KR20240098255A - Method for manufaturing grain oriented electrical steel sheet - Google Patents

Abstract

A method for manufacturing a grain-oriented electrical steel sheet is provided.
The method for manufacturing a grain-oriented electrical steel sheet of the present invention includes the steps of reheating a steel slab to 1200°C or lower and hot rolling; Manufacturing a cold-rolled steel sheet with a final thickness by cold-rolling the hot-rolled steel sheet once or two or more times including intermediate annealing; Primary recrystallization annealing of the cold rolled steel sheet; Applying an annealing separator to the primary recrystallization annealed cold-rolled steel sheet and then drying it; and forming a forsterite film on the surface of the steel sheet by performing secondary recrystallization annealing on the cold rolled steel sheet coated with the annealing separator. In the primary recrystallization annealing process, the temperature is 750°C. In the temperature increase section from the above to the cracking temperature, annealing is performed by controlling the P _H2O /P _H2 value in the furnace atmosphere to 40% or more compared to the P _H2O /P _H2 value in the furnace atmosphere in the crack zone.

Description

Method for manufacturing grain oriented electrical steel sheet}

The present invention relates to a method of manufacturing grain-oriented electrical steel sheets with excellent surface and magnetic properties used as iron core materials for transformers or rotating machines, etc., by controlling the internal and external oxide compositions in the decarbonization annealing process to achieve a very uniform force in the final product. It relates to a method of manufacturing a grain-oriented electrical steel sheet that can improve iron loss characteristics by enabling the formation of a terite film.

Grain-oriented electrical steel is a soft magnetic material that is mainly used as an iron core material for transformers or rotating machines. In terms of magnetic properties, it is important to have a high magnetic flux density and excellent core loss and magnetostrictive properties. The forsterite film formed during finishing annealing and the insulating film are applied to the surface of these grain-oriented electrical steel sheets during the final heat flattening process to create the final product. This forsterite film not only serves the purpose of providing surface insulation, but also has the effect of improving iron loss and magnetostrictive properties by applying tensile stress generated by the difference in thermal expansion properties from the base metal to the steel sheet. The forsterite film formed on the surface of this steel sheet not only has an effect of improving insulation performance and magnetic properties, but also determines product value such as workability in the iron core processing process and the appearance of the product, depending on the state of its formation, making it uniform and stable. The formation of a quality forsterite film is required.

To form a forsterite film in the production of grain-oriented electrical steel sheets, coils cold rolled to the final thickness are decarbonized and annealed in a humid atmosphere at a temperature of 800 to 900°C in a continuous line to form primary recrystallization and a forsterite film. Treatment is performed to form oxides containing Fe ₂ SiO ₄ and SiO ₂ as main components, which play an important role in oxidation. Afterwards, the annealing separator containing MgO as the main ingredient is stirred in water to form a slurry, applied to the steel sheet using a roll coater, etc., dried, wound into a coil, and subjected to high-temperature finishing annealing at a temperature of about 1200°C. When this happens, a forsterite film is formed.

In the process of fine annealing of grain-oriented electrical steel sheets, the forsterite film is formed through a reaction between MgO, the main component of the annealing separator, and SiO _{2 ,} the main component of the oxide formed in decarburization annealing (2MgO + SiO ₂ → Mg ₂ SiO ₄ ). At this time, when AlN is used as an inhibitor, spinel-structured compounds such as Al ₂ O ₃ , MgO, and SiO ₂ are formed near the bottom of the forsterite film. At this time, the forsterite film formation behavior also affects the behavior of inhibitors such as MnS and AlN in the steel, and thus also affects the secondary recrystallization behavior, which is an essential process for having excellent magnetic properties.

In other words, if the forsterite film formation reaction is delayed or progresses unevenly during the temperature increase process of finishing annealing, or if the quantity and quality of the formed film are inadequate, O and N easily penetrate into the steel in the annealing atmosphere, thereby acting as a steel inhibitor. Decomposition and coarsening occur, affecting the inhibitor strength. Moreover, the forsterite film formed during the polishing annealing process serves to purify the inhibitor that has become unnecessary after secondary recrystallization is completed, by pulling it out of the film, thereby reducing hysteresis loss. Therefore, the uniform formation of the forsterite film and the control process during its formation are one of the important points that determine product quality.

In order to improve magnetic properties, Patent Document 1 provides a grain-oriented electrical steel sheet with excellent magnetic properties by including Sn: 0.03-0.07% by weight, Sb: 0.01-0.05% by weight, and P: 0.01-0.05% by weight in the steelmaking components. Manufacturing is reported. In addition, Patent Document 2 reports the manufacture of grain-oriented electrical steel sheets with excellent magnetic flux density by adding Bi or Bi-containing materials at an amount of 100 to 1500 g/T of molten steel, converted to Bi.

Additionally, Patent Document 3 and Patent Document 4 report improving magnetic properties by adding Ni and Cr or Sb, Sn, and Cr in combination.

