JPS6270525A - Manufacture of grain oriented electrical sheet having good forsterite film - Google Patents

Abstract

PURPOSE:To obtain the good titled film even in coil having large simplex weight, by controlling oxygen partial pressure in atmosphere at finish annealing and electrostatically coating MgO on annealing separator material when grain oriented electrical sheet is manufactured by usual method. CONSTITUTION:Slab contg. by weight 3.0-4.5% Si, <=0.010% S + 0.405 Se, {0.05 + 7 (S + 0.45 Se)}-0.8% Mn is hot and cold rolled, and decarburization annealed in wet hydrogen atmosphere. Next, annealing separator material composed mainly of MgO is coated to the sheet and it is finish annealed to manufacture grain oriented electric sheet. Hereupon, slurry state annealing separator material of <=4g/m<2> per one side of steel sheet is coated, dried and 3-6g/m<2> MgO per one side of steel sheet is electrostatically coated thereon. Further oxygen partial pressure (PH2O/PH2) in atmosphere from finish annealing starting to 650 deg.C is controlled to <=0.015 to carry out annealing. Thereby, the cause of pepper and salt fault in forsterite film on steel sheet surface can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention particularly relates to a method for manufacturing a unidirectional electrical steel sheet with a good forsterite coating.

[Conventional technology]

Unidirectional electrical steel sheet is a soft magnetic material mainly used for transformer cores. This type of steel sheet uses crystal grains ((110) C00 whose axes of easy magnetization are aligned within a range of several degrees with respect to the rolling direction) in order to significantly increase magnetic permeability only in the direction of magnetic flux flow.
(L) oriented grains), and contains Si as a component to increase hardness resistance and reduce core loss caused by Joule heat. On its surface, forsterite, MgSiO4, produced by a solid phase reaction between SiO□, which was selectively oxidized during decarburization annealing during the steel sheet manufacturing process, and MgO coated on it during final annealing, is present in a thickness of several μm. It acts as an insulating film and subdivides magnetic domains. It also plays an important role in terms of magnetic properties. Usually, it is used as a transformer core after being coated with a secondary coating mainly made of colloidal silica for the purpose of adding tension. From this perspective, a unidirectional electrical steel sheet is a composite material that is covered with crystal grains with (110) [001) orientation in the rolling direction and has a ceramic coating mainly composed of forsterite and a secondary coating on the surface layer. I can say that there is.

Now, (110) in such a unidirectional electrical steel sheet
Achieving a high degree of integration in the (001) orientation and forming a forsterite film in oxide-based ceramics usually occur at about the same time during Box annealing, which is called final annealing. The former is called secondary recrystallization (1
10) Abnormal grain growth of (001) oriented grains, the latter being achieved by SiO□-MgO solid phase reaction on the surface of the copper plate, and although these two reactions are essentially completely different phenomena, they are indirectly Real reactions progress while mutually interfering with each other.

As is well known, forsterite, Mg25iOn, is 12.505 (1965)). In the research field related to the production of grain-oriented mm plates, Mn0z, T
It has been empirically known that the presence of trace amounts of substances such as iO□, B2O3, CaO, and Sr compounds changes the properties of the produced forsterite. For example, in Japanese Patent Publication No. 51-12450, the addition of MnO□
The addition of TiO□ was disclosed in the same publication No. 51-12451. Also, Japanese Patent Publication No. 57-32716, Japanese Patent Application Laid-Open No. 55-89422, and Japanese Patent Application Laid-open No. 56-7
No. 5577 discloses the effect of Sr compounds on forsterite film properties. Unexamined Japanese Patent Publication 1987-1966
Publication No. 935 discloses a method for controlling the amount of water brought in mainly in the form of magnesium hydroxide depending on the amount of CaO component contained in an annealed and separated product containing MgO as a main component.

