JP5040131B2 - Manufacturing method of unidirectional electrical steel sheet - Google Patents

Description

  The present invention relates to a method capable of producing a unidirectional electrical steel sheet having excellent magnetic properties and coating properties at a low cost.

  The grain-oriented electrical steel sheet is mainly used as an iron core material for transformers and other electric devices, and is required to have excellent magnetic properties such as magnetic flux density and iron loss value. As a general manufacturing method, a slab having a thickness of 100 to 300 mm is heated to a high temperature of about 1350 ° C. or more, hot-rolled, and then subjected to hot-rolled sheet annealing as necessary, or once or A complex process in which the final sheet thickness is obtained by cold rolling at least twice with intermediate annealing, and after decarburization annealing, an annealing separator is applied, followed by final finishing annealing for the purpose of secondary recrystallization and purification. The crystal grains of {110} <001> orientation are grown by secondary recrystallization during final finish annealing.

  In order to effectively develop such secondary recrystallization, it is necessary to first disperse a precipitated dispersed phase called an inhibitor that suppresses the growth of primary recrystallized grains to a uniform and appropriate size. . As such an inhibitor, those having low solubility in steel such as sulfides, Se compounds and nitrides represented by MnS, MnSe, AlN and BN are used, and slab heating before hot rolling is used. At times, a method in which the inhibitor is completely dissolved and finely precipitated in the subsequent steps is employed. In this case, in order to sufficiently dissolve the inhibitor, it is necessary to perform slab heating at a temperature of about 1350 to 1400 ° C., which is about 200 ° C. higher than the slab heating temperature of ordinary steel.

High temperature slab heating as described above has the following drawbacks.
(A) The energy intensity is high for high temperature heating.
(B) Melt scale is likely to occur and slab sag is likely to occur, so that surface defects of the product are likely to occur.
(C) Overdecarburization of the slab surface layer is likely to occur.

  In order to solve the problems (b) and (c), an induction heating furnace is employed, but the problem of an increase in energy cost remains. Therefore, many studies have been made to reduce the slab heating temperature in order to save energy and reduce costs.

  For example, Patent Document 1 discloses a technique for lowering the slab heating by setting Mn to 0.08 to 0.45% and S to 0.007% or less, and Patent Document 2 discloses adding Cr to this. A technique for stabilizing secondary recrystallization is disclosed. All of these are characterized in that the amount of S is reduced to achieve solid solution of MnS during slab heating. However, these techniques have a problem that magnetic characteristics are likely to vary in the coil width direction and the longitudinal direction, and are limited to manufacturing means on a laboratory scale. The cause is destabilization of secondary recrystallization due to insufficient function of an inhibitor that substitutes for MnS. In other words, the above-mentioned technique contains 0.010 to 0.060% acid-soluble Al and 0.0030 to 0.0130% N, and uses AlN as an inhibitor. The magnetic properties were not stabilized due to the lack of inhibitory inhibition or partial fluctuations in inhibition.

  As means for making up for such drawbacks, Patent Document 3 discloses a technique for stabilizing secondary recrystallization by promoting nitrogen absorption during secondary recrystallization annealing. A similar technique for nitriding during secondary recrystallization annealing by adding nitride in the annealing separator and stabilizing secondary recrystallization is also disclosed in Patent Document 4. However, the technique of nitriding during secondary recrystallization annealing still cannot sufficiently stabilize the expression of secondary recrystallization due to differences in the amount of nitriding in the longitudinal and width directions of the coil. .

  In order to solve the above-mentioned problem, after decarburization annealing and before secondary recrystallization annealing, a technique for nitriding the steel sheet to stabilize secondary recrystallization is disclosed in Patent Document 5, Patent Document 6, and Patent Document. 7. However, the method of performing the nitriding treatment before the secondary recrystallization annealing has a problem of requiring new equipment and increasing the cost.

  On the other hand, various attempts have been made to produce grain-oriented electrical steel sheets without using inhibitors that have been considered essential so far. For example, Patent Literature 8, Patent Literature 9, Patent Literature 10, and Patent Literature 11 disclose techniques that utilize tertiary recrystallization. However, since these are all methods that utilize a surface energy difference, Limited to thin thickness. Therefore, the thickness of the grain-oriented electrical steel sheet currently used as a product is almost 0.20 mm or more, and it is difficult to manufacture a normal product by the above method.

However, in recent years, as an important point in the development of secondary recrystallization, in addition to the presence of an inhibitor, the orientation difference angle between adjacent crystal grains in the primary recrystallization structure has attracted attention. That is, it is reported in Non-Patent Document 1 that a grain boundary (high energy grain boundary) having an azimuth difference angle of 20 to 45 ° plays an important role, and based on this, a directional electromagnetic without using an inhibitor is reported. Steel plate research has been actively conducted again.
For example, Patent Document 12 discloses a technique (inhibitorless method) capable of industrially producing a grain-oriented electrical steel sheet without including an inhibitor component in a steel slab.

In order to improve and stabilize the properties of grain-oriented electrical steel sheets produced by this inhibitorless method, the following techniques have been proposed.
That is, in Patent Document 13, the N and S contents are suppressed in accordance with [ppmN] ² + [ppmS] ² ≦ 6400, and the rate of temperature increase from 600 ° C. to 750 ° C. for decarburization annealing is 15 ° C./s. The atmospheric oxidation (P [H ₂ O] / P [H ₂ ]), which is the ratio of the partial pressure of water vapor to the partial pressure of hydrogen in the soaking process of decarburization annealing, is controlled in the range of 0.6 or less. Technology has been proposed.
Patent Document 14 uses an annealing separator containing 0.1 to 9.0 parts by weight of Ti oxide with respect to 100 parts by weight of MgO, and the final finish annealing is a temperature range of 900 ° C. or higher and 1050 ° C. or lower. Including the step of holding for 5 hours to 15 hours in an atmosphere with an inert gas content of 50 vol% or more, and retaining in the temperature range of 950 ° C. or higher in this step for 2 hours or more and 10 hours or less Technology has been proposed.
Further, in Patent Document 15, the crystal grain size in the steel sheet after the primary recrystallization annealing is in the range of 8 to 25 μm, and the average heating rate of 800 to 900 ° C. in the temperature raising process of the secondary recrystallization annealing is 0.5 to 5. A technique has been proposed which is characterized in that the difference in the amount of nitrogen in the steel sheet between 900 ° C. and 800 ° C. is in the range of −10 ppm to +25 ppm in the temperature increase process of secondary recrystallization annealing in the range of ° C./h. .

