JP3336555B2 - Method for producing grain-oriented electrical steel sheet without glass coating with excellent surface properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a (glass-less) grain-oriented electrical steel sheet having no glass coating (forsterite, spinel coating) having excellent surface properties, and has excellent workability such as cutting properties and punching properties. Especially the surface appearance,
The present invention relates to a method of treating an insulating film having excellent adhesion and excellent magnetic properties.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are generally used as soft magnetic materials, mainly as core materials for transformers and other electric equipment, and are required to have good magnetic characteristics such as excitation characteristics and iron loss characteristics. In order to obtain good magnetic properties, it is important that <001>, which is the axis of easy magnetization, be highly aligned in the rolling direction. Further, the plate thickness, crystal grain size, specific resistance, and film properties are also important because they have a great influence on the magnetic properties.

[0003] The directionality of the crystal has been greatly improved by the method characterized by the final cold rolling reduction under high pressure using AlN as an inhibitor. At present, it is possible to produce a magnetic flux density close to the theoretical value. ing. On the other hand, when the grain-oriented electrical steel sheet is used by a consumer, the film properties and workability are important together with the magnetic properties. Normally, the grain-oriented electrical steel sheet is surface-treated by a glass coating and an insulating coating formed at the time of final finish annealing.

The glass film contains forsterite (Mg ₂ SiO ₄ ) as a main component, which is a reaction product of an annealing separator, MgO, and an oxide, SiO ₂ , formed during decarburizing annealing, and Al formed by decomposition of AlN used as an inhibitor. ₂ O ₃
And a film made of a spinel compound such as SiO ₂ , MgO or the like.

[0005] The glass coating is hard and has high wear resistance, and significantly affects the wear resistance of tools such as slits, cuts, and punches in processing of transformer cores, motor core materials for rotating machines, and the like. . For example, when punching a grain-oriented electrical steel sheet having a glass coating,
Abrasion of the mold occurs, and the return of the sheet punched out by punching several thousand times becomes large enough to cause a problem in use.

[0006] For this reason, it is necessary to re-polish the mold or replace it with a new one, which leads to a reduction in work efficiency and cost increase in iron core processing at the customer. Similarly, the adverse effect of the glass coating is also a problem on the slitting property, the cutting property and the like.

With respect to the magnetic properties of the grain-oriented electrical steel sheet, iron loss can be improved by the film tension of the glass coating. This effect is remarkable in the case of a material having a high magnetic flux density.
An iron loss improving effect of about 20% can be obtained as compared with a case without a coating. However, the state of formation, particularly the increase in the thickness of the coating and the presence of the internal oxide layer, have a negative effect on the reduction of the magnetic flux density and the effect of improving iron loss at the time of magnetic domain refining. For this reason, by applying a tension imparting type insulating coating to the surface without a glass coating, in recent years, manufacturing technology for products having good workability and excellent iron loss characteristics has come to the spotlight, and various proposals have been made. Became.

However, on the other hand, the glass coating plays an important role in the adhesion to the steel sheet surface as the whole insulating coating due to its structure that is finely and densely developed during the formation process. In a grain-oriented electrical steel sheet having no glass coating, the weakening of the inhibitor becomes more remarkable than that of a normal material with a glass coating due to a surface reaction in the glassless process. For this reason, secondary recrystallization tends to be unstable. Furthermore, since there is no anchor effect by the glass coating, the adhesion of the insulating coating is disadvantageous.

Further, depending on the manufacturing conditions in the treatment of the insulating film, the steel sheet may be oxidized to impair the appearance of the product, or the adhesiveness of the insulating film may not be sufficiently obtained. In addition, peeling may occur due to bending or strain relief annealing, or in extreme cases, may fall off the steel sheet surface during baking of the insulating coating in a production line. Therefore, it is important to develop a baking treatment technique centering on stabilization of secondary recrystallization and improvement of adhesion of an insulating coating in the production of a grain-oriented electrical steel sheet having no glass coating.

