JPH0762443A - Method for producing grain-oriented electrical steel sheet with high-tensile glass coating and excellent magnetic properties - Google Patents

Abstract

(57) [Summary] [Purpose] Having a high-strength glass coating by controlling the oxide film in decarburization annealing, the annealing separator additive, and the final annealing conditions.
Manufacture grain-oriented electrical steel sheets with excellent magnetic properties. [Structure] The steel sheet after the final cold rolling is subjected to decarburization annealing and nitriding treatment to be annealed so that the oxygen amount of the steel sheet is 350 to 650 ppm, and then sulfated sulfide, borate, chlorinated as Sb compound with respect to 100 parts by weight of MgO. One or two or more kinds of materials and oxides are added and mixed with 0.05 to 1.5 parts by weight of an annealing separator, and the temperature rising rate up to 1200 ° C. is 20 ° C./Hr or less, and the N ₂ partial pressure of atmospheric gas is It has a high-strength glass coating formed by performing finish annealing by raising the temperature in one or more atmospheres of 0.25 or more of N ₂ , H ₂ and other inert gases, and has excellent magnetic properties. Method for manufacturing grain-oriented electrical steel sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented electrical steel sheet and provides a high tensile strength by providing an oxide film forming method in decarburizing annealing-nitriding treatment-final finish annealing, an annealing separator and a final finish annealing control method. The present invention relates to a method for producing a grain-oriented electrical steel sheet having a glass coating and excellent magnetic properties.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are generally used as a soft magnetic material, mainly as an iron core material for transformers and other electrical equipment, and are required to have good magnetic excitation characteristics and iron loss characteristics. In order to obtain good magnetic properties, it is important to highly align the <001> axis, which is the easy axis of magnetization, in the rolling direction. Further, the plate thickness, the grain size, the specific resistance, the coating film, etc. have a great influence on the magnetic properties and are important. The crystallographic direction has been significantly improved by a method characterized by final cold rolling under high pressure using AlN and MnS as inhibitors, and at present, magnetic flux densities have come close to theoretical values.

Further, in recent years, the technology for thinning the plate thickness and for increasing the Si steel has advanced, and the iron loss characteristics have been improved to a considerable level. When the grain-oriented electrical steel sheet is used in a consumer's house, it is the coating characteristics that are important together with the magnetic characteristics. This has a great effect not only on the coating characteristics such as corrosion resistance, insulation, and adhesion in the transformer core using the grain-oriented electrical steel sheet, but also on the magnetostriction and strain sensitivity that affect building factors and noise. Because. The coating properties of the grain-oriented electrical steel sheet thus have an important role in controlling the inhibitor in the steel sheet during the formation process while influencing the product characteristics. Therefore, in order to obtain a grain-oriented electrical steel sheet having a high magnetic flux density and a low iron loss, it is important to strictly control the formation rate, quantity and quality of the coating film during the manufacturing process.

Generally, grain-oriented electrical steel sheets include a glass coating (primary coating; forsterite + spinel) formed in the final finish annealing process and an insulating coating (secondary coating; phosphate + colloidal silica) formed during heat flattening. The surface treatment is performed by a two-layer coating of (system). The glass coating contains, as a main component, a forsterite (Mg ₂ SiO ₄ ) film formed by the reaction of MgO, which is the main component of the annealing separator, with the SiO ₂ -based oxide film formed during decarburization annealing. When Al is used as a steel component as in the present invention, Al ₂
It is composed of oxide components provided by O ₃ and other additives for annealing separators and spinel-like substances derived from them. This glass coating improves iron loss, magnetostriction, etc. due to its tension effect, while depending on the state of formation, it reduces the insulating properties, space factor, magnetic flux density, adhesion, etc. in addition to the appearance of the coating and the above-mentioned tension effect. Differences occur in the effect of improving iron loss, etc. Further, when (Al, Si) N is used as an inhibitor as in the present invention, this glass coating controls the invasion of N from the atmospheric gas at the steel sheet interface by the formation timing, formation rate, formation amount, etc. On the contrary, it has a great influence on the decomposition behavior of the inhibitor from the steel. Therefore, it is important to form an appropriate amount of glass film at an appropriate time in order to obtain a product having both film properties and magnetic properties, and there is an increasing need for new technology development for this purpose.

