KR20240098854A - Grain oriented electrical steel sheet and method for the same - Google Patents

Abstract

A method for manufacturing grain-oriented electrical steel is provided.
The method for manufacturing a grain-oriented electrical steel sheet of the present invention includes manufacturing a steel slab; Manufacturing a hot-rolled sheet by hot-rolling the steel slab; Annealing the hot-rolled sheet; manufacturing a cold-rolled sheet by cold-rolling the annealed hot-rolled steel sheet; Primary recrystallization annealing of the cold-rolled sheet; It includes the step of applying an annealing separator to the cold-rolled sheet subjected to primary recrystallization annealing and drying it, and the step of performing secondary recrystallization annealing of the cold-rolled sheet coated with the annealing separator.

Description

Grain oriented electrical steel sheet and method for the same}

The present invention relates to a grain-oriented electrical steel sheet with excellent Goss orientation integration, low surface roughness, and smooth magnetic domain movement, and a method for manufacturing the same.

Grain-oriented electrical steel sheet contains 3.2% Si and has a texture in which the grains are aligned in the (110)[001] direction. It is mainly used as an iron core material for transformers, motors, generators, and other electronic devices, and utilizes its extremely excellent magnetic properties in the rolling direction.

Recently, as high magnetic flux density grain-oriented electrical steel sheets have been commercialized, materials with low iron loss are in demand. This can be mainly approached through four technical methods: i) a method of accurately orienting the {110} <001> grain orientation, which includes the magnetization axis of grain-oriented electrical steel sheet, in the rolling direction, ii) a method of thinning the material, iii) a magnetic domain refinement method that refines the magnetic domain through chemical and physical methods, and iv) a method of improving surface properties or imparting surface tension by chemical methods such as surface treatment.

The last method above is a method of improving the magnetic properties of the material by actively improving the surface properties of the grain-oriented electrical steel sheet. As a representative example, there is a method of removing the oxide layer inevitably generated during the decarburization annealing process and the forsterite (Mg ₂ SiO ₄ ), that is, the base coating layer, generated through a chemical reaction of MgO slurry, which is an anti-fusion agent for coils. . [Reference: Y. Ushigami et al., "Recent Development of low-loss Grain-Oriented Silicon Steel", JMMM, pp307-314, 254-255 (2003)]

The technology for removing the base coating layer is a method of forcibly removing a typical product with a base coating layer already formed with sulfuric acid or hydrochloric acid, and a technology of removing or suppressing the base coating layer in the process of being created (hereinafter referred to as glassless technology). This was proposed (patent document 1).

To date, the main research directions for the glassless technology include technology that uses the surface etching effect in a high-temperature annealing process after adding chloride to MgO, an annealing separator, and applying Al ₂ O ₃ powder as an annealing separator in the high-temperature annealing process. Technology that does not form the base coating layer itself has progressed in two directions.

The ultimate direction of this technology is to eliminate surface pinning sites that cause magnetic deterioration by intentionally preventing the base coating layer in the manufacturing of electrical steel sheets, and ultimately improve the magnetic properties of grain-oriented electrical steel sheets. .

As described above, both of the two glassless methods proposed above, that is, the method of suppressing the formation of the forsterite layer and the technology of separating the base coating layer from the base material in the high-temperature annealing process, produce oxygen in the furnace through hydrogen and nitrogen gases and dew point changes during the decarbonization annealing process. There is a problem in the process that the oxidation ability (PH ₂ O/PH ₂ ) must be controlled very low (Patent Document 2). The reason for controlling the oxidation ability to a low level is to minimize the oxidation layer formed on the surface of the base material during decarburization and to suppress the formation of a base coating layer as much as possible. In addition, when the oxidation capacity in the furnace is low, the oxidation layer generated is mostly silica (SiO ₂ ) oxide, which can suppress the formation of iron-based oxides, so there is an advantage that iron-based oxides do not remain on the surface after high-temperature annealing. However, in this case, it is difficult to secure an appropriate primary recrystallized grain size due to poor decarburization, and problems may also occur in secondary recrystallized grain growth during high-temperature annealing. Therefore, a decarburization process is usually used to thin the oxide layer while appropriately securing decarburization. It took longer than the reprocessing process, and as a result, productivity decreased (Patent Document 3). In addition, due to the thin oxide layer, the amount of nitrate due to subsequent nitriding annealing is reduced, so NH ₃ Gas must be added excessively to secure the normal amount of nitrate of about 200ppm, which can also cause a decrease in productivity.

US Patent No. 4543134 Japanese Patent No. 6-63036 Japanese Patent Laid-Open No. 6-256848

The purpose of the present invention is to provide a method for manufacturing a grain-oriented electrical steel sheet in which a forsterite removal process (hereinafter referred to as “base coating free” process), which has excellent magnetic flux density and excellent productivity, is introduced.

The object of the present invention is not limited to the above-described content. Anyone skilled in the art to which the present invention pertains will have no difficulty in understanding the additional problems of the present invention from the overall details of the present invention specification.

