Coating material, grain-oriented silicon steel sheet having a coating formed from the coating material, and method for manufacturing the same.

Abstract

The present invention relates to a coating material for surface coating of grain-oriented silicon steel. The coating material has: a phosphate; colloidal silica; and at least one vanadate selected from vanadates of Ce, Mn, Co, Cu or Fe. The coating material does not have Cr. The present invention further relates to grain-oriented silicon steel having a surface coating formed from the coating material. The present invention further relates to a method for manufacturing grain-oriented silicon steel having a surface coating formed from the coating material. The coating material of the present invention does not have chromium. The coating formed from the coating material can provide sufficient moisture absorption resistance while protecting the environment, and can apply sufficient tension to the grain-oriented silicon steel sheet, so that the iron loss and magnetostriction of the grain-oriented silicon steel are further reduced, and a high-quality iron core material for transformers can be obtained.

Description

[Technical Field]

[0001] The present invention relates to the field of steel sheet coating, and more particularly to coating materials for surface coating of grain-oriented silicon steel, grain-oriented silicon steel sheets having the surface coating, and methods for manufacturing the same. [Background technology]

[0002] Grain-oriented silicon steel sheet is obtained through cold rolling and heat treatment processes, and has a silicon content in the range of 2.8 wt% to 3.5 wt%. {110} <001> This refers to a steel sheet having a grained texture. Its magnetic properties along the rolling direction are significantly better than its magnetic properties in the transverse direction. Grained silicon steel sheets are mainly used as core materials for transformers. To reduce energy loss and noise levels in transformers, grained silicon steel sheets are preferably low iron loss and low noise. It is currently known that the iron loss and magnetostriction values ​​of grained silicon steel sheets can be reduced by applying appropriate tensile stress to them.

[0003] Prior art typically solves the above problem by applying a chromium-containing coating to the surface of grain-oriented silicon steel sheets. Chromium-containing coatings have good insulating properties. Furthermore, the coating generates tensile stress on the steel sheet, thereby reducing iron loss and magnetostriction in the steel sheet due to the difference in thermal expansion coefficients between the coating and the steel sheet during heat treatment. However, since the coating solution used contains hexavalent chromium, the waste liquid generated during its manufacture contains large amounts of hexavalent chromium, which is harmful to the environment and will cause serious environmental pollution.

[0004] In recent years, with growing concern for environmental protection, there has been an increased demand for products that do not contain harmful substances such as chromium and lead. The development of chromium-free coatings (coatings that do not contain chromium) for grain-oriented silicon steel is also anticipated. However, grain-oriented silicon steel using chromium-free coatings typically suffers from significantly reduced moisture resistance and insufficient tensile strength. Therefore, chromium-free coatings are rarely used, or at least not feasible.

[0005] A Chinese patent document titled "Insulating Coating Solution for Grain-Grain Electrical Steel Sheets and Method for Manufacturing Grain-Grain Electrical Steel Sheets with Insulating Coating" (Publication Number: CN101790599A, Publication Date: July 28, 2010) discloses a chromium-free insulating coating solution for grain-grain electric steel sheets, comprising at least one phosphate of Mg, Ca, Ba, Sr, Zn, Al, and Mn, and chelates of colloidal silica and titanium. It can improve adhesion and coating tension. However, the chelates tend to decompose during heat treatment to produce carbon, which adversely affects the coating tension.

[0006] A Chinese patent document titled "Grain-oriented electrical steel sheet having a chromium-free insulating coating and insulating coating agent therefor" (Publication number: CN101223300A, Publication date: July 16, 2008) discloses a chromium-free insulating coating agent for grain-oriented electrical steel sheets. Its main components are phosphates, colloidal silica, and inorganic compounds of Fe, Ni, Co, Cu, Sr, or Mo with particle sizes of 15 nm or less, such as hydroxides, oxides, carbonates, silicates, and molybdates. However, hydroxide colloids are not stable in phosphate solution systems and do not have sufficient ability to fix their free phosphate radicals, which can easily reduce the moisture resistance and anti-adhesion properties of grain-oriented silicon steel sheets.

