of Si+Al contents of 0.2 to less than 3.0 wt%, although the oxide film thickness of the substrate is small, the surface energy of the substrate interface will be obviously reduced because the inorganic nonmetallic oxides on the substrate surface modify the micro-morphology of the substrate surface. The substrate is more covalently bonded than metallicly bonded in contact with the coating, which is beneficial to improve the comprehensive performance of the coating. Therefore, the amount of Ti+Zr in the conversion film required for such substrate is relatively small. In actual applications, it is found that for the non-oriented high-grade silicon steel, even if the amount of conversion film generated is small, some performance 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.

[0050] However, for the low-grade silicon steel substrate, the amount of oxides formed on its surface is rare or even absent, it must rely on the conversion film to play its role as an interface layer. Therefore, it is necessary to significantly increase the Ti+Zr content in the conversion film, so that the subsequent coating applied on the conversion film can have relatively good performance.

[0051] Preferably, in the method described in 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 temperature of the surface of the steel sheet) of the steel sheet at the outlet of the hot-air drying oven is controlled to be 50-85 °C, and the air dew point D.P. in the hot-air drying oven is < 40 °C. The lower limit of the air output volume received by each surface per square meter of the substrate is 300 m 3< / h, and preferably the upper limit of the air output volume is 500 m 3< / h.

[0052] Preferably, in the method described in the present invention, the surface of the silicon steel substrate is cleaned before the immersing step.

[0053] One of the purposes of surface cleaning is to clean off contaminants such as floating dust adhering to the surface of the silicon steel substrate in the annealing furnace. Another purpose is to cool down the silicon steel substrate to prepare for subsequent surface conversion treatment.

[0054] The surface cleaning method described above can be one or more of immersion washing by cooling water, spraying, brushing by a brush roll, and electrolytic cleaning. Preferably, one or more pairs of wringing rollers are provided at the outlet of the cleaning tank to wring out the residual water on the surface of the cleaned silicon steel substrate. More preferably, a ventilating and air drying device is also provided at the outlet of the cleaning tank.

[0055] 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 Grade 2 or better (referring to ISO 8502-3 standard, pressure-sensitive tape method), or the total amount of residues on the surface of the silicon steel substrate is ≤ 100 mg / m 2< (referring to determination method of residues on the surface of cold-rolled sheets disclosed in CN102226767A). There is no water stain clearly visible to the naked eye on the surface of the silicon steel substrate before the immersing step.

[0056] The silicon steel substrate that meets the above conditions can be subjected to the immersing step. If the production unit of the silicon steel substrate has a high degree of cleanliness, the surface cleaning step of the obtained silicon steel substrate can also be omitted.

[0057] After the above treatment, a conversion film is formed on the surface of the silicon steel substrate, and then an insulating coating is applied on the conversion film to obtain a finished non-oriented silicon steel sheet.

[0058] The insulating coating formed on the surface of the conversion film of the present invention can be a C-5 (referring to ASTM A976) or EC-5 (referring to IEC 60404-1-1) coating, or can be a C-6 (referring to ASTM A976) or EC-6 (referring to IEC 60404-1-1) coating.

[0059] The C-5 or C-6 insulating coating formed on the conversion film of the C-4 category (referring 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 - 7 µm, and the peak metal temperature range during the baking and curing is preferably 240-300 °C.

[0060] The conversion liquid and method for forming a conversion film on the surface of the non-oriented silicon steel according to the present invention have the following advantages and beneficial effects: In the present invention, although a process is added after annealing and before applying the insulating coating to form a conversion film on the surface of the silicon steel substrate, it has no influence on the coating process and baking-curing process of the insulating coating.

[0061] The conversion liquid of the present invention is environmentally friendly and is a water-based, wash-free, short-process, green and environmentally friendly liquid used for forming a conversion film on a metal surface.

[0062] 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 forming time is usually less than 10 seconds, and no additional water treatment processes such as washing or rinsing are required. The production process is simple and convenient.