What is the mechanism by which these trace additives cause MgO-
It affects the reaction mechanism of 5iO□ solid phase reaction,
Furthermore, it is not clear at present whether various properties such as the crystal grain size of the produced forsterite and the adhesion between the so-called forsterite film composed of forsterite crystal grains and the steel sheet are changed. However, these substances commonly contain MgO, SiO□, and Mg
These additives have the property of lowering the melting point of MgO-3iO□-based oxides such as 2SiO4, so these additives
It is thought that it contributes to the reaction by accelerating the diffusion rate of `` and 0-''.In some cases, at around the maximum temperature of 1200°C for finish annealing of ordinary grain-oriented electrical steel sheets, some liquid It is speculated that the reaction rate of the system is significantly increased by forming a phase.

Now, the present inventors first investigated the Mn activity in the steel and the atmospheric oxygen partial pressure (P II□
0/P) (represented by 12), the forsterite crystal grain size is small and the adhesion of the film is good.
A method for forming a forsterite film in which the tension exerted by the film on a steel plate is greater than that obtained by conventional techniques has been disclosed (Japanese Patent Application No. 59-53819). This method differs from previous methods in which the properties of the coating were improved by adding small amounts of additives to the annealed separator.This method uses the ingredients in the steel, that is, the Mn activity and the oxygen partial pressure in the external atmosphere, to improve the properties of the coating. The aim is to improve. The key point of the mechanism is that MgO-3iO□ is produced by high-temperature oxidation during the solid phase reaction.
It is believed that this method involves the generation of O, and can be said to have a different feature from the conventional technology from an industrial standpoint, since it requires fewer types of trace additives.

It was found that when testing was carried out on a coil with a large unit weight of 10 tons or 20 tons, there were many film defects where bare metal was exposed, generally called shimofuri, near the good forsterite film.

These film defects not only deteriorate the appearance of the finished product, but also have an unfavorable effect on the magnetic properties, such as deterioration of the insulation properties and the tension applied to the steel sheet.

[Means for solving problems]

The purpose of the present invention is to eliminate and improve these problems that occurred in Japanese Patent Application No. 59-53819 by the present inventors for the purpose of producing a good forsterite film, and to improve the production of a good forsterite film in a coil with a large unit weight. An object of the present invention is to provide a finish annealing method capable of forming a film of 1 to 100%.

That is, in the present invention, Si: 3.0% or more and 4.5% or less, S + 0.405 Se: 0.010% or less,
Mn: {0.05+7(S+0.4055e)}
% or more and 0.8% or less, and create a unidirectional electrical steel sheet by the usual method, the oxygen partial pressure (P H2O /P11□) is limited to 0.015 or less, and in the process of applying an annealing separator mainly composed of magnesia to a decarburized annealed plate, the amount of undercoat applied after the annealing separator is made into a slurry and then applied and dried. 4g per side
/ rl or less, and also uses a so-called electrostatic coating method in which 3 to 6 g/m (one side) of magnesia is applied electrostatically on the forsterite film. . In addition to this method, by inspecting the steel plate at a temperature range of 800-900℃ for 10-30 hours during final annealing, the removal of film defects becomes more complete. It has become clear that the film properties can be improved by regulating the oxygen partial pressure during temperature rise to a specific range for Mn, S, and 5eil in the steel.

The present invention will be explained in detail below.

Figure 2 shows C: 0.055%, Si: 3.25%, Mn:
0.18%, S: 0.006%, P: 0.
02%, AI! : 0.03%, N: 0.0
After decarburizing and annealing a cold-rolled sheet of 8C1ll x 3 cm size containing 0.07% in a wet hydrogen atmosphere, an annealing separation material mainly composed of magnesia containing 5 parts by weight of TiO□ was applied on one side at 7 g/ This figure shows the frequency of occurrence of lame-like film defects that appeared in the forsterite film obtained after applying m2 and finishing annealing. In this experiment, the final annealing atmosphere was N25% and 8275%, and the oxygen partial pressure up to 650° C. was set to various values as a parameter. From this experiment, the frequency of occurrence of frost-like film defects was determined by the oxygen partial pressure of the atmosphere during the first half of finish annealing being P H20/ P I+□
It was found that this is particularly significant when the value exceeds 0.015.