These patents are characterized by improving the magnetic properties of the final product by adding a certain amount of segregation elements or precipitates to the steelmaking components. In particular, recently, grain-oriented electrical steel sheets with components containing these segregation elements or precipitates have been developed. This accounts for most of it.

In addition, in order to form a uniform forsterite film, in Patent Document 5, in order to form a decarburizing and excellent forsterite film, the decarbonization annealing conditions are wet with P _H2O /P _H2 of 0.60 to 0.90 in a temperature range of 940 to 980 ° C. It is suggested that it be done in an atmosphere. Additionally, Patent Document 6 discloses a method of forming a defect-free forsterite film by controlling the amount and composition of the surface oxide of the decarbonized annealed plate within a specific range. In other words, the amount of surface oxide formed is set in the range of 1.0 to 2.5 g/m ² , and Fayalite (Fe ₂ SiO ₄ ) present in the oxide is managed at a weight ratio of 0.05 to 0.3 compared to Silica (SiO ₂ ). is suggesting that

As a method of improving the film properties through atmosphere control in the final finishing annealing process, in Patent Document 7, the heating time in the temperature range of 750℃~1050℃ is set to 8.3℃/hr~50℃/hr, and P _H2O /P _H2 A method of annealing in an N ₂ 50% atmosphere of 0.001 to 0.02 is proposed.

Recently, in line with the global energy saving trend, transformer customers continue to request low core loss grain-oriented electrical steel sheets to miniaturize devices. In order to meet these customer demands, as mentioned above, grain-oriented electrical steel sheets with components containing complex grain segregation elements or precipitates such as Sb, Sn, P, and Cr were developed to ensure excellent magnetic properties. there is. However, steel grades containing large amounts of grain segregation elements or precipitates such as Sb, Sn, P, and Cr may be advantageous in improving magnetic properties in the final product, but the forsterite film in the final product Because it is formed unstable, there are problems with film defects such as metal spots and gas mark-like discoloration occurring on the outer coil and both edges, and thin film phenomenon on the inner coil, so it can be said that the stability of quality is still sufficient. It is impossible. In addition, when this phenomenon occurs, it can seriously affect the stability of the inhibitor in the steel and cause problems such as deterioration of the magnetic properties.

Republic of Korea Patent Publication No. KR2009-0072116 Japanese Patent Publication No. 1994-88171 Republic of Korea Patent Publication No. KR2020-0035752 Republic of Korea Patent Application No. KR2021-0184134 Korean Patent Publication No. 1999-026909 Japanese Registered Patent Publication No. S59-41480 Japanese Patent Publication No. 1999-256242

The purpose of the present invention is to provide a method for manufacturing a grain-oriented electrical steel sheet that can not only stably form a forsterite film with excellent adhesion but also stably obtain excellent magnetic properties.

The object of the present invention is not limited to the above-described contents. 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,

In weight percent, Si: 2.5-4.0%; C: 0.070% or less; Sol.Al: 0.015~0.040%; Mn: 0.50% or less; N: 0.0055% or less; S: 0.0055% or less; Sum of one or more of Sn: 0.03 to 0.10%, Sb: 0.01 to 0.05%, Cu: 0.01 to 0.2%, and P: 0.01 to 0.10%: 0.05 to 0.20%; Cr: 0.03~0.15%; Reheating the slab containing the remaining Fe and other unavoidable impurities to 1200°C or lower and hot rolling; Manufacturing a cold-rolled steel sheet with a final thickness by cold-rolling the hot-rolled steel sheet once or two or more times including intermediate annealing; Primary recrystallization annealing of the cold rolled steel sheet; Applying an annealing separator to the primary recrystallization annealed cold-rolled steel sheet and then drying it; In the method of manufacturing a grain-oriented electrical steel sheet, comprising forming a forsterite film on the surface of the steel sheet by performing secondary recrystallization annealing on the cold-rolled steel sheet coated with the annealing separator,

In the primary recrystallization annealing process, the P _H2O /P _H2 value in the furnace atmosphere in the temperature increase section from 750 ℃ or higher to the cracking temperature is controlled to 40% or more compared to the P _H2O /P _H2 value in the furnace atmosphere of the crack zone, and annealing is performed. It relates to a manufacturing method of grain-oriented electrical steel sheet.

In the primary recrystallization annealing process, it is better to control the P _H2O /P _H2 value in an atmosphere of 40 to 100% of the P _H2O /P _H2 value in the crack zone within the temperature rise atmosphere from 750 ℃ or higher to the cracking temperature. desirable.

In the present invention, the oxide formed in the surface layer of the cold rolled steel sheet by performing the primary recrystallization annealing was measured using a glow discharge spectrometer (GDS), and as a result, the content profile of the Cr element in the steel sheet in the depth direction was determined. The following relational expression 1 can be satisfied.

