EP4640919A1

EP4640919A1 - Insulation coating composition, grain-oriented electrical steel sheet comprising same, and method of manufacturing grain-oriented electrical steel sheet

Info

Publication number: EP4640919A1
Application number: EP23907564.1A
Authority: EP
Inventors: Hyunjong KIM; Heonjo CHOI; Minserk KWON
Original assignee: Posco Co Ltd
Current assignee: Posco Holdings Inc
Priority date: 2022-12-19
Filing date: 2023-12-13
Publication date: 2025-10-29
Also published as: JP2026501245A; KR20240096116A; CN120283081A; WO2024136278A1

Abstract

An insulation coating composition for a grain-oriented electrical steel sheet according to an embodiment of the present disclosure includes: phosphate; silica; nitrate; and an oxidizer. The silica includes 50 to 400 parts by weight of a solid content based on 100 parts by weight of the phosphate, a mixing ratio of a solid content of the silica to a solid content of the phosphate is 0.3 to 3.9, and the oxidizer includes 0.5 to 10.0 parts by weight of a solid content based on 100 parts by weight of the phosphate.

Description

[Technical Field]

The present disclosure relates to an electrical steel sheet, and more particularly, to an insulation coating composition, a grain-oriented electrical steel sheet including the same, and a method of manufacturing the grain-oriented electrical steel sheet.

[Background Art]

An electrical steel sheet is a product used as a material for a transformer, a motor, and an electrical device, and unlike a general carbon steel that emphasizes processability such as a mechanical characteristic, the electrical steel sheet is a functional product that emphasizes an electrical characteristic. The electrical characteristic required for the electrical steel sheet includes low iron loss, high magnetic flux density, high permeability, and a high space factor. The electrical steel sheet is classified into a grain-oriented electrical steel sheet and a non-oriented electrical steel sheet. The grain-oriented electrical steel sheet is an electrical steel sheet with an excellent magnetic characteristic in a rolling direction by forming a Goss structure ({110}<001> texture) throughout the steel sheet using an abnormal grain growth phenomenon called secondary recrystallization. In contrast, the non-oriented electrical steel is an electrical steel of which a magnetic characteristic is uniform in all directions on a rolled sheet. In order to secure stability over time in the grain-oriented electrical steel sheet, it is important to secure a physical property such as surface roughness, glossiness, chromaticity, or uniformity of an insulation coating. For example, in the grain-oriented electrical steel sheet, it is necessary to have excellent durability in an extremely high-temperature and high-humidity environment such as SRA processing, have a higher effect than before in an extreme corrosion resistance environment, and secure heat resistance at a high temperature. The grain-oriented electrical steel sheet has a general coating configuration including a MgO coating on a base material and an insulation coating on an upper surface thereof. The insulation coating generally includes phosphate, silica, and nitrate. A general condition of conventional corrosion resistance is 5% NaCl, 60 °C, and 8 hours. An extreme condition of corrosion resistance for an accessory of a vehicle used for a long time is 5% NaCl, 65 °C, and 100 hours when salt water is sprayed. A general condition of weather resistance is 72 hours at 98% moisture and 60 °C, but an extreme condition of weather resistance is 100 hours at 98% moisture and 65 °C. A general insulation coating has excellent corrosion resistance, but has a disadvantage of being vulnerable to weather resistance and having a sticky surface. The sticky characteristic may cause a problem in an adhesive property when a wound coil is wound. Therefore, in the insulation coating, it is necessary to develop a chromium-free phosphate coating for the grain-oriented electrical steel sheet in which a layer and a material are not separated even in a high-humidity environment, and to develop an insulation coating composition that solves a problem of being vulnerable to a high-humidity environment with a sticky nature of a surface caused by phosphate.

[Disclosure]

[Technical Problem]

A technical problem to be solved by the present disclosure provides an insulation coating composition for a grain-oriented electrical steel sheet including a coating material in which a layer (or a film) and a material are not separated even in a high-temperature and high-humidity environment.
Another technical problem to be solved by the present disclosure provides a grain-oriented electrical steel sheet coated with the insulation coating composition having the above-described advantage.
Another technical object to be solved by the present disclosure provides a method of manufacturing the grain-oriented electrical steel sheet having the above-described advantage.

[Technical Solution]