Starting from the component materials of the invention,
Many methods have been proposed for obtaining a good glass coating and excellent magnetic properties by improving decarburization annealing and nitriding treatment conditions. Japanese Unexamined Patent Publication (Kokai) No. 2-259017 discloses annealing of a steel sheet by a surface oxide layer formed in the nitriding process from decarburization annealing so that the oxygen content is in the range of 500 to 750 ppm.
A method has been proposed in which an annealing separator is applied and final finishing annealing is performed, and thus there are no film defects such as shimofuri and scale, and both magnetic properties and film properties are excellent. However, in the component-based material of the present invention, the annealing separator Mg
The coating and magnetic properties may be affected and deteriorated depending on the physical properties of O and the conditions of the final annealing, which is not a sufficient technique. In addition, Japanese Patent Laid-Open No. 60-096770 discloses Sb.
One or more of ₁₃ , SrC ₁₂ , TiC ₁₂ , and ZnC ₁₂ is added in an amount of 0.02 to 100 parts by weight of magnesium oxide.
It is stated that 1.5 parts by weight are added. further,
Japanese Examined Patent Publication No. 63-3022 discloses that as an annealing separator, 100 parts by weight of magnesium oxide is used, and 1 part of chloride of Sb, Sr, Ti and Zr is contained in the antimony sulfate.
There is described a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties by using an annealing separator containing 5 to 20% by weight of chlorine as one kind or two or more kinds.

All of these techniques for improving MgO additives include C: 0.03 to 0.100%, Si: 2.5 to 4.
If necessary, a hot rolled sheet containing 0% and at least one of sulfide and / or nitride as a primary recrystallized grain suppressor is annealed, and the final sheet thickness is obtained by cold rolling once or twice or more, It comprises a step of decarburizing and annealing and applying an annealing separating agent. That is, any of these techniques is a technique developed for the purpose of improving the coating film and magnetism of the conventional grain-oriented electrical steel sheet process material different from the process of the present invention.
In the case of the component-based materials and processes of the present invention, there are differences in the oxide film components and film formation reactivity, deinhibitor reaction, etc., and these techniques are not sufficient. In particular, when these techniques are applied, there is a problem that the secondary recrystallization becomes unstable and the magnetic properties are rather deteriorated. Therefore, low temperature slab heating-decarburization annealing-nitriding treatment-annealing separating agent application-
In the grain-oriented electrical steel sheet consisting of finish annealing, there is a further demand for the development of a technique for achieving both stable glass coating and magnetic properties by improving the decarboxylation film, annealing separator, final finishing annealing atmosphere and the like.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a grain-oriented electrical steel sheet having high tensile strength and excellent magnetic properties.

[0008]

The method for producing a grain-oriented electrical steel sheet according to the present invention is as a steel component C by weight;
0.075%, Si; 2.5-4.5%, Mn; 0.0
5 to 0.45%, S; ≤ 0.014%, acid-soluble Al;
0.010-0.040%, N; 0.0030-0.0
Slab containing 130%, Sn; 0.03 to 0.50%, the balance being Fe and unavoidable impurities at 1280 ° C.
After heating at a temperature of less than 1, then hot rolling, cold rolling at least once between annealing or annealing to obtain the final plate thickness, then decarburizing annealing, nitriding treatment, applying an annealing separator, and final finishing annealing. This is the basic process. In the method for producing a grain-oriented electrical steel sheet having a high-strength glass coating of the present invention in such components and steps and having excellent magnetic properties, decarburization annealing,
It is in the final finishing annealing process with the additive of annealing separator.