[Relationship 1]

0.40≤b /a≤1.0

Here, a refers to the Cr intensity value (Intensity) representing the highest Cr content within a depth of 0.01 ㎛ or more and within 0.1 ㎛ from the surface of the cold-rolled steel sheet after the primary recrystallization annealing and before the final annealing, and b is the Cr intensity value (Intensity) of the cold-rolled steel sheet It refers to the Cr intensity value that represents the highest Cr content at a depth of 0.1㎛ or more from the surface.

In the present invention, the annealing separator is Li, F, Na, K, Cu, Ba, Br, Mg, Ca, Zn, Sr, Cd, B, Al, with a melting point of 900°C or lower, based on 100 parts by weight of MgO. Hydroxides, carbonates, amides, chromates, oxides and antimony compounds of Y, Ga, In, Tl, Ti, Sn, P, Nb, Sb, Bi, S, Cr, Te, V, W, Fe, Co and Ni. , chlorine compounds, chloride oxides, sulfur compounds, nitrogen compounds, bromides, bromates, nitrides, telluric acid, vanadates, borates, and phosphorus compounds. It is preferable to mix 0.01 to 0.50 parts by weight of one or two or more additives. .

The present invention, configured as described above, can not only stably form a forsterite film with excellent adhesion through a final finishing annealing process, but can also effectively provide a grain-oriented electrical steel sheet with excellent magnetic properties.

Figure 1 shows the results of measuring the oxide formed in the surface layer of a steel sheet by performing primary recrystallization annealing according to an embodiment of the present invention using a glow discharge spectrometer (GDS), showing the Cr component in the steel sheet. This is a picture showing changes according to depth.

Hereinafter, the present invention will be described.

The present inventors have developed an excellent force in the forsterite film formation process from the decarburization annealing process to the polishing annealing process for steel grades containing a large amount of grain segregation elements or precipitates such as Sb, Sn, P, and Cr. The process conditions for obtaining the forsterite film were reviewed, and among them, it was discovered that the composition of the internal and external oxides of the decarburized plate for which the decarburization annealing process was completed had an effect on the forsterite film characteristics of the final product. In particular, among the components of the oxides of the decarburized plate, Cr is determined by the oxidation capacity (P _H2O /P _H2 ) within the temperature increase section within the decarburization annealing process, and if an appropriate amount of Cr-based oxide is controlled, the forsterite film characteristics of the final product can be improved. The present invention is presented after confirming that this is formed very uniformly.

This method of manufacturing a grain-oriented electrical steel sheet of the present invention contains, in weight percent, Si: 2.5 to 4.0%; C: 0.70% or less; Sol.Al: 0.015~0.040%; Mn: 0.50% or less; N: 0.0055% or less; S: 0.0055% or less; Sum of one or more of Sn: 0.03 to 0.10%, Sb: 0.01 to 0.05%, Cu: 0.01 to 0.2%, and P: 0.01 to 0.10%: 0.05 to 0.20%; Cr: 0.03~0.15%; Reheating the slab containing the remaining Fe and other unavoidable impurities to 1200°C or lower and hot rolling; Manufacturing a cold-rolled steel sheet with a final thickness by cold-rolling the hot-rolled steel sheet once or two or more times including intermediate annealing; Primary recrystallization annealing of the cold rolled steel sheet; Applying an annealing separator to the primary recrystallization annealed cold-rolled steel sheet and then drying it; and forming a forsterite film on the surface of the steel sheet by performing secondary recrystallization annealing on the cold rolled steel sheet coated with the annealing separator. In the primary recrystallization annealing process, the temperature is 750°C. In the temperature increase section from the above to the cracking temperature, annealing is performed by controlling the P _H2O /P _H2 value in the furnace atmosphere to 40% or more compared to the P _H2O /P _H2 value in the furnace atmosphere in the crack zone.

First, the present invention, in weight percent, Si: 2.5 to 4.0%; C: 0.70% or less; Sol.Al: 0.015~0.040%; Mn: 0.50% or less; N: 0.0055% or less; S: 0.0055% or less; Sum of one or more of Sn: 0.03 to 0.10%, Sb: 0.01 to 0.05%, Cu: 0.01 to 0.2%, and P: 0.01 to 0.10%: 0.05 to 0.20%; Cr: 0.03~0.15%; The slab containing the remaining Fe and other inevitable impurities is reheated to 1200°C or lower, hot rolled, and the hot rolled hot rolled steel sheet is cold rolled once or twice or more including intermediate annealing to achieve the final thickness. A steel sheet is manufactured, followed by primary recrystallization annealing of the cold-rolled steel sheet, followed by applying an annealing separator to the primary recrystallization-annealed cold-rolled steel sheet and drying it, and finally, the cold-rolled steel sheet onto which the annealing separator is applied. A typical method of manufacturing a grain-oriented electrical steel sheet can be used to form a forsterite film on the surface of the steel sheet by performing secondary recrystallization annealing, and the present invention is not limited to a specific manufacturing process or process conditions.