[0007] A Chinese patent document titled "Chromium-free coating agent for grain-oriented electrical steel sheets, method for preparing the same, electrical steel sheet using the same, and method for manufacturing the same" (Publication number: CN102119239A, Publication date: July 6, 2011) discloses a chromium-free coating agent for grain-oriented electrical steel sheets having phosphate, colloidal silica, and hematite silicon sol. However, hematite silicon sol is difficult to maintain stably in a phosphate-based system, and its preparation is also difficult, making industrial production challenging.

[0008] In light of the above-mentioned problems, there is a need to obtain a coating material for grain-oriented silicon steel sheets that meets industrial production requirements, is chromium-free, remains stable during heat treatment, and has good coating performance. Furthermore, the surface coating of grain-oriented steel sheets obtained with this coating material will have good moisture resistance, corrosion resistance, heat resistance, and anti-adhesion properties, and will also provide sufficient tensile effect, further reducing iron loss and magnetostriction in grain-oriented silicon steel. [Overview of the project]

[0009] The object of the present invention is to provide a coating material for surface coating of grain-oriented silicon steel. This coating material does not contain chromium. This provides grain-oriented silicon steel with good moisture resistance, tensile strength, corrosion resistance, heat resistance, and anti-adhesion properties, and further reduces iron loss and magnetostriction of grain-oriented silicon steel while protecting the environment.

[0010] To achieve the above objective, the inventors unexpectedly discovered that by using a combination of at least one vanadate selected from Ce, Mn, Co, Cu, and Fe and a phosphate in the coating material, the phosphate radicals in the vanadate and phosphate form an insoluble substance during the heat treatment of the coating material. This provides the effect of fixing the phosphate radicals and applying tension to the grain-oriented silicon steel, thus forming a coating on the surface of the grain-oriented silicon steel with good moisture resistance, tension, corrosion resistance, heat resistance, and anti-adhesion properties, thereby obtaining grain-oriented silicon steel with good iron loss and magnetostriction.

[0011] The present invention relates to a coating material for surface coating of grain-oriented silicon steel, wherein the coating material is: It contains phosphate; It has colloidal silica; Furthermore, it has at least one vanadate selected from vanadates of Ce, Mn, Co, Cu, or Fe; The coating material does not contain chromium (Cr).

[0012] After applying the above-described coating material onto a grain-oriented silicon steel sheet, the coating material is subjected to heat treatment to form a coating, and the phosphate can form a phosphate coating having a network or chain structure on the steel sheet surface after heat treatment. In the present invention, colloidal silica is used as a filler, and after heat treatment, a ceramic layer with a low coefficient of thermal expansion is formed, providing tension to the coating, which is beneficial in improving the coating performance of the coating material. In the present invention, "colloidal silica" generally refers to an aqueous dispersion of nanoscale silica having silanol groups. During heat treatment, Ce, Mn, Co, Cu, Fe, and V in the vanadate can form insoluble phosphate compounds with phosphate radicals in the phosphate, thereby fixing phosphate radicals on the grain-oriented silicon steel and preventing free phosphate radicals from remaining in the coating. Therefore, the moisture resistance, tension, corrosion resistance, and anti-adhesion of the coating can be improved.

[0013] The vanadate salt used in this invention is not particularly limited as long as it can form insoluble vanadium phosphate with a phosphate radical. Examples of vanadates include orthovanadate, pyrovanadate, or metavanadate. Preferably, the vanadate salt is an orthovanadate of Ce, Mn, Co, Cu, or Fe (VO4 3- ), pyrovanadinate (V2O7 4- ), and / or metavanadate (VO3 - )

[0014] Preferably, the coating material comprises, by mass%, 25-50% phosphate, 25-50% colloidal silica, and 10-50% vanadate.

[0015] Preferably, the phosphate is at least one selected from the phosphates of Mg, Al, Ca, Zn, and Mn.

[0016] Preferably, the phosphate is magnesium dihydrogen phosphate, aluminum dihydrogen phosphate, calcium dihydrogen phosphate, zinc dihydrogen phosphate, and manganese dihydrogen phosphate.

[0017] Preferably, the mass ratio of colloidal silica to phosphate is 0.5 to 1.5, more preferably 1.0 to 1.5. Within this range, good coating performance can be obtained, which is beneficial for improving the coating performance of the coating material of the present invention.

