KR102080168B1 - Annealing separating agent composition for grain oriented electrical steel sheet, method for manufacturing magnesium oxide for annealing separating agent, and method for manufacturing grain oriented electrical steel sheet - Google Patents

Abstract

The annealing separator composition for a grain-oriented electrical steel sheet according to an embodiment of the present invention includes magnesium oxide, and the hydration water slope of magnesium oxide represented by the following Formula 1 is 0.28 to 0.50.
[Equation 1]
[Hydration Moisture Gradient] = ([Ig.loss2]-[Ig.loss1]) / ([T2]-[T1])
(In Formula 1, [Ig.loss1] and [Ig.loss2] are the weight loss rate (% by weight) of magnesium oxide when the hydrated magnesium oxide is raised to the temperature of [T1] and [T2], respectively, [T1] and [T2] is the temperature (° C.) selected at 550 to 1000 ° C. respectively. [T1] and [T2] are different from each other.)

Description

Annealing separator composition for oriented electrical steel sheet, manufacturing method of magnesium oxide for annealed separator and manufacturing method of oriented electrical steel sheet ORIENTED ELECTRICAL STEEL SHEET}

An annealing separator composition for grain-oriented electrical steel sheet, a method for producing magnesium oxide for annealing separator and a method for producing a grain-oriented electrical steel sheet. Specifically, by the control of the degree of hydration and physical properties of magnesium oxide in the annealing separator composition, the annealing separator composition for grain-oriented electrical steel sheet having excellent surface quality and uniformity, the manufacturing method of magnesium oxide for annealing separator and a method for producing the grain-oriented electrical steel sheet will be.

A grain-oriented electrical steel sheet includes an Si component in a steel sheet and has an aggregate structure in which crystal grains are aligned in the {110} <001> direction, and refers to an electrical steel sheet having extremely excellent magnetic properties in the rolling direction.

Recently, as the high magnetic flux density oriented electrical steel sheet is commercialized, a material having low iron loss is required. Improving iron loss in electrical steel can be approached in four technical ways: firstly, to orient the {110} <001> grain orientation in the rolling direction, including the axis, for magnetization of oriented electrical steel; Thirdly, the magnetic micronization method of refining the magnetic domain through chemical and physical methods, and finally, the improvement of surface properties or the provision of surface tension by chemical methods such as surface treatment and coating.

In order to improve the surface properties or impart the surface tension, a method of forming the primary film and the insulating film has been proposed. The primary coating is a forsterite (2MgO? IO ₂ ) layer, which is an oxide used as an annealing separator and silicon oxide (SiO ₂ ) formed on the surface of the material during the primary recrystallization annealing of electrical steel sheets. It is known to consist of the reaction of magnesium (MgO). The primary film formed during the high temperature annealing should have a uniform color without defects in appearance, and functionally prevent fusion between the plates in the coil state, and tensile stress on the material due to the difference in thermal expansion coefficient between the material and the primary film. By providing it can bring about the effect of improving the iron loss of the material.

First of all, however, excellent primary coating properties should basically have a uniform color without defects on the surface of the material. Especially, since commercial products are manufactured in the form of large coils, it is very difficult to maintain uniform coating properties over the entire length of the coil. The biggest cause of this is an annealing separator containing water. Magnesium oxide slurry is applied to the steel sheet and wound in a coil to undergo a final finishing hot annealing process. At this time, since the amount of heat transferred from the annealing furnace to the coil is different and accordingly, the discharge of hydration water varies according to the coil position and part, the innermost part of the coil is not generally desired to discharge the hydrated water in the coil as compared to the outer part. Phosphorous black spot defects will occur.

An annealing separator composition for grain-oriented electrical steel sheet, a method for producing magnesium oxide for annealing separator, and a method for producing a grain-oriented electrical steel sheet are provided. Specifically, through the control of the degree of hydration and physical properties of magnesium oxide in the annealing separator composition, providing an annealing separator composition for a grain-oriented electrical steel sheet, a method for producing a magnesium oxide for annealing separator and a method for producing a grain-oriented electrical steel sheet having excellent surface quality do.

The annealing separator composition for a grain-oriented electrical steel sheet according to an embodiment of the present invention includes magnesium oxide, and the hydration water slope of magnesium oxide represented by the following Formula 1 is 0.28 to 0.50.

[Equation 1]

[Hydration Moisture Gradient] = ([Ig.loss2]-[Ig.loss1]) / ([T2]-[T1])

(In Formula 1, [Ig.loss1] and [Ig.loss2] are the weight loss rate (% by weight) of magnesium oxide when the hydrated magnesium oxide is raised to the temperature of [T1] and [T2], respectively, [T1] and [T2] is the temperature (° C.) selected at 550 to 1000 ° C. respectively. [T1] and [T2] are different from each other.)

[T1] may be selected from 550 to 600 ° C, and [T2] may be selected from 850 to 900 ° C.