That is, the material coil cold-rolled to the final plate thickness is decarburized and annealed in a continuous line. By this decarburization annealing, C in the steel is removed and primary recrystallization is performed, and at the same time, an oxide film mainly composed of SiO ₂ is formed on the surface of the steel sheet. The quality and quantity of this oxide film plays an important role in the reaction with the annealing separating agent and the change of the inhibitor in the subsequent finish annealing. In the present invention, at that time, Fe ₂ SiO which does not form FeO in thermochemical equilibrium as decarburization annealing temperature and atmosphere.
₄₎ Inhibitors are formed by performing nitriding treatment under the condition that a heating pattern of one or more steps is provided in the formation region. In the component system of the present invention, Fe ₂ SiO _{2 is formed on} the outermost surface layer of the oxide film by the decarburization annealing under such a thermal cycle and atmospheric conditions and the surface modification by the subsequent nitriding treatment.
₄ , Fe compound coating such as FeSiO ₃ , SiO _{2 on the} inner layer
However, the total oxygen content of the steel sheet is 350 to 650 pp.
Annealed to m.

In the present invention, the decarburization annealing is performed in order to control the oxide film as described above, and the former stage of the soaking section is 800 to 850.
_{℃, P H 2 O / P} H 2; 0.30~0.57, the subsequent second part _{820~950 ℃, P H 2 O /} P H 2; ≦ 0.
The secondary control of the oxide film component is performed by setting it to 1 and the soaking time ratio of the front part and the rear part to be the rear part / the front part; 0.01 to 0.20. Next, a nitriding treatment is performed as an inhibitor forming treatment, and the nitriding amount at that time is 15
Annealed to 0-300ppm. As an annealing separator for the steel sheet after this nitriding treatment, one or more of Sb compounds such as sulfate, sulfide, borate, chloride, and oxide as 0.05 to 1. 5
An annealing separator, which is added by adding parts by weight, is applied and wound on a coil. Then, final finish annealing at 1200 ° C. × 20 Hr is performed.

In the present invention, the atmosphere gas and heat cycle of this final finish annealing are extremely important together with the decarburization annealing oxide film forming conditions and the annealing separator, and the temperature rising rate up to 1200 ° C. is 20 ° C./hr or less, In addition, final finish annealing is performed in an atmosphere of one or two or more of N ₂ , H ₂ and other inert gases having an N partial pressure of 0.25 or more. After reaching 1200 ° C., purification treatment and glass film formation are performed in a dry atmosphere of H ₂ 100%. The glass-coated coil thus obtained is subjected to an insulating coating baking process and heat flattening in a continuous line. In the grain-oriented electrical steel sheet, especially in a material having a high magnetic flux density, it is effective for improving the iron loss characteristic and the magnetostrictive characteristic due to the tension of the glass coating and the insulating coating. Therefore, for example, Japanese Patent Publication No.
Phosphates as described in 28375.
A colloidal silica-based tension-imparting coating material is applied and baked to obtain a product.

The present inventors carried out nitriding treatment after decarburization annealing to form an oxide film and an inhibitor mainly composed of (Al, Si) N, and to form a high-strength glass film by an annealing separator and final finishing annealing, In order to obtain magnetic properties, the amount and quality of the oxide film of decarburization annealing, MgO as an annealing separator and additives,
It was determined by enormous experiments and research that it is important to control the heat cycle and the atmospheric conditions at the time of temperature rise in the final annealing to a specific range. That is, by appropriately controlling these process conditions, the glass film formation is started on the lower temperature side at the time of the final finish annealing temperature rise, and the additional oxidation and the additional nitridation in the latter stage at the time of temperature rise are suppressed to obtain a uniform high temperature. This has led to the development of a manufacturing technique for forming a tension film and appropriately smoothing the deinhibitor to obtain good secondary recrystallization. Next, the reasons for limiting the configuration technology in the present invention will be described. The starting slab is C by weight;
0.021-0.075%, Si; 2.5-4.5%,
Mn; 0.05 to 0.45%, S; ≤ 0.014%, A
1; 0.010 to 0.040%, N; 0.0030 to
0.0130%, Sn; 0.03 to 0.50%, and the balance Fe and unavoidable impurities. If the content of C is less than 0.021%, the secondary recrystallization becomes unstable, and the magnetic flux density of the product is often B ₈ lower than 1.8 Tesla even when the secondary recrystallization is performed. On the other hand, 0.
If it exceeds 075%, it takes a long time for the decarburization annealing step, which impairs the productivity. The specific resistance of Si varies depending on the content of Si. If it is less than 2.5%, a good iron loss value cannot be obtained. On the other hand, if it is more than 4.5%, cracks and fractures frequently occur during cold rolling, making stable rolling operation impossible.