However, in the present invention, when using the general grain-oriented electrical steel manufacturing process described above, in the primary recrystallization annealing process, the P _H2O / P _H2 value in the furnace atmosphere in the temperature increase section from 750 ℃ or higher to the cracking temperature is measured in the furnace in the crack zone. It is characterized in that annealing is performed by controlling the P _H2O /P _H2 value to 40% or more in the atmosphere.

In the end, the alloy composition of the steel slab of the present invention and the reason for limiting its content are explained, where the content is in units of weight percent.

Si: 2.5~4.0%

Silicon (Si) plays a role in reducing iron loss by increasing the resistivity of steel. If the Si content is too small, the resistivity of the steel becomes small, which deteriorates the iron loss characteristics and a phase transformation section exists during high-temperature annealing, making secondary recrystallization unstable. Problems may arise. If the Si content is too high, brittleness may increase, making cold rolling difficult. Therefore, the Si content can be adjusted within the above-mentioned range. More specifically, Si may be included in an amount of 2.5 to 4.0%.

Al: 0.015~0.040% by weight

Aluminum (Al) is a component that ultimately becomes nitride in the form of AlN, (Al,Si)N, and (Al,Si,Mn)N and acts as an inhibitor. If the Al content is too low, it is difficult to expect sufficient effect as an inhibitor. Additionally, if the Al content is too high, the Al-based nitride precipitates and grows too coarsely, which may result in insufficient effectiveness as an inhibitor. Therefore, the Al content can be adjusted within the above-mentioned range.

Mn: 0.50% or less

Mn has the effect of reducing iron loss by increasing resistivity in the same way as Si, and reacts with nitrogen introduced through nitriding treatment with Si to form precipitates of (Al, Si, Mn) N, thereby growing primary recrystallized grains. It is an important element in suppressing and causing secondary recrystallization. However, if the Mn content is too high, it promotes austenite phase transformation during hot heating, thereby reducing the size of primary recrystallized grains and making secondary recrystallization unstable. In addition, when the content of Mn is too low, as an austenite forming element, the austenite fraction is increased during hot rolling reheating to increase the solid capacity of the precipitates, which has the effect of preventing the primary recrystallization grains through refining of the precipitates and formation of MnS from being too excessive during re-precipitation. It may happen insufficiently. Therefore, the content of Mn can be adjusted within the above-mentioned range.

Sum of one or more of Sn: 0.03 to 0.10%, Sb: 0.01 to 0.05%, Cu: 0.01 to 0.2%, and P: 0.01 to 0.10%: 0.05 to 0.20%

The steel slab of the present invention may also further include the sum of one or more of Sn: 0.03-0.10%, Sb: 0.01-0.05%, Cu: 0.01-0.2%, and P: 0.01-0.10% in the range of 0.05-0.20%. It may be possible. Sb, Sn, Cu, or P are grain boundary segregation elements that interfere with the movement of grain boundaries, so as an inhibitor, they promote the creation of Goss crystal grains in the {110}<001> orientation and allow secondary recrystallization to develop well, thereby controlling the grain size. It is an important element in If the amount added alone or in combination is too small, the effect resulting from the addition cannot be expected. On the other hand, if the content added alone or in combination is too high, it excessively segregates at the grain boundaries during the manufacture of grain-oriented electrical steel sheets, which acts to excessively suppress the growth of primary recrystallized grains, or does not properly cause the decarburization reaction in which carbon in the steel is removed. This may occur and deteriorate the magnetic properties, so it is limited.

Cr: 0.03~0.15%

Cr not only has the effect of promoting the formation of internal and external oxides in the decarbonization annealing process due to the use of a large amount of segregation elements in the steel, but also creates fine Cr-based nitrides, such as (Cr, Al, By forming Si)N, it also has the effect of playing the role of a grain growth inhibitor in the polishing annealing process. If the Cr content is less than 0.03%, the formation of oxides and fine nitrides formed in the decarburization annealing process may not be smooth. On the other hand, if the Cr content exceeds 0.15%, excessive Cr-based nitrides are formed during the decarburization annealing process, which may cause deterioration of magnetic properties due to a change in the secondary recrystallization initiation temperature during the finishing annealing process.

The steel slabs of the present invention may further include C, S or N.

It is desirable to control the C content to 0.07% or less. If the content exceeds 0.07%, it should be avoided as it may significantly damage productivity because a lot of decarbonization time is required in the decarbonization process.

It is desirable to control the N content to 0.0055% or less. If the content exceeds 0.0055%, not only may defects on the surface of the steel sheet called brister occur, but it may also be difficult to control the grain size of the primary recrystallized grains generated in the decarbonization annealing process.

It is desirable to control the S content to 0.0055% or less. S is known to be used as a forming element of MnS, a precipitate necessary to generate secondary recrystallization. However, if the content exceeds 0.0055%, a lot of purification annealing time is required to remove it after the secondary recrystallization annealing is completed.

Other remaining components are Fe and inevitable impurities. 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.

In the present invention, a cold rolled steel sheet of the final thickness is manufactured by heating a slab of the above composition, hot rolling, and then cold rolling the hot rolled steel sheet once or twice or more including intermediate annealing.

