JPS633007B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention applies to the surface of a high magnetic flux density unidirectional silicon steel plate.
The present invention relates to a method of forming an MgO-SiO ₂ -based insulating film. (Prior art) The MgO-SiO ₂ insulating film mainly composed of forsterite on the surface of the unidirectional silicon steel sheet not only improves the appearance of the product, but also provides the necessary interlayer resistance between the steel sheets. It also plays an important role in terms of magnetic properties, reducing product iron loss due to the tensile stress that acts between them. This forsterite film is usually produced by the following method. First, a material for unidirectional silicon steel containing about 3 to 4% by weight of silicon is cold rolled once or twice or more with intermediate annealing to the final thickness, and then heated at 700 to 900°C in wet hydrogen. Decarburization annealing is performed within the range of 100 to 100 ml, and at the same time an oxide film containing SiO ₂ is formed on the surface of the steel sheet. Next, a slurry-like annealing separation material containing MgO as the main component is applied to the surface of the steel sheet, then wound into a coil and subjected to final annealing. The MgO-SiO ₂ solid phase reaction that occurs during this process is used to form forsterite. (Mg ₂ SiO ₄ ) is formed. However, the properties of the forsterite film produced at this time depend on the properties of the decarboxylated film, the type of magnesia, the amount and properties of trace additives to the magnesia powder, or the atmosphere during final annealing, and are affected by mechanical and Many studies have been conducted on methods for forming forsterite films with excellent magnetic properties. For example, Japanese Patent Publication No. 51-12451 reports that a forsterite film with excellent adhesion and uniformity can be obtained by adding TiO ₂ to magnesia powder. Also, JP-A-54-
In Publication No. 66935, in order to obtain a forsterite film with good adhesion consisting of forsterite particles with a small average particle size, magnesia powder is
Appropriate management of CaO and water content is disclosed. Further, JP-A-55-58331 discloses a method for obtaining a good forsterite film by limiting the activity of magnesia used. What these methods have in common is that they all propose improvements to annealed separators whose main component is magnesia, and although many of them are recognized to be effective, from an industrial perspective, they lead to high costs. In many cases, process control is difficult.
Furthermore, the more fundamental problem is that the steel plate surface
When forming a forsterite film by MgO-SiO ₂ solid-phase reaction, there is a limit to the improvement in the properties of the resulting forsterite film even if only the annealing separation material, that is, the MgO side is unilaterally specified. That's what it means. For example, the steel plate tension of the forsterite film obtained by this method is very high.
It is ^about 400g/mm2, and in the actual process
As disclosed in Japanese Patent No. 28375, it is necessary to further improve the tension of the steel plate by applying a secondary coating mainly composed of colloidal silica or the like on the forsterite film. On the other hand, methods for regulating the atmosphere during finish annealing include the inert neutral gas introduction method for iron and iron oxides disclosed in JP-A-50-116998 and JP-A-55-110726; There is a dew point control method as found in Japanese Unexamined Patent Publication No. 53-5800. These methods were mainly proposed to solve the problems of the forsterite film forming method in the method of manufacturing unidirectional silicon steel sheets with high magnetic flux density, as disclosed in Japanese Patent Application Laid-Open No. 49-61019. That is, in the method disclosed in JP-A No. 49-61019, it is necessary to heat at a constant temperature of 800 to 920°C for 10 to 100 hours during final annealing, but during the final annealing, the oxidation in the oxide scale It was discovered that applying a reducing atmosphere to iron causes significant defects in the forsterite film, and therefore it was necessary to make the atmosphere neutral or inert (Japanese Patent Application Laid-Open No. 116998/1983). , No. 55-110726). In addition, after constant temperature maintenance between 800 and 920℃, 1150~
By using hydrogen gas as the atmosphere when the temperature is raised to 1250℃, keeping the dew point at that time in the range of -20 to +20℃, and then keeping the average dew point below +10℃,
A method for reducing the average grain size of forsterite to 0.7 μm or less was disclosed in JP-A-53-5800. The former proposal is based on the suitability of the steel plate during the MgO− _SiO2 reaction.