One aspect of the present invention is,

By weight%, Si: 2~4%, C: 0.01~0.07%, Al: 0.02~0.04%, N: 0.01% or less, P: 0.01~0.05%, Mn: 0.2% or less (excluding 0%), S : manufacturing a slab containing 0.015% or less (excluding 0%), Cu: 0.0005 to 0.1%, the balance Fe and other unavoidable impurities; Manufacturing a hot-rolled sheet by hot-rolling the slab; Annealing the hot-rolled sheet; Manufacturing a cold-rolled sheet by cold-rolling the annealed hot-rolled steel sheet; Primary recrystallization annealing of the cold-rolled sheet; In the method of manufacturing a grain-oriented electrical steel sheet, comprising the steps of applying an annealing separator to the primary recrystallization annealed cold-rolled sheet and drying it, and secondary recrystallization annealing the cold-rolled sheet coated with the annealing separator,

After the primary recrystallization annealing, the content of carbon remaining in the steel sheet is controlled to be within 150 ppm, the oxidation amount of the steel sheet is controlled to be within 500 ppm, the amount of oxidation is controlled to be within the range of 120 to 180 ppm, and the thickness of the oxidation layer formed on the surface of the steel sheet is controlled to be within 0.1 to 2.0 ppm. It relates to a method of manufacturing a grain-oriented electrical steel sheet, controlling the primary recrystallization annealing process to satisfy the ㎛ range, and removing the forsterite (Mg ₂ SiO ₄ ) film formed on the surface of the steel sheet in the secondary recrystallization annealing step.

The slab may further contain Se: 0.015% or less.

The annealed separator may be composed of 10 to 20 parts by weight of an oxychloride material and 1 to 5 parts by weight of a sulfate-based antioxidant, based on the weight of MgO with an activation degree of 400 to 3000 seconds.

The oxychloride material may be one or more selected from antimony oxychloride (SbOCl) and bismuth oxychloride (BiOCl).

The sulfate-based antioxidant may be one or more selected from antimony sulfate (Sb ₂ (SO ₄ ) ₃ ), strontium sulfate (SrSO ₄ ), and barium sulfate (BaSO ₄ ).

The surface roughness of the produced grain-oriented electrical steel sheet may satisfy Ra of 0.2㎛ or less.

The range of the average value of the steinmetz index value (α) obtained by measuring the area of the magnetization curve of the manufactured electrical steel sheet at each sweeping speed while changing the field sweeping speed (dH/dt) of the magnetic field up to 150Oe/sec is 0.5. ~0.7 can be satisfied.

In addition, another aspect of the present invention is,

By weight%, Si: 2~4%, C: 0.01~0.07%, Al: 0.02~0.04%, N: 0.01% or less, P: 0.01~0.05%, Mn: 0.2% or less (excluding 0%), S : 0.015% or less (excluding 0%), Cu: 0.0005~0.1%, contains remaining Fe and other inevitable impurities, and changes the field sweeping speed (dH/dt) of the magnetic field up to 150Oe/sec for each sweeping It relates to a grain-oriented electrical steel sheet in which the average value of the steinmetz index value (α), obtained by measuring the area of the magnetization curve of the steel sheet at speed, satisfies the range of 0.5 to 0.7.

According to one embodiment of the present invention described above, magnesium oxide (MgO) present in the oxide layer generated in the primary recrystallization annealing process and the annealing separator are forsterite (MgO) generated through a chemical reaction in the secondary recrystallization annealing process. ₂ SiO ₄ ) After forming the film, the surface properties of the grain-oriented electrical steel sheet can be controlled by uniformly removing it.

Alternatively, in this process, in order to control the oxidation layer on the surface to be uniform and thin, carbon in the steel is not completely removed but remains up to 150 ppm, which not only increases productivity by reducing the annealing time, but also increases surface forsterite during the secondary recrystallization formation process. By smoothly exfoliating the layers, the magnetic properties of the final product can be improved.

Furthermore, in the grain-oriented electrical steel sheet from which the forsterite film has been removed, the pinning point, which is a major element limiting magnetic domain movement, can be excluded, and the effect of hysteresis loss among the elements constituting the iron loss of the grain-oriented electrical steel sheet can be reduced. . However, due to the excessively removed pinning points and the improved integration of the Goss orientation, the width of the magnetic domain increases, resulting in an effect of increasing iron loss due to magnetic domain movement, resulting in fewer elements constituting iron loss compared to ordinary grain-oriented electrical steel sheets. It should be noted that this has the effect of changing the ratio.

1 is a schematic process flow chart of a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention.
Figure 2 is a diagram showing the change in area of the MH loop according to the frequency of the applied magnetic field of the grain-oriented electrical steel sheet according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein.

Figure 1 schematically shows a process flow chart of a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention. The flowchart of the method for manufacturing a grain-oriented electrical steel sheet in Figure 1 is merely for illustrating the present invention, and the present invention is not limited thereto. Therefore, the manufacturing method of grain-oriented electrical steel can be modified in various ways.

The method of manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention is by weight percentage, Si: 2-4%, C: 0.01-0.07%, Al: 0.02-0.04%, N: 0.01% or less, P: 0.01-0.01% Manufacturing a steel slab containing 0.05%, Mn: 0.02-0.2%, S: 0.015% or less (excluding 0%), Cu: 0.0005-0.1%, the balance Fe and other inevitable impurities; Manufacturing a hot-rolled sheet by hot-rolling a steel slab; Manufacturing a cold-rolled sheet by cold rolling a hot-rolled sheet; Primary recrystallization annealing of the cold rolled sheet; Applying an annealing separator to a cold-rolled sheet subjected to primary recrystallization annealing and drying it; and secondary recrystallization annealing of the cold-rolled sheet to which the annealing separator has been applied.