[0063] The insulating coating formed on the conversion film of the present invention not only enhances the properties such as rust prevention / corrosion resistance and adhesion, but also improves the overall scratch resistance, punching and shearing processability, and heat resistance of the substrate surface coating, thus exhibiting improved comprehensive performance.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0064] The conversion liquid and method for forming a conversion film on the surface of non-oriented silicon steel described in the present invention will be further explained and described below in conjunction with specific examples. However, these explanation and description do not constitute an improper limitation on the technical solution of the present invention.Examples 1-11 and Comparative Examples 1-4

[0065] The conversion films of Examples 1-11 were obtained by the following steps: (1) Silicon steel materials of grades B50A290 (sum of Si+Al content is 3.8 wt%) and B50A800 (sum of Si+Al content is 1.3 wt%) were selected as substrates respectively. (2) After the substrate was subjected to the final annealing process, the substrate surface was sprayed and scrubbed with brush rollers using industrial pure water. A pair of wringing rollers was arranged at the outlet of the cleaning tank. The substrate temperature at the outlet was about 25°C, the surface cleanliness was Grade 1 (referring to ISO 8502-3 standard, pressure-sensitive tape method), and there were no clearly visible water stains on the surface. (3) The cleaned substrate was placed in a conversion tank containing conversion liquid for surface immersion treatment. A pair of wringing rollers was arranged at the inlet of the conversion tank and two pairs of wringing rollers were arranged at the outlet of the conversion tank. The pressure between each pair of wringing rollers was 3-4 kg.

[0066] Comparative Examples 1 and 2 employed steps basically similar to those in the above Examples, except that the solid fraction in the conversion liquid of Comparative Example 1 did not meet the limitations of the present invention, and the conversion liquid of Comparative Example 2 did not contain inorganic conversion film components.

[0067] Comparative Examples 3 and 4 employed processing steps completely different from those in the Examples of the present invention. In these Comparative Examples, the silicon steel substrate was not immersed in the conversion liquid of the present invention, but was immersed in phosphoric acid for phosphating pretreatment.

[0068] Table 1 lists the components of solid fraction of the conversion liquids for each Example and Comparative Example and the mass percentage of the corresponding components. Table 1CategoryConversion liquid componentsInorganic conversion film componentsAqueous organic resinAdditiveSolid fraction (wt%)ComponentContent (wt%)ComponentContent (wt%)ComponentContent (wt%)Example 1Hexafluorozirc onic acid1.0%Phenolic resin12%Manganese dihydrogen phosphate2%17.5%Hexafluorotitan ic acid2.5%Example 2Hexafluorozirc onic acid2.0%Phenolic resin20%Manganese dihydrogen phosphate2%26.5%Hexafluorotitan ic acid2.5%Example 3Hexafluorozirc onic acid3.0%Polyurethane resin2%Nano silica sol6%15.5%Hexafluorotitan ic acid1.5%Silane coupling agent3%Example 4Hexafluorozirc onic acid4.0%Polyurethane resin2%Nano silica sol6%18%Hexafluorotitan ic acid3.0%Silane coupling agent3%Example 5Hexafluorotitan ic acid5.0%Polyester resin5%Silane coupling agent5%15%Example 6Hexafluorotitanic acid5.0%Polyester resin5%Silane coupling agent5%15%Example 7Hexafluorozirc onic acid5.0%Polyurethane resin5%Nano silica sol7.5%30%Hexafluorotitan ic acid5.0%Silane coupling agent7.5%Example 8Hexafluorotitan ic acid6.0%--Ferric dihydrogen phosphate5%16%Silane coupling agent5%Example 9Hexafluorozirc onic acid1.0%Phenolic resin9%--10%Example 10Hexafluorotitan ic acid4.0%Polyester resin5%Manganese dihydrogen phosphate4%16%Fluorosilicic acid1.0%Silane coupling agent2%Example 11Hexafluorozirc onic acid4.5%Phenolic resin10%Cobalt phosphate2%19%Fluorohafnic acid0.5%Silane coupling agent2%Comparative Example 1Hexafluorozirc onic acid4.0%----7%Hexafluorotitan ic acid3.0%Comparative Example 2--Phenolic resin15%Manganese dihydrogen phosphate6%24%Silane coupling agent3%Comparative Example 3Phosphoric acid15.0%--Comparative Example 4Phosphoric acid15.0%--