As a method for producing a grain-oriented electrical steel sheet having no glass coating, Japanese Patent Application Laid-Open No. Sho 64-62417 discloses a decarburizing annealing at a temperature of 800 to 850 ° C. in an atmosphere of PH ₂ O / P H.
₂ was set to 0.25 to 0.55, and magnesia 100
A metallic luster characterized by applying an annealing separator composed of 2 to 40 parts by weight of one or more alkali metal or alkaline earth metal chlorides per part by weight and finish annealing. A method for producing a grain-oriented electrical steel sheet having the following is described.

As a result, the chloride in the annealing separator decomposes SiO _{2 in} the oxide and does not lead to the formation of a glass film, so that a remarkable improvement in punchability is obtained. Further, in recent years, Japanese Patent Application No. 6-101014 has filed an application as a method for obtaining a unidirectional magnetic steel sheet having excellent magnetic properties and a large thickness and a small glass coating.

In this method, the slab is heated at a low temperature of less than 1280 ° C., then continuously subjected to cold rolling at a rolling reduction of 60 to 79% without performing hot rolling and hot-rolled sheet annealing, followed by decarburizing annealing and an annealing separator. In the method for producing a thick unidirectional magnetic steel sheet having a thickness of 0.4 to 1.0 mm, which is subjected to finish annealing and applying an insulating coating agent, the hot rolling end temperature is set to 800 to 1100 ° C.
The cumulative rolling reduction of the last three passes of hot rolling is set to 40% or more, the temperature of the steel sheet between the passes of cold rolling is set to 250 ° C or less, and the average grain size of the primary recrystallized grains from the decarburizing annealing to the start of the final finishing annealing is determined. 1
8 to 30 μm, and after the hot rolling and before the start of final finish annealing, nitriding treatment is performed.
Li, K, Na, Ba, Ca, Mg, Z
chlorides, nitrates of n, Fe, Zr, Sr, Sn, Al;
One or two or more selected from sulfides and sulfates
An object of the present invention is to provide a method for producing a unidirectional magnetic steel sheet having excellent magnetic properties and a small thickness and a small glass coating by applying an annealing separator added to 30 parts by weight.

[0013] Next, with regard to the technology in the insulating coating treatment of the grain-oriented electrical steel sheet, as disclosed in JP-A-59-104431, phosphate after forming a forsterite coating on the grain-oriented electrical steel sheet surface is disclosed. It has been proposed that in annealing for baking a system coating, baking is carried out in a weakly reducing atmosphere containing 15% or less of H ₂ and CO gas and the balance substantially consisting of N ₂ .

Thus, red discoloration of the steel sheet caused by baking of the conventional colloidal silica-Mg phosphate-chromic anhydride coating can be prevented. However, a technology for treating an insulating film in glassless is not disclosed, and development of a new technology is expected.

As described above, none of these prior arts by the present inventors have a thick glass coating having a glass coating or a so-called glassless directional electromagnetic coating having a small glass coating. Related to steel plate,
Significant improvement in workability such as punching property and cutting property has been obtained by the glassless process. However, in the treatment of the insulating film in these conventional techniques, depending on the surface condition, sufficient workability and adhesion of the insulating film cannot be obtained.
Considering cost, manufacturing control and overall film performance of the product in the field manufacturing process, it cannot be said that the technology is still sufficient.

[0016]

DISCLOSURE OF THE INVENTION The present invention relates to the production of a glass-less grain-oriented electrical steel sheet, in which the surface appearance abnormality peculiar to the glassless material in the treatment of an insulating film, the poor adhesion caused by oxidation of the steel sheet, the poor workability, and the magnetic properties. An object of the present invention is to provide a method for producing a glassless grain-oriented electrical steel sheet having excellent surface properties by solving the problem of defects.