One of the characteristics of the component system of the starting material of the present invention is S
Is 0.014% or less. As a known technique, for example, in the technique disclosed in Japanese Examined Patent Publication No. 47-25220, S is an element that forms a precipitate necessary for causing secondary recrystallization as MnS, and is most effective in the above-mentioned known techniques. There is a range of the amount of S that develops MnS in the slab heating step performed prior to hot rolling.
Was defined as the amount of solid solution. However, in recent studies, as precipitates necessary for secondary recrystallization (Al,
In the manufacturing process of the grain-oriented electrical steel sheet using Si) N, it was found that S promotes secondary recrystallization failure when the slab containing a large amount of Si in the material is heated at a low temperature and hot-rolled. S when the Si content in the material is 4.5% or less
Is 0.014% or less, preferably 0.0070% or less, no secondary recrystallization occurs.

In the present invention, (Al, Si) N is used as a precipitate necessary for secondary recrystallization. Therefore, in order to secure the necessary minimum amount of AlN, acid-soluble Al is 0.010.
%, N is required to be 0.0030%. However, when the acid-soluble Al exceeds 0.040%, A during hot rolling
Inappropriate 1N makes secondary recrystallization unstable. Therefore, it is limited to 0.010 to 0.040%. On the other hand, N
When the content of Cr exceeds 0.0130%, cracks on the surface of the steel plate called blister occur, and the grain size of primary recrystallization cannot be adjusted, so 0.0030% to 0.013%
Limited to 0%. If Mn is less than 0.025%, secondary recrystallization becomes unstable. However, when the amount of Mn added increases, B
_{Although the} value of ₈ is high, the addition of a certain amount or more is disadvantageous in terms of cost. Therefore, it is limited to 0.05 to 0.45%.

The first feature of the present invention using such a component as a starting material lies in the amount and forming conditions of the oxide film in the steps of decarburization annealing to nitriding. As a component of the oxide film after the nitriding annealing, the total oxygen amount of the oxide film is 350 to 650 ppm. In the present invention, the reaction between the SiO ₂ component contained in the oxide film and the annealing separating agent described later is carried out very effectively by the MgO additive and the final finishing annealing to form a dense and uniform glass film. . Therefore, the SiO in the decarboxylated film
₂ contributes to the film formation reaction more effectively than in the prior art.

When the amount of [O] is 350 ppm or less, a uniform glass film is formed, but the glass film thickness is too small, and the inhibitor stabilizing function in the final annealing temperature rising process is deteriorated and the adhesion property after the insulating film treatment is performed. This causes deterioration of magnetism due to decrease in film tension and film tension. On the other hand, when it is 650 ppm or more, excessive oxidation causes pinhole-like metallic luster spots and scale-like defects. Further, another problem in the case where the steel sheet has a large oxygen content is that in the present invention, the magnetic level is lowered even if the film formation is successfully performed. This is because the annealing separator of the present invention forms a dense film on the lower temperature side as a result of film formation, and as a result, N is not supplied into the steel during the temperature rise, and Al removal eliminates oxygen in the oxide film. It is considered that as a result of abruptly occurring, problems of magnetic deterioration and generation of fine particles are caused.

In the decarburizing annealing of the present invention for controlling the oxide film amount as described above, the temperature in the front stage of the soaking section is 800 to 850 ° C.
₂ O / P H ₂ ; 0.30 to 0.57, the subsequent stage is 820 to 950 ° C., P H ₂ O / P H ₂ ; ≤0.1,
Moreover, the time ratio of the front part and the rear part is 0.01 to 0.2.
It is done at zero. The front part is 800-850 ° C, PH ₂ O /
PH ₂ ; 0.30 to 0.57 is because the decarburization reaction and the oxidation reaction are performed at this time, and the decarburization and the oxide film formation to a certain level are completed, so that such conditions are applied. To be done. If the temperature is lower than 800 ° C, decarburization at this time is insufficient, or the oxidation reaction is extremely low, and it becomes difficult to obtain the oxidation amount and oxide film component of the present invention. 850
If the temperature exceeds 850 ° C., the oxidation proceeds before the decarburization reaction, decarburization is inhibited, and grain growth of primary recrystallized grains occurs. When P H ₂ O / P H ₂ is also less than 0.30, decarburization and oxidation reaction are disadvantageous, and it is difficult to obtain the oxide film component targeted by the present invention, so 0.30 or more is desirable. on the other hand,
If it exceeds 0.57, it becomes a FeO formation region due to thermochemical equilibrium,
Excess FeO is contained in the surface layer of the oxide film.