[0069] Table 2 lists the specific process parameters for the surface immersion treatment in each Example and Comparative Example. Table 2CategoryImmersing timeImmersing temperatureSubstrate (Si+Al) content(Ti+Zr) content in conversion filmExample 15 s5 °C3.8%28 mg / m 2< Example 28 s25 °C1.3%117 mg / m 2< Example 37s15 °C3.8%46 mg / m 2< Example 410 s30 °C1.3%243 mg / m 2< Example 58 s20 °C3.8%76 mg / m 2< Example 612 s35 °C1.3%424 mg / m 2< Example 715 s30 °C1.3%734 mg / m 2< Example 83 s25 °C3.8%17 mg / m 2< Example 915 s38 °C3.8%3 mg / m 2< Example 108 s25 °C1.3%291 mg / m 2< Example 1114 s25 °C1.3%426 mg / m 2< Comparative Example 113 s30 °C3.8%26 mg / m 2< Comparative Example 230 s 25 °C1.3%-Comparative Example 3Before coating, the substrate was immersed in phosphoric acid for phosphating pretreatment, wherein the [P] content in the phosphating layer was 78 mg / m 2< . 3.8%-Comparative Example 4Before coating, the substrate was immersed in phosphoric acid for phosphating pretreatment, wherein the [P] content in the phosphating layer was 78 mg / m 2< . 1.3%-

[0070] After the surface immersion treatment was completed, the conversion liquid in the conversion tank could be recovered and concentrated for waste liquid treatment. The waste liquid could be diluted 20 to 50 times with water, and then calcium hydroxide was added to make the pH value of the diluted liquid ≥ 12. After sufficient mixing and standing, the precipitate was centrally treated and the remaining wastewater was discharged. The discharged wastewater met the following: fluoride ion concentration < 20 mg / L, phosphorus ion concentration < 10 mg / L, chemical oxygen demand (COD) < 500 mg / L.

[0071] (4) After the silicon steel substrate was immersed in the conversion tank to form a wet conversion film layer on its surface, it was put into a hot-air drying oven for drying and curing to form a conversion film on the surface of the substrate. In a specific embodiment, the air dew point D.P. in the drying oven was 20 °C, the drying oven air output volume per square meter of each surface of the substrate was 450 m 3< / h, and the peak temperature PMT of the steel sheet surface at the outlet was 70-75 °C.

[0072] Table 2 also lists the Ti and Zr content in the conversion films formed in each Example and Comparative Example. The Ti and Zr contents were determined by X-ray fluorescence analysis (XRF).

[0073] In some embodiments of the present invention, after the conversion film is formed on the surface of the silicon steel substrate, an insulating coating, for example a C-6 insulating coating (referring to ASTM A976 standard), is preferably applied on the surface of the conversion film. The single-sided dry film thickness of the insulating coating can be 4.5+1.2 µm, and the peak temperature of the steel sheet surface during the baking and curing is 260-280 °C to obtain a finished non-oriented silicon steel plate.