An insulation coating composition for a grain-oriented electrical steel sheet according to an embodiment of the present disclosure includes: phosphate; silica; nitrate; and an oxidizer. The silica includes 50 to 400 parts by weight of a solid content based on 100 parts by weight of the phosphate, a mixing ratio of a solid content of the silica to a solid content of the phosphate is 0.3 to 3.9, and the oxidizer includes 0.5 to 10.0 parts by weight of a solid content based on 100 parts by weight of the phosphate. In an embodiment, the nitrate may include at least one of aluminum nitrate (Al(NO₃)₃), cobalt nitrate (Co(NO₃)₂), calcium nitrate (Ca(NO₃)₂), strontium nitrate (Sr(NO₃)₂), zinc nitrate (Zn(NO₃)₂), manganese nitrate (Mn(NO₃)₂), magnesium nitrate (Mg(NO₃)₂), and silver nitrate (AgNO₃).
In an embodiment, the nitrate may include at least two of aluminum nitrate (Al(NO₃)₃), cobalt nitrate (Co(NO₃)₂), calcium nitrate (Ca(NO₃)₂), strontium nitrate (Sr(NO₃)₂), zinc nitrate (Zn(NO₃)₂), manganese nitrate (Mn(NO₃)₂), magnesium nitrate (Mg(NO₃)₂), and silver nitrate (AgNO₃). In an embodiment, the nitrate may include 5 to 100 parts by weight of a solid content based on 100 parts by weight of the phosphate. In an embodiment, the oxidizer may include at least one of HClO₄, NaClO, NaClO₄, KMnO₄, NalO₄, OsO₄, H₂O₂, and Ca(ClO)₂.
A grain-oriented electrical steel sheet according to an embodiment of the present disclosure includes: an electrical steel sheet substrate; and an insulation coating that is disposed on a surface of the electrical steel sheet substrate. The insulation coating includes phosphate, silica, nitrate, and an oxidizer, the silica includes 50 to 400 parts by weight of a solid content based on 100 parts by weight of the phosphate, a mixing ratio of a solid content of the silica to a solid content of the phosphate is 0.3 to 3.9, and the oxidizer includes 0.5 to 10.0 parts by weight of a solid content based on 100 parts by weight of the phosphate.
A method of manufacturing the grain-oriented electrical steel sheet according to an embodiment of the present disclosure includes: preparing an electrical steel sheet substrate; applying an insulation coating composition to a surface of the electrical steel sheet substrate; and curing the insulation coating composition. The insulation coating composition includes phosphate, silica, nitrate, and an oxidizer, the silica includes 50 to 400 parts by weight of a solid content based on 100 parts by weight of the phosphate, a mixing ratio of a solid content of the silica to a solid content of the phosphate is 0.3 to 3.9, the oxidizer includes 0.5 to 10.0 parts by weight of a solid content based on 100 parts by weight of the phosphate, and the curing of the insulation coating composition is performed in a range of 800 to 900 °C for a range of 30 to 180 seconds.
In an embodiment, the applying of the insulation coating composition to the surface of the electrical steel sheet substrate may include mixing the phosphate and the silica, adding the nitrate to a mixed solution, and adding the oxidizer after the adding of the nitrate to the mixed solution. In an embodiment, the preparing of the electrical steel sheet substrate may include: preparing a steel slab; heating the steel slab; hot-rolling the heated steel slab to manufacture a hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet; performing primary recrystallization annealing on the cold-rolled steel sheet; applying an annealing separator on the primary recrystallization-annealed steel sheet; and performing secondary recrystallization annealing.
In an embodiment, the applying of the annealing separator on the primary recrystallization-annealed steel sheet may include applying the annealing separator in a range of 1 to 5 g/m². In an embodiment, the performing of the secondary recrystallization annealing may include cracking and temperature raising, and the cracking may be performed in a range of 650 to 750 °C, and the temperature raising may be performed in a range of 1,100 to 1,250 °C.
In an embodiment, the temperature raising may be performed at a temperature raising speed in a range of 10 to 20 °C/hr. In an embodiment, the cracking may be performed in two or more gas atmospheres among a hydrogen gas atmosphere, a nitrogen gas atmosphere, and an inert gas atmosphere. In an embodiment, the temperature raising may be performed in a hydrogen atmosphere.

[Advantageous Effects]

An insulation coating composition according to an embodiment of the present disclosure may provide an insulation coating composition for a grain-oriented electrical steel sheet having excellent durability and extreme corrosion resistance in a high-temperature and high-humidity environment and having excellent heat resistance at a temperature in which processability such as SRA is very high by adding an oxidizer for removing a hydrogen group of phosphate to the grain-oriented electrical steel sheet.
A grain-oriented electrical steel sheet according to an embodiment of the present disclosure may provide a grain-oriented electrical steel sheet coated with the above-described insulation coating composition.
According to an embodiment of the present disclosure, a method of manufacturing the grain-oriented electrical steel sheet having the above-described advantage may be provided.

[Mode for Invention]