Magnesium oxide is 30 to 70 parts by weight of highly active magnesium oxide having a degree of activation (Citric Acid Activity 70%, hereinafter referred to as activation degree) of 50 to 180 seconds and a low activity of 200 to 1000 seconds, based on 100 parts by weight of magnesium oxide. 30 to 70 parts by weight of magnesium oxide may be included.

The activation degree of the entire magnesium oxide may be 50 to 500 seconds.

The high active magnesium oxide may have a D50 of 2.0 to 3.5, and the low active magnesium oxide may have a D50 of 2.5 to 4.0.

D50 of the entire magnesium oxide may be 2.75 to 3.25.

The ceramic powder may further include 1 to 10 parts by weight based on 100 parts by weight of magnesium oxide.

The ceramic powder may include at least one selected from Al ₂ O ₃ , SiO ₂ , TiO _2, and ZrO ₂ .

The boron compound may further include 0.1 to 20 parts by weight based on 100 parts by weight of magnesium oxide.

The solvent may further include 500 to 1500 parts by weight of solvent based on 100 parts by weight of magnesium oxide.

Method for producing a magnesium oxide for a grain-oriented electrical steel sheet annealing separator according to an embodiment of the present invention comprises the steps of preparing magnesium hydroxide; Calcining magnesium hydroxide at 800 to 1200 ° C. to produce highly active magnesium oxide; Calcining magnesium hydroxide at 1300 to 1500 ° C. to produce low activity magnesium oxide; And mixing the high active magnesium oxide and the low active magnesium oxide.

Preparing magnesium hydroxide may include preparing magnesium hydroxide by reacting magnesium chloride and calcium hydroxide.

Method for producing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises the steps of preparing a steel slab; Heating the steel slab; Hot rolling the heated steel slab to produce a hot rolled sheet; Cold rolling the hot rolled sheet to produce a cold rolled sheet; Primary recrystallization annealing of the cold rolled sheet; Applying an annealing separator on the surface of the primary recrystallized annealed steel sheet; And secondary recrystallization annealing the steel sheet to which the annealing separator is applied.

The annealing separator includes magnesium oxide, and the hydrated water gradient of magnesium oxide represented by the following formula 1 is 0.28 to 0.50.

[Equation 1]

[Hydration Moisture Gradient] = ([Ig.loss2]-[Ig.loss1]) / ([T2]-[T1])

(In Formula 1, [Ig.loss1] and [Ig.loss2] are the weight loss rate (% by weight) of magnesium oxide when the hydrated magnesium oxide is raised to the temperature of [T1] and [T2], respectively, [T1] and [T2] is the temperature (° C.) selected at 550 to 1000 ° C. respectively. [T1] and [T2] are different from each other.)

After applying the annealing separator, it may further comprise the step of drying to 300 to 700 ℃.

The secondary recrystallization annealing may include: raising the temperature at a temperature rising rate of 18 to 75 ° C / hr in a temperature range of 700 to 950 ° C; Heating at a temperature increase rate of 10 to 15 ° C./hr in a temperature range of 950 to 1200 ° C .; And a cracking step.

The step of raising the temperature at a temperature rising rate of 18 to 75 ℃ / hr and the step of raising the temperature at a heating rate of 10 to 15 ℃ / hr is carried out in an atmosphere containing 20 to 30% by volume of nitrogen and 70 to 80% by volume of hydrogen. In addition, the cracking step may be performed in an atmosphere containing 90% by volume or more of hydrogen.

According to one embodiment of the present invention, by adjusting the hydration moisture discharge during the high temperature annealing process of magnesium oxide, it is possible to suppress the occurrence of black spot defects, which is the innermost oxidative defect that can occur in the large coil unit.

According to one embodiment of the present invention, a very uniform primary film (forsterite film, base film) can be obtained over the entire coil length.

In addition, according to an embodiment of the present invention, it is possible to obtain a primary film excellent in tension and adhesion to the steel sheet.

1 is a graph for explaining the gradient of hydration moisture of magnesium oxide according to an embodiment of the present invention.
2 and 3 are photographs of steel sheets manufactured in Examples (Sample No. 4) and Comparative Example (Sample No. 1), respectively.

Terms such as first, second, and third are used to describe various parts, components, regions, layers and / or sections, but are not limited to these. These terms are only used to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, the first portion, component, region, layer or section described below may be referred to as the second portion, component, region, layer or section without departing from the scope of the invention.

The terminology used herein is for reference only to specific embodiments and is not intended to limit the invention. As used herein, the singular forms “a,” “an,” and “the” include plural forms as well, unless the phrases clearly indicate the opposite. As used herein, the meaning of “comprising” embodies a particular property, region, integer, step, operation, element, and / or component, and the presence of another property, region, integer, step, operation, element, and / or component, It does not exclude the addition.

When a portion is referred to as "on" or "on" another portion, it may be directly on or on the other portion or may be accompanied by another portion therebetween. In contrast, when a part is mentioned as "directly above" another part, no other part is intervened in between.

In addition, 1 ppm in the present invention means 0.0001%.

In an embodiment of the present invention, the meaning of further including an additional component means to include the balance by adding an additional amount of the additional component.