[0074] The finished non-oriented silicon steel sheets (including the substrates and the coatings on the surface thereof) 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. (1) Bending adhesion: The test was conducted according to GB / T 2522 standard, and the bending adhesion was evaluated by 4 grades: "Excellent" (Grade A), "Good" (Grade B), "Fair" (Grade C) and "Poor" (Grade D). (2) Scratch resistance: A one-yuan coin with no edge wear was used, and the coin was held by hand at an angle of about 45 degrees with the sample, and a force of 1 kg was applied, and the coin was moved at a speed of 1 cm / s perpendicular to the rolling direction of the steel sheet, wherein a moving distance was 2 cm. Parallel scratches were made in the selected test area for 5 times, and the coin scratch resistance of the finished non-oriented silicon steel sheet was evaluated according to the number of visible scratches on the substrate. The test was evaluated by 4 grades: "Excellent" (scratch number was 0), "Good" (scratch number was 1-2), "Fair" (scratch number was 3), and "Poor" (scratch number was 4-5). (3) Punching and shearing processability: The finished non-oriented silicon steel sheet was punched or sheared, the dropping off status of the coating on the steel sheet surface within 1 mm of the edge was observed under the same conditions to evaluate punching and shearing processability of the coating. Punching and shearing processability was evaluated by 4 grades: "Excellent" (cumulative dropping off area within 1 mm of the edge < 25%), "Good" (25% ≤ cumulative dropping off area within 1 mm of the edge < 50%), "Fair" (50% ≤ cumulative dropping off area within 1 mm of the edge < 75%), and "Poor" (cumulative dropping off area within 1 mm of the edge ≥ 75%). (4) Salt-spray corrosion resistance: Salt-spray corrosion resistance was tested using a neutral salt spray (NSS) test method for 7 hours (referring to GB / T 6458-1986). Salt-spray corrosion resistance was evaluated by 4 grades: "Excellent" (corrosion area of the sample < 10%), "Good" (10% ≤ corrosion area of the sample < 20%), "Fair" (20% ≤ corrosion area of the sample < 40%), and "Poor" (corrosion area of the sample ≥ 40%). (5) Heat resistance: The sample was first heated to 180°C and held for 48 hours. After cooling, the sample was immersed in pure water for 24 hours. Changes such as blistering on the coating surface, wrinkling on the coating surface, and substrate corrosion were observed to evaluate the compactness of the coating after heat resistance test. The heat resistance was evaluated by 4 grades: "Excellent" (no change in the coating on the steel sheet surface), "Good" (the area of the coating with changes on the steel sheet surface in the total area < 5%), "Fair" (5% ≤ the area of the coating with changes on the steel sheet surface in the total area < 10%), and "Poor" (the area of the coating with changes on the steel sheet surface in the total area ≥ 10%).

[0075] Table 3 lists the coating properties of the non-oriented silicon steel sheets of Examples 1-11 and Comparative Examples 1-4. Table 3CategoryTest performanceΦ5mm bending adhesionScratch resistancePunching and shearing processabilitySalt-spray corrosion resistanceHeat resistanceEvaluation RequirementPeeling off by 3M tape tearingCoin scratch resistanceDropping off status of coating within 1 mm of punched / sheared edge7 hours NSS corrosionImmerse in water after heating at 180°C for 48 hoursExample 1⊚○⊚⊚⊚Example 2⊚○○⊚○Example 3○⊚⊚○⊚Example 4○⊚⊚○⊚Example 5⊚⊚○△○Example 6⊚⊚○△○Example 7○⊚△○△Example 8⊚○○○○Example 9○△△△△Example 10⊚○○○⊚Example 11⊚○○○○Comparative Example 1△○×○△Comparative Example 2○××○△Comparative Example 3○××△×Comparative Example 4○××△×Note: In Table 3, ⊚ represents "Excellent"; O represents "Good"; △ represents "Fait"; × represents "Poor".

[0076] As can be seen from Table 3, the coatings of the finished non-oriented silicon steel sheets of Examples 1-11 of the present invention have good bending adhesion, scratch resistance, punching and shearing processability, heat resistance, and corrosion resistance.

[0077] However, in Comparative Example 1, the solid fraction of the conversion liquid was lower than the lower limit defined in the present invention, and as a result, the coating performance was poor.

[0078] In Comparative Example 2, there was no inorganic conversion film component, which also resulted in poor coating performance.

[0079] In Comparative Examples 3 and 4, no conversion film or insulating coating was formed on the surface of the silicon steel substrate, but phosphoric acid was used to pre-treat the substrate for phosphating, which was 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 were not good.

[0080] It should be noted that combinations of the various technical features in this case are not limited to the combinations described in the specific embodiments. All technical features recorded in this case can be freely combined or associated in any way unless a contradiction occurs.

[0081] 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 the contents disclosed by those skilled in the art from the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A conversion liquid for forming a conversion film on a surface of a non-oriented silicon steel, wherein the conversion liquid is acidic and has a content of solid fraction of 10-30 wt%, and the solid fraction comprises: an inorganic conversion film component, being selected from at least one of fluorides of titanium, zirconium, hafnium, and silicon, and having a mass percentage content of 1-10 wt% in the conversion liquid; an aqueous organic resin, having a mass percentage content of 0-20 wt % in the conversion liquid.

2. The conversion liquid according to claim 1, wherein the solid fraction of the conversion liquid consists of: an inorganic conversion film component, being selected from at least one of fluorides of titanium, zirconium, hafnium, and silicon, and having a mass percentage content of 1-10 wt% in the conversion liquid; an aqueous organic resin, having a mass percentage content of 0-20 wt % in the conversion liquid.