First, in the present invention, in weight percent, Si: 2 to 4%, C: 0.01 to 0.07%, Al: 0.02 to 0.04%, N: 0.01% or less, P: 0.01 to 0.05%, Mn: 0.2% or less ( Steel slabs containing 0% or less (excluding 0%), S: 0.015% or less (excluding 0%), Cu: 0.0005 to 0.1%, the balance Fe and other inevitable impurities are manufactured (S10).

Hereinafter, the composition of the steel slab for manufacturing the grain-oriented electrical steel sheet of the present invention and the reasons for limiting its content will be described, where the content of each element is based on weight percent.

Si: 2~4%

Si is the basic composition of electrical steel and plays a role in lowering core loss by increasing the specific resistance of the material.

If the Si content is too low, the resistivity decreases, eddy current loss increases and iron loss characteristics deteriorate, and phase transformation between ferrite and austenite becomes active during decarbonitriding annealing, which may severely damage the primary recrystallization texture. In addition, during high-temperature annealing, a phase transformation occurs between ferrite and austenat, which not only makes secondary recrystallization unstable but also severely damages the {110} Goss texture.

On the other hand, if the Si content is too high, excessive and dense SiO ₂ and Fe ₂ SiO ₄ oxide layers are formed during the primary recrystallization annealing, which delays decarburization behavior and causes phase transformation between ferrite and austenite to continuously occur during the primary recrystallization annealing process. This causes the first recrystallization assembly to be severely damaged. In addition, the nitriding behavior is delayed due to the effect of delaying the decarburization behavior due to the formation of the dense oxide layer described above, and nitrides such as (Al, Si, Mn)N and AlN are not sufficiently formed, so that sufficient grain suppression power required for secondary recrystallization during secondary recrystallization annealing is required. becomes impossible to secure. Therefore, the Si content can be adjusted to the above-mentioned range.

C: 0.01~0.07%

C is an element that causes phase transformation between ferrite and austenite, and is an essential element for improving the rolling performance of electrical steel sheets, which are highly brittle and have poor rolling properties. However, if it remains in the final product, carbides formed due to the magnetic aging effect. Since it is an element that worsens magnetic properties, it can be controlled to an appropriate content.

If the C content is too low, the phase transformation between ferrite and austenite does not occur properly, causing non-uniformity in the slab and hot rolling microstructure. In addition, if the phase transformation between ferrite and austenite is excessive or insufficient during the hot-rolled sheet annealing heat treatment, the re-dissolved precipitates are coarsely precipitated when the slab is reheated, causing the primary recrystallization microstructure to become uneven, and the secondary recrystallization annealing due to the lack of a grain growth inhibitor. Secondary recrystallization behavior becomes unstable.

On the other hand, if the C content is too high, a problem may arise in which it is not easy to remove it because it cannot be sufficiently decarburized in a normal primary recrystallization process. Furthermore, if decarburization is not sufficient, deterioration of magnetic properties due to self-aging may occur when the final product is applied to power equipment. Therefore, the content of C can be adjusted to the above-mentioned range. In particular, in the primary recrystallization formation process of the present invention, the process of thinning the surface oxide layer is important, so it is necessary to reduce the C content compared to usual and set it in a range not exceeding a maximum of 700 ppm.

Al: 0.02~0.04%

In addition to AlN, which is finely precipitated during hot rolling and hot-rolled sheet annealing, nitrogen ions introduced by ammonia gas during the annealing process after cold rolling combine with Al, Si, and Mn present in a solid solution in the steel (Al, It acts as a strong grain growth inhibitor by forming nitrides in the form of Si, Mn)N and AlN.

If the Al content is too low, sufficient effect as an inhibitor may not be expected because the number and volume formed are quite low.

If the Al content is too high, coarse nitrides are formed, thereby reducing the ability to inhibit grain growth. Therefore, the Al content can be adjusted to the above-mentioned range.

N: 0.01% or less (excluding 0%)

N is an important element that reacts with Al to form AlN.

If the N content is too high, a surface defect called blister will occur due to nitrogen diffusion in the process after hot rolling, and too much nitride is formed in the slab state, making rolling difficult and making the next process complicated. This may cause the unit price to rise.

Meanwhile, N, which is additionally required to form nitrides such as (Al, Si, Mn) N and AlN, can be reinforced by nitriding the steel using ammonia gas in the first recrystallization annealing step (S40), which will be described later. . Therefore, the N content can be adjusted to the above-mentioned range.

P: 0.01~0.05%

P promotes the growth of primary recrystallized grains in low-temperature heating type oriented electrical steel sheets, thus increasing the secondary recrystallization temperature and increasing the integration of the {110}<001> orientation in the final product. If the primary recrystallization grains are too large, secondary recrystallization becomes unstable, but as long as secondary recrystallization occurs, it is advantageous for magnetism to have large primary recrystallization grains in order to increase the secondary recrystallization temperature.

Meanwhile, P not only lowers the iron loss of the final product by increasing the number of grains with {110}<001> orientation in the primary recrystallized steel sheet, but also strongly develops {111}<112> texture in the primary recrystallized steel sheet. As the {110}<001> integration of the final product is improved, the magnetic flux density also increases.

In addition, P segregates at grain boundaries up to a high temperature of about 1000°C during secondary recrystallization annealing, and has the effect of delaying the decomposition of precipitates and reinforcing the suppressing force.

If the P content is too high, the size of the primary recrystallized grains is reduced, which not only makes secondary recrystallization unstable, but also increases brittleness, which may impair cold rolling properties. Therefore, the content of P can be adjusted to the above-mentioned range.