JP 59-56522 JP 59-190325 A JP 62-70521 A Japanese Patent Laid-Open No. 62-40315 JP-A-2-200732 JP-A-4-183817 JP-A-4-235222 JP-A-64-55339 JP-A-2-57635 Japanese Unexamined Patent Publication No. 7-76732 Japanese Unexamined Patent Publication No. 7-197126 JP 2000-129356 JP Japanese Patent Laid-Open No. 2001-158919 Japanese Patent Laid-Open No. 2004-190053 JP 2004-218024 A Act Material 45 (1997) 1285

  However, when compared to grain-oriented electrical steel sheets manufactured using conventional inhibitors, there are still inferior magnetic properties and stability of the coating properties, especially when the steel sheet is wound into a coil and subjected to final finish annealing. Due to the fact that the magnetic properties and film properties may deteriorate in the width direction or longitudinal direction of the strip, it is still necessary to stably produce products with excellent quality and further improve the yield. It left room for improvement.

  The present invention has been developed in view of the above-described situation, and has a uniform forsterite insulating coating having no defects over the entire width and length of the coil and having excellent adhesion, and has excellent magnetic properties. It aims at proposing the method which can manufacture a steel plate at low cost.

The elucidation process of the present invention will be described below.
The inventors first tried to improve and stabilize the magnetic characteristics and film characteristics based on the techniques of Patent Documents 14 and 15 already proposed. Unless otherwise specified, “%” in relation to ingredients means mass%.

  First, regarding the material components, the upper limit of acid-soluble Al and N was required to be less than 100 ppm and less than 60 ppm, respectively, as in the above technology, but for acid-soluble Al, a trace amount of 40 ppm or more should be included. Therefore, the oxide film formed on the steel sheet surface during decarburization annealing becomes dense, the increase and decrease in nitrogen during secondary recrystallization annealing is suppressed, and the accumulation of secondary recrystallized grains in the Goss orientation improves, and the magnetic It has been found that the properties are improved. Therefore, the component range of acid-soluble Al is set to 40 ppm or more and less than 100 ppm. Further, N was found to be contained in an amount of 30 ppm or more in order to suppress the increase or decrease in nitrogen during secondary recrystallization annealing, so the component range was set to 30 ppm or more and less than 60 ppm. Furthermore, in order to produce a grain-oriented electrical steel sheet by the inhibitorless method, the upper limit of (S + 0.405Se) needs to be less than 50 ppm. This is because, when the total amount of these is 50 ppm or more, secondary recrystallization becomes difficult and the magnetic properties deteriorate.

Furthermore, Sb very effectively suppresses the increase in the amount of steel sheet nitrogen during secondary recrystallization annealing, so it is an indispensable element for obtaining excellent magnetic properties and stabilizing magnetic properties. In order to exert the effect sufficiently, it is necessary to add 0.035% or more. However, if it exceeds 0.30%, decarburization during decarburization annealing becomes very bad and unsuitable for industrial mass production, so the component range must be 0.035% or more and 0.30% or less. .
However, Sb, on the other hand, is very effective in reducing the oxidation rate of the steel sheet during decarburization annealing, so increasing the amount of Sb is thought to result from a decrease in the amount of oxide in the decarburized annealing plate subscale. Increased product coating defects.

Thus, as a result of intensive studies on means for suppressing the coating defects, it has been newly found that increasing the Mn content in steel according to the Sb content is effective for suppressing the defects.
That is, when Sb: 0.035% or more and 0.30% or less and Mn: {0.04 + Sb (%)}% or more and 0.50% or less, it is found that a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties can be produced stably. It was. Since the upper limit of the Mn amount is 0.30%, the upper limit of the Mn amount should be at least the lower limit (0.34%) in that case, and addition of a certain amount or more is a cost. This is not only disadvantageous in terms of surface, but also causes a decrease in magnetic flux density.

  Secondly, regarding the composition of the annealing separator, as disclosed in Patent Document 14, even in the inhibitorless component system, it is effective to improve the film properties by adding a Ti compound to magnesia. Therefore, as a result of examining the proper blending amount of the Ti compound in the component system of the present invention, as a result of applying an annealing separator containing 0.3 to 8 parts by mass of the Ti compound in terms of Ti with respect to 100 parts by mass of magnesia. Has been found to be effective in improving coating properties.

  Thirdly, the secondary recrystallization annealing pattern is disclosed in Patent Document 15 as “the average temperature increase rate from 800 ° C. to 900 ° C. in the temperature increase process of secondary recrystallization annealing is 0.5 to 5 ° C./h. As a result of examining the temperature increase pattern of secondary recrystallization annealing in the component system of the present invention based on the technology of `` to be in the range of It was found that this is effective in improving the magnetic properties.

In addition to this, the inventors have further studied the influence of the powder characteristics of magnesia, which is the main component of the annealing separator in the inhibitorless component system, on the film characteristics and magnetic characteristics of the forsterite insulating film.
This is because many proposals have been made to improve the film properties and magnetic properties by controlling the powder properties of magnesia, but most of them are MnS, MnSe, AlN, etc. This is because those using an inhibitor component and those that form an inhibitor such as (Al, Si) N by nitriding after decarburization annealing, and in the inhibitorless component system, there has been little research on these.

  As a result, especially as the powder characteristics of magnesia, the concentration of Cl, which is an impurity, and the CAA 40% value are important. After limiting these to a predetermined range, the amount of hydrated water of magnesia after coating and drying is predetermined. It was found that it is extremely effective to control within the above range.

In addition, the inventors also examined additives other than the Ti compound to be blended in the annealing separator. In addition to the Ti compound, 0.2 to 5 parts by mass of the Sr compound in terms of Sr with respect to 100 parts by mass of magnesia. It has been found that blending is effective in further improving magnetic properties and film properties.
That is, as long as the steel sheet is wound into a coil shape and subjected to final finish annealing, there is a certain difference in annealing conditions such as heat history and atmosphere in the inner, middle, and outer winding portions of the coil. However, in order to suppress the difference in magnetic properties and film properties due to the difference as much as possible and further improve the properties, it is effective to control the additive in the annealing separator as described above. It turns out.

The present invention has been completed based on the above knowledge, and the gist of the present invention is as follows.
(1) By mass%, C: 0.01 to 0.10%, Si: 2.5 to 4.5%, acid-soluble Al: 40 ppm or more and less than 100 ppm, N: 30 ppm or more and less than 60 ppm, Sb: 0.035 to 0.30%, Mn: {0.04 + Sb ( %)}% Or more and 0.50% or less and (S + 0.405Se): Hot rolling after heating a silicon steel slab containing less than 50 ppm and the balance of Fe and inevitable impurities at a temperature of 1250 ° C or less Then, after performing hot-rolled sheet annealing as necessary, perform cold rolling one or more times with intermediate annealing, followed by decarburization and primary recrystallization annealing, and then an annealing separator mainly composed of magnesia In manufacturing a unidirectional electrical steel sheet by a series of steps of applying final finishing annealing consisting of secondary recrystallization annealing and purification annealing after applying it in a slurry form with water and applying it to the steel sheet surface,
a) As magnesia, which is the main component of the annealing separator, select a powder whose powder characteristics are the concentration of impurities Cl: 0.01-0.05%, CAA 40% value: 40-90 seconds. slurried to coating, the annealing separating agent is hydrated such that the water of hydration content of magnesia after drying is below 1.0 mass% or more 3.0 mass%, applied to the surface of the primary recrystallization plate and dried ,
b) In the annealing separator, magnesia: 100 parts by mass , one or more selected from TiO ₂ , TiO ₃ .H ₂ O, TiO. (OH) ₂ and Ti (OH) ₄ Containing 0.3-8 parts by mass of Ti compound in terms of Ti,
c) A method for producing a unidirectional electrical steel sheet, wherein a residence time of 800 ° C. or more and 900 ° C. or less is set to 40 hours or more and 150 hours or less in a temperature raising process of secondary recrystallization annealing.

