Insulating coating composition for electrical steel sheet, electrical steel sheet, and method for producing same

Abstract

An insulating coating composition for an electrical steel sheet according to one embodiment of the present invention contains 100 parts by weight of a metal phosphate, 25 to 150 parts by weight of silica, 15 to 60 parts by weight of a metal oxyhydroxide, and 0.5 to 10 parts by weight of a reducing agent.

Description

Technical Field

[0001] One embodiment of the present invention relates to an insulating film composition for an electrical steel sheet, an electrical steel sheet, and a method for manufacturing the same. Specifically, the present invention relates to an insulating film composition for an electrical steel sheet, an electrical steel sheet, and a method for manufacturing the same. By appropriately combining the components of the insulating film composition, the composition exhibits excellent durability and extreme corrosion resistance in high-temperature and high-humidity environments, as well as excellent heat resistance at very high temperatures, such as during stress relief annealing (SRA). Background Art

[0002] Electrical steel sheet is used as a material for transformers, motors, and electrical equipment. Unlike ordinary carbon steel, which prioritizes mechanical properties and workability, electrical steel sheet is a functional product that prioritizes electrical properties. Required electrical properties include low iron loss, high magnetic flux density, high magnetic permeability, and a high space factor.

[0003] Electrical steel sheets are divided into oriented electrical steel sheets and non-oriented electrical steel sheets. Oriented electrical steel sheets use the abnormal grain growth phenomenon called secondary recrystallization to form a Gaussian texture ({110} <001> Non-oriented electrical steel sheets are electrical steel sheets that have uniform magnetic properties in all directions of the rolled sheet.

[0004] Meanwhile, the insulation coating formation process, which corresponds to the final manufacturing process of the product, requires not only electrical properties that suppress eddy currents but also continuous punching processability to minimize die wear when punching into a predetermined shape and then stacking multiple layers to create an iron core. Furthermore, the SRA process, which eliminates processing stress in the steel sheets and restores their magnetic properties, prevents adhesion between the core steel sheets and maintains surface adhesion. In addition to these fundamental properties, coating solutions are also required to exhibit excellent coating workability and long-term stability after preparation. Coating solutions used for these purposes include chromium coating solutions based on chromic acid and phosphate coating solutions based on phosphates.

[0005] Such coating solutions have the disadvantage of poor corrosion resistance. In addition, it is known that if chromium is not added, the physical properties of various solutions are relatively poor. Therefore, it is hoped that an environmentally friendly and relatively excellent corrosion-resistant insulating coating will be developed. Summary of the Invention

[0006] (1) Technical issues to be resolved

[0007] One embodiment of the present invention provides an insulating film composition for an electrical steel sheet, an electrical steel sheet, and a method for manufacturing the same. Specifically, one embodiment of the present invention provides an insulating film composition for an electrical steel sheet, an electrical steel sheet, and a method for manufacturing the same. By appropriately combining the components of the insulating film composition, the composition exhibits excellent durability and extreme corrosion resistance in high-temperature and high-humidity environments, as well as excellent heat resistance at very high temperatures, such as during stress relief annealing (SRA).

[0008] (2) Technical solution

[0009] According to one embodiment of the present invention, the insulating coating composition for an electrical steel sheet comprises 100 parts by weight of a metal phosphate, 25 to 150 parts by weight of silicon dioxide, 15 to 60 parts by weight of a metal oxyhydroxide, and 0.5 to 10 parts by weight of a reducing agent.

[0010] The metal phosphate may contain one or more of Mg, Ca, Ba, Sr, Zn, and Al.

[0011] The silica may have a pH of 8 to 12.

[0012] The metal oxyhydroxide may include one or more of TiOOH, ZrOOH, and MnOOH.

[0013] The reducing agent may include one or more of ammonia, glycol, polyol, and sulfate.

[0014] The reducing agent may include one or more of ammonia, ethylene glycol, propane-1,2,3-triol, and sodium sulfate.