Although not defined otherwise, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Commonly defined terms used are additionally interpreted as having a meaning consistent with the related technical literature and the presently disclosed contents, and are not interpreted as ideal or very formal meaning unless defined.

Hereinafter, exemplary embodiments of the present invention will be described in detail so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

The annealing separator composition for a grain-oriented electrical steel sheet according to an embodiment of the present invention includes magnesium oxide, and the hydration water slope of magnesium oxide represented by the following Formula 1 is 0.28 to 0.50.

[Equation 1]

[Hydration Moisture Gradient] = ([Ig.loss2]-[Ig.loss1]) / ([T2]-[T1])

(In Formula 1, [Ig.loss1] and [Ig.loss2] are the weight loss rate (% by weight) of magnesium oxide when the hydrated magnesium oxide is raised to the temperature of [T1] and [T2], respectively, [T1] and [T2] is the temperature (° C.) selected at 550 to 1000 ° C. respectively. [T1] and [T2] are different from each other.)

In the manufacturing of oriented electrical steel sheet, when the cold rolled sheet passes through a furnace controlled by a wet atmosphere for primary recrystallization, Si 2 having the highest oxygen affinity in the steel reacts with oxygen supplied from the steam in the furnace to form SiO ₂ on the surface. do. Oxygen penetrates into the steel afterwards to form Fe-based oxides. The SiO ₂ thus formed forms a forsterite (Mg ₂ SiO ₄ ) layer through a chemical reaction such as magnesium oxide or magnesium hydroxide in the annealing separator as in Scheme 1 below.

Scheme 1

2 Mg (OH) ₂ + SiO ₂ → Mg ₂ SiO ₄ + 2H ₂ O

In the oriented electrical steel sheet process for commercial production, the first recrystallization annealing process is performed in a coil state. After the decarburization and annealing annealing process, the slurry mixed with magnesium oxide and water, which is an annealing separator, is coated on the steel sheet, dried and wound in a coil shape to be charged into a secondary recrystallization annealing furnace. Annealing or hot annealing herein means secondary recrystallization annealing.

The reaction process of magnesium oxide in the annealing process is as follows. First, a condensation reaction in which magnesium hydroxide (Mg (OH) ₂ ), which is substituted while magnesium oxide is applied in a slurry state at the beginning of the annealing process, reacts with intramolecular hydroxyl groups (-OH) to generate water, as shown in Scheme 2 below. The water thus generated induces mass transfer in the coil to achieve thermal equilibrium in the coil.

Scheme 2

2Mg (OH) ₂ + Heat → 2MgO + 2H ₂ O

Thereafter, a reaction as in Scheme 1 occurs later in the annealing process, and water is produced from magnesium hydroxide as in the early stage of the annealing process. Therefore, in the process of forming the primary coating, magnesium hydroxide and water are always present in the coil, which affects the coating properties.

In the case of electrical steel sheet produced on a commercial scale, the high temperature annealing process is carried out in coil units, and during the annealing process, defects due to FeO-based oxide called black spots occur. The reason for the generation of the FeO oxide is that the coil inner winding portion is gradually increased in temperature to the sequence portion when the annealing coil is annealed, and thus the residence time at 550 ° C. or more, which is a temperature at which the FeO oxide production is accelerated, is relatively long.

Such oxidative defects tend to occur when the discharged moisture does not fall out of the annealing furnace smoothly when the amount of hydrated water discharged from the magnesium oxide rapidly increases when the coiling unit is advanced in the coil unit.

In one embodiment of the present invention, attention was paid to the relationship between the amount of hydrated moisture of magnesium oxide, in particular, the gradient of hydrated moisture with temperature, and the formation of a primary film and the occurrence of defects. Generally, the degree of hydration is defined as the weight increased by dispersing magnesium oxide in water and then hydration with Mg (OH) ₂ . In addition, when the hydrated magnesium oxide is heated to a specific temperature, a volatile component exists, and volatile components include carbon, magnesium trioxide component, and hydrated moisture, which is usually a magnesium oxide itself. At this time, the amount of hydrated water represents a weight loss rate when the temperature is raised to a specific temperature with respect to the total weight of the hydrated magnesium oxide.

The amount of hydrated water of the conventional magnesium oxide is to emit a small amount in the low temperature region of 550 to 900 ℃ and a large amount in the high temperature region above 900 ℃. Therefore, in the early stage of annealing, the amount of hydration water generated in the coil is relatively small, and in the latter stage of annealing, an environment in which the hydration moisture suddenly increases in the annealing furnace is created.

In the case of electrical steel sheet produced on a commercial scale, a high temperature annealing process is performed in coil units, and as described above, time is required to achieve thermal equilibrium with the coil according to the finish annealing temperature pattern. In addition, the temperature deviation for each coil position is generated until the temperature balance between the annealing furnace set temperature and the coil is achieved, and in terms of coil standards, thermal equilibrium is achieved from the outer coil to the inner coil.