The _latter proposal attempts to control the generation of forsterite grains at the start of the reaction and subsequent grain growth by controlling the oxygen partial pressure of the atmosphere. All of these methods are based on the premise of final annealing, which is characterized by constant temperature maintenance at a constant temperature between 800 and 920°C, as shown in Japanese Patent Application Laid-Open No. 49-61019. This method cannot necessarily be said to be general to other finish annealing cycles. Further, even if the average crystal grain size of the forsterite film obtained is 0.7 μm or less, the bending adhesion of the film is about 10 mm at the minimum peeling radius, and it cannot be said that sufficient adhesion is necessarily ensured. Furthermore, in such a method, the tension applied to the steel sheet by the coating is insufficient, and a secondary coating mainly composed of colloidal silica is often required, leading to an increase in manufacturing costs. (Objective of the Invention) The purpose of the present invention is to eliminate and improve the various drawbacks of the conventional forsterite film production method, and to provide a method for producing a forsterite film that has high adhesion and tension on steel sheets, and has extremely excellent magnetic properties. Our goal is to provide the following. According to the present invention, since the nucleus of forsterite is formed as MnO in the oxidized scale on the surface of the steel sheet, the forsterite structure digs into the inside of the steel sheet, resulting in extremely good adhesion, and as a result, high tension is applied to the steel sheet. Therefore, the magnetic properties can be improved. (Structure of the Invention) The present invention will be described in detail below. The characteristics of the forsterite film obtained by the present invention are that the tension is 500 g/mm ² or more, the average forsterite particle size is 0.5 μm or less, and the minimum peeling radius is 3 mm.
It is to have adhesion equivalent to . Figure 2 shows the improvement in iron loss due to such a forsterite film in comparison with conventional materials. As shown in the figure _, the improvement in iron loss due to the forsterite film obtained in the present invention is approximately
0.2W/Kg, which is compared to conventional technology.
It is also larger than 0.1W/Kg. The present inventors believe that in order to obtain such a forsterite film,
The Mn activity is sufficiently increased, and during final annealing, Mn
We have newly discovered that it is important to provide a constant oxygen partial pressure depending on the activity, and for this purpose, S +
0.405Se≦0.010 and 0.8≧Mn≧0.05+7 (S+
0.405Se), and the appropriate oxygen partial pressure in the temperature range of 850 to 1100℃ during final annealing is Mn-1.719 (S
+0.405Se), and specifically, it was concluded that it is necessary to secure it in the diagonally shaded area in Figure 1 (the area surrounded by ABCDE in the figure). Further, the present invention will be explained in detail. The forsterite film on the surface of grain-oriented silicon steel is composed of an oxide scale mainly composed of SiO ₂ formed during decarburization annealing, and an annealing separation material mainly composed of MgO applied afterward, which undergoes a solid phase reaction during finish annealing. It is generated by causing . The present inventors investigated the shape and crystal grain size of this forstellite film by direct observation using a scanning electron microscope (hereinafter referred to as scanning electron microscope) and indirect observation using a transmission electron microscope using a two-stage replica method. It was newly discovered that the average grain size of tellite depends on the amount of free Mn in the steel (the amount of Mn that is not fixed as MnS or MnSe) and the atmosphere at 850℃ to 1100℃ during final annealing, especially the oxygen partial pressure. . Furthermore, they found that there is a clear relationship between the amount of free Mn and the surface tension of the forsterite film, and found that in order to form a forsterite film that has an extremely excellent effect of improving magnetic properties, it is necessary to It was confirmed that it was necessary to limit the amounts of Mn, S, and Se and the final annealing atmosphere. Figure 3 shows that magnesia containing 5% TiO ₂ was applied to the decarburized annealed surface of 3.3% Si steel with different amounts of Mn and S in an