In the present invention, the cold rolled steel sheet is subjected to primary recrystallization annealing. At this time, in the temperature increase section from 750°C or higher to the cracking temperature, the P _H2O /P _H2 value in the furnace atmosphere is 40% compared to the P _H2O /P _H2 value in the furnace atmosphere in the crack zone. It is characterized by annealing while controlling to % or more.

That is, as a preferred decarbonization annealing condition in the present invention, in the decarbonization annealing process, the P _H2O /P _H2 value is 40% or more compared to the P _H2O /P _H2 value in the crack zone within the temperature rising atmosphere from 750 ℃ or higher to the cracking temperature. It must be controlled by atmospheric conditions. In general, in the process of reaching the cracking zone from the temperature rise zone, the moisture consumption of atmospheric gas is extremely high up to the cracking temperature, so the P _H2O /P _H2 value is likely to decrease. For this reason, in addition to the problem of decarburization defects due to P _H2O /P _H2 during temperature increase, it also affects the quantity and quality of the oxide film in the crack section. In particular, in the component system used in the present invention, the oxidation ability in the temperature rise zone, P _H2O /P _H2 , is very important. This is because not only the content of segregation elements but also the Cr content is high, so it is used for the formation of oxides in the temperature rise zone. Assuming that the line speed is kept constant during operation, if the P _H2O /P _H2 value in the temperature rise area is less than 40% compared to the P _H2O /P _H2 value in the crack area, the oxidation ability decreases, causing a certain amount of oxidation in addition to decarburization defects. It is limited because it is difficult to obtain.

More preferably, in the decarbonization annealing process, the P _H2O /P _H2 value is controlled under an atmosphere condition of 40 to 100% of the P _H2O /P _H2 value in the crack zone within the temperature rise atmosphere from 750℃ or higher to the cracking temperature. will be. If it exceeds 100%, a dense oxide may be formed on the surface, which may cause problems in which carbon emissions within the steel do not occur smoothly.

Meanwhile, in the present invention, as a result of measuring the oxide formed in the surface layer of the cold rolled steel sheet by performing the primary recrystallization annealing using a glow discharge spectrometer (GDS), the depth direction of the Cr element in the steel sheet was measured. The content profile may satisfy the following relational expression 1.

[Relationship 1]

0.40≤b /a≤1.0

Here, a refers to the Cr intensity value (Intensity) representing the highest Cr content within a depth of 0.01 ㎛ or more and within 0.1 ㎛ from the surface of the cold-rolled steel sheet after the primary recrystallization annealing and before the final annealing, and b is the Cr intensity value (Intensity) of the cold-rolled steel sheet It refers to the Cr intensity value that represents the highest Cr content at a depth of 0.1㎛ or more from the surface.

In equation 1, b/a is less than 0.40, which means that the Cr-based oxide among the internal oxides in the strip is relatively small compared to the amount of Cr-based oxide in the surface layer oxide. In this case, it promotes the formation of decarburized plate oxide. Since it means that the effect is small, it is not preferable for steel types containing a lot of segregation elements, such as the present invention. On the other hand, if b/a is greater than 1.0, it means that the Cr-based oxide of the internal oxide in the strip is relatively very large compared to the amount of Cr-based oxide in the surface layer oxide. In this case, chromite (FeCr ₂ O ₄ ) ] It is necessary to limit it because it forms other oxides in addition to oxides such as oxides, which has a disadvantageous effect on the formation of oxides in the final product.

The glow discharge luminescence spectrometer used in the present invention was model number GDS850A manufactured by Leco. The conditions for analysis were that the lamp type was RF (Radio Frequency) and the analysis area was 4 mϕ. Calibration Factor was set to 0.7, and analysis conditions were set to 700V, 30mA, and 21W. In addition, the depth setting was 0~end sec 40 points/sec, the plot point was 8000, and smoothing of the analysis results was performed three times. When analyzing the electrical steel sheet under the conditions set in this way, the depth was approximately 7 to 10㎛.

For the results measured in this way, the Cr item may be used for analysis as is, but for ease of analysis, in the present invention, the Cr results obtained from the measuring device were magnified 5 to 30 times and the results for Cr Peak were analyzed.

Next, in the present invention, an annealing separator is applied to the cold-rolled steel sheet subjected to primary recrystallization annealing and then dried.