As a result, the coil inner circumference is not only discharged of hydration water for a long time compared to the outer circumference, but also affected by the amount of hydration water discharged from the coil outer circumference. In other words, due to the fact that hydrated water is discharged in a relatively fast time with respect to the coil coated with magnesium oxide, the hydration moisture characteristics are not significantly affected, whereas in the coiled inner part, the moisture is discharged from the coil for a long time. Will receive. In particular, when a large amount of hydrated water discharged in the latter part of the annealing is present in the annealing furnace atmosphere, oxidative defects are more likely to occur because the primary coating is not completely formed in the inner winding part.

From this point of view, since magnesium oxide having a conventional hydration moisture gradient has a relatively high emission at a high temperature, the coil inner portion easily causes oxidative defects.

On the contrary, when the hydration moisture content is increased as a whole without considering the hydration water slope, a large amount in the low temperature region is discharged relatively low in the high temperature region. That is, the hydration water slope becomes small. In this case, on the contrary, in the low temperature region, the amount of hydration moisture in the coil inner portion increases rapidly, and the hydration moisture generated in the coil cannot be sufficiently discharged out of the annealing furnace. As a result, because of this, since the hydrated water generated in the outer winding portion is not properly discharged, oxidative defects easily occur in the coil outer winding portion.

Therefore, by appropriately adjusting the hydration moisture gradient as in the embodiment of the present invention, it is possible to significantly improve the oxidative defects of the inner winding portion. Specifically, the amount of water hydrated is when the magnesium oxide is sufficiently hydrated at room temperature (25 ° C.), and then heated to a specific temperature and maintained at that temperature for 5 minutes ([weight of magnesium oxide before temperature increase]-[magnesium oxide after temperature increase) Weight)] // [weight of magnesium oxide before temperature rising] x 100 (%).

Specifically, in one embodiment of the present invention it is possible to control the hydration moisture gradient of magnesium oxide in the range 0.28 to 0.50, it is possible to prevent the oxidative defects of the coil inner portion in the above range. Furthermore, the primary film which is excellent in tension and adhesiveness with a base steel plate can be obtained.

In one embodiment of the present invention, the hydration water gradient of magnesium oxide may be satisfied when two arbitrary temperatures T1 and T2 are set at 550 to 1000 ° C, but specifically, [T1] is selected from 550 to 600 ° C. [T2] may be selected from 850 to 900 ° C.

In FIG. 1, the hydration moisture slope of magnesium oxide is schematically shown. The X axis shows the temperature at which the hydrated water of magnesium oxide is measured, and the Y axis shows the amount of hydrated water when the hydrated water is measured at the X axis temperature. As shown in Fig. 1, the amount of hydrated water of magnesium oxide increases as the measurement temperature increases. When measuring the amount of hydration moisture at any two temperatures, a straight line passing through two points can be derived, and the slope of the linear equation for X and Y of the straight line becomes the hydration water slope. The measurement temperature can be two or more, and when the measurement temperature is more than two, the slope in the first equation where the sum of the points and the error is small becomes the hydration slope. In FIG. 1, for example, the amount of hydrated water measured at four temperatures is calculated and displayed by calculating a first-order equation with the smallest error.

The hydration gradient of the magnesium oxide may be controlled by controlling one or more factors of the magnesium oxide manufacturing method, particle size, and activation.

Specifically, in one embodiment of the present invention, magnesium oxide is 30 to 70 parts by weight of highly active magnesium oxide having an activation degree of 50 to 180 seconds and low active magnesium oxide having an activation degree of 200 to 1000 seconds, based on 100 parts by weight of the total magnesium oxide. It may include 30 to 70 parts by weight.

In this case, the activation degree (CAA 70%) means the ability of the MgO powder to chemically react with other components. Activation is measured by the time it takes for MgO to completely neutralize a certain amount of citric acid solution. If the activation degree is high, the time taken for neutralization is short, and if the activation degree is low, it can be said that it is high. Specifically, it is measured as the time taken for the solution to turn from white to pink when 100 ml of 0.4N citric acid solution to which 2 ml of 1% phenolphthalein reagent was added at 30 ° C. and 1.17 g of MgO were stirred. Since activation method is well known in the art, a detailed description thereof will be omitted.

If too high magnesium oxide is included, the reactivity may be insufficient to form a smooth film. When too much high active magnesium oxide is included, moisture discharge cannot be properly controlled, and oxidative defects may occur.

By mixing the high active magnesium oxide and the low active magnesium oxide, the activation degree of the entire magnesium oxide can be 50 to 500 seconds.

Hydration moisture gradient of magnesium oxide can be controlled by controlling the particle size. Specifically, the high active magnesium oxide may have a D50 of 2.0 to 3.5, and the low active magnesium oxide may have a D50 of 2.5 to 4.0. By using a mixture of low active magnesium oxide having a relatively large particle size and high active magnesium oxide having a relatively small particle size in an appropriate range, the hydration moisture gradient of magnesium oxide can be controlled.

D50 of the entire magnesium oxide may be 2.75 to 3.25. If the D50 value of the entire magnesium oxide is too small, the particulate fraction is increased, so the hydration moisture discharge is not smooth at low temperatures, if too large, on the contrary, the hydration moisture discharge is too fast at low temperatures may cause oxidative defects in the outer region. Here, D50 is defined as the particle diameter at the point where the particles accumulate from the smaller side to 50%, that is, the cumulative frequency of the volume distribution reaches 50%.