In addition, when similar experiments were conducted with different decarburization annealing dew points for steel materials with different Mn' activities, it was found that this type of film defect occurs more frequently in materials with high Mn activities. Furthermore, it was found that decarburization tends to occur when the oxygen partial pressure during decarburization annealing is high.

The present inventors investigated in detail the occurrence of these film defects and came to the following conclusion. In other words, these film defects are 1
During high-temperature annealing at around 200°C, MgO and SiO□, which constitute forsterite, TiO□ and B, which are intentionally added to the annealing separation material, and alkali or alkaline earth elements such as NazO, which are unavoidably mixed, are removed. F generated by high-temperature oxidation of oxides and components in steel
eO, Mn01A 62(h, etc.) This is due to the formation of a melt that occurs when the composition of these composite oxides satisfies a eutectic composition with a eutectic point of 1200°C or less. An excessive increase in the oxygen partial pressure in the annealing atmosphere generates excessive (Fe, Mn)0-based oxides,
It was concluded that the presence of these oxides causes the melting point of the composite oxide system to be below 1200''c even after forsterite is formed, resulting in the formation of chilblain film defects.

Now, based on these findings, the present inventors conducted a similar experiment using a 10-ton coil while maintaining the final annealing atmosphere at P IIzO/P Hz of 0.015 or less.

However, as a result, the present inventors faced a new problem in that the grain-like film defects that disappeared in the small sample test were not removed in the 10-ton coil test.

In order to solve this problem, the present inventors continued to conduct experiments based on the following considerations. Usually, the annealing separation material is applied by dissolving magnesia and various additives in pure water, applying it to the steel plate as a slurry, and drying it. At this time, the hydration reaction of magnesia progresses, and Mg
(OH) z is partially formed. This hydration component is released during the final annealing in the temperature range of 400-500°C and increases the oxygen partial pressure between the coil plates. Even if the oxygen partial pressure in the atmosphere outside the coil is controlled to 0.015 or less using P H20/PH2, it takes time for the oxygen partial pressure in the atmosphere directly above the steel plate to actually reach such a value, resulting in This induces a flaky film defect. FIG. 3 shows an example in which the change in oxygen partial pressure (in this case, water vapor partial pressure) between the coil plates over time is simulated using a computer. In order to prevent such an excessive increase in the oxygen partial pressure between the coil plates, there are two measures: to reduce as much as possible the hydration components that are unnecessarily carried between the coil plates, and to increase the gas permeability between the plates. Basically valid. The method disclosed in JP-A No. 58-67871 by the present inventors, in which non-hydratable dead-burned magnesia powder is electrostatically attached after applying a suspension liquid containing magnesia as a main component (hereinafter referred to as electrostatic This method (referred to as coating method) serves the purpose of controlling the amount of hydration components introduced into the coil. Table 1 shows 10 m of the inside of the coil when the above external atmosphere conditions are satisfied.
Normal magnesia coating method (coating amount: 7 g/n on one side) and electrostatic coating method (coating amount: 3 g/n on one side)
g/rd, electrostatic coating (5 g on one side) to apply magnesia and finish annealing. By employing the electrostatic coating method in this way, it has become possible to prevent the occurrence of frizz-like film defects even when final annealing is performed on an actual coil.

As mentioned above, it has become clear that a forsterite film is stably formed by adopting the electrostatic coating method.
By testing the steel plate in a temperature range of 900°C for 10 to 30 hours, defects in the forsterite film can be more reliably reduced. This will be explained next.