At this time, in the present invention, as the annealing separator, for 100 parts by weight of MgO, Li, F, Na, K, Cu, Ba, Br, Mg, Ca, Zn, Sr, Cd, B, Al, Y, Ga, In, Tl, Ti, Sn, P, Nb, Sb, Bi, S, Cr, Te, V, W, Fe, Mn, Co, Ni hydroxides, carbonates, amide compounds, chromates, 0.01 to 0.50 parts by weight of one or two or more additives among oxides, antimony compounds, chlorine compounds, chloride oxides, sulfur compounds, nitrogen compounds, bromides, bromates, nitrides, telluric acid, vanadates, borates, and phosphorus compounds. It is desirable to use

First, the present inventors sought to uniformize the forsterite film by improving its reactivity with the decarburized oxide film, and second, to improve the thickness, uniformity, and color deviation of the forsterite film due to additional oxidation or nitriding that occurs during polishing annealing. In order to achieve the two objectives of minimizing the effect on primary recrystallization, a study was conducted considering that it would be desirable to add an additive that can start the forsterite film formation temperature before additional oxidation or nitridation occurs. As a result, it was discovered that a very large improvement effect was obtained by applying additives with a melting point of 900°C or lower. In addition, as a more preferable condition, if more than 30% of all additives contain additives with a melting point of 750°C or lower, additional oxidation and additional nitridation hardly occur, and a uniform forsterite film is formed over the entire length and width of the coil. It was confirmed that stabilization of magnetic properties was achieved.

If the amount of the additive added is less than 0.01 parts by weight based on 100 parts by weight of MgO, the effect of promoting the formation of a low melting point glassy layer or forsterite film cannot be sufficiently obtained. On the other hand, if it exceeds 0.50 parts by weight, the effect of the low-melting point additive may be excessive depending on the atmosphere conditions of the annealing separator or polishing annealing, and local melting defects on the pinhole may occur.

Thereafter, in the present invention, a forsterite film with excellent adhesion and magnetic properties can be formed on the surface of the steel sheet by annealing the cold rolled steel sheet coated with the annealing separator using a commonly known secondary recrystallization annealing process.

Hereinafter, the present invention will be described in detail through examples.

(Example 1)

In weight percent: C: 0.058%, Si: 3.4%, Mn: 0.110%, Al: 0.028%, Cr: 0.08%, and Sb: 0.04%, Cu: 0.02%, Sn: 0.05%, P: 0.03%, The steel slab, the remainder of which was composed of Fe and other inevitably mixed components, was hot-rolled, annealed, and cold-rolled to a final thickness of 0.27 mm. Next, in the continuous decarburization annealing line, as shown in Table 1 below, P _H2O /P _H2 of the atmospheric gas in the temperature rise section and crack section was changed to form oxides inside and outside the decarburization plate, and then measured with a glow discharge luminescence spectrometer. The difference in profile of the Cr element in the depth direction is shown.

Figure 1 shows the results of measuring the oxide formed on the surface layer of the steel sheet by performing primary recrystallization annealing using a glow discharge spectrometer (GDS), showing the Cr component in the steel sheet of Invention Example 2 in Table 1 below. This is a picture showing changes according to depth. As shown in Figure 1, it can be seen that as the steel plate goes deeper along the depth direction, the Cr intensity value increases in the surface layer (a value), then decreases somewhat, and then increases again after a certain depth (b value).

Afterwards, an annealing separator containing 5 parts by weight of TiO ₂ , 0.3 parts by weight of Na ₂ B ₄ O ₇ , and 0.05 parts by weight of low melting point compound MnCl ₂ and 0.05 parts by weight of CoSO ₄ as additives based on 100 parts by weight of MgO was placed at water temperature. The slurry stirred at 10°C was applied to the surface of the decarbonized annealed steel sheet at a rate of 6.0 g/m ² per side based on the dried weight, dried, and wound into a coil. The hydration moisture value at this time was 1.50-2.10%.

Subsequently, after final finishing annealing under the conditions of 1200℃ The formed grain-oriented electrical steel sheet was manufactured.

In this way, the film adhesion and magnetic properties of the manufactured electrical steel sheets were measured, and the results are shown in Table 2 below.

Here, the film adhesion is 20mm after forming the insulating film. It was evaluated as a result of the bending test, and depending on the degree, it was judged as excellent (◎), good (○), and poor (X).

And 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.

division Decarbonization conditions GDS results Heating temperature range Heating stand P _H2O /P _H2 Crack zone temperature conditions Crack zone P _H2O /P _H2 Cr Peak[b/a] Invention Example 1


750~850℃ 0.50


850℃×130 seconds 0.58 0.83 Invention Example 2 0.45 0.58 0.76 Invention Example 3 0.40 0.58 0.62 Invention Example 4 0.38 0.58 0.58 Invention Example 5 0.35 0.58 0.50 Invention Example 6 0.52 0.58 0.88 Comparative Example 1 0.60 0.58 1.20 Comparative Example 2 0.20 0.58 0.25

*In Table 1, P _H2O /P _H2 means the minimum value of P _H2O /P _H2 in the heat treatment temperature range.