Also by the manufacturing method of magnesium oxide, the gradient of hydration moisture of magnesium oxide can be controlled.

The method for producing magnesium oxide includes preparing magnesium hydroxide and calcining magnesium hydroxide to produce magnesium oxide. At this time, the firing temperature at the time of firing magnesium hydroxide is controlled to produce high active magnesium oxide and low active magnesium oxide, and the prepared high active magnesium oxide and low active magnesium oxide are mixed and produced. Specifically, magnesium hydroxide is calcined at 800 to 1200 ° C. when producing high active magnesium oxide, and magnesium hydroxide is calcined at 1300 to 1500 ° C. when producing low active magnesium oxide.

In the preparation of highly active magnesium oxide, if the annealing temperature is too low, it is easy to hydrate in the air due to the presence of a large number of hydroxyl groups (-OH) in the particle after the production of magnesium oxide, resulting in agglomeration of particles, resulting in constant quality of 1 A problem may occur in which a secondary coating is not formed. In the manufacture of highly active magnesium oxide, if the annealing temperature is too high, the activation of the entire magnesium oxide is low, there may be a problem that the primary coating is not produced smoothly. More specifically, when preparing high active magnesium oxide, it may be calcined at 900 to 1100 ℃.

In the manufacture of low-active magnesium oxide, if the annealing temperature is too low, it becomes similar to the case containing only high-active magnesium oxide, in which case it becomes impossible to adequately control the hydration moisture gradient of magnesium oxide, and for the above reason, Alternatively, an oxidative defect may occur in the outer winding part. If the annealing temperature is too high, there is a problem that the activation of the entire magnesium oxide is too low, the primary film is not produced smoothly. More specifically, when preparing low activity magnesium oxide, it may be calcined at 1350 to 1450 ℃.

In one embodiment of the present invention, the annealing separator composition may be present in the form of a slurry for easy application to the surface of the grain-oriented electrical steel sheet substrate. When water is included as the solvent of the slurry, magnesium oxide is easily dissolved in water and may be present in the form of magnesium hydroxide. Therefore, in one embodiment of the present invention, magnesium oxide and magnesium hydroxide are treated as one component. Meaning of including 100 parts by weight of magnesium oxide means that 100 parts by weight of magnesium oxide is included when including magnesium oxide alone, and 100 parts by weight in total when magnesium oxide and magnesium hydroxide are included simultaneously. do.

The annealing separator composition for a grain-oriented electrical steel sheet may further comprise 1 to 10 parts by weight of ceramic powder based on 100 parts by weight of magnesium oxide. The ceramic powder may be at least one selected from Al ₂ O ₃ , SiO ₂ , TiO _2, and ZrO ₂ . When the ceramic powder is further contained in an appropriate amount, the insulating properties of the coating may be further improved. Specifically, the ceramic powder may further include TiO ₂ . The weight part means here the weight contained relatively with respect to each component.

The annealing separator composition may further comprise a solvent for even dispersion and easy application of the solids. Water, alcohol, and the like may be used as the solvent, and may include 500 to 1500 parts by weight based on 100 parts by weight of magnesium oxide. As such, the annealing separator composition may be in the form of a slurry.

In addition, the annealing separator composition according to an embodiment of the present invention further comprises a boron compound. The boron compound lowers the coefficient of thermal expansion in the primary coating and improves the adhesion between the primary coating and the steel sheet.

In one embodiment of the present invention, the annealing separator composition may further include 0.1 to 20 parts by weight of a boron compound based on 100 parts by weight of magnesium oxide. The boron compound may include one or more of boron trioxide (B ₂ O ₃ ), boric acid (H ₃ BO ₃ ), and sodium borate (Na ₂ B ₄ O ₇ ). If too little boron compound is added, it is difficult to sufficiently obtain the effect of the above-described boron compound addition. If the boron compound is added too much, problems may occur when the boron compound is aggregated and applied in the annealing separator. Therefore, the boron compound may be included in the above range. More specifically, the boron compound may include 1 to 5 parts by weight.

Method for producing a magnesium oxide for a grain-oriented electrical steel sheet annealing separator according to an embodiment of the present invention comprises the steps of preparing magnesium hydroxide; Calcining magnesium hydroxide at 800 to 1200 ° C. to produce highly active magnesium oxide; Calcining magnesium hydroxide at 1300 to 1500 ° C. to produce low activity magnesium oxide; And mixing the high active magnesium oxide and the low active magnesium oxide.

First, magnesium hydroxide is prepared. Preparing magnesium hydroxide may include preparing magnesium hydroxide by reacting magnesium chloride and calcium hydroxide.

Next, high active magnesium oxide is produced and low active magnesium oxide is produced. The step of preparing the high active magnesium oxide and the step of producing the low active magnesium oxide do not exist before or after time. The reason for limitation of the annealing temperature conditions in the step of preparing the high active magnesium oxide and the step of producing the low active magnesium oxide is the same as that described above, and thus redundant description is omitted.