In (2) above (1), further in the annealing separator, magnesia respect to 100 parts by weight, selected from among the _{SrSO 4, Sr (OH) 2} · 8H 2 O, SrCO 3 and Sr (NO) ₃ A method for producing a unidirectional electrical steel sheet, comprising adding 0.2 to 5 parts by mass of one or more Sr compounds in terms of Sr.

(3) In the above (1) or (2), the silicon steel slab is further mass%, Sn: 0.03-0.50%, Cu: 0.03-0.50%, Ni: 0.03-0.50%, Cr: 0.03-0.30 %, P: 0.01 to 0.10%, and Mo: 0.005 to 0.10%, one or more selected from the above, and a method for producing a unidirectional electrical steel sheet.

  According to the present invention, a grain-oriented electrical steel sheet excellent in magnetic properties and coating properties is obtained by low-temperature slab heating using a material in which an inhibitor component is not contained in a steel slab, that is, Al, S, Se or the like is an impurity level. It can be manufactured at low cost.

Hereinafter, the experimental results that led to the present invention will be described.
Now, the inventors have worked on the development of means capable of stably producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties by using Sb in an inhibitorless component system. As a result, the present invention has been completed. This knowledge has been obtained after various experiments and examinations at the laboratory level described below.

Hereinafter, the experimental results that led to the present invention will be described.
(Experiment 1)
C: 0.02 to 0.06%, Si: 3.0 to 3.5%, acid-soluble Al: 40 ppm to less than 100 ppm, N: 30 ppm to less than 60 ppm, Sb: 0.01 to 0.30%, Mn: 0.05% to 0.50%, (S + 0.405Se ): Less than 50 ppm, Cu: 0.01 to 0.50%, Cr: 0.01 to 0.30%, P: 0.002 to 0.10% of the component range, with the balance being a large number of vacuum steel ingots with a composition of Fe and inevitable impurities, 1200 After heating to ° C., hot rolling was performed, and hot-rolled sheet annealing was performed at a temperature of 950 to 1100 ° C., followed by cold rolling to a final thickness of 0.29 mm. Then, after decarburization and primary recrystallization annealing at a temperature of 800 to 900 ° C. in H ₂ —H ₂ O—N ₂ , magnesia is the main component, and magnesia: 0.1 to 20.0 mass relative to 100 mass parts Secondary recrystallization annealing with a residence time of 800 ° C or more and 900 ° C or less of 10 hours or more and 200 hours or less in the temperature rising process of secondary recrystallization annealing after applying an annealing separator containing a part of TiO ₂ And a final finish annealing consisting of purification annealing. Thereafter, the sample was washed with water to remove the unreacted annealing separator, and after the appearance of the coating film of the sample was examined, a coating containing magnesium phosphate, colloidal silica and chromic acid as main components was applied.
The magnetic properties (magnetic flux density B ₈ , iron loss W _17/50 ) and film adhesion of the samples thus obtained were investigated. The coating adhesion was evaluated by the minimum diameter at which the coating was not peeled off by winding a test piece around a round bar having various diameters at intervals of 5 mm as the bending adhesion of the coating.

First, among the many samples, the components satisfying Mn of 0.08 to 0.14% and Sb of 0.04 to 0.06%, the results of examining the effect of the amount of TiO ₂ added in the annealing separator on the film adhesion are shown in the figure. It is shown in 1.
As shown in the figure, although there are some exceptions, magnesia: When 0.3 to 8 parts by mass of TiO ₂ in terms of Ti is added to 100 parts by mass, relatively good film adhesion is obtained. I understand that.

Similarly, it is a component that satisfies Mn: 0.08-0.14% and Sb: 0.04-0.06%. During the temperature increase process of secondary recrystallization annealing, the residence time in the temperature range of 800 ° C or higher and 900 ° C or lower becomes the magnetic property. The result of investigating the effect is shown in FIG.
As shown in the figure, although there are some exceptions, it can be seen that relatively excellent magnetic properties are obtained when the residence time between 800 ° C. and 900 ° C. is between 40 hours and 150 hours.

Based on the above analysis results, magnesia: 0.3 to 8 parts by mass of TiO ₂ in terms of Ti is added to 100 parts by mass, and the residence time is 800 ° C. or more and 900 ° C. or less in the temperature raising process of secondary recrystallization annealing. The effect of the amount of Mn and Sb in the material on the magnetic properties and coating properties was investigated under the conditions of 40 hours to 150 hours. The obtained results are shown in FIGS. 3 (a) and 3 (b).
According to the figure, when Sb is 0.035% or more and Mn: {0.04 + Sb (%)}% or more, it is understood that a grain-oriented electrical steel sheet excellent in both magnetic properties and film properties can be obtained.

  In addition, as a technique for improving the film properties by increasing the amount of Mn in steel, there is a technique disclosed in Patent Document 3 and the like. However, according to examples, these contain 0.02 to 0.03% of acid-soluble Al as an inhibitor. A material using AlN, a material containing 0.02 to 0.03% of acid-soluble Al was subjected to nitriding after decarburization annealing, or nitrogen absorption was promoted during secondary recrystallization to use AlN as an inhibitor. The purpose of increasing the amount of Mn was to improve the tension and adhesion of the forsterite film by forming an appropriate amount of MnO by high-temperature oxidation on the steel sheet surface layer during finish annealing.

However, unlike the above technique, the inhibitor-less component system of the present invention contains less than 100 ppm of acid-soluble Al in the raw material component. The film formation process when the acid-soluble Al content is about 0.02% or more is described in “Journal of Materials Engineering and performance Vol.3 (1994) p. 214” (“Glass Film Structure of Grain-Oriented Silicon Steel Using Aluminum Nitride as an Inhibitor ”)” And “Materials and Processes CAMP-ISIJ, Vol.6 (1993) -676 (Structural Analysis of Finished Annealed Coating of Oriented Silicon Steel Sheet)”, there is little or little acid-soluble Al. Different from the case. Therefore, it can be estimated that the influence of the amount of Mn in steel is different between the case where the acid-soluble Al content is 0.02 to 0.03% and the case where it is not.
That is, the above-described findings are novel findings obtained particularly in relation to the amount of Sb under an inhibitorless component system different from the material component of the grain-oriented electrical steel sheet using the conventional inhibitor.