division Forsterite film exterior Adhesion magnetic properties B8(T) W17/50
(W/kg) Invention Example 1 Uniform and good, black gray, color difference from the center of the inner circle ○ 1.92 0.92 Invention Example 2 Good uniformity, black gray, glossy ◎ 1.92 0.90 Invention Example 3 Very uniform, very good with no color difference between the outer circle and the edge. ◎ 1.94 0.85 Invention Example 4 Dark gray, there is a weak color difference between the outer circle and the edge. ◎ 1.94 0.86 Invention Example 5 Thin gray, with weak scaling in the exosphere and edges ○ 1.92 0.91 Invention Example 6 Black gray, weak gloss, presence of gas mark color difference ○ 1.91 0.93 Comparative Example 1 Very severe scaling defects in the outer shell and edges.
Extreme color deviation due to gas marks in the inner coil of the coil X 1.89 1.02 Comparative Example 2 Bare spot defects and base metal visible in overall length/width X 1.85 1.25

As shown in Table 1-2 above, 0.08% by weight of Cr in the steelmaking components was added and 0.8 to 2.0% by weight of segregation elements including Sn, Sb, P, etc. were added, and hot rolled steel sheets were subjected to temperature rise and cracking during the decarbonization annealing process. The results of GDS analysis of the maximum value of Cr content along the depth direction of the steel sheet by controlling the oxidation capacity, P _H2O /P _H2, are shown.

Specifically, in the case of Inventive Examples 1-6, the b/a ratio of the Cr Peak analyzed by GDS satisfies the range of 0.4 to 1.0, showing that it has excellent film appearance, adhesion, and excellent magnetic properties in all cases. In particular, as in Example 3-4 of the present invention, it can be confirmed that in the case of a steel sheet with a Cr Peak b/a ratio of around 0.6, excellent results can be obtained in not only the appearance quality of the final product but also the magnetic properties.

On the other hand, in Comparative Example 1-2, the oxidation capacity between the temperature rise zone and the crack zone of the decarburization annealing process was outside the values suggested by the present invention, resulting in very poor appearance quality and magnetic properties. In particular, in Comparative Example 2, the Cr Peak b/a ratio was less than 0.4, the coil specimen had extreme bare spot defects across the full length/width, base metal was visible in some parts, and the magnetic properties were also very poor. indicated.

(Example 2)

By weight percentage, C: 0.060%, Si: 3.4%, Mn: 0.090%, Al: 0.030%, Cr: 0.15%, Sb: 0.03%, Cu: 0.02%, Sn: 0.08%, P: 0.04%, the rest Steel slabs composed of Fe and other inevitably mixed components were hot-rolled, annealed, and cold-rolled to a final thickness of 0.23 mm. Afterwards, in the continuous decarburization annealing line, the P _H2O /P _H2 ratio of the atmospheric gas in the temperature rising zone and the cracking zone was maintained at 60% and the cracking temperature was maintained at 850°C for 130 seconds to secure oxides inside and outside the decarburization plate. At this time, when the decarbonization annealing process was completed, the specimen was collected and the difference in the profile of the Cr element in the depth direction measured with a glow discharge luminescence spectrometer was measured, and the b/a ratio of Cr Peak was 0.63.

Afterwards, as shown in Table 3 below, the slurry was stirred at a water temperature of 10°C and dried with an annealing separator containing 100 parts by weight of MgO, 5 parts by weight of TiO ₂ , and low melting point compounds of different contents and types as additives. The weight was applied to the decarbonized steel sheet at a rate of 6.5 g/m ² per side, dried, and then wound into a coil.

Then, final finishing annealing was performed on the coil. Specifically, when the temperature is raised in the final finishing annealing process, P _H2O /P _H2 is 0.32 below 900℃, and an atmosphere of 25% N ₂ is maintained, and then, in the range from 900℃ to 1200℃ cracking temperature, P _H2O /P _H2 is 0.01. , Annealed with 25% N ₂ H ₂ + N ₂ atmosphere gas, continuously maintained at 100% H ₂ for more than 20 hours at 1200°C, cooled, and then Al phosphate and colloidal silica as insulating film components in a continuous line. After applying a solution containing as the main ingredient, annealing was performed at 850°C.

In this way, the film adhesion and magnetic properties of the manufactured electrical steel sheets were measured, and the results are shown in Table 4 below. At this time, the specific property evaluation criteria were the same as in Example 1.

division Hydration moisture (%) Low melting point additive (parts by weight) additive 1 additive 2 additive 3 Additive 4 Invention Example 7


1.50~2.2% SrCl ₂ 0.10 Sb ₂ O ₃ 0.05 FeBr ₂ 0.05 - Invention Example 8 Sb ₂ O ₃ 0.15 CuCl 0.05 - - Invention Example 9 MnCl ₂ 0.05 B ₂ O ₃ 0.10 NiSO ₄ 0.08 COSO ₄ 0.02 Invention Example 10 MNCl ₂ 0.10 COSO ₄ 0.05 CuBr 0.15 - Invention Example 11 SrCl ₂ 0.10 _Sb2O30.2 SnS 0.15 - Comparative Example 3 - - - - Comparative Example 4 MnCl ₂ 0.15 B ₂ O ₃ 0.30 NiSO ₄ 0.25 -

division Forsterite film exterior Adhesion magnetic properties B8(T) W17/50
(W/kg) Invention Example 7 Very uniform, good, black gray, shiny ◎ 1.93 0.83 Invention Example 8 Uniform color difference, less gray, glossy ○ 1.92 0.85 Invention Example 9 Very uniform, outer circle and edges very good, glossy ◎ 1.94 0.79 Invention Example 10 Very good, black gray, shiny ◎ 1.93 0.82 Invention Example 11 Dark gray, color difference exists between inner circle edge and central part ○ 1.91 0.86 Comparative Example 3 Bare spot defect in the vestibule, base metal visible X 1.87 0.95 Comparative Example 4 Color difference and local bare spot defects occur in the vestibule
Extreme color deviation due to gas marks in the coil inner winding area X 1.86 0.95