Mn: 0.2% or less (excluding 0%)

Mn, like Si, has the effect of reducing total iron loss by increasing resistivity and reducing eddy current loss, and reacts with nitrogen introduced through nitriding treatment with Si to form precipitates of (Al, Si, Mn) N. It is an important element in suppressing the growth of primary recrystallized grains and causing secondary recrystallization. When adding more than 0.20%, if too much Mn is added to the surface of the steel sheet, a large amount of (Fe, Mn) and Mn oxides in addition to Fe ₂ SiO ₄ are formed in the oxide layer on the surface of the steel sheet, which interferes with the formation of the base coating formed during high temperature annealing. This deteriorates the surface quality and causes phase transformation between ferrite and austenite during the secondary recrystallization annealing process, which can severely damage the texture and greatly deteriorate magnetic properties. Therefore, the Mn content can be adjusted to the above-mentioned range.

S: 0.015% or less (excluding 0%)

S is an important element that reacts with Mn to form MnS.

In the present invention, the strength of the restraining force due to AlN precipitates is smaller than that of a typical grain-oriented electrical steel sheet, so it is important to add auxiliary restraining force by precipitates such as MnS. The addition of S forms MnS precipitates and serves to reinforce the insufficient suppressing power of AlN. In the present invention, it is necessary to limit the S content to 0.015% or less for complete solidification of MnS precipitates at a reheating temperature of 1200°C.

Cu: 0.0005~0.1%,

Since Cu is an element that forms CuS precipitates to make up for insufficient suppression power, it is advantageous to add a certain amount. However, it needs to be limited to 0.1% or less in order to ensure full employment during the slab reheating process and not to interfere with secondary recrystallization due to excessive precipitate formation.

Se: 0.015% or less

The slab of the present invention may contain Se as needed.

Se is an important element that, similar to S, reacts with Mn to form MnSe. In the present invention, the strength of the restraining force due to the AlN precipitate is smaller than that of a typical grain-oriented electrical steel sheet, so it is important to add an auxiliary suppressing force by precipitates such as MnSe along with MnS. In the present invention, it is necessary to limit the S content to 0.015% or less for complete solidification of MnSe precipitates at a reheating temperature of 1200°C.

In the present invention, the remaining components include Fe and other unavoidable components. In one embodiment of the present invention, the addition of elements other than the above-described alloy components is not excluded, and various elements may be included within a range that does not impair the technical spirit of the present invention. If additional elements are included, they are included by replacing the remaining Fe.

Next, in step S20, a hot rolled sheet is manufactured by hot rolling the steel slab. At this time, the thickness of the hot rolled sheet may be 2.0 to 2.8 mm.

Then, in step S30, annealing of the hot rolled sheet is performed in the same manner as manufacturing a conventional grain-oriented electrical steel sheet.

Thereafter, in step S40, a cold rolled sheet is manufactured by cold rolling the hot rolled sheet. At this time, the thickness of the cold rolled sheet may be 0.15 to 0.35 mm.

Next, in step S50, the cold rolled sheet is subjected to primary recrystallization annealing.

When a cold rolled sheet passes through a heating furnace controlled by a wet atmosphere for decarburization and quenching, Si, which has the highest oxygen affinity among the composition of the cold rolled sheet, reacts with oxygen supplied from the water vapor in the heating furnace and is the first to appear on the surface. Silica oxide (SiO ₂ ) is formed. Afterwards, oxygen penetrates into the cold rolled sheet and Fe-based oxide is generated. The silica oxide formed in this way forms a forsterite (Mg ₂ SiO ₄ ) film (base coating layer) on the surface of the steel sheet through the following chemical equation 1 in the subsequent secondary recrystallization annealing process.

[Scheme 1]

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

As shown in the chemical reaction equation above, in order to achieve a complete chemical reaction when silica oxide reacts with solid magnesium slurry, a catalyst material that connects the two solids is required, and in this case, payalite (Fe ₂ SiO ₄ ) is responsible for this. do. Therefore, in the case of a typical grain-oriented electrical steel sheet with a base coating, it was important not only to form silica oxide but also to form an appropriate amount of payalite.

Meanwhile, after primary recrystallization annealing (decarburization annealing) of electrical steel, the shape of the oxide layer is such that the oxide in the black part is embedded in the metal matrix. This layer has been formed to be 3 to 6㎛ in order to ensure that the base coating is well formed by controlling the temperature, atmosphere, dew point, etc. of the furnace.

However, the glassless process has the concept of forming a minimum base coating layer, which ultimately impedes the magnetic domain movement of the material, at the front end of the high-temperature annealing process and then removing it at the back end, so a minimum amount of silica oxide is usually produced in the primary recrystallization annealing process. After it is formed, it is reacted with an annealing slurry substituted with magnesium hydroxide (Mg(OH) ₂ ) to form a forsterite layer, which then induces separation from the base material.

Therefore, in the case of a typical glassless manufacturing process, it is advantageous to form a small amount of silica oxide layer on the surface of the material and to generate a very small amount of payalite by controlling the dew point, cracking temperature, and atmospheric gas during decarburization and quenching. The reason is that payalite, a substance that promotes the reaction between silica oxide and magnesium, is an iron-based oxide. When forming a base coating, an iron-based oxide hill (hereinafter referred to as Fe mound) is formed and the glassless-based additive is vaporized and does not fall off from the base material. In this case, not only is it impossible to obtain a product with a beautiful surface, which is what the glassless process aims for, but its magnetic properties are also very poor.