Furthermore, in the inhibitorless component system, the reason why the coating properties are improved when the amount of Mn in steel is increased in accordance with the amount of Sb is also different from the mechanism of the prior art described above. That is, as described above, Sb is very effective in reducing the oxidation rate of the steel sheet during decarburization annealing. Therefore, when the amount of Sb increases, as shown in FIG. And the defects of the product coating presumed to be increased.
On the other hand, when the amount of Mn in the steel is increased, as shown in FIG. 5, the amount of oxide generated during the decarburization annealing increases, so that the reduction in the subscale amount due to the increase in the Sb amount can be compensated.

In addition, as sub-scale oxides, the amount of firelite and silica produced increases as Mn increases. Especially in the component system in which the amount of (S + 0.405Se) is less than 50 ppm, when the amount of Mn is increased, (Fe, An increase in the amount of firelite generated represented by the chemical formula of Mn) ₂ SiO ₄ also contributes to the improvement of the coating. That is, in the secondary recrystallization annealing in which the residence time of the temperature rising process of 800 ° C. or more and 900 ° C. or less, which is one of the constituent elements of the present invention, is 40 hours or more and 150 hours or less, in the temperature range of 800 ° C. or more and 900 ° C. or less. The main reaction of film formation is not the reaction of the following formula (1) in which magnesia and silica react directly to form forsterite, but a part of Fe or Mn in the firelite is substituted with Mg (2) Since the reaction is an olivine formation reaction (olivine formation reaction), it is considered that the formation of a film is more likely to proceed when a certain amount of firelite is present in the decarburized annealed plate subscale, and the final film characteristics are improved.
Further, when the Mn ratio is increased in (Fe, Mn) ₂ SiO ₄ , the substitution of Mg is more likely to proceed in the olivine formation reaction, that is, the olivine formation reaction is likely to proceed, and the amount of Mn in the steel is increased. This is considered to be one of the reasons why the film properties are improved. In addition, when the amount of Sb is increased while keeping the amount of Mn constant, the olivine formation reaction becomes slower. Therefore, the reason why the coating properties deteriorate when the Sb content is increased is thought to be due to the fact that the oxide content of the decarburized annealing plate subscale decreases and the olivine formation reaction slows down during the secondary recrystallization annealing process. However, the fact that both can be improved at the same time by increasing the Mn content is considered to be a reason why the increase in Mn can compensate for the deterioration of the coating properties due to the increase in Sb.
2MgO + SiO ₂ → Mg ₂ SiO ₄ --- (1)
(Fe, Mn) ₂ SiO ₄ + MgO → (Fe, Mn) _2-X Mg _X SiO ₄ + [Mg _1-X , (Fe, Mn) _X ] O --- (2)

Fig. 6 shows that after applying an annealing separator mainly composed of magnesia to a decarburized annealing plate with different raw material components, holding the sample at 850 ° C for 50 hours, and then extracting the sample surface by Fourier transform infrared absorption spectroscopy (FT- (IR).
(a) Compared to the sample with Mn: 0.09% + Sb: 0.04%, the sample at (b) Mn: 0.09% + Sb: 0.06% stopped at the low wavenumber side at about 1030cm ^-1 in (a). It can be seen that olivine formation is slow, but in the sample of (c) Mn: 0.12% + Sb: 0.06%, olivine formation progresses more than (b), and it is understood that (a) is equal to or higher.

In JP-A-6-184638, the Fe and Mn content in the oxide film component {(Fe, Mn) O} a · {SiO ₂ } b generated in the decarburization annealing step is (FeO + MnO) / oxide film. It has a total SiO ₂ as 0.10 to 0.50, and the total SiO ₂ is in the oxide film by decarburization annealing as a 0.6~1.7g / m ^2, a uniform glass film in excellent direction of the magnetic properties Although the technology for producing a tempered electrical steel sheet is disclosed, the purpose of this technique is good in the method of producing a directional electrical steel sheet in which a nitriding treatment is performed after decarburization annealing to form an (Al, Si) N-based inhibitor. Therefore, the technical contents are different from those of the present invention which is intended to produce a grain-oriented electrical steel sheet having excellent magnetic characteristics and film characteristics in an inhibitorless component system.

(Experiment 2)
Based on the result of Experiment 1, the amount of material Mn and Sb was tested in the component system with Sb: 0.035% or more and Mn: {0.04 + Sb (%)}% or more respectively. In some cases, the film properties were greatly deteriorated. Further, the coating characteristics are remarkably deteriorated in a large coil, and the appearance of the coating may be poor particularly at the center of the coil.
As for the deterioration of the coating properties accompanying the increase in the size of the coil, refer to Japanese Patent Application Laid-Open No. 11-158558 and Japanese Patent Application Laid-Open No. 11-181525, “When the coil becomes larger, the atmosphere between the coil layers at the center of the coil becomes excessive. It becomes higher, and the tendency to generate film defects and deterioration of magnetic properties becomes stronger. ” And the coil interlayer atmosphere at the time of final finish annealing changes depending on the partial pressure of H ₂ O generated from the hydrated water of MgO in the annealing separator and the H ₂ partial pressure of the inlet atmosphere, and the atmosphere is highly oxidizing It is shown that the film formation reaction is suppressed and the film deterioration is likely to occur.
In order to improve the coating deterioration as described above, Japanese Patent Application Laid-Open No. 11-158558 and Japanese Patent Application Laid-Open No. 11-181525 describe the MgO production method and powder characteristics (CAA 40%, CAA 80%, specific surface area, Ig .loss etc.) has been proposed. Further, Japanese Patent No. 3707144 proposes a technique for setting the hydrated water content of MgO after being applied to and dried on a steel sheet to 1.0 mass% or more and 3.9 mass% or less with respect to MgO.

Thus, magnesia, the main component of the annealing separator that is one of the raw materials for forsterite film formation, is known to have a significant effect on the film formation reaction. Has been studied.
However, most of them relate to those that use inhibitors such as MnS, MnSe, and AlN, and those that apply to manufacturing methods that form inhibitors such as (Al, Si) N by nitriding after decarburization annealing. In the loess component system, little research has been done on magnesia.
Therefore, a study was conducted on magnesia suitable for manufacturing inhibitorless component-based electrical steel sheets.

That is, it contains C: 0.043%, Si: 3.34%, acid-soluble Al: 63ppm, N: 39ppm, Sb: 0.047%, Mn: 0.105% and (S + 0.405Se): 13ppm, the balance from Fe and inevitable impurities A plurality of directional slabs for directional silicon steel sheets were heated to 1200 ° C. and hot rolled to form hot rolled sheets having a thickness of 2.4 mm. Next, after hot-rolled sheet annealing at 1050 ° C. for 30 seconds, the final cold-rolled sheet thickness was set to 0.29 mm by cold rolling, and these cold-rolled sheets were degreased to clean the surface, and then H ₂ -H ₂ Decarburization annealing was performed in a 0-N ₂ atmosphere.
In this way, 10 coils (sheet width: 1200 mm, mass of each coil: 15 tons) of steel plates after decarburization annealing were prepared, and the annealing separator mainly composed of 10 types of magnesia shown in Table 1 was used as the steel sheet surface. After being applied to and wound up, it was subjected to a final finish annealing consisting of secondary recrystallization annealing and purification annealing in which the residence time of 800 ° C. or more and 900 ° C. or less was 60 hours in the temperature raising process of secondary recrystallization annealing. .
In the annealing separator, 4 parts by mass of TiO ₂ was blended with 100 parts by mass of magnesia. Further, the amount of hydrated water of magnesia was controlled to be within a certain range shown in Table 1 by changing the hydration temperature and hydration time of the slurry.