Terms such as "first", "second", and "third" are used herein to describe various portions, components, regions, layers, and/or sections, but are not limited thereto. The terms are used only to distinguish one portion, component, region, layer, or section from another portion, component, region, layer, or section. Accordingly, a first portion, component, region, layer, or section described below may be referred to as a second portion, component, region, layer, or section within a scope that does not depart from a scope of the present disclosure.
A technical term used herein is intended only to refer to a specific embodiment, and is not intended to limit the present disclosure. Singular forms used herein also include plural forms unless phrases clearly indicate an opposite meaning. A term "include" used in the specification specifies a specific characteristic, region, integer, step, operation, element, and/or component, and does not exclude presence or addition of another characteristic, region, integer, step, operation, element, and/or component.
When it is said that a portion is "on" or "above" another portion, the portion may be disposed directly on or above the other portion, or another portion may be interposed therebetween.
In contrast, when a portion is said to be "directly above" another portion, no other portion is interposed therebetween.
Although not otherwise defined, all terms used herein, including a technical term and a scientific term, have the same meanings as those generally understood by a person of ordinary skill in the art to which the present disclosure belongs. Terms defined in a dictionary commonly used are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed contents, and are not interpreted in an ideal or very formal sense unless otherwise defined.
Unless otherwise stated, % means wt%, and 1 ppm is 0.0001 wt%.
In an embodiment of the present disclosure, inclusion of an additional element means replacing the balance of iron (Fe) by an additional amount of the additional element.
Hereinafter, an embodiment of the present disclosure will be described in detail so that a person of ordinary skill in the art to which the present disclosure belongs may easily implement the present disclosure. The present disclosure may be modified in various ways, all without departing from the spirit or scope of the present disclosure.
An insulation coating composition for a grain-oriented electrical steel sheet according to an embodiment of the present disclosure may include phosphate, silica, nitrate, and an oxidizer. The phosphate may be metal phosphate, and may satisfy M(H₂PO₄) or M(HPO₄). The M may include Mg, Al, Zn, Ca, or a combination thereof. For example, the M may be a phosphate including Mg and Al.
The silica may be a component necessary to reduce iron loss by providing tension to the steel sheet. In addition, the phosphate may act as a binder for the silica so that it improves a film-forming property of the coating and enhances a close contacting property of the coating. In an embodiment, the silica may be a basic or acidic material.
In an embodiment, the silica may include 50 to 400 parts by weight of a solid content based on 100 parts by weight of the phosphate. For example, the silica may include 80 to 200 parts by weight, 135 to 180 parts by weight, or 145 to 160 parts by weight based on 100 parts by weight of the phosphate.
If a range of the silica is out of an upper limit value, it may be confirmed that the silica has a poor effect in a sticky property or solution stability. If the range of the silica is out of a lower limit value, there may be a problem in which an effect of applying tension to the steel sheet is insufficient.
In an embodiment, the silica may have an average particle diameter in a range of 5 to 20 nm. If the average particle diameter of the silica is out of the upper limit value of the range, a surface area per unit mass may be decreased so that a speed of a condensation reaction is decreased, and there may be an uneconomic problem because a heat treatment temperature should be increased to increase the reaction speed. If the average particle diameter of the silica is out of the lower limit value of the range, the speed of the condensation reaction may be fast so that an agglomeration phenomenon occurs, and there may be a problem that causes a color deviation defect on a surface thereof.
In an embodiment, the silica may include at least one nanoparticle having different average particle diameters. For example, the silica may be used by mixing at least one silica nanoparticle having different average particle diameters to form an insulation coating having an excellent coating characteristic.
In an embodiment, a mixing ratio of a solid content of the silica to a solid content of the phosphate may be 0.3 to 3.9. For example, the mixing ratio may be 0.5 to 2.0. Because the silica and the phosphate are mixed at the mixing ratio, adhesion to a base material may be excellent and an advantage of excellent heat resistance, weather resistance, and corrosion resistance may be realized when the electrical steel sheet is manufactured.
If a ratio of the phosphate in the mixing ratio is excessively high, there may be a problem in which durability is degraded in a high-temperature and high-humidity environment. If a ratio of the silica in the mixing ratio is excessively high, there may be a problem in which adhesion to the base material is lowered.
The nitrate may play a role due to corrosion resistance and weather resistance. In an embodiment, the nitrates may be any one of aluminum nitrate (Al(NO₃)₃), cobalt nitrate (Co(NO₃)₂), calcium nitrate (Ca(NO₃)₂), strontium nitrate (Sr(NO₃)₂), zinc nitrate (Zn(NO₃)₂), manganese nitrate (Mn(NO₃)₂), magnesium nitrate (Mg(NO₃)₂), and silver nitrate (AgNO₃).
In an embodiment, the nitrate may include 5 to 100 parts by weight of a solid content based on 100 parts by weight of the phosphate. For example, the nitrate may include 15 to 80 parts by weight of a solid content, 20 to 60 parts by weight of a solid content, 22 to 51 parts by weight of a solid content, or 22 to 28 parts by weight of a solid content based on 100 parts by weight of the phosphate.
If a content of the nitrate is out of an upper limit value of the range, there may be a risk of fire. If the content of the nitrate is out of a lower limit value of the range, there may be a problem with weather resistance.
The oxidizer may serve as an additive for removing a hydrogen group (H) from the phosphate such as M(H₂PO₄) or M(HPO₄). The oxidizer may remove the hydrogen group from the phosphate so that it serves to remove H from the phosphate such as M(H₂PO₄) or M(HPO₄) having a sticky property or M(HPO4) to generate M(PO₄) having no sticky property.
In an embodiment, the oxidizer may include at least one of HClO₄, NaClO, NaClO₄, KMnO₄, NalO₄, OsO₄, H₂O₂, and Ca(ClO)₂. As described above, the oxidizer may oxidize the phosphate to remove the hydrogen group.
In an embodiment, the oxidizer may include 0.5 to 10.0 parts by weight of a solid content based on 100 parts by weight of the phosphate. The oxidizer may include 0.8 to 5.0 parts by weight or 1.0 to 3.0 parts by weight based on 100 parts by weight of the phosphate. The oxidizer may be included in the range described above so that It has an advantage of lowering a sticky property shown by the phosphate.
If a content of the oxidizer is out of an upper limit value of the range, it may have a poor effect in stickiness resistance or solution stability. If the content of the oxidizer is out of a lower limit value of the range, there may be a problem in which an advantage of lowering the sticky property due to addition of the oxidizer is not realized.
In an embodiment, the silica may be an acidic material. If a basic material is used as the silica, there may be a problem in which the phosphate and the nitrate are not stable and are gelled.
A grain-oriented electrical steel sheet according to an embodiment of the present disclosure may include an electrical steel sheet substrate and an insulation coating disposed on a surface of the electrical steel sheet substrate. The insulation coating may include phosphate, silica, nitrate, and an oxidizer, and a detailed description of the phosphate, the silica, the nitrate, and the oxidizer is the same as the contents of the insulation coating composition described above within a range not contradicting the contents of the insulation coating composition described above.
A method of manufacturing the grain-oriented electrical steel sheet according to an embodiment of the present disclosure may include a step of preparing an electrical steel sheet substrate, a step of applying the insulation coating composition to a surface of the electrical steel sheet substrate, and a step of curing (or hardening) the insulation coating composition.