[0018] Preferably, the mass ratio of vanadate to phosphate is 0.2 to 2.0, more preferably 0.2 to 1.5, more preferably 0.2 to 1.0, and even more preferably 0.2 to 0.5.

[0019] In the technical solution of the present invention, when the mass ratio of at least one vanadate (such as orthovanadate, pyrophosphate vanadate, metavanadate, etc.) to the phosphate is 0.2 or more, the moisture absorption resistance of the coating can be significantly improved. However, when the mass ratio of vanadate to phosphate exceeds 2.0, the tension and corrosion resistance of the coating will decrease. Therefore, in the coating material for the grain-oriented silicon steel sheet of the present invention, the mass ratio of vanadate to phosphate is limited to 0.2 to 2.0.

[0020] Preferably, the coating material for the surface coating of the grain-oriented silicon steel also has boric acid. By adding boric acid to the coating material, the sintering densification, tension, and heat resistance of the coating can be further improved.

[0021] Preferably, the content of boric acid is 0.02 to 0.2 parts by mass with respect to 100 parts by mass of colloidal silica.

[0022] By adding an appropriate amount of boric acid, the sintering densification, tension, and heat resistance of the coating can be further improved. However, when the mass ratio of boric acid to colloidal silica exceeds 0.2, the tension effect, heat resistance, and corrosion resistance will decrease. Therefore, in the coating material of the present invention, the mass ratio of boric acid to colloidal silica is limited to the range of 0.02 to 0.2.

[0023] Preferably, the particle size of the colloidal silica is 5 to 50 nm. Adjusting the particle size of the colloidal silica is beneficial for forming a dense ceramic layer after heat treatment and obtaining a better tension effect and coating surface morphology.

[0024] The present invention also provides a grain-oriented silicon steel sheet. The grain-oriented silicon steel sheet comprises a substrate and a coating formed on the surface of the substrate. The coating is formed from the coating material described above. The coating material formed on the surface of the grain-oriented silicon steel sheet of the present invention reduces the iron loss and magnetostriction of the grain-oriented silicon steel sheet, and the tensile stress exerted by the coating of the grain-oriented silicon steel sheet is utilized to make it suitable as a core material for transformers, and to effectively reduce the energy loss and noise level of the transformer.

[0025] Preferably, the phosphates in the coating form a network or chain-like structure.

[0026] Preferably, the coating has vanadium phosphate.

[0027] Preferably, in the grain-oriented silicon steel sheet of the present invention, the dry film amount of the coating is 2 to 10 g / m² on each side. 2 The dry film thickness on one side of the coating is 2 g / m². 2 Below this level, the coating cannot provide sufficient tension, and the dry film thickness on one side of the coating is 10 g / m². 2 If this amount is exceeded, the amount of coating material becomes too large, which can lead to uneven coating thickness after heat treatment and a decrease in the lamination coefficient of the steel sheet.

[0028] The grain-oriented silicon steel substrate of the present invention is not particularly limited. Grain-oriented silicon steel substrates commonly used in the art can be used. For example, a grain-oriented silicon steel substrate with a Si element content of 2 to 4 wt% can be used.

[0029] Preferably, the thickness of the substrate is 0.18 to 0.35 mm.

[0030] Preferably, the grain-oriented silicon steel sheet also has a magnesium silicate base layer, which is formed by the reaction of a separating agent (usually MgO) on the surface of the steel sheet with silicon oxide (SiO2) under high-temperature annealing conditions (e.g., 1200°C). The silicon oxide base layer is located between the substrate and the coating of the grain-oriented silicon steel sheet, thereby improving the adhesion between the coating and the steel sheet.

[0031] Preferably, the coating of the grain-oriented silicon steel sheet is subjected to a tension of 7.1 to 10.5 MPa and 75 μg / 150 cm 2 It has a lower phosphorus elution content.

[0032] The present invention further provides a method for manufacturing a grain-oriented silicon steel sheet, wherein the surface of the grain-oriented silicon steel sheet has a coating formed from the above-mentioned coating material, and the manufacturing method comprises the following steps: 1) A step of applying the above-mentioned coating material onto a substrate of grain-oriented silicon steel sheet to form a coating on the surface of the substrate of grain-oriented silicon steel sheet; and, 2) Sintering process.