Then, after washing with water and removing the unreacted annealing separator, a coating containing magnesium phosphate, colloidal silica and chromic acid as main components was applied.
The magnetic properties (magnetic flux density B ₈ , iron loss W _17/50 ), coating appearance and coating adhesion at the center of each product coil thus obtained were investigated. The coating adhesion was evaluated by the minimum diameter at which the coating was not peeled off by winding a test piece around a round bar having various diameters at intervals of 5 mm as the bending adhesion of the coating.
The obtained results are summarized in Table 1.

As shown in the table, the concentration of Cl, which is an impurity in magnesia, is 0.01 to 0.05%, the CAA 40% value is 40 to 90 seconds, and the amount of hydrated water is 1.0 mass% or more and 3.0 mass%% or less. When manufactured, a product excellent in magnetic characteristics and film characteristics could be obtained.
CAA 40% is citric acid: 28.0 g, sodium benzoate anhydrous: 0.25 g, 1% phenolphthalein alcohol solution: 2.0 ml of pure water dissolved in 1000 ml, and 100 ml in a 200 ml beaker. , Raise the temperature to 30 ± 0.5 ℃, put the rotor of the magnet of plastic outer with diameter: 8mm, length: 35mm, set it in the mug mixer with thermostat adjusted to the temperature of 30 ± 0.5 ℃, The electrode is put into a citric acid solution, and 2.0 g of MgO is put into the solution, and after 10 seconds, the rotor is rotated at 900 rpm to stir the solution. It measured by the method of measuring the time to become.

As described above, the reason why good product characteristics can be obtained at the center of the coil, especially when the hydrated water content of magnesia is 1.0% or more and 3.0% or less, is considered as follows.
As described above, application of this component system increases the amount of firelite expressed by the chemical formula (Fe, Mn) ₂ SiO ₄ as an oxide in the subscale. It contributes to. And, in the secondary recrystallization annealing in which the residence time of 800 ° C. or more and 900 ° C. or less, which is one of the requirements of the present invention, is 40 hours or more and 150 hours or less, in the temperature range of 800 ° C. or more and 900 ° C. or less. The main reaction for film formation is not a reaction in which magnesia and silica react directly to form forsterite, but a reaction in which part of Fe or Mn in firelite is replaced with Mg (olivine formation reaction). It is considered that when a certain amount of firelite is present in the annealed plate subscale, the film formation proceeds more easily, and the final film characteristics are improved. Further, when the Mn ratio is increased in (Fe, Mn) ₂ SiO ₄ , the substitution of Mg is more likely to proceed in the olivine formation reaction, that is, the olivine formation reaction is more likely to proceed. This is considered to be one of the reasons for improving the film properties.

However, in order to favorably advance the above-described olivine formation reaction and subsequent forsterite formation reaction with magnesia and silica, it results from the hydration water of magnesia applied to the steel sheet surface after decarburization annealing. It is necessary to sufficiently suppress the surface oxidation reaction (mainly iron oxidation). In other words, since the annealing separator mainly composed of magnesia is applied to the steel sheet as a slurry suspended in water, it retains physically adsorbed H ₂ O after drying and partly hydrates. To Mg (OH) ₂ . Therefore, a small amount of H ₂ O continues to be released up to about 800 ° C. during the secondary recrystallization annealing. This H ₂ O oxidizes the steel sheet surface during secondary recrystallization annealing. If this oxidation reaction proceeds excessively, it may cause the occurrence of point defects in which the ground iron is partially exposed. As described above, this phenomenon becomes significant at the coil central portion where the flowability between the coil layers is poor.
On the other hand, in the inhibitorless component system of the present invention, the surface of the steel sheet is more easily oxidized than when using conventional inhibitors such as MnS, MnSe, AlN, etc. It is considered that it is necessary to sufficiently suppress the oxidation of the steel sheet surface layer until the temperature immediately before the olivine formation reaction occurs in order to form a uniform and good film at the coil central portion.

(Experiment 3)
C: 0.036%, Si: 3.25%, Acid-soluble Al: 75ppm, N: 45ppm, Sb: 0.053%, Mn: 0.11%, (S + 0.405Se): 21ppm, Cu: 0.08% and Cr: 0.05%, The balance was a hot rolled sheet having a thickness of 2.2 mm by hot rolling a plurality of grain-oriented silicon steel sheet slabs composed of Fe and inevitable impurities, after heating to 1250 ° C. Next, after hot-rolled sheet annealing at 1025 ° C. for 60 seconds, the final cold-rolled sheet thickness was 0.29 mm by cold rolling. Subsequently, these cold-rolled sheets were degreased to clean the surface, and then decarburized and annealed in an H ₂ —H ₂ O—N ₂ atmosphere.
In this way, 8 coils of steel plate after decarburization annealing (plate width: 1200 mm, mass of each coil: 15 tons), impurity Cl content: 0.03%, CAA 40% value: 70 seconds of magnesia, By changing the hydration temperature and the hydration time, the amount of hydrated water is changed as shown in Table 2, applied to the surface of the steel sheet, wound up, and then heated in the secondary recrystallization annealing process. The sample was subjected to final finish annealing consisting of secondary recrystallization annealing and purification annealing with a residence time of 80 ° C to 900 ° C. In the annealing separator, 2 parts by mass of TiO ₂ was blended with 100 parts by mass of magnesia.

Then, after washing with water and removing the unreacted annealing separator, a coating containing magnesium phosphate, colloidal silica and chromic acid as main components was applied.
The magnetic properties (magnetic flux density B ₈ , iron loss W _17/50 ), coating appearance and coating adhesion at the center of each product coil thus obtained were investigated. The coating adhesion was evaluated by the minimum diameter at which the coating was not peeled off by winding a test piece around a round bar having various diameters at intervals of 5 mm as the bending adhesion of the coating.
The obtained results are summarized in Table 2.

  As can be seen from the table, when the hydrated water content is 1.0 mass% or more and 3.0 mass% or less, a product excellent in magnetic properties and film properties is obtained.