atmosphere of P _H2O /P _H2 = 4 × 10 ^-3 . This figure shows the relationship between the surface tension of the forsterite film and the amount of Mn in the steel (total amount of Mn) when finish annealing is performed. It has been experimentally confirmed that a surface tension of 550 g/mm ² or more can be obtained by increasing the amount of Mn in the steel. Furthermore, as shown in the figure, it has become clear that the tension increasing effect of Mn becomes even more pronounced as the amount of S in the steel decreases. This indicates that the amount of Mn in the steel, especially the amount of free Mn other than those trapped in the form of MnS and MnSe, and more precisely the Mn activity, are important in determining the properties of forsterite. be. This experiment revealed that the amount of Mn is important, but although a certain tendency was observed regarding the relationship between the amount of Mn and trap elements such as S or Se, a quantitative determination could not be made. As a result of observing the forsterite film using a scanning electron microscope and a two-stage replica, it was found that the forsterite particle size changes depending on the conditions. Generally, the forsterite grain size has a very large effect on glass tension, but the mechanism by which glass tension is produced on the steel plate is thought to be as follows. While the steel plate tends to shrink during the cooling process of final annealing, the forsterite crystals, which have a small amount of shrinkage, act as resistance to the shrinkage of the steel plate, and as a result, give tension to the steel plate. This resistance increases when the forsterite structure has high high-temperature strength, that is, when the forsterite crystal grain size is small, and a strong tension is applied to the steel sheet. As a result of experiments, it was found that if the forsterite crystal grain size is 0.5 μm or less, a steel plate tension of 500 g/mm ² or more can be applied. However, it is an essential condition that the glass does not peel off under such conditions, and this condition can be satisfied in the present invention because the adhesiveness is extremely good as described above. FIG. 4 shows scanning electron microscope images and two-stage replica photographs of forsterite coatings on steel sheets with different amounts of Mn and S (the amounts of Mn and S correspond to FIGS. 5 a to d). The magnesia powder used at this time contained 5% TiO ₂ , and the oxygen partial pressure during final annealing was P _H2O /P _H2 =4×10 ⁻³ . In this way, the appearance and grain size of the forsterite film are
It became clear that it strongly depends on the amount of Mn and S. FIG. 5 collectively shows the results of a wide range of such analyzes conducted for other Mn and S contents. As shown in the figure, in order to make the forsterite crystal grain size 0.5μm or less, Mn≧
It is necessary that it is 0.05+7S (Mn, s: weight %). Next, to investigate the effect of the atmosphere during finish annealing,
Finish annealing was performed by changing the atmospheric oxygen partial pressure to various values based on the amount of free Mn in the steel, and the properties of the resulting forsterite films were investigated. As an example, Fig. 6 shows a material with Mn = 0.2wt% and S = 0.005wt%.
Between 850 and 1100℃, (a) P _H2O /P _H2 = 2.5×10 ^-4 , (b)
A two-stage replica photograph of the forsterite film annealed at P _H2O /P _H2 =1.5×10 ^-2 is shown. Also,
Table 1 shows the characteristics of the forsterite film obtained in this example.

【table】

[Table] The final annealing atmosphere is P _H2O /P _H2 1.5×
It was found that by making the material weakly oxidizing at 10 ^-2 , the forsterite crystal grain size became smaller and the film tension improved. From the above experimental results, it is clear that the combination of the Mn activity in the steel and the final annealing atmosphere is important in order to form a forsterite film with a grain size of 0.5 μm or less and high tension and adhesion. Summer. The present inventors considered and examined these results as follows, and determined the limited range of elements such as Mn, S, and Se necessary to obtain a good forsterite film and the corresponding finish annealing atmosphere (especially oxygen (partial pressure). In order to promote the MgO-SiO ₂ system solid-phase reaction, it was reported in Japanese Patent Publication No. 1973-1 that it is useful to add trace amounts of additives such as TiO ₂ and MnO to magnesia powder.