[0015] An electrical steel sheet according to one embodiment of the present invention includes an electrical steel sheet substrate and an insulating coating located on a surface of the electrical steel sheet substrate, wherein the insulating coating includes 100 parts by weight of a metal phosphate, 25 to 150 parts by weight of silicon dioxide, 15 to 60 parts by weight of a metal oxyhydroxide, and 0.5 to 10 parts by weight of a reducing agent.

[0016] According to one embodiment of the present invention, a method for manufacturing an electrical steel sheet includes: preparing an electrical steel sheet substrate; applying an insulating coating composition on a surface of the electrical steel sheet substrate; and heat-treating the electrical steel sheet substrate, wherein the insulating coating composition includes 100 parts by weight of a metal phosphate, 25 to 150 parts by weight of silicon dioxide, 15 to 60 parts by weight of a metal oxyhydroxide, and 0.5 to 10 parts by weight of a reducing agent.

[0017] The heat treatment step may be performed at a temperature of 750 to 1000° C. for 10 to 300 seconds.

[0018] (3) Beneficial effects

[0019] According to one embodiment of the present invention, the present invention has excellent durability and extreme corrosion resistance in a high-temperature and high-humidity environment, and has excellent heat resistance at a temperature with very high workability such as stress relief annealing (SRA).

[0020] According to one embodiment of the present invention, it has a very excellent insulation effect in a high-frequency magnetic field environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 FIG. 4 is a schematic cross-sectional view of an electrical steel sheet according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The terms "first," "second," and "third" are used to describe various parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, and / or segment from another part, component, region, layer, and / or segment. Therefore, a first part, component, region, layer, and / or segment described below could also be described as a second part, component, region, layer, and / or segment without departing from the scope of the present invention.

[0023] The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention. Unless the context clearly indicates otherwise, the singular forms used herein are intended to include the plural forms. As used in the specification, "comprising" may specifically refer to a certain characteristic, field, integer, step, action, element and / or component, but does not exclude the presence or addition of other characteristics, fields, integers, steps, actions, elements, components and / or groups.

[0024] If a part is described as being "on" another part, then the other part may be directly on the other part or there may be another part therebetween. If a part is described as being "directly on" another part, then there may not be another part therebetween.

[0025] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Dictionary-defined terms should be interpreted as having the same meaning as that in the relevant technical literature and disclosed herein, and should not be interpreted in an idealized or overly formal sense.

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various ways and is not limited to the embodiments described herein.

[0027] The insulating coating composition for an electrical steel sheet according to one embodiment of the present invention includes 100 parts by weight of a metal phosphate, 25 to 150 parts by weight of silicon dioxide, 15 to 60 parts by weight of a metal oxyhydroxide, and 0.5 to 10 parts by weight of a reducing agent.

[0028] The following describes each component in detail. In one embodiment of the present invention, parts by weight refer to relative weight ratios based on 100 parts by weight of the metal phosphate, and are based on the solid content of each component. Solid content refers to the weight of each component when dried to a state free of volatile substances such as solvents. Specifically, it refers to the weight remaining after heat treatment, assuming that a heat treatment process is performed during the formation of the insulating coating.

[0029] The metal phosphate acts as a binder in the insulating coating composition. If the metal phosphate is not included in an appropriate amount, the adhesion of the insulating coating will deteriorate or the tension cannot be fully obtained. The metal phosphate can be manufactured by a manufacturing process in which a metal oxide is added to pure phosphoric acid (H3PO4) to react. In order to improve the adhesion of the metal phosphate, boric acid can be further added during the reaction and maintained for more than 3 hours to induce a condensation reaction between the metal phosphate and the boric acid, and the condensation reactant can also be used instead of the metal phosphate. In one embodiment of the present invention, the metal phosphate includes not only the metal phosphate, but also the condensation reactant of the metal phosphate and boric acid. The manufactured metal phosphate has a strong acidity.

[0030] The metal phosphate can be added to the composition using a solution having a solid content of 50 to 70% by weight. If the solid content of the solution is too low, free phosphoric acid in the metal phosphate may increase, potentially leading to surface moisture absorption after the metal phosphate is produced. If the solid content is too high, the excess solid content relative to pure phosphoric acid may result in poor reaction and precipitation.