(Experiment 4)
C: 0.047%, Si: 3.42%, acid-soluble Al: 55ppm, N: 36ppm, Sb: 0.04%, Mn: 0.10%, (S + 0.405Se): 27ppm, Cu: 0.12%, Cr: 0.04% and P: A plurality of grain-oriented silicon steel sheet slabs containing 0.012% and the balance consisting of Fe and inevitable impurities were heated to 1150 ° C. and hot rolled to form a hot rolled sheet having a thickness of 2.0 mm. Subsequently, after hot-rolled sheet annealing was performed at 1050 ° C. for 45 seconds, the final cold-rolled sheet thickness was 0.285 mm by cold rolling. At this time, the final cold rolling was performed so that the steel plate temperature immediately after the rolling roll exit side was 150 to 250 ° C. for at least one pass. Subsequently, these cold-rolled sheets were degreased to clean the surface, and then decarburized and annealed in an H ₂ —H ₂ O—N ₂ atmosphere.
Then, magnesia is the main component, magnesia: 100 to 10 parts by mass of 0 to 10 parts by mass of TiO _{2 in} terms of Ti and 0 to 8 parts by mass of SrSO ₄ or Sr (OH) ₂ · 8H ₂ O in terms of Sr After the applied annealing separator, it is used for the final finish annealing consisting of secondary recrystallization annealing and purification annealing with a residence time of 800 ° C or more and 900 ° C or less of 70 hours in the temperature increase process of secondary recrystallization annealing. did. For magnesia, the amount of impurities Cl: 0.02%, CAA 40% value: 80 seconds so that the water hydration amount is 2.0-2.5mass% by controlling the hydration temperature and hydration time of the slurry. Applied.

Then, after washing with water and removing the unreacted annealing separator, a coating containing magnesium phosphate, colloidal silica and chromic acid as main components was applied.
The magnetic properties (magnetic flux density B ₈ , iron loss W _17/50 ), coating appearance and coating adhesion at the center of each product coil thus obtained were investigated. The coating adhesion was evaluated by the minimum diameter at which the coating was not peeled off by winding a test piece around a round bar having various diameters at intervals of 5 mm as the bending adhesion of the coating.
The obtained results are shown in FIG. 7 with the horizontal axis representing magnesia: TiO ₂ content relative to 100 parts by mass (Ti conversion) and the vertical axis representing Sr compound content relative to 100 parts by mass magnesia (Sr conversion).

From the figure, it can be seen that excellent product characteristics are obtained when 0.3 to 8 parts by mass of TiO ₂ in terms of Ti is mixed with 100 parts by mass of magnesia. Among these, it can be seen that particularly excellent product characteristics are obtained when 0.2 to 5 parts by mass of Sr compound in terms of Sr is used in combination with 100 parts by mass of magnesia.

Next, the reason why the component composition is limited to the above range in the electrical steel sheet of the present invention will be described.
C: 0.01-0.10%
C is an element necessary for improving the primary recrystallization structure. However, if the content is less than 0.01%, a good primary recrystallization structure cannot be obtained. On the other hand, if it exceeds 0.10%, decarburization annealing is not possible. Since the decarburization load increases and the productivity decreases, the C amount is limited to 0.01 to 0.10%.

Si: 2.5-4.5%
Si is an element useful for increasing the electrical resistance of steel and reducing eddy current loss, and in the present invention, it is necessary to contain 2.5% or more. However, if it exceeds 4.5%, cold rolling becomes extremely difficult, so the Si content is limited to 2.5-4.5%.

Acid-soluble Al: 40 ppm or more and less than 100 ppm In order to produce a grain-oriented electrical steel sheet by producing secondary recrystallization by an inhibitorless method, the impurity element Al needs to be less than 100 ppm. However, a small amount of acid-soluble Al of 40 ppm or more densifies the oxide film formed on the steel sheet surface during decarburization annealing, suppresses the increase and decrease of nitrogen during secondary recrystallization annealing, and reduces the gossip of secondary recrystallized grains. Since it is effective for improving the accumulation in the orientation and improving the magnetic properties, in the present invention, the acid-soluble Al is contained in the range of 40 ppm or more and less than 100 ppm.

N: 30 ppm or more and less than 60 ppm Similarly, in order to produce a grain-oriented electrical steel sheet by causing secondary recrystallization by an inhibitorless method, N as an impurity element needs to be less than 60 ppm. However, in order to suppress the increase and decrease of nitrogen during the secondary recrystallization annealing, it is better to contain 30 ppm or more. Therefore, in the present invention, N is contained in the range of 30 ppm or more and less than 60 ppm.

Sb: 0.035-0.30%
Sb very effectively suppresses the increase in the amount of steel sheet nitrogen during secondary recrystallization annealing, so it is an indispensable element for obtaining excellent magnetic properties and stabilizing magnetic properties. It is necessary to add 0.035% or more in order to fully exhibit. However, if the content exceeds 0.30%, the decarburization property at the time of decarburization annealing becomes very poor and unsuitable for industrial mass production, so the Sb content is limited to 0.035 to 0.30%.

Mn: {0.04 + Sb (%)}% or more and 0.50% or less The problem with producing grain-oriented electrical steel sheets with excellent magnetic properties and coating properties using Sb in an inhibitorless component system is the amount of Sb added. It is in the deterioration of the film properties when increased. In order to solve this problem, it is effective to increase the amount of Mn according to the amount of Sb, so the lower limit of the amount of Mn was set to {0.04 + Sb (%)}%. Since the upper limit of the Sb amount is 0.30%, the upper limit of the Mn amount should be at least the lower limit (0.34%) in that case, and addition of a certain amount or more is disadvantageous in terms of cost. Not only that, but also caused a decrease in magnetic flux density, so 0.50%.

(S + 0.405Se): less than 50 ppm Impurity elements S and Se are made less than 50 ppm with (S + 0.405Se) in order to produce a grain-oriented electrical steel sheet by producing secondary recrystallization by an inhibitorless method. There is a need. This is because when the amount of (S + 0.405Se) is 50 ppm or more, secondary recrystallization becomes difficult and the magnetic properties are deteriorated.

The basic components have been described above. In the present invention, the following elements can be appropriately contained for the purpose of improving magnetic properties and film properties.
Sn: 0.03-0.50%
Sn is an element that improves and stabilizes magnetic properties. However, if the content is less than 0.03%, the effect of addition is poor. On the other hand, if it exceeds 0.50%, a good primary recrystallized structure cannot be obtained. , Sn content is preferably in the range of 0.03-0.50%.

Cu: 0.03-0.50%
Cu is an element having an action of suppressing deterioration of magnetic properties by suppressing oxynitriding of the steel sheet surface layer. However, if the content is less than 0.03%, the effect of addition is poor. On the other hand, if it exceeds 0.50%, defects called “baldness” tend to occur on the surface, so the Cu content is in the range of 0.03 to 0.50%. Is preferred.

Ni: 0.03-0.50%
Ni is an element having an effect of improving the texture and improving the magnetic flux density. However, if the content is less than 0.03%, the effect of addition is poor. On the other hand, even if added over 0.50%, not only the effect is poor, but also the rollability may be deteriorated. It is preferable to be in the range of ~ 0.50%.

Cr: 0.03-0.30%
Cr is an element effective for improving the film properties, but if it is less than 0.03%, a remarkable improvement effect cannot be obtained. On the other hand, if it exceeds 0.30%, the magnetic properties tend to deteriorate, so the Cr content is 0.03 to 0.30. % Is preferable.