It is publicly known from Publication No. 12450 and the like. These TiO ₂ ,
The reason why MnO etc. have a catalytic effect in the progress of solid-state reactions is not necessarily clear, but one reason is that the melting point of substances that contribute to the MgO-SiO ₂ reaction decreases in the vicinity of TiO ₂ and MnO. It is conceivable that the diffusion rate of molecules such as ⁺⁺ increases, and as a result, forstellite is likely to be generated in the vicinity of TiO ₂ and MnO, that is, a condition for a type of heterogeneous nucleation is satisfied. If the melting point decreases significantly, the final annealing temperature range (900℃~1200℃)
A liquid phase such as MgO−SiO ₂ −TiO ₂ −MnO system is generated,
It is presumed that this has a significant effect on the sintering of forsterite. Until now, the known technology of adding various small amounts of additives to MgO powder has been to generate forsterite nuclei on the outside of the steel sheet, that is, on the MgO side of the MgO-SiO ₂ solid phase reaction interface, and to improve the film properties. There was naturally a limit to the degree of contribution. However, according to the present invention, by selecting the Mn activity in the steel and the final annealing atmosphere, it is possible to form MnO in the SiO ₂ scale through high-temperature oxidation, thereby producing forsterite nuclei on the side of the steel sheet, and thereby making it possible to generate forsterite nuclei on the side of the steel sheet. Tension of tellite film,
It can be understood that it has become possible to significantly improve properties such as adhesion. The conditions for such MnO formation can be determined by the Mn activity in the steel and the oxygen partial pressure during final annealing. That is, Mn + H ₂ O = MnO + H ₂ , ΔG ... (1) ΔG = ΔG゜ + RTlnξ ^-1 ... (2) (Here, ξ = a _Mo・P _H2O /P _H2 (a _Mo is Mn activity) and ΔG゜ is the standard formation free energy change of reaction (1). (R is the gas constant, T is the absolute temperature)) In order for reaction (1) to proceed to the left, it is necessary that ΔG < 0. Therefore, as is clear from equation (2), it is necessary to maintain the oxygen partial pressure P _H2O /P _H2 at a certain value or higher relative to the Mn activity. Figure 1 shows the lowest temperature at which forsterite formation can begin.
The amount of free Mn in such a region at 850℃ is
Illustrated for Mn-1.719 (S+0.405Se). In the figure, points corresponding to the atmosphere at the time of film formation corresponding to the replica photographs shown in FIGS. 6a and 6b are also shown.
It has thus been found that the differences in the properties of the forsterite films shown in FIG. 6 and Table 1 can be rationally explained by the presence or absence of MnO formation. Based on the above experimental results and considerations, the present inventors have arrived at the minimum value of the required oxygen partial pressure during finish annealing as shown in FIG. By the way, in order to ensure sufficient Mn activity in steel, it is necessary to reduce elements such as S and Se that trap Mn in the form of precipitates such as MnS and MnSe. This is contrary to conventional knowledge in terms of the stability of secondary recrystallization. For example, in Japanese Patent Publications No. 30-3651 and No. 47-25250, MnS
The use of is essential for stabilizing secondary recrystallization. In addition, S
The necessity of this was applied as shown in Japanese Patent Publication No. 15644/1973. However, the inventors have S+
It was separately discovered that it is possible to perform secondary recrystallization with sufficient stability even in the range of 0.405Se≦0.010. That is, acid-soluble Al and N are desirable as the main inhibitor components, but other inhibitor components such as TiN,
If secondary recrystallization can be performed using NbC, NbN, etc., these may be used. By combining this AlN-based inhibitor and finish annealing, it is possible to secure a magnetic flux density of B ₈ =1.9 (T) or higher, as shown in the examples of the present invention. Next, the reasons for limiting the constituent elements of the present invention will be described. If the S+Se content exceeds 0.010wt% in terms of S content, it takes a meaninglessly large amount of Mn to obtain the necessary Mn activity.
It becomes necessary to add it at the time of tapping, which is not economical.
(Here, Se has the same effect as S in the sense that it traps Mn. Therefore, in order to secure the necessary Mn activity, the amount of Se must also be regulated. The S equivalent of Se is its Atomic weight from 0.405Se
(Se: weight%), so for S+0.405Se
The amount of Mn was regulated. ) Furthermore, S and Se during purification annealing
MgS, MnS,
Since S and Se are mixed in the form of MnSe and impair the adhesion and uniformity of the film, the amount of S and Se needs to be 0.010wt% or less in terms of S amount, that is, S+0.405Se≦0.010 (wt%). More preferably S+0.405Se≦
By setting the amount to 0.007 (wt%), the film tension is stabilized and the adhesion and uniformity are improved, as shown in Figure 3. As is clear from the results in Figure 5, in order to obtain the necessary Mn activity, Mn must be ≥0.05+7 (S+0.405Se) relative to the amount of S and Se in the steel. The upper limit of the Mn content is determined not from the properties of the film but from the stability of secondary recrystallization of grain-oriented silicon steel. That is, as shown in FIG. 7, as the amount of Mn increases, the degree of directional integration of secondary recrystallized grains deteriorates, making it difficult to ensure magnetic flux density. The cause of this is not clear, but at present Mn
Adding more than the required amount of Mn is harmful, so the upper limit for Mn was set at 0.8wt%. The temperature at which forsterite crystal nucleation and growth occurs is approximately 850-1100℃ during finishing annealing.