The step of preparing the electrical steel sheet substrate may include a step of preparing a steel slab, a step of heating the steel slab, a step of hot-rolling the heated steel slab to manufacture a hot-rolled steel sheet, a step of cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet, a step of performing primary recrystallization annealing on the cold-rolled steel sheet, a step of applying an annealing separator on the primary recrystallization-annealed steel sheet, and a step of performing secondary recrystallization annealing.
The step of heating the steel slab may heat the steel slab to a temperature of 1,300 °C or less. If the steel slab is heated in the temperature range described above, a crack of the sheet may be prevented from occurring during a hot rolling process by preventing a columnar crystal structure of the slab from coarsely growing. For example, the step of heating the steel slab may be heated to a temperature of 1,050 to 1,300 °C.
Thereafter, the heated steel slab may be hot-rolled to manufacture the hot-rolled steel sheet. The hot rolling temperature may be not limited, and in an embodiment, the hot rolling may be terminated at a temperature of 950 °C or less.
In an embodiment, after the step of manufacturing the hot-rolled steel sheet, the step of annealing the hot-rolled steel sheet may be performed. In the step of annealing the hot-rolled steel sheet, a non-uniform microstructure and a precipitate of the hot-rolled steel sheet may be homogenized. For example, the step of annealing the hot-rolled steel sheet may be performed in a temperature range of 800 to 1,300 °C.
Thereafter, the step of cold-rolling the hot-rolled steel sheet to manufacture the cold-rolled steel sheet may be performed. In the step of cold-rolling the hot-rolled steel sheet, one cold rolling or two or more cold rollings including intermediate annealing may be performed.
Thereafter, the step of performing the primary recrystallization annealing on the cold-rolled steel sheet may be performed. In this case, the step of performing the primary recrystallization annealing on the cold-rolled steel sheet may include a decarbonization step and a nitriding step. The decarbonization step and the nitriding step may be performed regardless of an order. For example, the nitriding step may be performed after the decarbonization step, or the decarbonization step may be performed after the nitriding step.
In an embodiment, in the step of performing the primary recrystallization annealing on the cold-rolled steel sheet, decarbonization annealing and nitriding treatment may be simultaneously performed on the cold-rolled steel sheet obtained through the cold rolling. For example, the decarbonization step and the nitriding step may be simultaneously performed. The nitriding step may be a step for nitrification within the steel sheet, may be a step for introducing a nitrogen ion into the steel sheet, and may be a step for generating a precipitate such as (Al, Si, Mn)N or AIN that is a crystal growth inhibitor. Nitrification may be performed through the nitriding step so that nitrogen of the grain-oriented electrical steel sheet is 0.01% or less.
In the step of performing the primary recrystallization annealing on the cold-rolled steel sheet, an annealing temperature may be heat-treated in a range of 800 to 950 °C. If a range of the annealing temperature is out of an upper limit value, there may be a problem in which stable secondary recrystallization is not formed because grains coarsely grow so that a driving force for crystal growth is degraded. If the range of the annealing temperature is out of a lower limit value, there may be a problem in which excessive time is required during decarbonization.
The step of performing the primary recrystallization annealing on the cold-rolled steel sheet may be performed in a nitrogen atmosphere, a hydrogen atmosphere, or a mixed gas atmosphere thereof. For example, the gas atmosphere may be an ammonia gas atmosphere. The gas atmosphere may be performed in a wet atmosphere or a dry atmosphere.
After the step of performing the primary recrystallization annealing on the cold-rolled steel sheet, an annealing separator may be applied to the steel sheet. For example, the annealing separator may be an annealing separating agent including MgO as a primary component. In an embodiment, in the step of applying the annealing separator, an application amount of the annealing separator may be performed in a range of 1 to 5 g/m².
If the application amount of the annealing separator is out of an upper limit value of the range, there may be a problem in which secondary recrystallization is affected. If the application amount of the annealing separator is out of a lower limit value of the range, there may be a problem in which it is difficult to smoothly form the coating.
The step of performing the secondary recrystallization annealing may form a {110}<001> texture by the secondary recrystallization, may impart insulation by forming a glassy coating by reaction of MgO with an oxide layer formed during the primary recrystallization annealing, and may remove an impurity that inhibits a magnetic characteristic.
In an embodiment, the step of performing the secondary recrystallization annealing may include a cracking step and a temperature raising step. The cracking step may be performed in a range of 650 to 750 °C, and the temperature raising step may be performed in a range of 1,100 to 1,250 °C. If a temperature is out of the temperature range, there may be a problem in which it is difficult to form an appropriate coating.
In an embodiment, the temperature raising step may be performed at a temperature raising speed in a range of 10 to 20 °C/hr. For example, the temperature raising speed may be performed in a range of 13 to 17 °C/hr.
If the temperature raising speed is out of an upper limit value of the range, there may be a problem in which a coating (or a coating film) is decomposed by decomposition of the phosphate. If the temperature raising speed is out of a lower limit value of the range, there may be a problem of poor corrosion resistance and weather resistance due to non-curing of the silica.
In an embodiment, the cracking step may be performed in at least two gas atmospheres among a hydrogen gas atmosphere, a nitrogen gas atmosphere, and an inert gas atmosphere. In an embodiment, the temperature raising step may be performed in the hydrogen gas atmosphere. For example, in the temperature raising step of a method of the secondary recrystallization annealing before the secondary recrystallization occurs, a mixed gas of nitrogen and hydrogen may be maintained to protect nitride that is a particle growth inhibitor so that secondary recrystallization develops well, and in the cracking step of the method of the secondary recrystallization annealing after the secondary recrystallization is completed, an impurity may be removed by maintaining it in a 100% hydrogen atmosphere for a long time.
In an embodiment, the step of applying the insulation coating composition to the surface of the electrical steel sheet substrate may include a step of mixing the phosphate and the silica, a step of adding the nitrate to the mixed solution, and a step of adding the oxidizer after the adding of the nitrate to the mixed solution. The phosphate, the silica, the nitrate, and the oxidizer are the same as the contents described in the above-described insulating coating composition within a range that does not contradict the contents described in the above-described insulating coating composition.
In an embodiment, a step of curing the insulation coating may be performed in a temperature range of 800 to 900 °C. If a temperature is out of an upper limit value of the temperature range, there may be a problem of deterioration in weather resistance and corrosion resistance of the insulation coating. If a temperature is out of a lower limit value of the temperature range, curing of a silica sol may not occur so that a problem with respect to corrosion resistance and weather resistance occurs.
In an embodiment, the step of curing the insulation coating may be performed for a time of 30 to 240 seconds. For example, the time may be performed for a time of 45 to 180 seconds.
If a time is out of an upper limit value of the time, there may be a problem of decomposition of the phosphate. If a time is out of a lower limit value of the time, there may be a problem in which corrosion resistance and weather resistance are deteriorated due to non-curing of the silica.
Hereinafter, a specific embodiment of the present disclosure will be described. However, the following embodiment is only the specific embodiment of the present disclosure, and the present disclosure is not limited to the following embodiment.