Next, high active magnesium oxide and low active magnesium oxide are mixed. The mixing ratio of the high active magnesium oxide and the low active magnesium oxide is the same as that described in the above-described annealing separator composition, and thus redundant description is omitted.

Method for producing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises the steps of preparing a steel slab; Heating the steel slab; Hot rolling the heated steel slab to produce a hot rolled sheet; Cold rolling the hot rolled sheet to produce a cold rolled sheet; Primary recrystallization annealing of the cold rolled sheet; Applying an annealing separator on the surface of the primary recrystallized annealed steel sheet; And secondary recrystallization annealing the steel sheet to which the annealing separator is applied. In addition, the method for producing a grain-oriented electrical steel sheet may further comprise other steps.

First prepare a steel slab. In one embodiment of the present invention, the effect is due to the composition of the annealing separator composition irrespective of the alloy composition of the steel slab. Supplementally, the composition of the steel slab is as follows. Steel slab is 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), carbon (C) 0.01% by weight or less (excluding 0%), N: 0.005 to 0.05% by weight and 0.01 to 0.15% by weight of antimony (Sb), tin (Sn), or a combination thereof, the balance being Fe and other unavoidable impurities It may include. Description of each component of the steel slab is generally the same as the known content, detailed description thereof will be omitted.

Next, the steel slabs are heated. At this time, the slab heating may be heated by a low temperature slab method at 1,200 ℃ or less.

Next, the heated steel slab is hot rolled to prepare a hot rolled sheet. Thereafter, the manufactured hot rolled sheet may be hot rolled and annealed.

Next, the hot rolled sheet is cold rolled to produce a cold rolled sheet. In the step, cold rolling may be performed once, or two or more cold rolling may be performed including intermediate annealing.

Next, the cold rolled sheet is subjected to primary recrystallization annealing. In the first recrystallization annealing process, the cold rolled sheet may be simultaneously subjected to decarburization annealing and nitriding annealing, or after decarburization annealing, may include nitriding annealing.

Next, an annealing separator is applied on the surface of the steel sheet subjected to primary recrystallization annealing. Since the annealing separator is specifically described above, repeated descriptions are omitted.

The application amount of the annealing separator may be 6 to 20 g / m ² . If the application amount of the annealing separator is too small, the film may not be formed smoothly. If the application amount of the annealing separator is too high, it may affect the secondary recrystallization. Therefore, the coating amount of the annealing separator can be adjusted to the above-mentioned range.

After applying the annealing separator, it may further comprise the step of drying. The drying temperature may be 300 to 700 ° C. If the temperature is too low, the annealing separator may not dry easily. If the temperature is too high, secondary recrystallization may be affected. Therefore, the drying temperature of the annealing separator can be adjusted to the above-mentioned range.

The secondary recrystallization annealing can raise the temperature increase rate at 18-75 degreeC / hr in the temperature range of 700-950 degreeC, and can raise the temperature increase rate at 10-15 degreeC / hr in the temperature range of 950-1200 degreeC. After that, it cracks. By adjusting the temperature increase rate in the above-described range, the primary coating can be formed smoothly. In addition, the temperature rising process of 700 to 1200 ° C is carried out in an atmosphere containing 20 to 30% by volume of nitrogen and 70 to 80% by volume of hydrogen, and after reaching 1200 ° C in a cracking step is carried out in an atmosphere containing 90% by volume or more of hydrogen. can do. By adjusting the atmosphere in the above-described range, the primary coating can be formed smoothly.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, these examples are only for illustrating the present invention, and the present invention is not limited thereto.

Example

By weight% Si: 3.2%, C: 0.055%, Mn: 0.12%, Al: 0.026%, N: 0.0042%, S: 0.0045% and Sn: 0.04%, Sb: 0.03%, P: 0.03% and cup As a result, steel slabs containing Fe and unavoidable impurities were produced.

The slab was heated at 1150 ° C. for 220 minutes and then hot rolled to a thickness of 2.8 mm to prepare a hot rolled sheet.

The hot rolled plate was heated to 1120 ° C., held at 920 ° C. for 95 seconds, quenched with water, pickled, and cold rolled to a thickness of 0.23 mm to prepare a cold rolled plate.

The cold rolled plate was placed in a furnace maintained at 875 ° C., and then maintained in a mixed atmosphere of 74% by volume of hydrogen, 25% by volume of nitrogen, and 1% by volume of dry ammonia gas for 180 seconds to simultaneously decarburize and nitride.

As the annealing separator composition, a high activity magnesium oxide having an activation degree of 75 seconds and a low active magnesium oxide having an activation degree of 250 seconds were mixed at the weight shown in Table 1 to prepare an annealing separator composition. Highly active magnesium oxide was prepared by firing magnesium hydroxide at 850 ° C., and lowly active magnesium oxide was prepared by firing magnesium hydroxide at 1350 ° C. The hydration moisture slope of the total magnesium oxide was measured and shown in Table 1. Hydration Moisture Gradients Hydrated Magnesium was heated to 550 ° C, 650 ° C, 750 ° C, and 850 ° C for 5 minutes, and then the amount of hydrated water was measured. , To find the slope of the equation.