[0017]

In order to obtain the product of the present invention, a steel material is used as a starting material and C: 0.021 by weight ratio.
0.075%, Si: 2.5 to 4.5%, acid soluble A
l: 0.010-0.040%, N: 0.0030-
0.0130%, S ≦ 0.0140%, Mn: 0.05
An electromagnetic steel slab containing ０．４0.45%, the balance being Fe and unavoidable impurities was used.
After heating to a temperature below, hot rolling is performed, and cold rolling is performed once or two or more times with intermediate annealing, after final thickness, then decarburizing annealing, nitriding, and applying an annealing separator After that, a high-temperature finish annealing is performed, and a manufacturing method comprising performing heat flattening and application and baking of an insulating film is performed.

That is, according to the present invention, in the slab heating step, the inhibitor element, for example, Al, N, Mn, S, etc. is not dissolved in steel, and after decarburization annealing, the material is subjected to nitriding treatment in a strong reducing atmosphere. By doing so, an inhibitor containing (Al, Si) N as a main component is formed. Next, as an annealing separator, for example, one or more selected from chloride, nitrate, sulfide, sulfate, etc. were added to MgO from the prior application technology proposed by the present inventors. An annealing separator is used. After applying these annealing separators in the form of slurry to a steel sheet, finish annealing is performed.

Thus, a good glassless surface and secondary recrystallization can be obtained in the finish annealing process. Next, as an insulating coating agent, MgO, A was added to 100 parts by weight of phosphoric acid.
one or two selected from l ₂ O ₃ , CaO and ZnO
After applying an aqueous solution containing 15 to 35 parts by weight of at least one species and 1 to 20 parts by weight of one or more of a chromium compound, a boric acid compound, and a silicate compound, the oxygen content in the atmosphere gas is 200
The baking process is performed at 800 to 900 ° C. at 0 ppm or less.

At this time, the coating amount of the insulating coating agent is set within a certain range, and the temperature of the steel sheet on the outlet side of the drying furnace and the addition of a small amount of H ₂ as an atmosphere gas in the baking furnace or the dew point are controlled. A glassless product having extremely good surface condition, workability and magnetic properties can be obtained. As described above, the present invention is characterized by the components of the insulating coating in the production of the glassless grain-oriented electrical steel sheet and the application amount thereof, the atmosphere gas during the baking treatment, and the heat cycle.

[0021] The final cold rolled material is first decarburized and annealed in a continuous line. By this decarburizing annealing, removal of C in the steel and primary recrystallization are performed, and at the same time, SiO
An oxide film containing ₂ as a main component is formed. P H ₂ O in N ₂ + H ₂ atmosphere at this decarburization annealing eight hundred to eight hundred and seventy-five ° C.
/ P H ₂ is controlled.

Next, a nitriding treatment is performed in the latter half of the decarburizing annealing, after the end of the decarburizing annealing, or in another line. The nitriding treatment, NH ₃ to N ₂ + H ₂ at a sheet temperature 700-850 ° C.
Is annealed in a dry atmosphere in which the desired nitriding amount is obtained. At this time, the nitriding amount is set at 150 to 300 ppm. Thereafter, an annealing separating agent is applied, dried, and wound around a coil.

Next, as an annealing separator, for example, as proposed in JP-A-5-31353, M
For 100 parts by weight of gO, Li, K, Na, Ba, C
a, Mg, Zn, Fe, Zr, Sr, Sn, Al Annealing separator containing 2 to 30 parts by weight of one or more selected from chlorides, nitrates, sulfides, and sulfates of glass. Used as a wrestling agent. These annealing separators are applied as a water slurry to the surface of a steel sheet by a roll or the like, dried, and wound around a coil.

[0024] By the subsequent finish annealing, the glassless reaction and the secondary recrystallization are performed, and a steel sheet having metallic luster and good crystal orientation is obtained. At this time, in order to obtain a good secondary recrystallization structure, for example, 2N ₂ + H ₂ containing 50% or more of N is used as an atmosphere gas at the time of raising the temperature of the finish annealing.
Is used.

As in the present invention, MnS is used as an inhibitor.
In a process in which (Al, Si) N is formed and AlN is changed later, the secondary recrystallization initiation temperature is higher than that of a normal grain-oriented electrical steel sheet, and
Above 0 ° C., the end is between 1125 and 1150 ° C.
Therefore, it is necessary to keep the inhibitor stable up to the secondary recrystallization start region while performing the glassless reaction and the oxidation suppression.