It is. Therefore, the atmosphere within this temperature range determines the properties of forsterite. The atmosphere in this temperature range will be described in detail below. The required oxygen partial pressure in the finish annealing atmosphere can be obtained by solving equation (2) for a _Mo , and its limit value is P _H2O /P _H2 = 1/a _Mo exp (-34200 + 7.25T/RT). Given. The thermodynamic values in equation (2) are given in the literature (O.
Kubaschewski & CAAlcook,
Metallurgical Thermochemistry5th.ed.(1979)
Pergamon Press, p. 294). What is difficult here is the evaluation of Mn activity, a _Mo. The current issue is the conditions for generating the minimum amount of MnO that contributes to the MgO-SiO ₂ solid phase reaction, which is considered to be different from the general Mn activity in silicon steel. For this reason, the present inventors experimentally determined this as follows. First, we assumed Henry's law and set a _Mo = γ _Mo・b _Mo ...(3). Here, b _Mo = [Mn−1.719(S+
0.405Se)]×0.01 (Mn, S, Se: weight %).
Next, magnesia was applied to the decarburized annealed plates with different b _Mo values, and finish annealing was performed in various P _H2O / P _H2 atmospheres in the range of 10 ^-1 to ^{10 -4} to investigate the formation of forsterite crystal grains. The average grain size was investigated. Then, from the change in the obtained forsterite average particle size, γ _Mo =
5 was obtained, and this value was substituted into equation (3) into equation (2).
The temperature to which equation (2) is applied is from 850℃, the initial stage of forsterite formation, and at this temperature
The value of P _H2O /P _H2 was taken as the lower limit. This value is the value indicated by the straight line BC in FIG. By maintaining the value of P _H2O /P _H2 in the final annealing atmosphere above this value, the necessary amount of MnO can exist in the SiO ₂ scale at the time of forsterite formation.
A dense forsterite film with fine crystal grains can be obtained. In addition, when considering the components in steel, the regulation for Mn against S and Se is Mn≧0.05+7 (S+
0.405Se), whereas the Mn activity when considering the required critical oxygen partial pressure is a _Mo = γ _Mo・(Mn−1.719
(S+0.405Se))×0.01. Here S+
The coefficient for 0.405Se is different, but its meaning in the present invention is that for the amount of Mn, S, and Se that satisfy Mn≧0.05+7 (S+0.405Se), the Mn activity that affects forsterite properties is expressed as the oxygen partial pressure. When considering the effect of a _Mo = γ _Mo・(Mn−1.179
(S+0.405Se))×0.01, which does not imply any contradiction. The upper limit value DE of P _H2O /P _H2 is such that if the Mn activity is increased further or the atmosphere is made oxidizing, film defects will occur that are thought to be caused by the excessively generated liquid phase, and the interlayer resistance of the product will decrease. Since this causes deterioration, the settings were made as shown in the figure. Further, the upper limit value AE is limited due to problems in on-site operations. That is, P _H2O /
In order to perform finish annealing with P _H2 of 5 x 10 ^-2 or more, a large-capacity humidifier is required, and it is also difficult to apply oxygen partial pressure evenly in the width and length directions of the coil, resulting in non-uniform Since the formation of a film becomes unavoidable and the product yield decreases, the upper limit must be set to AE. As mentioned above, due to the constraints on P _H2O /P _H2 and a _Mo , the oxygen partial pressure between 850 and 1100℃ during finish annealing is shown in Figure 1.
Must be kept within the range shown in ABCDE. By limiting the amount of Mn, S, and Se in the steel and the atmosphere within this range, it is possible to generate an appropriate amount of MnO in the SiO ₂ scale during final annealing.
As a result, the tension was 500 g/mm ² with a crystal grain size of 0.5 μm or less.