Experimental Examples 1 to 8

In order to manufacture the insulation coating composition for the grain-oriented electrical steel sheet of the present disclosure, an aluminum and magnesium phosphate solution in which 67% of a solid content of the phosphate having a content of the following Table 1 is mixed is manufactured, and then a colloidal silica solution in which 30% of a solid content having a content of the following Table 1 is mixed is added and mixed.
Thereafter, a nitrate solution in which 50% of a solid content such as aluminum nitrate or magnesium nitrate corresponding to a conversion coating material having a content of the following Table 1 is mixed is added, and then an oxidizer in which 50% of a solid content such as HClO₄, NaClO, or NaClO₄ having a content of the following Table 1 is mixed is added to manufacture an insulation coating composition solution having a composition of the following Table 1. The manufactured insulation coating composition solution is applied on a steel sheet treated with MgO. Thereafter, after the applied insulation coating composition is dried at a temperature between 700°C and 950 °C for 30 to 240 seconds, a sticky property, weather resistance, heat resistance, corrosion resistance, and solution stability are evaluated.
The sticky property, the weather resistance, the heat resistance, the corrosion resistance, and the solution stability are evaluated using the following method.

<Evaluation method>

Evaluation of stickiness resistance

The stickiness resistance evaluates how sticky it is, and the stickiness is evaluated by a friction coefficient obtained through Test 1 conducted with a sphere diameter of 12.7 mm, a pressurized load of 50 N, a rotation speed of 50 rpm, a rotation radius of 15 mm, and a slip distance of 200 m and a test conducted with the same load and rotation speed as those of Test 1, a rotation radius of 10 mm, and a slip distance of 10 m for comparing a wear amount according to the slip distance. In this case, the friction coefficient is calculated as a frictional force with respect to a vertical load (e.g., the frictional force/the vertical load). If the friction coefficient is lower than 0.4 and is good, it is indicated as "OK", and if the friction coefficient is higher than or equal to 0.4 and is defective, it is indicated as "NG".

Evaluation of coating property

If it is visually evaluated to be good due to no stain, it is indicated as "OK", and if it is defective due to a stain, it is indicated as "NG".

Evaluation of weather resistance

The weather resistance is evaluated under a condition of 98% moisture, 60 °C, and 72 hours, and if it is good, it is indicated as "OK", and if it is defective, it is indicated as "NG".

Evaluation of heat resistance

In the evaluation of the heat resistance, it is heated for 2 hours under a condition of 560 °C, 20% hydrogen, and 80% nitrogen. Thereafter, it is confirmed that it is 5B or higher through a cross-hatch cut test.
If a result of the test is 5B or higher and is good, it is indicated as "OK", and if the result of the test is less than 5B and is defective, it is indicated as "NG".

Evaluation of corrosion resistance

A salt water spray test of 5% NaCl, 100%RH, 65 °C, and 8 hours is performed.

Evaluation of solution stability

A 2x2 cm sized coating plate is dissolved in 100 ml of 10% NaOH and then the dissolved coating plate is filtered through a filter. A material that is not dissolved and exists as a powder is PO₄. If a weight of a powder remaining in the filter is measured and then a powder is present, it may be determined that HPO₄ is removed by the oxidizer.

In a Cl tracing method, if a Cl component is present in a solution after a 2x2 cm sized coating is dissolved in 100 ml of 10% NaOH, it may be seen that Cl is added.

(Table 1)

Clas sific atio n	Composition									Characteristic				Not e
	Pho sph ate	Wat er	Silic a solut ion	Mag nesi um nitra te	Alu min um nitra te	HCl O₄	NaC lO	NaCl O₄	Silica /phos phat e	Sticki ness resist ance	Weat her resist ance	Corr osion resist ance	Solut ion stabil ity
	[g]	[9]	[9]	[9]	[9]	[9]	[g]	[g]	-	Sticki ness resist ance	Weat her resist ance	Corr osion resist ance	Solut ion stabil ity
Exp erim enta l Exa mpl e 1	5.6	5.4	7.4	0	2	0	0	0	1.32	NG	NG	NG	OK	Co mpa rativ e Exa mpl e
Exp erimenta l Exa mpl e 2	5.6	5.4	7.4	0	2	0.1	0	0	1.32	OK	OK	OK	OK	Em bodimen t
Exp erim enta l Exa mpl e 3	5.6	5.4	7.4	0	2	0	0.1	0	1.32	OK	OK	OK	OK	Em bodi men t
Exp erim enta l Exa mpl e 4	5.6	5.4	7.4	0	2	0	0	0.1	1.32	OK	OK	OK	OK	Em bodi men t
Exp erim enta l Exa mpl e 5	5.6	5.4	7.4	2	0	0	0	0	1.32	NG	NG	NG	OK	Co mpa rativ e Exa mpl e
Exp erim enta l Exa mpl e 6	5.6	5.4	7.4	2	0	0.1	0	0	1.32	OK	OK	OK	OK	Em bodi men t
Exp erim enta l Exa mpl e 7	5.6	5.4	7.4	2	0	0	0.1	0	1.32	OK	OK	OK	OK	Em bodi men t
Exp erim enta l Exa mple 8	5.6	5.4	7.4	2	0	0	0	0.1	1.32	OK	OK	OK	OK	Em bodi men t

If Experimental Example 1 of Table 1 is compared with Experimental Examples 2 to 4 of Table 1, it is confirmed that the stickiness resistance, the weather resistance, the corrosion resistance, and the solution stability are good if an oxidizer such as HClO₄, NaClO, or NaClO₄ is additionally added and the stickiness resistance, the weather resistance, and the corrosion resistance are poor if the oxidizer is not added. In addition, it is confirmed that Experimental Examples 5 to 8 are different from Experimental Examples 1 to 4 in that the magnesium nitrate instead of the aluminum nitrate is used as nitrate and the same effect is obtained even when the magnesium nitrate instead of the aluminum nitrate is used as the nitrate.
For example, the oxidizer may be added so that a hydrogen group is removed from an oxidizer such as M(H₂PO₄) or M(HPO₄) by the following reaction formula.