This is because the condition of the interface and the atmosphere have a great influence on the absorption of nitrogen from the atmosphere gas and the decomposition of the inhibitor due to the denitrification in the glassless process due to the conditions of the temperature raising process. The conditions of the finish annealing include N ₂ 50 as a condition of the temperature raising process for performing uniform decomposition of the glass film.
%, The decomposition of the inhibitor is suppressed, and a steel sheet having good magnetic properties is obtained.

The glassless grain-oriented electrical steel sheet thus treated is subjected to an insulating coating treatment and a heat flattening treatment for both shape correction and distortion removal in a continuous line. The treatment of the insulating film at this time is intended by the present invention, and is important for obtaining good surface appearance, adhesion of the insulating film and good workability.

In the glassless grain-oriented electrical steel sheet such as the material of the present invention, the disadvantages of the absence of a glass coating include the problem of reduced adhesion after the treatment and baking of the insulating coating and the coating performance due to oxidation generated during the processing of the insulating coating. In addition, there is a problem that the magnetic characteristics are deteriorated.

For example, when an insulating coating agent of a tension imparting type as disclosed in Japanese Patent Publication No. 53-28375 is applied and baked, the insulating coating may fall off from the steel plate surface during a cooling process or the like and may not be resistant to bending or the like. Become. In particular, this tendency becomes remarkable depending on the atmosphere of the baking treatment conditions, the heat cycle, and the like.

In the present invention, as a novel insulating coating agent and a baking treatment method, the amount of the insulating coating agent applied, the temperature at the exit side of the drying furnace in the baking line, the oxygen concentration and the dew point of the atmospheric gas in the baking high temperature furnace are determined. By controlling, a steel sheet having extremely excellent appearance, excellent adhesion, workability, and magnetic properties can be obtained.

Next, the reasons for limiting the method for producing the glassless grain-oriented electrical steel sheet of the present invention will be described. First, the reasons for limiting the component composition of the material slab used as the starting material are as follows. C content thereof becomes unstable secondary recrystallization is less than 0.021%, the magnetic flux density of the product is intended 1.80Tesla as low as about at B ₈ even when the secondary recrystallization. On the other hand, if the content exceeds 0.075%, a long time is required for decarburization, which impairs productivity.

The specific resistance of Si changes depending on its content. For this reason, if it is less than 2.5%, good iron loss characteristics cannot be obtained. On the other hand, when the content exceeds 4.5%, cracks and breaks frequently occur during cold rolling, making stable cold rolling difficult. One of the characteristics of the component system of the starting material of the present invention is that S is set to 0.0
140% or less.

Conventionally known techniques, for example, JP-B-47-25
In the technology disclosed in Japanese Patent Publication No. 220, S is M
nS is an element that forms a precipitate necessary for causing secondary recrystallization to occur, and there is a content range in which S is most effective in the above-mentioned known technology, and it is MnS in a slab heating step performed prior to hot rolling. Was defined as an amount capable of forming a solid solution.

However, in a recent study, in a production process of a grain-oriented electrical steel sheet using (Al, Si) N as a precipitate required for secondary recrystallization, a slab containing a large amount of Si in a material is subjected to slab slab at a low temperature. When heating and hot rolling,
S has been found to promote secondary recrystallization failure. When the amount of Si in the material is 4.5% or less, S is 0.0140.
%, Preferably 0.0070% or less, no secondary recrystallization failure occurs at all.

In the present invention, (Al, Si) N is used as a precipitate necessary for the secondary recrystallization. Therefore, the minimum A
To secure 1N, acid-soluble Al must be 0.010% or more and N must be 0.0030% or more. However, if the acid-soluble Al exceeds 0.040%, the Al
N becomes inappropriate and secondary recrystallization becomes unstable.
Limited to 10-0.040%.