Due to the manufacturing problems of the glassless manufacturing process, the oxidation ability is controlled low during primary recrystallization annealing in a typical glassless process to generate a small amount of oxide layer, and the composition of the generated oxide layer is mostly silica oxide. On the other hand, the problem of decarburization of the material due to this decrease in oxidation ability is solved by increasing the decarburization treatment time. This not only reduces productivity in the primary recrystallization annealing process, but also requires strict control of the dew point temperature and furnace temperature to simultaneously form a low amount of oxidation and a trace amount of residual carbon (less than 30 ppm).

In other words, in order to decarburize the amount of carbon in the steel to less than 30ppm, the oxidation ability in the furnace must be increased, which causes the oxidation layer on the surface to become thicker. Since the thickened oxidation layer makes it difficult for FeCl ₂ gas to penetrate inside and is the main cause of lowering the hardness, it is necessary to carry out decarburization for a long time while lowering the oxidation ability in the furnace to maintain excellent hardness while completing decarburization. I would say there is.

At this time, in the present invention, the amount of carbon in the steel sheet is not decarburized to less than 30ppm, but controlled to less than 150ppm, and the oxidation amount is controlled to less than 500ppm, thereby creating a thin and dense surface oxide layer, thereby forming an oxide film due to internal penetration of FeCl ₂ gas. It is characterized by improving the mirror surface by smoothing the removal effect. Preferably, it can be said that it is advantageous to lower the oxidation amount to 300ppm or less to facilitate the removal of the oxide film. However, if the oxidation amount is too low, carbon in the steel is not removed and remains in large amounts of 150ppm or more, so high temperature annealing at 1200 degrees is required. If it is not removed afterward, it may cause magnetism to deteriorate.

At this time, in the present invention, it is preferable to control the thickness of the oxidation layer formed on the surface of the steel sheet to a range of 0.1 to 2.0 μm. As before, if the oxide layer is too thin, decarburization takes too much time and is uneconomical, and if it is too thick, it is undesirable because it promotes the chemical reaction 1 described above and promotes the formation of a forsterite layer.

Meanwhile, the carbon remaining up to the maximum of 150ppm undergoes oxide layer peeling in the 1000-1100°C range during high-temperature annealing, and additional decarburization occurs to the outside, resulting in less than 30ppm of carbon in the final product.

In addition, in the present invention, in order for surface oxide layer peeling to occur in a relatively low section and secondary recrystallization to form, it is advantageous to keep the total strength of the restraining force lower than that of a typical electrical steel sheet, so the amount of sediment formed during the primary recrystallization formation process is It is desirable to manage it below 150ppm.

Next, in step S60, an annealing separator is applied to the cold-rolled sheet subjected to primary recrystallization annealing and dried. Specifically, the annealing separator may include MgO, an oxychloride material, and a sulfate-based antioxidant.

MgO is the main component of the annealing separator, and reacts with SiO ₂ present on the surface to form a forsterite (Mg ₂ SiO ₄ ) film, as shown in the above-mentioned chemical equation 1.

The activation degree of MgO can be 400 to 3000 seconds. If the activation degree of MgO is too high, there may be a problem of leaving spinel-based oxide (MgOAl ₂ O ₃ ) on the surface after secondary recrystallization annealing. If the activation degree of MgO is too small, it may not react with the oxide layer and may not form a base coating layer. Therefore, the activation degree of MgO can be adjusted within the above-mentioned range.

The oxychloride material is thermally decomposed in the subsequent secondary recrystallization annealing process (S70). The oxychloride material may be one or more selected from antimony oxychloride (SbOCl) and bismuth oxychloride (BiOCl). For example, antimony oxychloride may undergo thermal decomposition at around 280°C according to the chemical reaction 1 below.

[Scheme 2]

2SbOCl → Sb ₂ (s) + O ₂ (g) + Cl ₂ (g)

In the case of chloride in the form of oxychloride, Cl groups are generated only through thermal decomposition. Accordingly, the roughness and gloss and ultimately iron loss are reduced during the process of preparing antimony oxychloride as a slurry in an aqueous solution and then applying and drying it. It generates less iron-based oxides that can inhibit

The chlorine (Cl) gas separated in this way does not escape out of the coil due to the pressure inside the heating furnace for final annealing acting on the coil, but diffuses back toward the surface and forms iron chloride (FeCl) at the boundary between the segregation layer and the oxidation layer as shown in Scheme 3 below. ₂ ) is formed. That is, during the step (S70) described later, a base coating is formed on the outermost surface by reaction of magnesium slurry and silica oxide at around 900°C according to Scheme 1 above. Afterwards, around 1025~1100℃, the iron chloride (FeCl ₂ ) formed at the interface between the segregation layer and the oxide layer begins to decompose, and as the decomposed chlorine gas escapes to the outermost surface of the material, forsterite (Mg ₂ SiO _{4 )} formed on top begins to decompose. ) The film (base coating) is peeled off from the material.

[Scheme 3]

Fe (segregation layer) + Cl ₂ → FeCl ₂ (interface between segregation layer and oxide layer)

In the present invention, the oxychloride material may be included in an amount of 10 to 20 parts by weight based on 100 parts by weight of MgO. If the amount of the oxychloride material is too small, Cl sufficient to form FeCl ₂ cannot be supplied, which may lead to limitations in improving the roughness and gloss after step (S70). If the amount of oxychloride material is too large, it may interfere with the formation of the base coating itself, affecting secondary recrystallization not only on the surface but also metallurgically. Therefore, the amount of oxychloride material can be adjusted to the above-mentioned range.