[0031] The metal phosphate and the metal oxide may contain various metals without limitation. Specifically, the metal of the metal phosphate and the metal oxide may contain one or more of Mg, Ca, Ba, Sr, Zn and Al. More specifically, the metal phosphate may contain one or more of a first magnesium phosphate (Mg(H2PO4)2) and a first aluminum phosphate (Al(H2PO4)3). More specifically, it may contain a first magnesium phosphate (Mg(H2PO4)2) and a first aluminum phosphate (Al(H2PO4)3). In this case, based on solids, the metal phosphate may contain 10 to 40 parts by weight of the first aluminum phosphate and 60 to 90 parts by weight of the first magnesium phosphate relative to a total of 100 parts by weight. If the content of the first aluminum phosphate is too little, the tension-enhancing effect brought about by the addition of the first aluminum phosphate may not be sufficient. When too much first aluminum phosphate is added, the Al component will increase the crystallization of silicon dioxide, which may cause cracks in the insulating coating. Specifically, based on solids, the metal phosphate may include 15 to 35 parts by weight of the first aluminum phosphate and 65 to 85 parts by weight of the first magnesium phosphate, more specifically 20 to 30 parts by weight of the first aluminum phosphate and 70 to 80 parts by weight of the first magnesium phosphate, relative to a total of 100 parts by weight.

[0032] The insulating coating composition for an electrical steel sheet according to one embodiment of the present invention includes 25 to 150 parts by weight of silicon dioxide relative to 100 parts by weight of the metal phosphate.

[0033] Silica is an essential component for imparting tension to the steel sheet and reducing iron loss. If the silica content is too low, it will be difficult to achieve a sufficient tension-imparting effect on the steel sheet. If the silica content is too high, problems with viscosity or solution stability may arise. More specifically, the silica content may be 30 to 130 parts by weight, and more specifically 35 to 100 parts by weight, per 100 parts by weight of the metal phosphate.

[0034] The silica can include both basic and acidic silica, more specifically basic silica. Including basic silica improves the stability of the insulating coating composition and enhances the shelf life of the solution. The basic silica can have a pH of 8 to 12. The silica can be dispersed in a colloidal form to measure pH.

[0035] The silicon dioxide can have an average particle size of 5 to 20 nm. If the average particle size of the silicon dioxide is too small, the condensation reaction speed is accelerated, thereby causing agglomeration, which may lead to color difference defects on the surface. If the average particle size is too large, the surface area per unit mass is reduced, the condensation reaction speed slows down, and defects may be generated. More specifically, the silicon dioxide can have an average particle size of 10 to 15 nm. In one embodiment of the present invention, the particle size can be measured using a particle size measuring instrument (Zeta Potential), and the average particle size is the arithmetic mean.

[0036] The silicon dioxide may be composed of at least one nanoparticle having different average particle sizes. Specifically, in order to form an insulating film having excellent film properties, the silicon dioxide may be mixed with at least one silicon dioxide nanoparticle having different average particle sizes.

[0037] The insulating coating composition for an electrical steel sheet according to one embodiment of the present invention comprises 15 to 60 parts by weight of a metal oxyhydroxide relative to 100 parts by weight of a metal phosphate. x (OOH) y A compound wherein M represents a metal and x and y represent a ratio according to the oxidation number of the metal. For conventional insulating coating compositions, oxide particles such as TiO2, ZrO2, and MnO2 are sometimes included as inorganic ceramic particles. However, in this case, the solution will gel, and there are problems with the stability of the solution. On the other hand, as described in one embodiment of the present invention, when the insulating coating composition is added in the form of a metal hydroxide oxide, it is dissolved in the solution in the composition state, and the stability of the solution has advantages. In addition, during the formation of the insulating coating, the metal hydroxide oxide reacts with the reducing agent to become an insoluble substance. That is, if it is present in the insulating coating composition in the form of a metal hydroxide oxide, the viscosity of the solution will remain close to the Newtonian fluid properties required for natural coater applications. Specifically, the viscosity of the insulating coating composition can be maintained below 10 c.p. More specifically, the viscosity can be 1 to 10 c.p. At this time, the viscosity can be measured based on a Brookfield viscometer at a temperature of 30°C.