[Reaction formula] 2Mx(HPO₄)_Y + NaClO → H₂O + NaCl + M_X(PO₄)_Y
It is confirmed that the stickiness resistance is good as the hydrogen group is removed from the phosphate by the reaction formula.

Experimental Examples 9 to 17

Experimental Examples 9 to 17 manufacture the insulation coating composition for the grain-oriented electrical steel sheet and evaluate the manufactured composition using the same method as that of Experimental Examples 1 to 8 except that a composition of the insulation coating composition is controlled (or adjusted) to a content range described in the following Table 2, aluminum nitrate is used as nitrate, and HClO₄ is used as the oxidizer.

(Table 2)

Clas sific atio n	Composition						Characteristic					Not e
	Phos phat e	Wate r	Silic a	Alum inum nitrat e	HCl O₄	Silica/ph osphate	Stickine ss resistan ce	Coati ng prope rty	Weat her resist ance	Corro sion resist ance	Soluti on stabili ty
	[g]	[g]	[g]	[g]	[g]	-	Stickine ss resistan ce	Coati ng prope rty	Weat her resist ance	Corro sion resist ance	Soluti on stabili ty
Exp erim enta l Exa mpl e 9	3	3	8	2	0.1	2.67	OK	OK	OK	OK	OK	Em bodi men t
Exp erim enta l Exa mple 10	3	3	8	1	0.1	2.67	OK	OK	OK	OK	OK	Em bodi men t
Exp erim enta l Exa mpl e 11	3	3	8	0.5	0.1	2.67	OK	OK	OK	OK	OK	Em bodi men t
Exp erim enta l Exa mpl e 12	3	3	8	2	0.5	2.67	OK	OK	OK	OK	NG	Co mpa rativ e Exa mpl e
Exp erim enta l Exa mpl e 13	3	3	12	2	0	4.00	NG	OK	OK	OK	OK	Co mpa rativ e Exa mpl e
Experim enta l Exa mpl e 14	3	3	12	2	0.1	4.00	NG	OK	OK	OK	OK	Compa rativ e Exa mpl e
Exp erim enta l Exa mpl e 15	3	3	12	1	0.1	4.00	NG	OK	OK	OK	OK	Co mpa rativ e Exa mpl e
Exp erim enta l Exa mpl e 16	3	3	12	2	0.5	4.00	NG	OK	OK	OK	NG	Co mpa rativ e Exa mpl e
Exp erim ental Exa mpl e 17	3	3	12	1	0.5	4.00	NG	OK	OK	OK	NG	Co mpa rativ

If Experimental Examples 9 to 12 of Table 2 where HClO₄ that is the oxidizer is added are compared with Experimental Example 13 of Table 2 where the oxidizer is not added, it is confirmed that Experimental Examples 9 to 12 have the stickiness resistance to be not sticky. In addition, it is confirmed that the solution stability of Experimental Example 12 is poor if the oxidizer is excessively added. In addition, if Experimental Examples 9 to 11 are compared with Experimental Examples 14 to 17, it is confirmed that the stickiness resistance or the solution stability is poor if a content of the silica is excessively high so that a mixing ratio of the phosphate and the silica is out of a target mixing ratio of the present disclosure.

Experimental Examples 18 to 26

Experimental Examples 18 to 26 manufacture the insulation coating composition for the grain-oriented electrical steel sheet and evaluate the manufactured composition using the same method as that of Experimental Examples 1 to 8 except that a composition of the insulation coating composition is controlled (or adjusted) to a content range described in the following Table 3.

(Table 3)

Clas sificatio n	Composition						Characteristic					Not e
Clas sificatio n	Phosphat e	Water	Silica	Alum inum nitrat e	HClO₄	Silica/phosphate	Stickiness resistan ce	Coating prope rty	Weather resist ance	Corrosion resist ance	Soluti on stabili ty
	[g]	[g]	[g]	[g]	[g]	-	Stickiness resistan ce	Coating prope rty	Weather resist ance	Corrosion resist ance	Soluti on stabili ty
Exp erim enta l Exa mpl e 18	3	3	8	2	0.1	2.67	OK	OK	OK	OK	OK	Em bodi men t
Exp erim enta l Exa mpl e 19	3	3	8	1	0.1	2.67	OK	OK	OK	OK	OK	Em bodi men t
Exp erim ental Exa mpl e 20	3	3	8	0.5	0.1	2.67	OK	OK	OK	OK	OK	Em bodi ment
Exp erim enta l Exa mpl e 21	3	3	8	2	0.5	2.67	OK	OK	OK	OK	NG	Co mpa rativ e Exa mpl e
Exp erim enta l Exa mpl e 22	12	3	3	2	0	0.25	NG	OK	OK	OK	OK	Co mpa rativ e Exa mpl e
Exp erim enta l Exampl e 23	12	3	3	2	0.1	0.25	NG	OK	OK	OK	OK	Co mpa rativ e Exampl e
Exp erim enta l Exa mpl e 24	12	3	3	1	0.1	0.25	NG	OK	OK	OK	OK	Co mpa rativ e Exa mpl e
Exp erim enta l Exa mpl e 25	12	3	3	2	0.5	0.25	NG	OK	OK	OK	NG	Co mpa rativ e Exa mpl e
Exp erim enta l Exa mpl e 26	12	3	3	1	0.5	0.25	NG	OK	OK	OK	NG	Co mpa rativ e Exa mpl e

If Experimental Examples 18 to 20 of Table 3 where HClO₄ that is the oxidizer is added are compared with Experimental Example 22 of Table 3 where the oxidizer is not added, it is confirmed that Experimental Example 22 has the stickiness resistance to be not sticky. In addition, it is confirmed that the stickiness resistance or the solution stability is poor if the oxidizer is excessively added as in Experimental Examples 23 to 26 so that a mixing ratio of the phosphate and the silica is out of a mixing ratio of the phosphate and the silica of the present disclosure.