Under such conditions, when the latter-stage oxidation conditions of the present invention are applied, the oxide film on the surface portion is reduced, and a large amount of Fe is exposed at the outermost surface layer portion and hinders film formation. Further, in such a case, the decarburization reaction is also disadvantageous, so 0.57 or less is desirable. The processing conditions of the subsequent stage of the decarburization annealing performed next are as follows: temperature 820 to 950 ° C. PH ₂ O / PH ₂ ; ≦ 0.1
Done in. In the annealing of the present invention, with respect to the front part of decarburization annealing,
The characteristic feature is that the temperature of the second-stage region is at least higher than that of the first-stage region, and the operation is performed in such a dry atmosphere. As a result, the densification of the oxide film and the Fe-based compound (Fe ₂ SiO ₄ , Fe ₂
SiO ₃ ) is effectively increased, and a highly reactive oxide is formed. If the post-stage temperature is less than 820 ° C, there is no effect of modifying the oxide film surface layer, while if it exceeds 950 ° C, grain growth of primary recrystallized grains occurs even if the oxidation time is limited as in the present invention, and good magnetic properties Is difficult to obtain, so it is preferable to limit it.

Next, P H ₂ O / P H _{2 at} this time is 0.1
The following is desirable. If it exceeds 0.1, the surface layer of the oxide film is insufficiently modified, and it is difficult to form a dense oxide film. When it is 0.1 or less, the Fe-based compound in the surface layer of the oxide film is increased and the SiO ₂ layer is densified, so that the glass film forming reaction is improved and the high tension film is easily formed. Another important condition for this decarburization annealing condition is the annealing time ratio of the first and second steps. That is, it is desirable that the rear / front ratio is 0.01 to 0.2. If the rear-stage ratio is less than 0.01, the oxide film cannot be sufficiently modified as described above, and the effect of the present invention cannot be sufficiently exerted. On the other hand, if it exceeds 0.2, the reduction reaction of the outermost layer becomes excessive, and Fe is exposed as a metal in the surface layer to form a porous oxide film or significantly impair the reactivity.

Further, the latter-stage region time affects the grain growth of the primary recrystallized grains, and therefore affects the secondary recrystallization depending on the conditions, and is therefore limited. The coil whose oxide film is controlled by decarburization annealing is then subjected to nitriding treatment. The nitriding treatment is 150 to 300 ppm. Inhibitors (Al,
The amount of Si) N is too small and the secondary recrystallization becomes unstable.
On the other hand, if it exceeds 300 ppm, coating defects may occur during decomposition at the start of secondary recrystallization, which is not preferable. At 150 to 300 ppm, there is no effect on such glass coating, and by controlling the annealing separator and the final annealing conditions, a product having good high-strength glass coating and magnetic properties can be obtained.

The second feature of the present invention is the following annealing separator. MgO, which is the main component of the annealing separator, reacts with the underlying oxide film to form a glass film. In this reaction, a low melting point agent is essential as a reaction accelerator, and in the present invention, one or more kinds of Sb compounds such as sulfate, sulfide, borate, chloride and oxide are used. Addition amount is 0.0
If it is less than 5 parts by weight, a sufficient effect of improving the glass film forming reaction cannot be obtained. On the other hand, if it exceeds 1.5 parts by weight, the effect of lowering the melting point is too strong, and excessive S, SO ₄ , Cl, O, etc. cause corrosion of the oxide film and the glass film, causing pinhole-like metallic gloss defects and scale. It is limited because it causes problems such as shape defects and uneven coating thickness.