P: 0.01-0.10%
P has a function of improving the magnetic flux density by improving the texture after cold rolling and recrystallization by grain boundary segregation. However, if the content is less than 0.01%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 0.10%, a good primary recrystallized structure cannot be obtained. Therefore, the P content is preferably in the range of 0.01 to 0.10%.

Mo: 0.005-0.10%
Mo has the effect of improving the surface properties. However, if the content is less than 0.005%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 0.10%, the decarburization property during decarburization annealing deteriorates, so the Mo amount is preferably in the range of 0.005 to 0.10%. .

Next, preferred production conditions for the grain-oriented electrical steel sheet according to the present invention will be described.
The molten steel adjusted to the above components is cast by a continuous steel casting method or an ingot-making method by a steel making method conventionally used, and a slab is produced with a lump process interposed as necessary. Further, a thin cast piece having a thickness of 100 mm or less may be directly produced using a direct casting method.

  Next, the slab is heated according to a normal method, and then hot rolled to form a hot rolled coil. The slab heating temperature at this time is preferably 1250 ° C. or lower in order to reduce energy costs. This is because high-temperature slab heating exceeding 1250 ° C. is meaningless in the present invention by the inhibitorless method and only increases the cost.

After the above-described hot rolling, hot-rolled sheet annealing is performed as necessary, and then a cold-rolled sheet having a final thickness is obtained by one or more cold rolling or two or more cold rollings sandwiching intermediate annealing.
Note that the cold rolling may be performed at room temperature, or may be warm rolling in which rolling is performed at a temperature higher than room temperature, for example, about 150 to 300 ° C. Moreover, you may perform the aging treatment in the range of 150-300 degreeC in the middle of cold rolling once or several times.

Next, decarburization and primary recrystallization annealing are performed on the final cold rolled sheet in a wet hydrogen atmosphere. It is desirable to reduce the residual C amount to 0.004% or less by this decarburization annealing.
Thereafter, an annealing separator mainly composed of magnesia is applied to the surface of the steel plate subjected to the decarburization annealing in a slurry form with water and then dried. Here, in order to obtain good film properties, as the magnesia powder properties, a powder having an impurity Cl concentration of 0.01 to 0.05% and a CAA 40% value of 40 to 90 seconds is selected. It is important to use an annealing separator that has been hydrated so that the hydrated water content of magnesia after it has been applied and dried in slurry form is 1.0 mass% or more and 3.0 mass% or less. Here, the amount of hydrated water needs to be controlled by the hydration temperature and average hydration time of the slurry.

  That is, in the production line, the annealing separator slurry is used by applying a certain amount and consuming it, and then adding a new amount almost commensurate with the consumption amount and adding it to the remaining slurry. Therefore, although the hydration temperature can be controlled to be constant, it is difficult to make the hydration time constant, and it is difficult to make the amount of hydrated water constant over the entire length of the coil. This is because the hydrated water content of magnesia increases as the hydration temperature increases or the hydration time increases (the increase in the hydrated water content is due to the progress of hydration. This is caused by partly becoming magnesium hydroxide). However, by controlling the hydration temperature and the average hydration time, it is possible to make the hydration amount within a certain range, for example, 2.3 ± 0.2%.

  Note that magnesia having an impurity Cl concentration of 0.01 to 0.05% and a CAA 40% value of 40 to 90 seconds is selected, and the hydrated water content of magnesia after applying and drying the powder into a slurry is 1.0. % To 3.0% or less, set the hydration temperature of the slurry to 5 to 22 ° C., and take into account the slurry consumption such as the line feed speed of the steel sheet and the annealing separator and coating amount. It is desirable that the hydration time be in the range of 20 to 90 minutes. The Cl concentration of impurities is more preferably 0.025 to 0.04%.

Moreover, in order to obtain a favorable film characteristic, it is necessary to apply | coat the annealing separator which mix | blended 0.3-8 mass parts Ti compound in Ti conversion with respect to magnesia: 100 mass parts. Here, as the Ti compound , one or more selected from TiO ₂ , TiO ₃ .H ₂ O, TiO. (OH) ₂ , and Ti (OH) ₄ can be used. Further, combining and combining 0.2 to 5 parts by mass of Sr compound in terms of Sr with respect to 100 parts by mass of magnesia is effective in further improving and stabilizing the magnetic characteristics and film characteristics. As such an Sr compound , one or more selected from SrSO ₄ , Sr (OH) ₂ .8H ₂ O, SrCO ₃ , and Sr (NO) ₃ can be used.

In addition, for the purpose of further improving the uniformity of the film properties, in the annealing separator, oxides such as CaO, sulfides such as MgSO ₄ .7H ₂ O and SnSO ₄ , Na ₂ B ₄ O ₇ 1 type or 2 types or more selected from B-type compounds such as Sb ₂ O ₃ and Sb ₂ (SO ₄ ) ₃ alone or in combination, and magnesia: 100 parts by mass It can also be added at 5 parts by mass or less.
In the present invention, “mainly magnesia” means that the annealing separator containing each compound as described above contains at least 80 mass% of magnesia.

Further, the annealing separator is preferably applied in a range of about 4 to 10 g / m ² per one side of the steel sheet. This is because if the coating amount is less than 4 g / m ^2, the formation of forsterite becomes insufficient. On the other hand, if it exceeds 10 g / m ² , the forsterite film is excessively formed and becomes thick. Because it invites.

After that, final finish annealing consisting of secondary recrystallization annealing and purification annealing is performed. Here, secondary recrystallization annealing is performed at a temperature rising process of 800 ° C to 900 ° C with a residence time of 40 hours to 150 hours. It is necessary to.
This is because, if the residence time at 800 ° C. or more and 900 ° C. or less is out of the above range, the magnetic characteristics are deteriorated as shown in FIG.

Thereafter, a phosphate-based insulating coating, preferably an insulating coating that imparts tension, is applied to the steel sheet surface to obtain a product. The type of insulating coating is not particularly limited, but any conventionally known insulating coating is suitable. For example, a coating solution containing phosphate-chromic acid-colloidal silica described in JP-A-50-79442 and JP-A-48-39338 is applied to a steel plate and baked at about 800 ° C. The method is preferred.
Furthermore, performing a known magnetic domain refinement treatment after the final cold rolling, after the final finish annealing, or after forming the insulating coating is effective in further reducing iron loss.

  A steel slab having the component composition shown in Table 3 was heated to 1180 ° C. with a gas heating furnace, and then hot rolled into a hot rolled sheet having a sheet thickness of 2.3 mm. Then, after hot-rolled sheet annealing at 1025 ° C. for 45 seconds, the final sheet thickness was 0.29 mm by cold rolling. Next, after decarburization and primary recrystallization annealing, an annealing separator mainly composed of magnesia was applied, and then final finish annealing including secondary recrystallization annealing and purification annealing was performed. Table 4 shows the powder characteristics of magnesia, the blending ratio of the annealing separator and the secondary recrystallization annealing conditions (retention time of 800 ° C. or more and 900 ° C. or less). Thereafter, an insulating coating mainly composed of magnesium phosphate, chromic acid and colloidal silica was applied.