The sulfate-based antioxidant is added to form a thin forsterite layer generated from the reaction of MgO and SiO ₂ . Specifically, the sulfate-based antioxidant may be one or more selected from antimony sulfate (Sb ₂ (SO ₄ ) ₃ ), strontium sulfate (SrSO ₄ ), and barium sulfate (BaSO ₄ ).

The sulfate-based antioxidant may be included in an amount of 1 to 5 parts by weight based on 100 parts by weight of MgO. If the amount of sulfate-based antioxidant is too small, it may not contribute to improving roughness and gloss. If the amount of sulfate-based antioxidant is too high, it may interfere with the formation of the base coating itself. Therefore, the amount of sulfate-based antioxidant can be adjusted to the above-mentioned range.

The annealing separator may further contain 800 to 1500 parts by weight of water for smooth application. Smooth application can be achieved within the above-mentioned range.

In step S60, the application amount of the annealing separator may be 6 to 20 g/m ² . If the amount of annealing separator applied is too small, the base coating may not be formed smoothly. If the amount of annealing separator applied is too large, secondary recrystallization may be affected. Therefore, the application amount of the annealing separator can be adjusted to the above-mentioned range.

The temperature for drying the annealing separator in step (S60) may be 300 to 700°C. If the temperature is too low, the annealing separator may not be easily dried, and if the temperature is too high, it may affect secondary recrystallization. Therefore, the drying temperature of the annealing separator can be adjusted to the above-mentioned range.

And in the present invention, the cold-rolled sheet coated with the annealing separator is subjected to secondary recrystallization annealing in step (S70). Specifically, the temperature raising process from 700 to 1200°C is performed in an atmosphere containing 10 to 50% by volume of hydrogen and 50 to 90% by volume of nitrogen, and after reaching 1200°C, 2 times in an atmosphere containing 100% by volume of hydrogen. Secondary recrystallization annealing can be performed.

That is, during step S70, a base coating is formed on the outermost surface by reaction of magnesium slurry and silica oxide at around 900°C according to Scheme 1 above. That is, in step S70, the upper part of the oxide layer changes into a forsterite layer by reacting with MgO, which is an annealing separator, and the lower part exists as silicon oxide, and the segregation layer is located below the silicon oxide to form an interface with the metal base material. . Afterwards, around 1000~1100℃, the iron chloride (FeCl ₂ ) formed at the interface between the segregation layer and the oxide layer begins to decompose, and the decomposed chlorine gas escapes to the outermost surface of the material, destroying the forsterite film (base coating) formed on the material. Remove it by peeling it off.

The time when this peeling occurs is similar to the time when secondary recrystallization occurs, and by matching this process well, it is possible to manufacture a grain-oriented electrical steel sheet with excellent magnetic properties. In other words, if peeling by FeCl ₂ gas occurs relatively quickly due to the thin oxide layer thickness, the surface of the base material is exposed to H ₂ gas whose dew point temperature is -40 degrees or less. At this time, the Goss orientation crystal grains have the effect of obtaining auxiliary energy for selective growth due to the low surface energy. In the present invention, unlike in ordinary grain-oriented electrical steel sheets, the strength of the restraining force caused by AlN is weak, so it can be said that the contribution of auxiliary energy to help the growth of Goss grains is essential.

The electrical steel sheet manufactured by the grain-oriented electrical steel sheet manufacturing method of the present invention described above has a surface roughness Ra of 0.1 μm or less and has excellent surface gloss.

In addition, according to the method of manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention described above, the thickness of the oxide layer during the primary recrystallization formation process in step (S40) is formed as thin as 50% or less compared to the normal material, and a secondary annealing step ( In S70), a metallic luster type grain-oriented electrical steel sheet in which the forsterite layer is easy to remove and thus the magnetic domain movement of the base material is easy can be obtained. Accordingly, the advantage of reducing the influence of hysteresis loss among the elements constituting the iron loss of grain-oriented electrical steel can be obtained. However, due to the excessively removed pinning points and the improved integration of the Goss orientation, the width of the magnetic domain increases, resulting in an effect of increasing iron loss due to magnetic domain movement, which is a factor that constitutes iron loss compared to ordinary grain-oriented electrical steel sheets. Because it has the effect of changing the ratio, it is necessary to classify the hysteretic loss, classical eddy current loss, and abnormal eddy current loss that make up the total iron loss separately from ordinary products.

In order to rationally classify such iron loss, the present invention attempted to distinguish the characteristics of the core loss components by analyzing the magnetization curve due to the movement of the magnetic domain in the local area. In general, energy loss is divided into intrinsic core loss (hysteresis loss, not dependent on the speed of the external magnetic field cycle), eddy current core loss (eddy current loss), and magnetic domain wall core loss (anomalous core loss) depending on the mechanism. Eddy current loss and magnetic domain wall core loss It is known that iron loss is proportional to the square and 1/2 power of the frequency, but the exact index may vary depending on the state of the material. In the present invention, the effect of iron loss due to the frequency of the magnetic field is calculated as the effect of the glossiness of the surface and the magnetic flux density of the product using the Steinmetz model (P. Steinmetz Trans. Amer. Electr. Eng. (1892)) as shown in the following relational equation 1. I would like to explain them separately.

[Relationship 1]

Direct magnetic domain observation was performed on the micro area rather than the entire macro area, and after analyzing the hysteresis curve for the magnetic field sweep speed (Ω), the iron loss change due to the change in surface gloss was confirmed by Steinmetz law as the index change determined in the micro area. It can be observed through.