On the other hand, if the N content exceeds 0.0130%, cracks on the steel sheet surface called blisters occur,
0.0030 ~ because the particle size of primary recrystallization cannot be adjusted
Limit to 0.0130%. If Mn is less than 0.050%, secondary recrystallization becomes unstable. However, B ₈
Although the value is high, addition over a certain amount is disadvantageous in cost. For this reason, it is limited to 0.05 to 0.45%.

In the treatment of the insulating coating agent, the coating composition is the first feature of the present invention. Selected coating composition to phosphoric acid 100 parts by _{weight, MgO, Al 2 O 3,} CaO, 1 or two or more 15-35 parts by weight and the chromium compound selected from the group consisting of ZnO, boric acid compound, from a silicate compound 1
1 to 20 parts by weight of CrO ₃ , B ₂ O ₃ , and SiO ₂ is used as a kind or two or more kinds. In the case of an insulating film having such a composition, a very beautiful appearance and good film characteristics can be obtained by baking under the following atmosphere conditions.

That is, when a conventional phosphate-colloidal silica-based coating is applied to a glassless surface, there is a problem that the coating peels off and falls off, especially when a thick coating is to be obtained. On the other hand, when baking the liquid of the present invention,
Since the composition can be selected by appropriately controlling the film tension, an insulating film having no peeling problem can be obtained.

Further, as another advantage, the iron loss characteristics in the direction perpendicular to the rolling direction can be improved as compared with the above-mentioned conventional high tensile strength coating. For this reason, when used as an iron core material for a large rotating machine, excellent punching properties and magnetic properties can be obtained at the same time. When applied to thin high magnetic flux density materials, local distortion due to laser, gear, press, etching, etc.,
There is no problem because a low iron loss can be obtained by the magnetic domain refining technique of providing minute recrystallized grains and grooves.

MgO, Al formulated in the insulating coating composition liquid
₂ O ₃ , CaO, ZnO is 15 parts per 100 parts by weight of phosphoric acid.
３５35 parts by weight. If the amount is less than 15 parts by weight, the amount of free phosphoric acid increases and foaming tends to occur during drying. In addition, stickiness due to moisture absorption easily occurs after baking. Furthermore, seizure called sticking tends to occur during the strain relief annealing. On the other hand, if the content exceeds 35 parts by weight, the undissolved oxide deteriorates the appearance of the coating film, occupies the space factor, and deteriorates the adhesion.

The amount of the chromium compound, boric acid compound and silicic acid compound is 1 to 20 parts by weight based on 100 parts by weight of phosphoric acid. These have the effect of densifying the insulating coating and improving the heat resistance.
In addition, it reacts with free phosphoric acid to produce an effect of improving hygroscopicity and heat resistance. As these additives, chromic acid, chromic acid compounds, dichromic acid, dichromic acid compounds, boric acid, borates, silicate substances and the like are used.

If the amount is less than 1 part by weight, such effects as densification, improvement of heat resistance and reduction of free phosphoric acid do not occur. Meanwhile, 2
If the amount is 0 parts by weight or more, stickiness due to its own hygroscopicity increases and the surface appearance deteriorates, so that the amount is limited.

Next, as a condition for baking the insulating coating agent, it is desirable that the amount of the insulating coating agent applied is 2.56 g / m ² as a weight after drying and baking. If it is less than 2.5 m ² , in the case of the composition liquid of the present invention, the composition is liable to be affected by oxidation or nitridation of the surface of the glassless material due to the atmospheric gas during the baking process, so that the composition liquid is limited.

If the amount is more than 6 g / m ^{2, the} space factor may be reduced due to an increase in the thickness of the coating, and powdering may easily occur, which is disadvantageous from the viewpoint of the magnetic surface. Within the range of 2.5 g / m ² , extremely good film properties and magnetic properties can be obtained under the baking conditions of the present invention.