A forsterite film with good adhesion as described above can be obtained. Examples Example 1 C: 0.060%, Si: 3.30%, P: 0.036%, S:
For molten steel containing 0.004%, acid-soluble Al: 0.030%, N: 0.0082%, Mn (a) 0.005%, (b) 0.02%,
Ingots were prepared by adding (c) 0.10% and (d) 0.20%. After heating at 1200°C, a hot rolled sheet with a thickness of 2.3 mm was produced by hot rolling. These hot-rolled plates were heated at 1120℃×2min,
After annealing, it was cold rolled to a final plate thickness of 0.30 mm, and after annealing, decarburization annealing was performed in wet hydrogen at 850°C for 1.5 min. After subsequent application of magnesia containing 5% _TiO2 , _N2 25%, _H2 75%, dew point -10 °C (P _H2O /P _H2
= 3.78×10 ^-3 ) in an atmosphere of 600°C to 1100°C at a heating rate of 8°C/hr to 1200°C,
Thereafter, it was maintained at the same temperature in a hydrogen atmosphere for 20 hours. The magnetic flux density, iron loss, properties of the forsterite film, etc. of the obtained product were as shown in Table 2. Two-stage replica photographs of the appearance of the forsterite film shown in this example are shown in FIGS. 4a to 4d, and scanning electron microscope images are shown in FIGS. 4a' to d'.

【table】
←Scope of the present invention→
Example 2 C: 0.052%, Si: 3.35%, Mn: 0.20%, P:
0.040%, S: 0.004%, acid-soluble Al: 0.027%,
After heating a continuous cast slab containing N: 0.0090% and Cr: 0.10% to a temperature of 1150°C, it was hot rolled to 2.3
mm hot-rolled sheets were made. This hot-rolled plate is heated to 1080℃×
After annealing for 2 minutes, it was cold rolled to a final thickness of 0.30 mm using a one-step method, and decarburized annealed at 850°C for 2 minutes in a wet hydrogen atmosphere. After that, magnesia containing 2% TiO ₂ was applied, and then the temperature was increased to 1200°C at a heating rate of 6°C/hr between 700 and 1200°C in an atmosphere of 25% N ₂ and 75% H ₂ .
It was heated to ℃ and then kept at the same temperature in a hydrogen atmosphere for 20 hours. At this time, the dew point from 800℃ to 1100℃ is -40℃ (P _H2O /P _H2 = 2.49 × 10 ^-4 ), +10℃
(P _H2O /P _H2 =0.0163). The magnetic properties and properties of the forsterite film obtained were as shown in Table 3.

【table】

[Table] Example 3 C: 0.053%, S: 3.45%, Mn: 0.28%, P:
For molten steel containing 0.035%, acid-soluble Al: 0.030%, N: 0.0085%, S was (a) 0.003%, (b) 0.009%,
(c) 0.015% and (d) 0.020% were added to prepare ingots. After heating at 1350°C, a 2.5 mm hot-rolled plate was produced by hot rolling. These hot-rolled plates were cold-rolled to a thickness of 1.8 mm, annealed at 1120°C for 2 minutes, and cold-rolled to a final plate thickness of 0.18 mm. Then, in wet hydrogen at 850℃
Decarburization annealing was performed for 2 minutes, magnesia containing 3% TiO ₂ was applied, and final annealing was performed. Atmosphere at this time was 75% _N2 , 25% _H2 , dew point -40℃
(P _H2O /P _H2 =7.5×10 ^-4 ), and the temperature increase rate from 600 to 1200°C was 10°C/hf. The magnetic flux density, iron loss, and properties of the forsterite film of the obtained product were as shown in Table 4.

[Table] ← Scope of this invention
Enclosure →
Example 4 C: 0.059%, Si: 3.33%, Mn: 0.35%, P:
0.038%, S: 0.008%, acid-soluble Al: 0.024%,
A continuous cast slab containing N: 0.0095% and Cr: 0.20% was heated to a temperature of 1200°C and then hot-rolled to 2.3
It was made into a hot rolled sheet of mm. This hot-rolled plate was heated to 1120℃×2min.
After annealing, plate thickness (a) 0.30mm, (b) 0.23mm,
(c) After cold rolling to 0.17mm, 850℃× in a humid atmosphere
Decarburization annealing was performed for 2 min. Then, magnesia containing 5% TiO ₂ was applied, and final annealing was performed in an atmosphere of 75% N ₂ , 25% H ₂ , and a dew point of −20° C. (P _H2O /P _H2 =4.96×10 ⁻³ ). At this time, the temperature increase rate from 600 to 1200°C was 15°C/hr. The properties of the forsterite film of the obtained product were good regardless of the thickness of the product, with an average grain size of 0.2 μm and a minimum peeling radius of 4 mm, and the appearance was blackish gray and dense. Magnetism (indicated by magnetic flux velocity B ₈ and iron loss W _17/50 ) is (a) 1.91, respectively.