That is, in the present invention, the steinmetz index value (α) obtained by measuring the area of the magnetization curve of the manufactured electrical steel sheet at each sweeping speed while changing the field sweeping speed (dH/dt) of the magnetic field up to 150Oe/sec The range of the average value can be satisfied from 0.5 to 0.7. If the index value (α) is less than 0.5, the magnetic domain wall does not exist or does not move, but in the case of grain-oriented electrical steel, this does not apply because magnetic domains exist. If it exceeds 0.7, the magnetic domain wall iron loss contribution due to magnetic domain movement is not applicable. This may cause problems such as increased hysteresis loss due to increased surface roughness. In the case of the present invention, since there is no pinning site that interferes with magnetic domain movement on the surface, the hysteresis loss has a relatively small value compared to the magnetic domain wall iron loss. Therefore, the exponent value (α) does not exceed 0.7.

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

(Example)

Steel slabs were prepared containing Si: 3.2%, C: 0.053%, Mn: 0.1%, Al: 0.028%, N: 0.0048%, S: 0.005, Cu 0.004%, balance Fe and inevitable impurities in weight percent. Next, the manufactured steel slab was reheated at 1150°C for 2 hours and then hot rolled to produce a 2.2 mm hot rolled sheet. Afterwards, the hot rolled sheet was annealed and then cold rolled to a final thickness of 0.22 mm.

Next, the cold rolled steel sheet was subjected to primary recrystallization annealing. Specifically, the cracking temperature was maintained at 850°C for 180 seconds in a mixed atmosphere of 61 vol% hydrogen, 38 vol% nitrogen, and 1 vol% dry ammonia gas. Simultaneous decarburization and nitriding treatment were performed. At this time, the amount of residual carbon in the steel sheet can be controlled by controlling the dew point temperature of the wet HN gas flowing into the annealing furnace, and the amount of oxygen formed during the decarburization process was adjusted to manufacture a steel sheet that underwent primary recrystallization. At this time, the carbon content, oxidation amount, and oxide layer thickness in the steel sheet subjected to primary recrystallization annealing were measured, and the results are shown in Table 1 below.

Then, on the primary recrystallization annealed steel sheet, 10 g/m ² of an annealing separator prepared by mixing 100 g of MgO with an activation degree of 500 seconds, 5 g of SbOCl, 2.5 g of Sb ₂ (SO ₄ ) ₃ and 1000 g of water was applied. It was dried.

Subsequently, the steel sheet coated with the annealing separator was subjected to secondary recrystallization annealing. Specifically, during the secondary recrystallization annealing, the first cracking temperature was 700°C, the second cracking temperature was 1200°C, and the cracking time at 1200°C was was treated for 15 hours. The atmosphere during final annealing was a mixed atmosphere of 75 vol% nitrogen and 25 vol% hydrogen up to 1200°C, and after reaching 1200°C, it was maintained in a 100 vol% hydrogen atmosphere and then furnace cooled.

The magnetic properties of iron loss and magnetic flux density for the electrical steel sheet on which the secondary recrystallization was completed were measured, and the results are shown in Table 1 below. Specifically, the magnetic properties of the electrical steel sheet manufactured as above were evaluated under the conditions of 1.7T and 50Hz. The magnetic properties of electrical steel sheets usually use W17/50 and B8 as representative values. W17/50 refers to the power loss that occurs when a magnetic field with a frequency of 50Hz is magnetized with alternating current up to 1.7Tesla. Here, Tesla is a unit of magnetic flux density, meaning magnetic flux per unit area. B8 represents the magnetic flux density flowing through the electrical steel sheet when a current of 800 A/m is passed through the winding wound around the electrical steel sheet.

In addition, the surface roughness of the electrical steel sheet on which the secondary recrystallization was completed was measured, and the results are shown in Table 1 below.

In addition, a composition with excellent iron loss improvement rate and insulation after SRA as a tension coating agent consisting of 50 to 250 g of colloidal silica, 5 to 15 g of chromium oxide, and 5 to 15 g of ultrafine solid silica per 100 g of metal phosphate solution is applied to the electrical steel sheet on which the secondary recrystallization has been completed. By applying it to the surface and measuring the iron loss, the influence of surface roughness on the magnetic domain refinement effect was analyzed.

In addition, the magnetization curve area was measured for each product plate using a magnetic domain observation microscope, and the average value (10 points) of the steinmetz index value (α) in equation 1 was obtained and shown in Table 1 below. As a method of measuring the magnetization curve area, the field sweeping speed (dH/dt) of the magnetic field was changed up to 150Oe/sec and the area of the magnetization curve at each sweeping speed was measured.

After 1st recrystallization annealing After secondary recrystallization annealing Iron loss (W/Kg) note residual carbon
(weight) Oxidation amount
(weight%) Oxide layer thickness (㎛) surface roughness
(Ra:㎛) magnetic flux density
(B ₈ ) Steinmetz Index
(α) Tension coating not applied Tension coating
apply Core loss improvement rate (%) 0.0025 0.0644 2.37 1.4 1.90 0.755 1.02 0.97 1.9 Comparative Example 1 0.0038 0.0552 2.05 0.9 1.95 0.724 1.00 0.93 7.0 Comparative example 2 0.0016 0.0781 2.78 1.7 1.93 0.831 0.94 0.89 5.3 Comparative Example 3 0.0085 0.0385 1.15 0.1 1.95 0.615 1.05 0.85 19.0 Invention Example 1 0.0065 0.0416 1.00 0.2 1.97 0.587 0.98 0.77 21.4 Invention Example 2 0.0110 0.0327 0.95 0.1 1.96 0.678 0.99 0.87 12.1 Invention Example 3

As shown in Table 1, in Comparative Examples 1-3, the oxidation amount exceeds 500 ppm, and the surface roughness of the steel sheet obtained after secondary recrystallization is high, as well as the Steinmetz index (α) value exceeds 0.7. there is. In addition, it can be seen that the iron loss improvement rate before and after applying the tension coating is less than 10%.