[0038] If the metal oxyhydroxide content is too low, the weather resistance and corrosion resistance of the insulating film may be deteriorated. If the metal oxyhydroxide content is too high, the solution stability may be affected. More specifically, the metal oxyhydroxide may be included in an amount of 20 to 55 parts by weight.

[0039] The metal oxyhydroxide may include one or more of TiOOH, ZrOOH, and MnOOH. More specifically, one or more of TiOOH and ZrOOH may be included. More specifically, both TiOOH and ZrOOH may be included. If both TiOOH and ZrOOH are included, 10 to 40 parts by weight of TiOOH and 10 to 40 parts by weight of ZrOOH may be included. More specifically, 10 to 15 parts by weight of TiOOH and 10 to 40 parts by weight of ZrOOH may be included.

[0040] The insulating coating composition for an electrical steel sheet according to one embodiment of the present invention includes 0.5 to 10 parts by weight of a reducing agent relative to 100 parts by weight of the metal phosphate.

[0041] The reducing agent is not limited, and any substance can be used as long as it causes the metal oxyhydroxide to undergo a reduction reaction during the film formation process and become an insoluble substance.

[0042] Specifically, it may contain one or more of ammonia, glycol, polyol, and sulfate. More specifically, it may contain one or more of ammonia, ethylene glycol, propane-1,2,3-triol, and sodium sulfate.

[0043] If the reducing agent is too little, it is difficult to fully reduce the metal oxyhydroxide. If the reducing agent is too much, the solution may gel, which may cause problems in the stability of the solution. More specifically, the reducing agent can be included in an amount of 1 to 5 parts by weight.

[0044] In addition to the aforementioned ingredients, the composition for forming an insulating coating may also include a solvent. The solvent facilitates application of the composition and ensures uniform dispersion of the ingredients. The amount of solvent is not particularly limited, but may range from 100 to 1000 parts by weight relative to 100 parts by weight of the metal phosphate.

[0045] Figure 1 FIG. 1 is a schematic cross-sectional view of an electrical steel sheet 100 according to an embodiment of the present invention. Figure 1 As shown, an electrical steel sheet 100 according to one embodiment of the present invention includes an electrical steel sheet substrate 10 and an insulating film 20 located on the electrical steel sheet substrate 10 .

[0046] The electrical steel sheet substrate 10 may be a general non-oriented or oriented electrical steel sheet without limitation. In one embodiment of the present invention, the main technical feature is the formation of an insulating film 20 of a special composition on the electrical steel sheet substrate 10, so a detailed description of the electrical steel sheet substrate 10 is omitted.

[0047] Supplementary description of the composition of the grain-oriented electrical steel sheet matrix is as follows.

[0048] The grain-oriented electrical steel sheet substrate may include 2.0 to 7.0 wt% of silicon (Si), 0.020 to 0.040 wt% of aluminum (Al), 0.01 to 0.20 wt% of manganese (Mn), 0.01 to 0.15 wt% of phosphorus (P), 0.01 wt% or less of carbon (C) and excluding 0%, 0.005 to 0.05 wt% of nitrogen (N), and 0.01 to 0.15 wt% of antimony (Sb), tin (Sn), or a combination thereof, with the remainder comprising Fe and other unavoidable impurities. The description of the components of the grain-oriented electrical steel sheet substrate 10 is the same as that generally known, and thus a detailed description is omitted.

[0049] A metal oxide layer (primer coating, primary coating) may exist between the oriented electrical steel sheet substrate and the insulating coating, formed during the secondary recrystallization process by reacting with the annealing separator and the steel sheet's oxide layer. An example of a metal oxide layer is a forsterite layer. By suppressing the formation of the metal oxide layer or removing the metal oxide layer during the manufacturing process of the oriented electrical steel sheet, the oriented electrical steel sheet substrate and the insulating coating can also be in contact.

[0050] The thickness of the insulating film 20 can be 0.5 to 10 μm. If the insulating film 20 is too thin, it can be difficult to ensure adequate insulation. If the insulating film 20 is too thick, the space factor can decrease. In one embodiment of the present invention, even with a thin insulating film 20, adequate insulation can be ensured. More specifically, the thickness of the insulating film 20 can be 1 to 5 μm.