(T), 0.98 (W/Kg), (b)1.92 (T), 0.87 (W/K
g),
(c) 1.92 (T), 0.84 (W/Kg). (Effects of the Invention) As detailed above, the present invention has been able to produce a forsterite film with an average grain size of 0.5 μm or less and excellent adhesion and steel sheet tension, which has been difficult until now, using 3% silicon steel. This method provides a method that enables this by combining Mn activity and oxygen partial pressure during final annealing.With this method, the amount of iron loss reduction due to the tension effect of the film reaches 0.2W/Kg. Adhesion was also achieved with a minimum peeling radius of approximately 3 mm. Therefore, since the present invention can provide a magnetic material with excellent magnetic properties, it is of great industrial benefit.

[Brief explanation of the drawing]

Figure 1 shows a crystal grain size of 0.5 μm or less and a tension of 500 g/
Amounts of Mn, S, and Se in steel necessary to obtain a forsterite film of mm ² or more and 850℃ to 1100℃ during final annealing.
Figure 2 shows the relationship between P _H2O /P _H2 in the atmosphere at temperatures between Figure 3 is a diagram showing the relationship between magnetic flux density B ₈ and iron loss W _17/50 , Figure 3 is a diagram showing the relationship between Mn content in steel and tension due to forsterite film, and Figure 4 is a diagram showing the relationship between magnetic flux density B 8 and iron loss W 17/50. Figure 5 is a two-stage replica photograph and scanning electron micrograph showing the grain structure of the forsterite film of the 3.3% Si steel. Figures 6a and b are two-stage replica photographs showing the particle structure of the forsterite film shown in Table 1. Figure 7 is the average crystal grain size (μm) of the forsterite grains. Figure 7 is the average crystal grain size (μm) of the forsterite grains. Quantity and magnetic flux density, B ₈
(T), and FIGS. 8a to 8d are scanning electron micrographs showing the particle structure of the forsterite film of the product obtained in Example 3.

Claims (1)

[Claims] 1% by weight, C: 0.025-0.075%, Si: 3.0-4.5
%, acid-soluble Al: 0.010~0.060%, N: 0.0030~
A silicon steel slab containing 0.0130%, S≦0.010%, P: 0.015 to 0.045%, and Mn satisfying the relationship of 0.8≧Mn≧0.05+7×S, with the remainder being Fe and unavoidable impurities, is heated. This is rolled into a hot-rolled plate. After continuous annealing, the final plate thickness is obtained by cold rolling with a reduction ratio of over 80%, followed by decarburization annealing to form a subscale containing SiO ₂ on the surface. In the method for forming a forsterite film on a grain-oriented silicon steel sheet, the temperature range of 850 to 1100°C during the final annealing is as follows: The oxygen partial pressure (expressed as P _H2O /P _H2 ) at Mn−
A method for forming a forsterite insulating film on a unidirectional silicon steel sheet, which is characterized by maintaining the forsterite insulating film in the area surrounded by ABCDE in FIG. 1 for 1.719×S. 2 Weight%: C: 0.025-0.075%, Si: 3.0-4.5
%, acid-soluble Al: 0.010~0.060%, N: 0.0030~
0.0130%, S≦0.010%, P: 0.015-0.045%,
Cr: 0.07~0.25%, and Mn 0.8≧Mn≧0.05+
A silicon steel slab containing so as to satisfy the relationship of 7×S and the remainder Fe and unavoidable impurities is hot-rolled into a hot-rolled plate, which is continuously annealed and then subjected to strong rolling with a rolling reduction of more than 80%. The final plate thickness is obtained by cold rolling, and then decarburization annealing is performed to improve the surface of the plate.
Generate subscales containing SiO ₂ and then MgO
In a method for forming a forsterite film on a unidirectional silicon steel sheet, in which final annealing is performed after applying an annealing separator mainly composed of
Oxygen partial pressure (P _H2O /P _H2
) in Fig. 1 for Mn−1.719×S.
A method for forming a forsterite insulating film on a unidirectional silicon steel sheet, which is characterized by maintaining the forsterite insulating film in a region surrounded by ABCDE.