On the other hand, in Example 1-3 of the present invention, it can be seen that the thickness of the oxidation layer can be reduced to less than 2㎛ by lowering the oxidation amount to 500ppm or less when the residual carbon is relatively high at 150ppm or less. Therefore, it can be seen that the electrical steel sheet of Inventive Example 1-3 not only has a low surface roughness of 0.2 μm or less in the final product for which secondary recrystallization has been completed, but also has a Steinmetz index (α) value of 0.7 or less.

In addition, it can be seen that the iron loss improvement rate before and after applying the tension coating of Example 1-3 of the present invention is more than 10%, which can be seen as the effect of the abnormal vortex loss, which was relatively high due to the low roughness of the surface, being drastically reduced by applying tension. there is. It can be seen that this increase in the iron loss improvement rate is in good agreement with the results of the Steinmetz index measured below 0.7 (the lower the index value, the greater the iron loss due to magnetic domain movement).

As described above, the detailed description of the present invention has described preferred embodiments of the present invention, but those skilled in the art can make various modifications without departing from the scope of the present invention. Of course this is possible. Therefore, the scope of rights of the present invention should not be limited to the described embodiments, but should be determined not only by the claims described later, but also by their equivalents.

Claims (10)

By weight%, Si: 2~4%, C: 0.01~0.07%, Al: 0.02~0.04%, N: 0.01% or less, P: 0.01~0.05%, Mn: 0.2% or less (excluding 0%), S : manufacturing a slab containing 0.015% or less (excluding 0%), Cu: 0.0005 to 0.1%, the balance Fe and other unavoidable impurities; Manufacturing a hot-rolled sheet by hot-rolling the slab; Annealing the hot-rolled sheet; manufacturing a cold-rolled sheet by cold-rolling the annealed hot-rolled steel sheet; Primary recrystallization annealing of the cold-rolled sheet; In the method of manufacturing a grain-oriented electrical steel sheet, comprising the steps of applying an annealing separator to the primary recrystallization annealed cold-rolled sheet and drying it, and secondary recrystallization annealing the cold-rolled sheet coated with the annealing separator,
After the primary recrystallization annealing, the content of carbon remaining in the steel sheet is controlled to be within 150 ppm, the oxidation amount of the steel sheet is controlled to be within 500 ppm, the amount of sediment is controlled to be within the range of 120 to 180 ppm, and the thickness of the oxidation layer formed on the surface of the steel sheet is controlled to be within 0.1 to 2.0 ppm. A method of manufacturing a grain-oriented electrical steel sheet, controlling the primary recrystallization annealing process to satisfy the ㎛ range, and removing the forsterite (Mg ₂ SiO ₄ ) film formed on the surface of the steel sheet in the secondary recrystallization annealing step.
The method of claim 1, wherein the slab further contains Se: 0.015% or less.
The method of claim 1, wherein the annealing separator includes 10 to 20 parts by weight of an oxychloride material and 1 to 5 parts by weight of a sulfate-based antioxidant, based on parts by weight of MgO with an activation degree of 400 to 3000 seconds. .
The method of claim 3, wherein the oxychloride material is at least one selected from antimony oxychloride (SbOCl) and bismuth oxychloride (BiOCl).
The method of claim 3, wherein the sulfate-based antioxidant is at least one selected from antimony sulfate (Sb ₂ (SO ₄ ) ₃ ), strontium sulfate (SrSO ₄ ), and barium sulfate (BaSO ₄ ).
The method of claim 1, wherein the surface roughness of the produced grain-oriented electrical steel sheet is 0.2㎛ or less in terms of Ra.
According to claim 1, the steinmetz index value (α) obtained by measuring the area of the magnetization curve of the manufactured electrical steel sheet at each sweeping speed while changing the field sweeping speed (dH/dt) of the magnetic field up to 150Oe/sec. A method of manufacturing a grain-oriented electrical steel sheet that satisfies the average value range of 0.5 to 0.7.
By weight%, Si: 2~4%, C: 0.01~0.07%, Al: 0.02~0.04%, N: 0.01% or less, P: 0.01~0.05%, Mn: 0.2% or less (excluding 0%), S : 0.015% or less (excluding 0%), Cu: 0.0005~0.1%, contains remaining Fe and other inevitable impurities, and changes the field sweeping speed (dH/dt) of the magnetic field up to 150Oe/sec for each sweeping A grain-oriented electrical steel sheet in which the average value of the steinmetz index value (α), obtained by measuring the area of the steel sheet's magnetization curve at speed, satisfies the range of 0.5 to 0.7.
The grain-oriented electrical steel sheet of claim 8, wherein the electrical steel sheet further contains Se: 0.015% or less.
The grain-oriented electrical steel sheet of claim 8, wherein the electrical steel sheet has a surface roughness of Ra of 0.2㎛ or less.

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