[0051] The insulating film 20 comprises 100 parts by weight of a metal phosphate, 25 to 150 parts by weight of silicon dioxide, 15 to 60 parts by weight of a metal oxyhydroxide, and 0.5 to 10 parts by weight of a reducing agent. The insulating film may have substantially the same solid content as the aforementioned insulating film composition.

[0052] According to one embodiment of the present invention, a method for manufacturing an electrical steel sheet includes the steps of preparing an electrical steel sheet substrate; coating an insulating coating composition on a surface of the electrical steel sheet substrate; and heat treating.

[0053] The electrical steel sheet substrate and the insulating film composition are described in detail above, and thus repeated description is omitted.

[0054] As an example, an electrical steel sheet substrate may be manufactured as follows.

[0055] Prepare a steel slab. In the next step, the steel slab is heated. At this time, for the slab heating, it can be heated at a temperature below 1200°C by a slab low-temperature heating method. Next, the heated steel slab is hot rolled to produce a hot-rolled plate. Then, the produced hot-rolled plate can be hot-rolled annealed. Next, the hot-rolled plate is cold rolled to produce a cold-rolled plate. For cold rolling, one cold rolling can be carried out or two or more cold rollings including intermediate annealing can be carried out. Next, a recrystallization annealing is performed on the cold-rolled plate. At this time, the step of performing a recrystallization annealing on the cold-rolled plate can include the step of performing decarburization annealing and nitriding annealing on the cold-rolled plate at the same time or the step of performing nitriding annealing after decarburization annealing. Next, an annealing separator is applied to the surface of the steel plate after the recrystallization annealing. The coating amount of the annealing separator can be 1 to 5 g / m 2 . If the coating amount of the annealing separator is too small, the coating may not be formed smoothly. If the coating amount of the annealing separator is too much, the secondary recrystallization may be affected. Therefore, the coating amount of the annealing separator can be adjusted to the aforementioned range. Next, the steel plate coated with the annealing separator is subjected to secondary recrystallization annealing. During the secondary recrystallization annealing, the primary soaking temperature may be 650 to 750°C, and the secondary soaking temperature may be 1100 to 1250°C. Within the temperature range of the heating section, it can be controlled under the condition of 15°C / hour (hr). In addition, for the gas environment, until the primary soaking step can be carried out in an environment containing 20 to 30 volume % nitrogen and 70 to 80 volume % hydrogen, the secondary soaking step can be kept in a 100% gas environment for 15 hours and then furnace cooled (furnace cooling).

[0056] During the heat treatment step, the heat treatment temperature may be 700 to 1000°C. If the temperature is too low, the time required to form the insulating coating may be too long, potentially resulting in poor continuous processing operability. If the temperature is too high, cracking may occur, leading to decreased heat resistance and bluing resistance. More specifically, the heat treatment temperature may be 750 to 950°C. More specifically, it may be 750 to 900°C. The heat treatment time may be 10 to 300 seconds. More specifically, it may be 30 to 180 seconds.

[0057] The heat treatment environment may be a nitrogen environment.

[0058] Hereinafter, preferred embodiments of the present invention, comparative examples thereof, and evaluation examples thereof will be described. However, the following embodiment is only a preferred embodiment of the present invention, and the present invention is not limited to the following embodiment.

[0059] Example

[0060] As the test material, oriented electrical steel sheets (300 60mm), which contains 3.1% Si by weight, has a thickness of 0.23mm, and has a primary coating after final annealing.

[0061] The components were mixed in the proportions shown in Table 1 below to produce an insulating coating composition. First, alkaline colloidal silica (average particle size 15 nm, pH 10) was added to a phosphate solution containing 50 parts by weight of aluminum phosphate and 50 parts by weight of magnesium phosphate, and the mixture was mixed. Then, a metal oxyhydroxide and a reducing agent were added to produce the insulating coating composition.

[0062] The prepared solution was heated at 3.1 g / mm 2 The coating was applied to both sides of an electrical steel sheet and heat treated at 850°C for 45 seconds to form an insulating film with a thickness of 1 μm.