3. The conversion liquid according to claim 1 or 2, wherein the inorganic conversion film component comprises at least titanium fluoride and / or zirconium fluoride.

4. The conversion liquid according to claim 1 or 2, wherein the content of the solid fraction of the conversion liquid is 15-20 wt%; and / or the conversion liquid has a pH value of 2-4.

5. The conversion liquid according to claim 1 or 2, wherein the aqueous organic resin is selected from one of water-soluble phenolic resin, water-soluble polyester resin, and water-soluble polyurethane resin.

6. The conversion liquid according to claim 1 or 2, wherein the solid fraction further comprises an additive, and the additive includes: phosphate and / or silicon-based auxiliary agent.

7. The conversion liquid according to claim 6, wherein the phosphate is selected from at least one of the phosphates of Mn, Fe, and Co.

8. The conversion liquid according to claim 6, wherein the silicon-based auxiliary agent is selected from nano-scale SiO2 sol and / or silane coupling agent.

9. The conversion liquid according to claim 6, wherein the additive has a mass percentage content of 2-15 wt% in the conversion liquid.

10. A non-oriented silicon steel, comprising a 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 according to any one of claims 1-9.

11. The non-oriented silicon steel according to claim 10, wherein a Ti+Zr content in the conversion film is 1-800 mg / m2; and / or the silicon steel substrate contains, in addition to Fe and inevitable impurities, the following elements in mass percentage: Si: 1.0-3.3 wt% and Al: 0.2-0.8 wt%.

12. The non-oriented silicon steel according to claim 11, wherein when 0.2 wt% ≤ (Si+Al) < 3.0 wt% in the silicon steel substrate, the Ti+Zr content in the conversion film is 80-800 mg / m2; when 3.0 wt% ≤ (Si+Al) ≤ 4.5wt% in the silicon steel substrate, the Ti+Zr content in the conversion film is 1-100 mg / m2.

13. The non-oriented silicon steel according to claim 12, wherein when 0.2 wt% ≤ (Si+Al) < 3.0 wt% in the silicon steel substrate, the Ti+Zr content in the conversion film is 100-500 mg / m2.

14. The non-oriented silicon steel according to claim 12, wherein when the Si+Al content in the silicon steel substrate is 3.0-4.5 wt%, the Ti+Zr content in the conversion film is 3-50 mg / m2.

15. A method for forming a conversion film on a surface of a silicon steel substrate, wherein the method comprises the following steps performed in sequence: immersing: immersing the silicon steel substrate into the conversion liquid according to any one of claims 1-9, wherein the immersing time is 2 to 15 seconds, and the immersing 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, applying an insulating coating on the surface of the conversion film to obtain a finished non-oriented silicon steel sheet; preferably, cleaning the surface of the silicon steel substrate before performing the immersing step.

16. The method according to claim 15, wherein the immersing time is 3-8 seconds; and / or the immersing temperature is 15-30 °C.

17. The method according to claim 15, wherein in the immersing step, the conversion liquid is placed in a conversion tank, wherein at least one pair of wringing rollers is arranged at an inlet of the conversion tank to wring out residual water on the surface of the silicon steel substrate, and at least two pairs of wringing rollers are arranged at an outlet of the conversion tank to wring out the silicon steel substrate immersed by the conversion liquid.

18. The method according to any one of claims 15-17, wherein the Ti+Zr content in the conversion film is 1-800 mg / m2; and / or the silicon steel substrate contains, in addition to Fe and inevitable impurities, the following elements in mass percentage: Si: 1.0-3.3 wt% and Al: 0.2-0.8 wt%.

19. The method according to claim 18, wherein when 0.2 wt% ≤ (Si+Al) < 3.0 wt% in the silicon steel substrate, the Ti+Zr content in the conversion film is 80-800 mg / m2, preferably 100-500 mg / m2; when 3.0 wt% ≤ (Si+Al) ≤ 4.5 wt% in the silicon steel substrate, the Ti+Zr content in the conversion film is 1-100 mg / m2, preferably 3-50 mg / m2.

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