In addition to magnesium oxide, TiO ₂ , Na ₂ B ₄ O ₇ and pure water were mixed in the amounts summarized in Table 1 below to prepare an annealing separator composition.

10 g / m ² of annealing separator was applied, and secondary recrystallization annealing was carried out on the coil. In the second recrystallization annealing, the first cracking temperature was 700 ° C and the second cracking temperature was 1200 ° C. 15 degreeC / hr. In addition, the cracking time in 1200 degreeC was processed into 15 hours. At the time of secondary recrystallization annealing, the atmosphere was mixed with 25% by volume of nitrogen and 75% by volume of hydrogen up to 1200 ° C. After reaching 1200 ° C, it was maintained in a 100% by volume hydrogen atmosphere and then cooled.

Table 2, after applying the annealing separator prepared in Table 1 to the specimen, summarized the presence or absence of oxidative defects, primary film tension, adhesion.

The presence or absence of oxidative defects was indicated by O when black spots (oxidative defects) having a size of 0.1 m or more were observed for a width of 1.05 m and a length of 1000 m, and X when no black spots were observed. 2 and 3 are photographs (measurement) of steel sheets manufactured in Examples (Sample No. 4) and Comparative Example (Sample No. 1), respectively. 2 shows no black spots, while FIG. 3 shows that black spots are formed.

In addition, the primary coating tension is obtained by measuring the radius of curvature (H) of the specimen generated after removing one side coating of the double-coated specimen, and substituting the value into the following equation.

E _c = Young's Modulus of coating layer

υ _RD = Poisson's ratio in rolling direction

T: thickness before coating

t: thickness after coating

I: specimen length

H: radius of curvature

In addition, the adhesion is shown by the minimum arc diameter without film peeling when the specimen is bent 180 ° in contact with a 10 to 100 mm arc.

Psalter
number Magnesium oxide Oxidation
titanium
(g) Na ₂ B ₄ O ₇
(g) pure
(g) Remarks High water
(g) Dehydration
(g) Granularity
(D50) Hydrating Moisture
inclination One 100 0 2.0 0.23 5 0.3 1000 Comparative material 2 90 10 2.23 0.26 5 0.3 1000 Comparative material 3 70 30 2.5 0.275 5 0.3 1000 Comparative material 4 60 40 2.8 0.3 5 0.3 1000 Example 5 50 50 3.0 0.38 5 0.3 1000 Example 6 40 60 3.1 0.42 5 0.3 1000 Example 7 30 70 3.25 0.45 5 0.3 1000 Example 8 10 90 3.5 0.52 5 0.3 1000 Comparative material 9 0 100 3.8 0.55 5 0.3 1000 Comparative material

Psalter
number Oxidative defect Film tension
(kgf / mm ² ) Adhesion
(mmf) Remarks Occurrence One O 0.30 25 Comparative material 2 O 0.35 25 Comparative material 3 O 0.32 25 Comparative material 4 X 0.45 20 Example 5 X 0.50 20 Example 6 X 0.48 20 Example 7 X 0.55 20 Example 8 O 0.31 20 Comparative material 9 O 0.23 30 Comparative material

As can be seen in Tables 1 and 2, the film tension and adhesion in Specimen Nos. 4 to 7 in which the hydrated water gradient of magnesium oxide was adjusted were shown to be superior to those of the comparative materials (Samples Nos. 1 to 3, 8, and 9). In particular, the occurrence of oxidative defects can be fundamentally reduced. The reason for this is that in the annealing separator proposed in the present invention, the hydration water discharge pattern is kept relatively high at the initial annealing stage and relatively low at the annealing stage.

In addition, as can be seen in Table 2, in the case of the specimen which does not generate an oxidative defect, the bond between the primary coating and the base material was also good, thereby improving the adhesion. Furthermore, the tension of the primary coating is improved. Therefore, it can be expected to affect iron loss improvement.

The present invention is not limited to the embodiments and can be manufactured in various different forms, and those skilled in the art to which the present invention pertains may change to other specific forms without changing the technical spirit or essential features of the present invention. It will be appreciated that it may be practiced. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims (16)