[0063] Weather resistance, corrosion resistance, solution stability, and adhesion were evaluated by the following methods and the results are shown in Table 2.

[0064] Evaluation of weather resistance

[0065] Weather resistance was evaluated under conditions of 98% moisture, 60° C., and 72 hours, with a good result being indicated as “OK” and a poor result being indicated as “NG”.

[0066] Evaluation of corrosion resistance

[0067] A salt spray test was conducted at 5% NaCl, 100 RH, and 65°C for 8 hours. Good results were indicated as "Good" and poor results were indicated as "Poor."

[0068] Evaluation of solution stability

[0069] The solution was allowed to stand at 30° C. for 72 hours and then measured with a Brookfield viscometer. A viscosity of 10 cp or less was considered good, and a viscosity of more than 10 cp was considered poor.

[0070] Evaluation of adhesion

[0071] Adhesion was evaluated by heating at 560°C for 2 hours in an atmosphere of 20% hydrogen and 80% nitrogen. Adhesion was then evaluated by a cross-hatch cut test.

[0072] When the test result is 5B or more, it is good and is indicated as "good", and when it is less than 5B, it is poor and is indicated as "poor".

[0073]

Table 1

[0074]

[0075]

Table 2

[0076]

[0077] As shown in Tables 1 and 2, when the components of the insulating coating composition are included in appropriate amounts, excellent weather resistance, corrosion resistance, solution stability, and adhesion are confirmed. On the other hand, when the components of the insulating coating composition are not included in appropriate amounts, some properties are confirmed to deteriorate. In particular, when TiO2 and ZrO2 powders are added instead of metal oxyhydroxides, gelation of the solution is confirmed, resulting in a decrease in solution stability.

[0078] The present invention can be implemented in various ways and is not limited to the above-described embodiments. A person skilled in the art will appreciate that the present invention can be implemented in other specific ways without changing the technical concept or essential features of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not restrictive.

[0079] [Explanation of Reference Signs]

[0080] 100: electrical steel sheet; 10: electrical steel sheet substrate

[0081] 20: Insulation coating

Claims

1. An insulating film composition for an electrical steel sheet, comprising: 100 parts by weight of metal phosphate; 25 to 150 parts by weight of silicon dioxide; 15 to 60 parts by weight of a metal oxyhydroxide; and 0.5 to 10 parts by weight of a reducing agent.

2. The insulating film composition for an electrical steel sheet according to claim 1, wherein The metal phosphate contains one or more of Mg, Ca, Ba, Sr, Zn and Al.

3. The insulating film composition for electrical steel sheets according to claim 1, wherein The silica has a pH of 8 to 12.

4. The insulating film composition for an electrical steel sheet according to claim 1, wherein The metal oxyhydroxide includes one or more of TiOOH, ZrOOH, and MnOOH.

5. The insulating film composition for electrical steel sheets according to claim 1, wherein The reducing agent includes one or more of ammonia, glycol, polyol and sulfate.

6. The insulating film composition for electrical steel sheets according to claim 1, wherein The reducing agent includes one or more of ammonia, ethylene glycol, propane-1,2,3-triol and sodium sulfate.

7. An electrical steel sheet comprising: an electrical steel sheet substrate; and an insulating film on the surface of the electrical steel sheet substrate, The insulating film includes 100 parts by weight of metal phosphate, 25 to 150 parts by weight of silicon dioxide, 15 to 60 parts by weight of metal oxyhydroxide, and 0.5 to 10 parts by weight of a reducing agent.

8. A method for manufacturing an electrical steel sheet, comprising: The step of preparing an electrical steel sheet substrate; The step of coating an insulating coating composition on the surface of the electrical steel sheet substrate; and The step of heat treating the electrical steel sheet substrate, The insulating coating composition includes 100 parts by weight of a metal phosphate, 25 to 150 parts by weight of silicon dioxide, 15 to 60 parts by weight of a metal oxyhydroxide, and 0.5 to 10 parts by weight of a reducing agent.

9. The method for manufacturing an electrical steel sheet according to claim 8, wherein: The heat treatment step is performed at a temperature of 750 to 1000° C. for 10 to 300 seconds.

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