[0033] Preferably, in step 2), sintering is performed under conditions that the substrate surface temperature is 800 to 900°C and the sintering time is 20 seconds or more. If the temperature is below 800°C, the flatness of the steel plate will be insufficient and the tensile effect that the coating imparts to the steel plate will not be significant. If the temperature exceeds 900°C, the silica in the coating will be more likely to crystallize, and the density and tensile effect of the coating will decrease.

[0034] Preferably, the coating material is applied to the substrate of the grain-oriented silicon steel sheet in the form of an aqueous solution.

[0035] Preferably, the manufacturing method satisfies at least one of the following conditions: The coating material is applied to the substrate at a rate of 2-10 g / m² on each side. 2 To be applied with a dry film thickness of [amount]; The manufacturing method also includes forming a magnesium silicate layer between the substrate and the coating.

[0036] Compared to prior art, the coating material of the present invention and the grain-oriented silicon steel sheet having a coating formed from the coating material have the following beneficial effects: (1) The coating material of the present invention does not contain the harmful metallic element chromium and has good environmental advantages, as it causes little pollution to the surrounding environment; (2) The coating material of the present invention has good stability and coating performance and can be used in industrial production; and, (3) The surface coating of the grain-oriented silicon steel sheet according to the present invention has good moisture resistance, tensile strength, corrosion resistance, heat resistance, and anti-adhesion, thereby further reducing iron loss and magnetostriction of the grain-oriented silicon steel. [Modes for carrying out the invention]

[0037] Detailed description of the embodiment A more detailed description of the present invention is provided by examples, which will increase clarity and facilitate a better understanding of its contents. However, it should be noted that the examples disclosed below are merely illustrative examples of the detailed description of embodiments of the present invention. The present invention is not limited to these examples.

[0038] 1. Preparation of coating materials for surface coating of grain-oriented silicon steel The coating materials for surface coating of oriented silicon steel in Examples 1-28 and Comparative Examples 1-6 of the present invention were prepared by the following method: A phosphate solution and colloidal silica were directly mixed according to the formulations listed in Table 1, and then boric acid was optionally added in the form of a solid reagent (boric acid was not added in Example 28). After stirring thoroughly to completely dissolve the boric acid, vanadate powder was added to the solution in the form of high-speed dispersion or ultrasonic dispersion to form the coating material.

[0039] Table 1 lists the mass % (wt%) of each component and the particle size of colloidal silica in the coating materials of Examples 1 to 28 and Comparative Examples 1 to 6. Of these, the amount of vanadate in Comparative Examples 1 to 6 does not satisfy the requirement of the present invention, which is that the mass ratio of vanadate to phosphate is 0.2 to 2.0.

[0040] [Table 1-1]

[0041] [Table 1-2]

[0042] [Table 1-3]

[0043] [Table 1-4]

[0044] 2. Manufacturing of grain-oriented silicon steel sheets with surface coatings The coating materials of Examples 1-28 and Comparative Examples 1-6 were applied to grain-oriented silicon steel sheet substrates. Each grain-oriented silicon steel sheet having a coating formed from the coating material was obtained by the following process (the main technical parameters are shown in Table 2), where the grain-oriented silicon steel sheet substrate had the following chemical elements, with the mass percentages being: C: 0.046%, Si: 3.32%, S: 0.006%, soluble Al: 0.027%, N: 0.006%, Mn: 0.012%, with the remainder being Fe and other unavoidable impurities: (1) A process of obtaining steel billets by smelting and casting based on the mass percentage of each of the above chemical elements. (2) A process in which the steel billet is heated to 1150°C and then hot-rolled into a hot-rolled sheet with a thickness of 2.8 mm. (3) A process of pickling the hot-rolled sheet and then cold-rolling it to produce a cold-rolled sheet with a thickness of 0.18 to 0.35 mm. (4) After decarburization annealing, subject the cold-rolled sheet to continuous nitriding treatment in a humid ammonia-filled nitrogen and hydrogen protective atmosphere. (5) Coat the steel sheet after nitriding treatment with a magnesium oxide-based separating agent. (6) After winding the steel sheet into a coil, perform secondary recrystallization annealing in a dry protective atmosphere (such as a mixture of nitrogen and hydrogen). The annealing temperature is maintained at 1200 °C for 20 hours to obtain a substrate with a Gaussian texture covered with a bottom layer of magnesium silicate on the surface. (7) Coat the surface of the substrate with the coating material of the present invention. (8) Sinter at 800 - 900 °C for 20 seconds or more to obtain a grain-oriented silicon steel sheet with a surface coating. The dry film coating amount of the surface coating is 2 - 10 g / m on one side. 2 It is.