Table 4 shows the results of examining the magnetic flux density (B ₈ ), iron loss (W _17/50 ), coating appearance, and coating adhesion at the coil center for each product thus obtained.
The coating adhesion was evaluated by the minimum diameter at which the coating was not peeled off by winding a test piece around a round bar having various diameters at intervals of 5 mm as the bending adhesion of the coating.

  As is apparent from Table 4, all of the inventive examples manufactured under the conditions according to the present invention have good magnetic properties and coating properties.

  A steel slab having the components shown in Table 5 was heated to 1200 ° C. in a gas heating furnace, and then hot rolled into a hot rolled sheet having a thickness of 2.5 mm. Thereafter, hot-rolled sheet annealing was performed at 1050 ° C. for 45 seconds, and then the final sheet thickness was 0.285 mm by cold rolling. At this time, in the final cold rolling, at least one pass was performed such that the steel plate temperature immediately after the drawing roll exit side was 150 to 250 ° C. Next, after performing primary recrystallization and decarburization annealing, an annealing separator mainly composed of magnesia was applied, and final finishing annealing consisting of secondary recrystallization annealing and purification annealing was performed. Table 6 shows the powder characteristics of magnesia, the blending ratio of the annealing separator and the secondary recrystallization annealing conditions (retention time of 800 ° C. or more and 900 ° C. or less). Thereafter, an insulating coating mainly composed of magnesium phosphate, chromic acid and colloidal silica was applied.

Table 6 shows the results of examining the magnetic flux density (B ₈ ), iron loss (W _17/50 ), coating appearance and coating adhesion of each product obtained in this way.
The coating adhesion was evaluated by the minimum diameter at which the coating was not peeled off by winding a test piece around a round bar having various diameters at intervals of 5 mm as the bending adhesion of the coating.

  As is apparent from Table 6, all the conforming examples manufactured under the conditions according to the present invention show good magnetic properties and coating properties.

  A steel slab having the components shown in Table 7 was heated to 1200 ° C. in a gas heating furnace, and then hot rolled into a hot rolled sheet having a thickness of 2.7 mm. Subsequently, the sheet thickness was 1.6 mm by cold rolling, followed by intermediate annealing at 1025 ° C. for 60 seconds, and then by cold rolling to a final sheet thickness of 0.22 mm. At this time, the final cold rolling was performed such that at least one pass, the steel plate temperature immediately after the rolling roll exit side was 150 to 250 ° C. Next, after performing primary recrystallization and decarburization annealing, an annealing separator mainly composed of magnesia was applied, and final finishing annealing consisting of secondary recrystallization annealing and purification annealing was performed. Table 8 shows the powder characteristics of magnesia, the blending ratio of the annealing separator and the secondary recrystallization annealing conditions (retention time of 800 ° C. or more and 900 ° C. or less). After that, an insulating coating composed mainly of magnesium phosphate, chromic acid and colloidal silica was applied.

Table 8 shows the results of examining the magnetic flux density (B ₈ ), iron loss (W _17/50 ), coating appearance, and coating adhesion of each product thus obtained.
The coating adhesion was evaluated by the minimum diameter at which the coating was not peeled off by winding a test piece around a round bar having various diameters at intervals of 5 mm as the bending adhesion of the coating.

  As is apparent from Table 8, all the conforming examples manufactured under the conditions according to the present invention show good magnetic properties and coating properties.

It is a figure which shows the influence which the amount of Ti compound addition in an annealing separation agent has on film adhesion. It is a figure which shows the influence which the residence time of 800 to 900 degreeC has on a magnetic characteristic in the temperature rising process of secondary recrystallization annealing. It is a figure which shows the influence which the amount of Mn and Sb in a raw material has on a magnetic characteristic and a film characteristic. It is a figure which shows the influence which the raw material Sb amount has on the oxygen basis weight (per one side) of a decarburized annealing board subscale. It is a figure which shows the influence which the raw material Mn amount has on the oxygen areal weight (per one side) of a decarburized annealing board subscale. It is a figure which shows the FT-IR measurement result of the steel plate surface after annealing for 50 hours at 850 degreeC during secondary recrystallization annealing. It is a figure which shows the influence which the addition amount of Ti compound and Sr compound in an annealing separation agent has on a product characteristic.

Claims (3)

In mass%, C: 0.01-0.10%, Si: 2.5-4.5%, acid-soluble Al: 40ppm or more, less than 100ppm, N: 30ppm or more, less than 60ppm, Sb: 0.035-0.30%, Mn: {0.04 + Sb (%)} % Or more and 0.50% or less and (S + 0.405Se): less than 50ppm, the balance is Fe and unavoidable impurities, silicon steel slab is heated at a temperature of 1250 ℃ or less, then hot-rolled and necessary Depending on the hot-rolled sheet annealing, after one or two or more cold rolling sandwiched between the intermediate annealing, then decarburization and primary recrystallization annealing, the annealing separator mainly composed of magnesia with water In producing a unidirectional electrical steel sheet by applying a final finishing annealing consisting of secondary recrystallization annealing and purification annealing after applying it to the steel sheet surface in a slurry state,
a) As magnesia, which is the main component of the annealing separator, select a powder whose powder characteristics are the concentration of impurities Cl: 0.01-0.05%, CAA 40% value: 40-90 seconds. slurried to coating, the annealing separating agent is hydrated such that the water of hydration content of magnesia after drying is below 1.0 mass% or more 3.0 mass%, applied to the surface of the primary recrystallization plate and dried ,
b) In the annealing separator, magnesia: 100 parts by mass , one or more selected from TiO ₂ , TiO ₃ .H ₂ O, TiO. (OH) ₂ and Ti (OH) ₄ Containing 0.3-8 parts by mass of Ti compound in terms of Ti,
c) A method for producing a unidirectional electrical steel sheet, wherein a residence time of 800 ° C. or more and 900 ° C. or less is set to 40 hours or more and 150 hours or less in a temperature raising process of secondary recrystallization annealing. According to claim 1, further in the annealing separating agent, magnesia respect to 100 parts by _{weight, SrSO 4, Sr (OH)} 2 · 8H 2 O, one or two chosen from among SrCO ₃ and Sr (NO) ₃ The manufacturing method of the unidirectional electrical steel sheet characterized by including 0.2-5 mass parts of Sr compounds of a seed | species or more in conversion of Sr.   3. The silicon steel slab according to claim 1, wherein the silicon steel slab is further mass%, Sn: 0.03-0.50%, Cu: 0.03-0.50%, Ni: 0.03-0.50%, Cr: 0.03-0.30%, P: 0.01- A method for producing a unidirectional electrical steel sheet, comprising one or more selected from 0.10% and Mo: 0.005 to 0.10%.

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