As the base MgO, MgO having a hydration water content of 2.5% or less is preferably applied in the finish annealing process with the highly reactive additive as in the present invention. This is because the hydrated water content of MgO increases the dew point between the steel plates in proportion to the amount. Therefore, in the present invention in which sufficient reactivity is obtained by controlling the decarboxylation film, controlling the Sb compound, and the final annealing condition, the water content is rather harmful, and if it exceeds 2.5%, it may cause a peroxidation phenomenon or cause uneven coating. There is.

With the component-based material of the present invention, it is possible to considerably improve the film characteristics by controlling the components and amount of the steel sheet oxide film and improving the reactivity by the Sb compound. In this process, stable secondary recrystallization cannot be obtained by this alone. For this reason,
The final finishing annealing condition, which is the third feature of the present invention, is essential. As a result of repeated studies on stabilization and improvement of secondary recrystallization, the inventors have found that remarkably good secondary recrystallized grains can be stably obtained by controlling the temperature rising conditions during annealing as follows. I found it. That is, the temperature rising rate is set to 20 ° C. or less and N ₂
Annealing with 25% or more of N ₂ + H ₂ + other inert gas is essential. If the annealing rate exceeds 20 ° C., the dehydration between the plates during the temperature rise is not sufficiently performed, and the steel plates are likely to be wet.

Therefore, even if the atmospheric gas is in an appropriate condition, a deinhibitor is generated, and stable secondary recrystallization is difficult to obtain. On the other hand, at a temperature rising rate of 20 ° C. or less, the drying between the steel sheets is sufficiently promoted to form a remarkably uniform glass film, and the inhibition of the deinhibitor due to the oxidation reaction is appropriately performed. Furthermore, the balance between the strengthening of the inhibitor by controlling the N ₂ gas by the atmosphere gas described below and the grain growth at the time of temperature rise is sufficiently maintained, and excellent secondary recrystallization is obtained. The atmosphere gas is important together with the temperature rising rate.

With the additive of the present invention and the final anneal, the glass coating forms at a lower temperature than in the prior art. For this reason, the inhibitor (Al, Si) N hardly obtains the reinforcing effect of the denitrification reaction by the atmospheric gas due to the sealing effect of the coating film, and the decarboxylation film component existing at the coating film interface causes deinhibition. Therefore, the inhibitor is likely to decrease. For this reason, it is particularly important to control the atmosphere when the deinhibitor occurs. It is desirable that N ₂ be 20% or more in the atmosphere gas in which one kind or a mixed gas of two or more kinds such as N ₂ + H ₂ + inert gas is used.

By keeping the N ₂ partial pressure at 20% or more,
The decomposition of the N compound of the inhibitor in steel is suppressed. As a result, (Al, Si) N is kept stable until the start of secondary recrystallization, and good secondary recrystallization is obtained. Appropriateness of this atmosphere gas may be applied to the entire area when the temperature is raised or may be applied to a specific area when the temperature is raised. In this case, application in a high temperature range of at least 700 ° C. or higher is desirable.

As a mechanism for obtaining a glass coating and a grain-oriented electrical steel sheet having excellent magnetic properties according to the present invention, first, the steel sheet oxygen amount is controlled to a constant amount as an oxide film amount formed by decarburization annealing. An annealing separator is applied on this steel sheet, and at this time, an Sb compound is added to MgO as a reaction accelerator. As a result, the formation of the forsterite coating is further lowered in temperature and uniformized. As a result, a surface sealing effect is generated and an additional oxidation suppressing effect is generated, and a glass film containing less internal oxide, which is harmful to magnetism, is stably formed. At the time of this finish annealing, by gradually heating at 20 ° C./Hr or less and applying a high N ₂ partial pressure, the inter-plate atmosphere at the time of temperature rise is uniformly dried, and the film is made uniform. In addition, the decomposition of the inhibitor is suppressed, and good secondary recrystallization is obtained.