[0045] Table 2 shows the main process parameters of the manufacturing methods of the grain-oriented silicon steel sheets of Examples 1 - 28 and Comparative Examples 1 - 6.

[0046]

Table 2-1

[0047]

Table 2-2

[0048] 3. Performance evaluation of grain-oriented silicon steel sheets with surface coatings The grain-oriented silicon steel sheets of Examples 1 - 28 and Comparative Examples 1 - 6 of the present invention were subjected to performance tests including tests on the tension, moisture absorption resistance, heat resistance, corrosion resistance, and anti-adhesion of the coating. The test methods are as follows: (1) Tension σ of the coating: With the rolling direction as the length direction, cut the grain-oriented silicon steel sheet into a sample plate with a length of 300 mm and a width of 30 mm. Then, remove the coating, bend the sample plate to measure the amount of warp, and calculate the tension σ of the coating using the following formula.

[0049]

Equation

[0050] In the above formula, σ represents the tension of the coating, and its unit may be MPa; E represents the Young's modulus of the steel sheet, and its unit may be GPa; t represents the thickness of the steel sheet, and its unit may be mm; H represents the amount of warping, and its unit may be mm; and L represents the length of the steel sheet, and its unit may be mm. (2) Moisture resistance: After boiling the grain silicon steel sheet in pure water at 100°C, the phosphorus content dissolved in the coating per unit area was measured in μg / 150cm². 2 Quantitative analysis was performed. (3) Heat resistance: The deterioration of the tensile strength and insulating properties of the surface coating of the grain-oriented silicon steel sheet after stress relief annealing treatment was tested. The stress relief annealing treatment conditions were 850°C under 100% N2 gas for 4 hours. Heat resistance was evaluated in four stages: excellent (decrease in tensile strength and insulating properties <20%), good (decrease in tensile strength and insulating properties <30% ≤ 20%), medium (decrease in tensile strength and insulating properties <40% ≤ 30%), and poor (decrease in tensile strength and insulating properties ≥ 40%). (4) Corrosion resistance: The corrosion resistance of the coating was evaluated by a salt spray test. The salt spray test solution was a 5% NaCl solution, the test temperature was 35°C, and the test time was 10 hours. The corrosion resistance was evaluated on a four-point scale: excellent (rust area < 5%), good (5% ≤ rust area < 10%), medium (10% ≤ rust area < 30%), and poor (rust area ≥ 30%). (5) Anti-adhesion: 80 kg / cm² of the same size grain-oriented silicon steel sheets are laminated and applied to the surface of the laminated grain-oriented silicon steel sheets. 2 A vertical pressure was applied. Then, the samples were heat-treated at 850°C for 4 hours in N2 gas with a dew point of 10°C. The average peel force F between each orientation silicon steel sheet was measured to evaluate the anti-adhesion of the coating. A smaller peel force indicates better anti-adhesion. Anti-adhesion was evaluated as excellent (F < 100g / m²). 2 ), Good (100≦F<250g / m 2 ), medium (250≦F<500g / m 2 ), and defective (F≧500g / m²) 2) This was divided into four stages.

[0051] Table 3 shows the test results of the grain-oriented silicon steel sheets obtained according to the above method for Examples 1 to 28 and Comparative Examples 1 to 6.

[0052] [Table 3]

[0053] Table 3 shows that the coatings on the grain-oriented silicon steel sheets of Examples 1 to 28 of the present invention exhibit excellent tensile strength (tensile strength in the range of 7.1 to 10.5 MPa) and moisture resistance (phosphorus elution content of 75 μg / 150 cm²). 2 It is also found to have excellent or good heat resistance, corrosion resistance, and anti-adhesion properties (as described below).