Experimental Examples 27 to 36

Experimental Examples 27 to 36 manufacture the insulation coating composition for the grain-oriented electrical steel sheet and evaluate the manufactured composition using the same method as that of Experimental Examples 1 to 9 except that a composition of the insulation coating composition is controlled (or adjusted) to a content range described in the following Table 4, aluminum nitrate and magnesium nitrate are used as nitrate, and HClO₄ is used as the oxidizer.

(Table 4)

Clas sific ation	Composition							Characteristic				Note
	Phos phate	Water	Silica	Mag nesi um nitrate	Alum inum nitrate	HCl O₄	Silica/ph osphate	Stickiness resistance	Weat her resist ance	Corro sion resist ance	Solution stability
	[g]	[g]	[g]	[g]	[g]	[g]	-	Stickiness resistance	Weat her resist ance	Corro sion resist ance	Solution stability
Exp erim enta l Exa mpl e 27	5.6	5.4	7.4	2	2	0.01	1.32	NG	OK	OK	OK	Co mp ara tive Ex am ple
Exp erim enta l Exa mpl e 28	5.6	5.4	7.4	2	2	0.5	1.32	OK	OK	OK	NG	Co mp ara tive Ex am ple
Exp erim enta l Exa mpl e 29	5.6	5.4	7.4	2	2	0.2	1.32	OK	OK	OK	OK	Em bod ime nt
Exp erim enta l Exa mpl e 30	5.6	5.4	7.4	0.5	0.5	0	1.32	NG	OK	OK	OK	Co mp ara tive Ex am ple
Exp erim enta l Exa mpl e 31	5.6	5.4	7.4	2	2	0.1	1.32	OK	OK	OK	OK	Em bod ime nt
Exp erim enta l Exa mpl e 32	5.6	5.4	7.4	1	1	0.1	1.32	OK	OK	OK	OK	Em bod ime nt
Exp erimenta l Exa mpl e 33	3	3	8	2	2	0	2.67	NG	OK	OK	OK	Co mpara tive Ex am ple
Exp erim enta l Exa mpl e 34	3	3	8	2	2	0.1	2.67	OK	OK	OK	OK	Em bod ime nt
Exp erim enta l Exa mpl e 35	3	3	8	1	1	0.1	2.67	OK	OK	OK	OK	Em bod ime nt
Exp erim enta l Exa mpl e 36	3	3	8	2	2	0.5	2.67	OK	OK	OK	NG	Co mp ara tive Ex am ple

If Experimental Example 29, Experimental Example 31, Experimental Example 32, Experimental Example 34, and Experimental Example 35 of Table 4 where the magnesium nitrate and the aluminum nitrate are simultaneously added as the nitrate and HClO₄ is included as the oxidizer are compared with Experimental Example 33 that does not include the oxidizer, it is confirmed that the stickiness resistance of Experimental Example 29, Experimental Example 31, Experimental Example 32, Experimental Example 34, and Experimental Example 35 is good. In addition, it is confirmed that the stickiness resistance or the solution stability is poor if a content of the oxidizer is excessively large or small as in Experimental Example 27 and Experimental Example 28. In addition, it is confirmed that the stickiness resistance is poor if a combined amount of magnesium nitrate and aluminum nitrate is 1 g and a content of the nitrate is excessively small as in Experimental Example 30. In addition, it is confirmed that the stickiness resistance and the solution stability are poor if a content of the oxidizer is excessively large as in Experimental Example 36.

Experimental Exampled 37 to 47 - Curing temperature test

The following Table 5 shows evaluation of stickiness resistance, weather resistance, and corrosion resistance when a curing temperature and a curing time for the insulation coating composition for the grain-oriented electrical steel sheet having the same composition are adjusted as in the following Table 4.

(Table 5)

Classif ication	Composition					Curing condition		Characteristic			Note
	Pho sph ate	Wat er	Silic a	Mag nesi um nitra te	HCl O₄	Curing temperat ure	Curing time	Stickines s resistanc e	Weath er resista nce	Corros ion resista nce
	[9]	[9]	[9]	[g]	[9]	[°C]	[second]	Stickines s resistanc e	Weath er resista nce	Corros ion resista nce
Experi mental Exam ple 37	5.6	5.4	7.4	2.0	0.1	750	45	NG	NG	NG	Com parati ve Exam ple
Experi mental Exam ple 38	5.6	5.4	7.4	2.0	0.1	800	45	OK	OK	OK	Emb odim ent
Experi mental Exam ple 39	5.6	5.4	7.4	2.0	0.1	850	45	OK	OK	OK	Emb odim ent
Experimental Exam ple 40	5.6	5.4	7.4	2.0	0.1	900	45	OK	OK	OK	Embodim ent
Experi mental Exam ple 41	5.6	5.4	7.4	2.0	0.1	950	45	OK	NG	NG	Com parati ve Exam ple
Experi mental Exam ple 42	5.6	5.4	7.4	2.0	0.1	800	20	OK	OK	OK	Emb odim ent
Experi mental Exam ple 43	5.6	5.4	7.4	2.0	0.1	900	20	OK	OK	OK	Emb odim ent
Experi mental Exam ple 44	5.6	5.4	7.4	2.0	0.1	800	180	OK	OK	OK	Emb odim ent
Experi mental Example 45	5.6	5.4	7.4	2.0	0.1	900	180	OK	OK	OK	Emb odim ent
Experi mental Exam ple 46	5.6	5.4	7.4	2.0	0.1	800	600	OK	NG	NG	Com parati ve Exam ple
Experi mental Exam ple 47	5.6	5.4	7.4	2.0	0.1	900	600	OK	NG	NG	Com parati ve Exam ple