[0028]

【Example】

[Example 1] C: 0.055% by weight, Si: 3.30
%, Mn; 0.13%, acid-soluble Al; 0.030%,
S; 0.0065%, N; 0.0070%, Sn;
A raw material composed of Fe and unavoidable impurities with the balance of 038% was hot-rolled to 2.0 mm, annealed at 1120 ° C. for 2 minutes, pickled, and cold-rolled to a plate thickness of 0.225 mm. The steel sheet was annealed at a temperature of 830 ° C. for 110 seconds in an atmosphere of N ₂ 25% + H ₂ 75% at a dew point of 60 ° C., and subsequently annealed at 850 ° C. × 10 seconds of N ₂ 25% + H ₂ 75% at a dew point of −10 ° C. N
_A sample was prepared by performing nitriding treatment in 225% + H ₂ 75% + NH ₃ so that the amount of nitrogen was 180 ppm. The oxygen content of the steel sheet at this time was 500 ppm. An annealing separator having the composition shown in Table 1 was applied to this steel sheet, and after drying, FIG.
Final finishing annealing was performed under the conditions shown in (B). The results are shown in Table 2.

[0029]

[Table 1]

[0030]

[Table 2]

As a result, when the annealing separator was the present invention and the final annealing condition was the cycle of FIG. 1 (A), the glass coating was uniform and excellent, and the magnetic properties were remarkably good. In particular, the amount of Sb ₂ (SO ₄ ) ₃ added is 0.25 to
When 1.0 g was added, very good film properties and magnetic properties were exhibited. However, even with the same annealing separator, when the finish annealing was as shown in the cycle of FIG. 1 (B), a good glass film was obtained, but a small amount of fine particles were mixed and the magnetic properties were considerably inferior. Became. On the other hand, when the annealing separator is a comparative example, the coating is uneven and thin regardless of the annealing conditions,
The magnetic properties were also poor, and the iron loss value was particularly poor.

Example 2 A 0.225 mm thick steel plate obtained in the same manner as in Example 1 was treated with N ₂ 25 at 820 ° C. for 120 seconds.
% + H ₂ 75% After annealing at a dew point of 65 ° C., annealing was subsequently performed in the latter half of the same furnace at a dew point of −5 ° C. for 870 ° C. for 2.5 seconds. After that, the furnace temperature is set to 750 so that the nitriding amount becomes 200 ppm.
Nitriding treatment was performed in a dry atmosphere of N ₂ 25% + H ₂ 75% + NH ₃ at 30 ° C. for 30 seconds to adjust the starting material. The oxygen content of the steel sheet at this time was 550 ppm. An annealing separator having a composition as shown in Table 3 was applied to this steel sheet, and then, as shown in FIG.
As shown in (1), (2), and (3), the atmosphere conditions of the final annealing were changed and the product was annealed to obtain a product. Table 4 shows the characteristics and magnetic characteristics of the glass coating at this time.

[0033]

[Table 3]

[0034]

[Table 4]

As a result, with the annealing separating agent of the present invention to which the Sb compound was added, all the glass coating films were uniformly formed in good condition and the coating film tension was very high. The magnetic characteristics are N at the time of temperature rise under the final annealing conditions C- (1) and C- (2).
_{When the two-} part pressure was increased, the magnetic flux density and iron loss value were remarkably good in all cases. However, the final annealing atmosphere is N ₂ 10%
Under the condition that the N partial pressure was low, the secondary recrystallization was unstable and the magnetic characteristics were also poor. On the other hand, under the conditions of the comparative example, the annealing separator has a nonuniform and thin glass coating film, and the magnetic properties are very inferior to those of the material of the present invention.

Example 3 A coil after final cold rolling having a thickness of 0.225 mm prepared in the same manner as in Examples 1 and 2 was heated at a temperature of 825 ° C. for 100 seconds and an atmosphere gas of N ₂ 25% + H _2.
After annealing by changing the dew point so that the oxygen content of the steel plate changes in 75%, then as a post-stage condition, 860 ° C x 15 seconds, N
And annealed as dew point -20 ° C. in _{2 25% + H 2 75%} . Then, nitriding treatment was performed in N ₂ 25% + H ₂ 75% + NH ₃ so that the amount of nitrogen was 220 ppm. On this steel sheet, TiO 2 was added to 100 parts by weight of hydrated water of 2% MgO.
₂ 5 parts by weight and Sb ₂ (SO _{4) 3} After coating an annealing separating agent consisting of 0.5 part by weight, by a final annealing under the conditions shown in FIG. 1C - (2). Table 5 shows the oxygen content of the oxide film after nitriding and the film components, and Table 6 shows the results of the glass film properties and magnetic properties after the final annealing.