[0054] The coatings on the grain-oriented silicon steel sheets of Comparative Examples 1-6 cannot simultaneously satisfy all the properties of Examples 1-28. Specifically, it has been shown that if the vanadate content is too low, the coating has the required tension, but the amount of phosphorus leaching becomes relatively high, resulting in poor moisture resistance. On the other hand, if the vanadate content is too high, although the excess vanadate fixes phosphate radicals in the coating material, the tension of the coating cannot satisfy the requirements of the present invention. Furthermore, the excellent or good heat resistance, corrosion resistance, and anti-adhesion properties required by the present invention cannot be ensured.

[0055] Preferred specific examples of the present invention have been described in detail above. Those skilled in the art should understand that various modifications and changes can be made based on the concept of the present invention without creative effort. Therefore, any technical solutions that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the prior art and in accordance with the concept of the present invention should fall within the scope of protection as defined by the claims.

[0056] Furthermore, the forms of combinations of technical features presented herein are not limited to those described in the claims or in the specific examples provided herein. All technical features described herein may be freely combined or incorporated in any form, provided they do not conflict with each other.

Claims

1. A coating material for surface coating of grain-oriented silicon steel, wherein the coating material is: It has a phosphate, wherein the phosphate is magnesium dihydrogen phosphate, aluminum dihydrogen phosphate, calcium dihydrogen phosphate, zinc dihydrogen phosphate, and / or manganese dihydrogen phosphate; It has colloidal silica; Having a vanadate, wherein the vanadate is an orthovanadate and / or metavanadate of Ce, Mn, Co, Cu, or Fe; and Here, the coating material does not contain Cr, and the mass ratio of the vanadate to the phosphate is 0.2 to 2.

0. The aforementioned coating material.

2. The coating material according to claim 1, comprising, by mass, 25-50% phosphate, 25-50% colloidal silica, and 10-50% vanadate.

3. The coating material according to claim 1, wherein the mass ratio of colloidal silica to the phosphate is 0.5 to 1.

5.

4. The coating material according to claim 1, wherein the mass ratio of colloidal silica to phosphate is 1.0 to 1.5, and / or the mass ratio of vanadate to phosphate is 0.2 to 1.

0.

5. The coating material further: It contains boric acid, wherein the boric acid content is 0.02 to 0.2 parts by mass per 100 parts by mass of colloidal silica. The coating material according to claim 1.

6. The coating material according to claim 1, wherein the particle size of the colloidal silica is 5 to 50 nm.

7. A grain-oriented silicon steel sheet having a substrate and a coating formed on the surface of the substrate, wherein the coating is formed using a coating material according to any one of claims 1 to 6.

8. The grain-oriented silicon steel sheet according to claim 7, wherein the phosphate in the coating forms a network or chain structure.

9. The grain-oriented silicon steel sheet according to claim 7, wherein the coating comprises vanadium phosphate.

10. The dry film amount on one side of the aforementioned coating is 2 to 10 g / m². ２ The grain-oriented silicon steel sheet according to claim 7.

11. The grain-oriented silicon steel sheet according to claim 7, wherein the grain-oriented silicon steel sheet further has a magnesium silicate layer, and the magnesium silicate layer is located between the substrate and the coating of the grain-oriented silicon steel sheet.

12. The coating on the grain-oriented silicon steel sheet is subjected to a tension of 7.1 to 10.5 MPa and 75 μg / 150 cm. ２ The grain-oriented silicon steel sheet according to claim 7, having a lower phosphorus elution content.

13. A method for manufacturing grain-oriented silicon steel sheets, the manufacturing method comprising the following steps, the steps being: 1) A step of applying the coating material according to any one of claims 1 to 6 onto the substrate of the grain-oriented silicon steel sheet; and, 2) A step of performing sintering to form a coating on the surface of the substrate of the grain-oriented silicon steel sheet, wherein the surface temperature of the substrate during sintering is 800 to 900°C, and the sintering time is 20 seconds or more. The aforementioned manufacturing method.

14. The manufacturing method satisfies one or more of the following conditions, and the conditions are: The coating material is applied to the substrate at a rate of 2 to 10 g / m² on each side. ２ To be applied with a dry film thickness of ; The manufacturing method further includes forming a magnesium silicate layer between the substrate and the coating. The manufacturing method according to claim 13.

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