As the heat cycle of the insulating film baking process, when the insulating film agent application-drying-baking process is performed in a continuous line, the temperature on the exit side of the drying furnace is preferably 550 ° C. or more. The liquid of the present invention has a number of advantages in terms of the properties of the insulating coating, but the coating material has a somewhat high vitrification temperature, and therefore, if the outlet temperature of the drying furnace is low, the coating component adheres to the roll in the subsequent baking furnace. This causes scratches on the coating surface, lowering the commercial value and lowering the coating properties.

When the temperature at the outlet side of the drying furnace is 550 ° C. or more, the vitrification of the insulating film proceeds, and the surface of the insulating film changes to a smooth film surface. As the atmosphere gas in the baking furnace, the amount of oxygen in the atmosphere gas was 20%.
It is below 00ppm.

In the baking of the insulating coating of the glassless material of the present invention, as described above, the oxidation of the glassless surface is apt to occur, and this atmospheric condition is the most important. If the atmosphere conditions are not appropriate, not only is the appearance of the insulating film glossy and color abnormal, but also the adhesion, workability and magnetic properties are degraded. As a method of adjusting this atmosphere,
It is controlled by the purity, composition, amount of gas, and gas flow (atmosphere sealing technology) of the atmosphere gas.

When the oxygen content of the atmosphere gas is more than 2000 ppm, in the case of the insulating coating agent of the present invention, the oxidation of the steel sheet cannot be suppressed, resulting in the deterioration of the coating performance and the deterioration of the magnetic properties as described above. In an extreme case, uneven color tone of the coating may occur, and the commercial value may be lost. If it is less than 2000 ppm, these problems can be avoided in most cases. Most preferably, the oxygen content is 500 ppm or less. In this case, a good surface state can be obtained stably.

Next, H ₂ 0.2 to 4%
And a dew point of 25 ° C. or less are more preferred in the present invention. As the atmosphere gas, usually, an N ₂ atmosphere is used.
₂ oxidation of the steel sheet when using an atmospheric gas containing a combination of H ₂ in the range of 0.2 to 10.0% is suppressed, good surface. If it is less than 0.2%, such an oxidation suppressing effect cannot be obtained. On the other hand, at 10.0% or more, there is no significant difference in the effect. In addition, when considering industrial equipment, it is not preferable in terms of safety and cost.

In the present invention, the dew point of the atmospheric gas is preferably 25 ° C. or less. Dew point of the atmosphere gas is oxygen, it is important with components of the atmosphere gas to be formulated as H _2. At 25 ° C. or higher, oxidation of the steel sheet due to the moisture is apt to occur, and the oxidation can be suppressed even by using other important technical elements of the present invention, such as the coating agent component, the amount of adhesion, the heat cycle, the baking atmosphere oxygen amount, and the like. Instead, a new oxide layer mainly composed of SiO ₂ is generated on the glassless surface, resulting in deterioration of insulating film characteristics, magnetic characteristics, and the like.
At 25 ° C. or lower, these problems hardly occur, and a good surface state can be obtained.

[0051]

【Example】

Example 1 C: 0.052% by weight, Si: 3.4% by weight
0%, Mn: 0.12%, acid-soluble Al: 0.030%,
S: 0.0068%, N: 0.0070%, the balance being Fe
And hot rolled a material consisting of unavoidable impurities to 2.0 mm
After annealing at 120 ° C. for 2 minutes, pickling and cold rolling were performed to obtain a final thickness of 0.225 mm. Then, N ₂ 25% + H ₂ 75
%, After decarburizing annealing at 840 ° C. for 120 seconds in an atmosphere with a dew point of 65 ° C., 750 ° C. for 30 seconds N ₂ 25% + H ₂ 75% + N
A nitriding treatment was performed in a dry atmosphere of H ₃ so that the nitrogen amount became 200 ppm.