[0037]

[Table 5]

As a result, the steel sheet of the present invention has an oxygen content of 380 to 6
All of the samples after nitriding in the range of 40 ppm were uniform and had good glass coating and magnetic properties. Particularly in the case of a material having a steel sheet oxygen content of 480 to 640 ppm, a remarkable improvement in the film tension and the effect of improving the magnetism were obtained. On the other hand, when the oxygen content of the steel sheet is as low as 300 ppm, the coating is very thin, and when the oxygen content of the steel sheet is as high as 750 ppm, scale-like defects are partially generated in the coating, and the magnetic properties are considerably deteriorated in both cases. Became a trend.

[0039]

[Table 6]

[0040]

According to the present invention, by controlling the oxide film amount and quality of decarburization annealing, the annealing separator and the temperature rising rate of final annealing,
The glass film is formed early, uniformly and densely. Further, the inhibitor is kept stable by appropriately controlling the N ₂ partial pressure of the atmospheric gas. As a result, a glass coating property and magnetic property are compatible with each other, and a remarkably excellent product is obtained.

[Brief description of drawings]

FIG. 1 is a table showing heat cycles and atmospheric conditions of final finish annealing of the present invention and a comparative example. (A) is the temperature rising rate of the present invention and the atmosphere gas at the time of temperature rising, (B) is the temperature rising rate of the comparative example and the atmosphere gas at the time of temperature rising, (C) is the temperature rising under the temperature rising conditions of the present invention. In the example of changing the atmosphere gas of (1), (2)
Is the atmospheric gas condition of the present invention, and (3) is the atmospheric gas condition of the comparative example with less N ₂ .

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C22C 38/06 (72) Inventor Go Hamata 1-1 No. 1 Hibatacho, Tobata-ku, Kitakyushu City Nippon Steel Inside Yawata Works

Claims (3)

[Claims] 1. C by weight; 0.021 to 0.075%; Si; 2.5 to 4.5%; Mn; 0.05 to 0.45%; S; ≤ 0.014%; Molten Al: 0.010 to 0.040%, N: 0.0030 to 0.0130%, Sn: 0.03 to 0.50%, and 128 slabs consisting of the balance Fe and unavoidable impurities.
After heating at a temperature of less than 0 ° C, hot rolling is performed, and cold rolling is performed once or twice with sandwiching annealing to obtain a final plate thickness. Then, decarburization annealing is performed, nitriding treatment is performed, and an annealing separator is applied, In the method for producing a grain-oriented electrical steel sheet, which comprises performing finish annealing, the oxidation amount of the steel sheet after decarburization and nitriding annealing is 350 to 650 ppm as the steel sheet oxygen amount, and the nitriding amount is 150 to 650 ppm as the steel sheet nitrogen amount. After decarburizing and nitriding treatment to 300 ppm, MgO was used as an annealing separator.
An annealing separator containing 0.05 to 1.5 parts by weight of one or more of Sb compounds such as sulfates, sulfides, borates, chlorides, and oxides as an Sb compound is applied to 100 parts by weight. Then, final finish annealing is performed in an atmosphere of one or two or more of N ₂ , H ₂ and other inert gases having a temperature rising rate up to 1200 ° C. of 20 ° C./Hr or less and a N ₂ partial pressure of 0.25 or more. A method for producing a grain-oriented electrical steel sheet having a high-tensile glass coating and excellent magnetic properties, the method comprising: 2. As a decarburizing annealing condition, the soaking part front stage is set to 80.
_{0~850 ℃, P H 2 O /} P H 2; 0.30~0.57
Subsequent subsequent part is 820 to 950 ° C, PH ₂ O / P
H ₂ ; ≦ 0.1, and the annealing is performed so that the soaking time ratio of the former part and the latter part is 0.01 to 0.20 for the latter part / the former part. A method for producing a grain-oriented electrical steel sheet having a tensile glass coating and excellent magnetic properties. 3. Mg used as a main component of an annealing separator
The hydrated water content of O is 2.5% or less, and the method for producing a grain-oriented electrical steel sheet having the high-strength glass coating according to claim 1 or 2, which has excellent magnetic properties.