Contains magnesium oxide,
Annealing separator composition for grain-oriented electrical steel sheet having a hydration water gradient of magnesium oxide represented by the following Formula 1 from 0.28 to 0.50.
[Equation 1]
[Hydration Moisture Gradient] = ([Ig.loss2]-[Ig.loss1]) / ([T2]-[T1])
(In Formula 1, [Ig.loss1] and [Ig.loss2] are the weight loss rate (% by weight) of magnesium oxide when the hydrated magnesium oxide is raised to the temperature of [T1] and [T2], respectively, [T1] and [T2] is the temperature (° C.) selected at 550 to 1000 ° C. respectively. [T1] and [T2] are different from each other.) The method of claim 1,
[T1] is selected from 550 to 600 ° C, and [T2] is selected from 850 to 900 ° C. The method of claim 1,
The magnesium oxide is aromatic, containing 30 to 70 parts by weight of highly active magnesium oxide having an activation degree of 50 to 180 seconds and 30 to 70 parts by weight of low active magnesium oxide having an activation degree of 200 to 1000 seconds, based on 100 parts by weight of the total magnesium oxide. Annealing separator composition for electrical steel sheet. The method of claim 3,
Annealing separator composition for a grain-oriented electrical steel sheet having an activation degree of the entire magnesium oxide is 50 to 500 seconds. The method of claim 3,
The high active magnesium oxide D50 is 2.0 to 3.5, the low active magnesium oxide D50 is 2.5 to 4.0 annealing separator composition for grain-oriented electrical steel sheet. The method of claim 5,
Annealing separator composition for grain-oriented electrical steel sheet having a total D50 of 2.75 to 3.25 of the magnesium oxide. The method of claim 1,
Annealing separator composition for grain-oriented electrical steel sheet further comprising 1 to 10 parts by weight of ceramic powder based on 100 parts by weight of the magnesium oxide. The method of claim 7, wherein
The ceramic powder is an annealing separator composition for a grain-oriented electrical steel sheet comprising at least one selected from Al ₂ O ₃ , SiO ₂ , TiO ₂ and ZrO ₂ . The method of claim 1,
Annealing separator composition for grain-oriented electrical steel sheet further comprising 0.1 to 20 parts by weight of the boron compound based on 100 parts by weight of the magnesium oxide. The method of claim 1,
Annealing separator composition for a grain-oriented electrical steel sheet further comprises 500 to 1500 parts by weight of solvent based on 100 parts by weight of magnesium oxide. Preparing magnesium hydroxide;
Calcining the magnesium hydroxide at 800 to 1200 ° C. to produce highly active magnesium oxide;
Calcining the magnesium hydroxide at 1300 to 1500 ° C. to produce low-active magnesium oxide; And
Mixing the high active magnesium oxide and the low active magnesium oxide,
Magnesium oxide prepared in the mixing step is a method for producing magnesium oxide for a grain-oriented electrical steel sheet annealing separator having a water hydration gradient of 0.28 to 0.50 represented by the following formula (1).
[Equation 1]
[Hydration Moisture Gradient] = ([Ig.loss2]-[Ig.loss1]) / ([T2]-[T1])
(In Formula 1, [Ig.loss1] and [Ig.loss2] are the weight loss rate (% by weight) of magnesium oxide when the hydrated magnesium oxide is raised to the temperature of [T1] and [T2], respectively, [T1] and [T2] is the temperature (° C.) selected at 550 to 1000 ° C. respectively. [T1] and [T2] are different from each other.) The method of claim 11,
Preparing the magnesium hydroxide,
A method for producing magnesium oxide for a grain-oriented electrical steel sheet annealing separator comprising the step of reacting magnesium chloride and calcium hydroxide to produce magnesium hydroxide. Preparing a steel slab;
Heating the steel slab;
Hot rolling the heated steel slab to produce a hot rolled sheet;
Cold rolling the hot rolled sheet to produce a cold rolled sheet;
Primary recrystallization annealing of the cold rolled sheet;
Applying an annealing separator on the surface of the first recrystallized annealing steel sheet; And
Secondary recrystallization annealing of the steel sheet coated with the annealing separator,
The annealing separator comprises magnesium oxide, the hydrated water gradient of magnesium oxide represented by the following formula 1 is 0.28 to 0.50 method for producing a grain-oriented electrical steel sheet.
[Equation 1]
[Hydration Moisture Gradient] = ([Ig.loss2]-[Ig.loss1]) / ([T2]-[T1])
(In Formula 1, [Ig.loss1] and [Ig.loss2] are the weight loss rate (% by weight) of magnesium oxide when the hydrated magnesium oxide is raised to the temperature of [T1] and [T2], respectively, [T1] and [T2] is the temperature (° C.) selected at 550 to 1000 ° C. respectively. [T1] and [T2] are different from each other.) The method of claim 13,
After applying the annealing separator, a method of manufacturing a grain-oriented electrical steel sheet further comprising the step of drying at 300 to 700 ℃. The method of claim 13,
The second recrystallization annealing step,
Heating at a temperature increase rate of 18 to 75 ° C./hr in a temperature range of 700 to 950 ° C .;
Heating at a temperature increase rate of 10 to 15 ° C./hr in a temperature range of 950 to 1200 ° C .; And
Method for producing a grain-oriented electrical steel sheet comprising a cracking step. The method of claim 15,
The step of raising the temperature at a temperature increase rate of 18 to 75 ℃ / hr and the step of increasing the temperature at a temperature increase rate of 10 to 15 ℃ / hr is in an atmosphere containing 20 to 30% by volume of nitrogen and 70 to 80% by volume of hydrogen Doing,
The cracking step is a method of producing a grain-oriented electrical steel sheet carried out in an atmosphere containing 90% by volume or more of hydrogen.

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