This steel sheet was treated with MgO10 as an annealing separator.
0 parts by weight, 5 parts by weight of CaCl ₂ and 0.5 parts by weight of MgF ₂
A slurry consisting of parts by weight was applied, dried, and wound around a coil. Next, a finish annealing condition of 1200 ° C. × 20 hours was performed to obtain a coil having a uniform glassless surface.
A sample was cut out from this coil, and after light-washing with 2% H ₂ SO ₄ at 80 ° C. × 10 seconds, an insulating coating agent having a composition shown in Table 1 was dried and baked at a weight of 4 g / m 2.
² was applied. Then, in a continuous annealing furnace, 8
N ₂ 97% × H ₂ as atmosphere gas at 50 ° C. × 30 seconds
A baking treatment was performed at 3% with an oxygen content of 200 ppm. Table 2 shows the properties of the insulating film and the magnetic properties at this time.

[0053]

[Table 1]

[0054]

[Table 2]

As a result of this test, when the coating composition of the present invention was baked, all of the properties, such as the appearance of the coating, adhesion, and seizure after strain relief annealing, were all good.
On the other hand, the comparative example containing less oxide than the present invention as a coating composition had stickiness after baking and more seizure during annealing. In the case of Comparative Example 2 of the high-tension type, the cutability and the adhesion were extremely poor.

Example 2 C: 0.052% by weight
Si: 3.22%, Mn: 0.10%, acid-soluble Al:
A slab consisting of 0.033%, S: 0.0070%, and the balance being Fe and unavoidable impurities is heated to a temperature of 1250 ° C., hot-rolled to a thickness of 3.0 mm, annealed at 1130 ° C., pickled and cooled. This was rolled into a cold-rolled coil having a final thickness of 0.5 mm. Next, decarburizing annealing was performed at 850 ° C. for 250 seconds in an atmosphere of N ₂ 25% + H ₂ 25% dew point of 67 ° C., and MgO 100 was used as an annealing separating agent for the nitrided steel sheet obtained in the same manner as in Example 1. N ₂ 25% + H ₂ 25% by weight
In a dry atmosphere of + NH ₃ , nitriding treatment was performed so that the N amount became 220 ppm, and the starting material was used.

This steel sheet was prepared by adding CaC to 100 parts by weight of MgO.
An annealing separator mixed with 15 parts by weight of l ₂ was applied and 1200
A finish annealing of 20 ° C. × 20 hours was performed. The steel sheet was subjected to light pickling at 85 ° C. × 15 seconds with 1% H ₂ SO ₄ in a continuous line, and then 100 parts by weight of phosphoric acid and Mg
15 parts by weight of O, 8 parts by weight of Al ₂ O ₃ , Al5 dichromate
As shown in Table 3, the solution of the present invention consisting of 2 parts by weight of boric acid and 2 parts by weight of boric acid was subjected to baking treatment by changing the weight after drying and baking and the temperature at the exit side of the drying furnace. Table 4 shows the results of the insulating film characteristics and the magnetic characteristics in this test.

[0058]

[Table 3]

[0059]

[Table 4]

As a result of this test, the amount of the insulating film of the present invention was 2.5 to 5.5 g / m ² , and the temperature on the exit side of the drying furnace was 600 to 7
In the case of 00 ° C., good film properties and magnetic properties were obtained in each case. In particular, the amount of the insulating coating is 4.5 to 5.5 g / m ^2.
In the case of (1), the surface appearance, punching properties, magnetic properties, etc. were good. On the other hand, in Comparative Example 1 in which the coating amount was small, red discoloration occurred during baking, and the coating characteristics and magnetic characteristics were poor.
When the temperature on the exit side of the drying oven was low, bumps-like surface flaws were generated in the baking oven, and the film appearance and magnetism were also inferior to those of the present invention.

Example 3 A sample was cut out from the steel sheet after the finish annealing obtained in Example 2 and washed with light acid in the same manner. As an insulating coating agent, 100 parts by weight of phosphoric acid, 22 parts by weight of MgO, and ₃ parts by weight of CrO _{3 were used.} , A baking treatment of an insulating coating agent consisting of 5 parts by weight of HBO ₂ . At this time, the temperature on the exit side of the drying furnace was kept constant at 650 ° C., and the baking treatment was performed by changing the conditions of the atmosphere gas as shown in Table 5. Table 6 shows the results of the film properties and magnetic properties at this time.