As shown in Table 3-4 above, as a result of measuring the Cr component with GDS along the depth direction of the steel sheet obtained through decarbonization annealing treatment, 100 parts by weight of MgO was added to the steel material satisfying the b/a ratio of 0.40 to 1.0. Inventive Examples 7-11, in which electrical steel sheets were manufactured by applying an annealing separator containing 0.01 to 0.50 parts by weight of a low melting point compound as a reaction accelerator, can be seen to have excellent film appearance, adhesion, as well as magnetic properties. .

On the other hand, as in Comparative Example 3-4, when the low melting point compound is not added to the annealing separator or is added beyond the scope of the present invention, a film so thin that the base metal is visible over the entire length is formed, or Color differences and local bare spot defects occurred over the entire length of the coil, extreme gas mark-like color deviation occurred in the inner part of the coil, and very poor results were obtained in terms of magnetic properties.

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 (4)

In weight percent, Si: 2.5-4.0%; C: 0.070% or less; Sol.Al: 0.015~0.040%; Mn: 0.50% or less; N: 0.0055% or less; S: 0.0055% or less; Sum of one or more of Sn: 0.03 to 0.10%, Sb: 0.01 to 0.05%, Cu: 0.01 to 0.2%, and P: 0.01 to 0.10%: 0.05 to 0.20%; Cr: 0.03~0.15%; Reheating the slab containing the remaining Fe and other unavoidable impurities to 1200°C or lower and hot rolling; Manufacturing a cold-rolled steel sheet with a final thickness by cold-rolling the hot-rolled hot-rolled steel sheet once or two or more times including intermediate annealing; Primary recrystallization annealing of the cold rolled steel sheet; Applying an annealing separator to the primary recrystallization annealed cold-rolled steel sheet and then drying it; In the method of manufacturing a grain-oriented electrical steel sheet, comprising forming a forsterite film on the surface of the steel sheet by performing secondary recrystallization annealing on the cold-rolled steel sheet coated with the annealing separator,
In the primary recrystallization annealing process, the P _H2O /P _H2 value in the furnace atmosphere in the temperature increase section from 750 ℃ or higher to the cracking temperature is controlled to 40% or more compared to the P _H2O /P _H2 value in the furnace atmosphere of the crack zone and annealing is performed. Manufacturing method of grain-oriented electrical steel sheet.
The method of claim 1, wherein in the primary recrystallization annealing process, the P _H2O /P _H2 value within the temperature-raising atmosphere from 750°C or higher to the cracking temperature is 40 to 100% of the P _H2O /P _H2 value in the crack zone. Method for manufacturing grain-oriented electrical steel sheets controlled by conditions.
The method of claim 1, wherein the oxide formed in the surface layer of the cold rolled steel sheet by performing the primary recrystallization annealing was measured using a glow discharge spectrometer (GDS), and as a result, the oxide formed in the surface layer of the cold rolled steel sheet was measured in the depth direction of the Cr element in the steel sheet. A method of manufacturing a grain-oriented electrical steel sheet, wherein the content profile satisfies the following equation 1.
[Relational Expression 1]
0.40≤b /a≤1.0
Here, a refers to the Cr intensity value (Intensity) representing the highest point of the Cr content within a depth of 0.01 ㎛ or more and within 0.1 ㎛ from the surface of the cold-rolled steel sheet after the primary recrystallization annealing and before the final annealing, and b is the Cr intensity value (Intensity) of the cold-rolled steel sheet It refers to the Cr intensity value that represents the highest Cr content at a depth of 0.1㎛ or more from the surface.
The method of claim 1, wherein the annealing separator is Li, F, Na, K, Cu, Ba, Br, Mg, Ca, Zn, Sr, Cd, B, with a melting point of 900°C or lower, based on 100 parts by weight of MgO. Hydroxides, carbonates, amides, chromates, and oxides of , Al, Y, Ga, In, Tl, Ti, Sn, P, Nb, Sb, Bi, S, Cr, Te, V, W, Fe, Co and Ni. , antimony compound, chlorine compound, chloride oxide, sulfur compound, nitrogen compound, bromide, bromate, nitride, telluric acid, vanadate, borate, and phosphorus compound, and mix 0.01 to 0.50 parts by weight of one or two or more additives. Method for manufacturing grain-oriented electrical steel sheets.

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