It is confirmed that the stickiness resistance, the weather resistance, and the corrosion resistance of Experimental Examples 38 to 40 in which the curing temperature of the curing condition of Table 5 is within the range of the present disclosure are good compared with those of Experimental Example 37 and Experimental Example 41 in which the curing temperature is out of the range of the present disclosure. It is confirmed that the stickiness resistance, the weather resistance, and the corrosion resistance of Experimental Examples 42 to 47 in which the curing time of the curing condition of Table 5 is within the range of the present disclosure are good but at least one of the stickiness resistance, the weather resistance, and the corrosion resistance of Experimental Example 46 and Experimental Example 47 in which the curing time is out of the range of the present disclosure is poor.
The present disclosure is not limited to the embodiments and/or the examples, may be manufactured in various different forms, and a person of ordinary skill in the art to which the present disclosure belongs will be able to understand that the present disclosure may be implemented in other specific forms without changing the technical idea or essential feature of the present disclosure. Therefore, it should be understood that the embodiments and/or the examples described above are illustrative and not limited in all respects.

Claims

An insulation coating composition for a grain-oriented electrical steel sheet, comprising:
phosphate;

silica;

nitrate; and

an oxidizer,

wherein the silica includes 50 to 400 parts by weight of a solid content based on 100 parts by weight of the phosphate, a mixing ratio of a solid content of the silica to a solid content of the phosphate is 0.3 to 3.9, and the oxidizer includes 0.5 to 10.0 parts by weight of a solid content based on 100 parts by weight of the phosphate.
The insulation coating composition of claim 1, wherein the nitrate includes at least one of aluminum nitrate (Al(NO₃)₃), cobalt nitrate (Co(NO₃)₂), calcium nitrate (Ca(NO₃)₂), strontium nitrate (Sr(NO₃)₂), zinc nitrate (Zn(NO₃)₂), manganese nitrate (Mn(NO₃)₂), magnesium nitrate (Mg(NO₃)₂), and silver nitrate (AgNO₃).
The insulation coating composition of claim 2, wherein the nitrate includes at least two of aluminum nitrate (Al(NO₃)₃), cobalt nitrate (Co(NO₃)₂), calcium nitrate (Ca(NO₃)₂), strontium nitrate (Sr(NO₃)₂), zinc nitrate (Zn(NO₃)₂), manganese nitrate (Mn(NO₃)₂), magnesium nitrate (Mg(NO₃)₂), and silver nitrate (AgNO₃).
The insulation coating composition of claim 1, wherein the nitrate includes 5 to 100 parts by weight of a solid content based on 100 parts by weight of the phosphate.
The insulation coating composition of claim 1, wherein the oxidizer includes at least one of HClO₄, NaClO, NaClO₄, KMnO₄, NalO₄, OsO₄, H₂O₂, and Ca(ClO)₂.
A grain-oriented electrical steel sheet, comprising:
an electrical steel sheet substrate; and

an insulation coating that is disposed on a surface of the electrical steel sheet substrate,

wherein the insulation coating includes phosphate, silica, nitrate, and an oxidizer, the silica includes 50 to 400 parts by weight of a solid content based on 100 parts by weight of the phosphate, a mixing ratio of a solid content of the silica to a solid content of the phosphate is 0.3 to 3.9, and the oxidizer includes 0.5 to 10.0 parts by weight of a solid content based on 100 parts by weight of the phosphate.
A method of manufacturing a grain-oriented electrical steel sheet, comprising:
preparing an electrical steel sheet substrate;

applying an insulation coating composition to a surface of the electrical steel sheet substrate; and

curing the insulation coating composition,

wherein the insulation coating composition includes phosphate, silica, nitrate, and an oxidizer, the silica includes 50 to 400 parts by weight of a solid content based on 100 parts by weight of the phosphate, a mixing ratio of a solid content of the silica to a solid content of the phosphate is 0.3 to 3.9, the oxidizer includes 0.5 to 10.0 parts by weight of a solid content based on 100 parts by weight of the phosphate, and the curing of the insulation coating composition is performed in a range of 800 to 900 °C for a range of 30 to 180 seconds.
The method of claim 7, wherein the applying of the insulation coating composition to the surface of the electrical steel sheet substrate includes mixing the phosphate and the silica, adding the nitrate to a mixed solution, and adding the oxidizer after the adding of the nitrate to the mixed solution.
The method of claim 7, wherein the preparing of the electrical steel sheet substrate comprises:
preparing a steel slab;

heating the steel slab;

hot-rolling the heated steel slab to manufacture a hot-rolled steel sheet;

cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet;

performing primary recrystallization annealing on the cold-rolled steel sheet;

applying an annealing separator on the primary recrystallization-annealed steel sheet; and

performing secondary recrystallization annealing.
The method of claim 9, wherein the applying of the annealing separator on the primary recrystallization-annealed steel sheet includes applying the annealing separator in a range of 1 to 5 g/m².
The method of claim 9, wherein the performing of the secondary recrystallization annealing includes cracking and temperature raising, and the cracking is performed in a range of 650 to 750 °C, and the temperature raising is performed in a range of 1,100 to 1,250 °C.
The method of claim 11, wherein the temperature raising is performed at a temperature raising speed in a range of 10 to 20 °C/hr.
The method of claim 11, wherein the cracking is performed in two or more gas atmospheres among a hydrogen gas atmosphere, a nitrogen gas atmosphere, and an inert gas atmosphere.
The method of claim 11, wherein the temperature raising is performed in a hydrogen atmosphere.