[0062]

[Table 5]

[0063]

[Table 6]

As a result of this test, good film characteristics and magnetic characteristics were obtained in all cases where the oxygen content in the atmosphere gas of the present invention was 1000 ppm or less. In particular, the amount of oxygen is 300ppm
In the following cases, oxidation of the glassless material surface does not occur at all,
The appearance, punching properties, adhesion, and magnetic properties were extremely good. On the other hand, in the comparative example having an oxygen content of 5000 ppm, the surface of the glassless material was significantly oxidized at the time of baking, and the film properties and the magnetic properties were considerably inferior to those of the present invention.

[0065]

According to the present invention, in the production of a glassless grain-oriented electrical steel sheet, oxidation of the steel sheet during baking of an insulating film is suppressed, and a product having excellent appearance, workability, and magnetic properties can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a cutting test method.

FIGS. 2A and 2B are explanatory diagrams of a method for evaluating the bakeability of a coating film in strain relief annealing.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kizu Ishibashi 1-1, Tobata-cho, Tobata-ku, Kitakyushu Nippon Steel Corporation Inside Yawata Works (72) Inventor, Kimihiko Sugiyama 1st, Tobita-cho, Tobata-ku, Kitakyushu No. 1 Inside Nippon Steel Corporation Yawata Works (72) Inventor Osamu Tanaka 46-59 Nakahara, Tobata-ku, Kitakyushu Nippon Steel Plant Design Co., Ltd. (56) References JP-A-4-337033 (JP, A) JP-A-6-73555 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 9/46 501 H01F 1/16

Claims (5)

(57) [Claims] 1. A weight ratio of C: 0.021 to 0.075%, Si: 2.5 to 4.5%, acid-soluble Al: 0.010 to 0.040%, N: 0.0030 to 0.0130%, S ≦ 0.0140%, Mn: 0.05 to 0.45% The remainder is hot-rolled on an electromagnetic steel slab consisting of Fe and unavoidable impurities, and cooled once or twice or more after annealing. The steel sheet which has been rolled to the final thickness is subjected to decarburizing annealing and nitriding treatment, a slurry composed of MgO and a halogen compound is applied as an annealing separator, finish annealing is performed, an insulating coating agent is applied, and drying and baking are performed. In the method for producing a grain-oriented electrical steel sheet having no glass coating, which comprises performing heat flattening with a phosphoric acid, 100 parts by weight of phosphoric acid is used as an insulating coating agent.
O, Al ₂ O _3, CaO, one or more 15-35 parts by weight and the chromium compound selected from the group consisting of ZnO, boric acid compound, 1-20 parts by blending one or more of the silicate compound A method for producing a grain-oriented electrical steel sheet having no glass coating with excellent surface properties, comprising applying the prepared aqueous solution, drying and baking at 800 to 900 ° C. with the oxygen content in the atmosphere gas at 2000 ppm or less. 2. A glass coating having excellent surface properties according to claim 1, wherein the temperature of the steel sheet on the exit side of the drying furnace is 550 ° C. or more as a drying condition in the drying and baking step of the insulating coating. Manufacturing method of grain-oriented electrical steel sheet. 3. The surface texture according to claim 1, wherein the atmosphere in the baking furnace is an atmosphere in which H ₂ is mixed in a range of 0.2 to 4% with respect to N ₂ with respect to N _2. Method of producing grain-oriented electrical steel sheet without glass coating with excellent quality. 4. The dew point of the atmospheric gas in the baking furnace is 25.
The method for producing a grain-oriented electrical steel sheet having no glass coating having excellent surface properties according to claim 1, 2 or 3, wherein the temperature is set to not more than ℃. 5. A method according to claim 1, 2, 3 or wherein the coating amount of the insulating coating agent in the range of weight after drying and baking process of 2.5g / m ² ~6.0g / m ² 4. A method for producing a grain-oriented electrical steel sheet having no glass coating having excellent surface properties according to 4.