Table 2 and Figure 4 show that after decarburizing a cold-rolled sheet containing 0.2% Mn and 0.004% S in an atmosphere of P HzO/PH 20,366, it was treated with magnesia containing 5 parts by weight of Tie. GDS (Glow Disch)
arge 0ptical EmissionSpac
troscopy). As can be seen from this figure, St gathers on the surface in the temperature range of 800 to 900°C. When the existence form was investigated using an infrared reflection spectrum, it was found that these Sis exist as 5i02. These findings revealed that the oxide film formed during the decarburization annealing undergoes a change in quality in the form of concentration of SiO□ in the temperature range of 800 to 900°C during the final annealing. Therefore, such concentration of SiO□, that is, a change in the composition of the complex oxide system to the SiO□rich side, increases the eutectic point of the system to 1200°C or higher, and as a result, suppresses the occurrence of chimney-like film defects. I came to the conclusion that In addition,
SiO at 800-900 °C during such final annealing
The conversion of □ to 4 is particularly noticeable in materials with high Mn activity. The inventors' views regarding this reason will be described below. As is well known, the high temperature oxidation behavior of the 3%5t-Re system is M
It varies depending on the n activity, and when the Mn amount is above a certain level,
The oxidation rate of the material increases significantly (N, Morito
&T.

rchida 1796H1977)). By exposing the film thus formed to a low oxygen partial pressure atmosphere such as during final annealing, the film composition is brought to a new equilibrium state, i.e. 5iOz/ (Fe, Mn) 2Si0
It is thought that the situation is approaching a state with a high ratio of 4. Such changes occur when the initial film is 5iOz/(Fe,Mn)zsi
It is thought that the lower the o4 ratio, the more strongly it appears.

The final annealing method described above can be further improved by combining it with Japanese Patent Application No. 59-53819 by the present inventors, which aims to control the oxygen partial pressure in the final annealing atmosphere according to the Mn activity in the steel. The effect can be effectively exhibited. Table 3 shows Mn: 0.18%, S: 0.006
% of the material was decarburized and annealed, magnesia containing 5 parts by weight of Ti01 was applied by a normal method and an electrostatic coating method, and the film defect occurrence rate and average fault that appeared in the forsterite film of the material obtained by final annealing were Shows the stellite crystal grain size.

Upper row: Shimofuri defect occurrence rate Lower row: Forsterite grain size Table 3 In this way, by increasing the dew point of the atmosphere at 850-1100°C to some extent during finish annealing, it is possible to reduce the grain size of the forsterite film. can. The reason for this is not necessarily clear, but the inventors of the present invention
As described in No. 19, an appropriate amount of MnO is generated on the oxide film side due to the combination of the Mn activity in the steel and the oxygen partial pressure in the atmosphere, and this MnO has a catalytic effect on the MgO-3iO□ system solid phase reaction. I think it is effective.

This method of applying a certain degree of oxygen partial pressure in the latter half of final annealing is at first glance contradictory to the idea of increasing the 5iOz/(Fe, Mn)zsi04 ratio by testing at 800 to 900°C and eliminating the sagging defects mentioned above. Looks like it does. However, as already mentioned, these methods are experimentally effective in producing good forsterite films on materials with high Mn activity. The present inventors' views regarding these phenomena will be described below.

First, from the viewpoint of promoting the solid phase reaction, an appropriate amount of MnO is added.
is effective for forming MgO-5i02 film. Therefore, Mn
The stability of MnO becomes a problem for materials with high activity. FIG. 5 shows the thermodynamic stability of Mn0O using Mn activity as a parameter. The numerical values required to create this diagram are “Metallurgica
l Thermochemistry” (5th6di
tion.

1979) Kubaschewski & Alcoc
Quoted from K (Pergamon Press).

As is clear from this figure, the equilibrium stability of MnO strongly depends on the oxygen partial pressure of the temperature atmosphere and the Mn activity in the steel. Moreover, in order to reduce MnO once formed, kinetic factors should work even more strongly. The present inventors' opinion is that an appropriate amount of MnO is necessary to improve the properties of the forsterite film, and that excess MnO1 is necessary to improve the properties of the forsterite film.
FeO or generally (Fe + M n ) 0-based oxides are undesirable in the sense that they lower the eutectic point of the composite oxide based on Mgo-5to and induce fraying defects. As is clear from Fig. 5, if a thermodynamic equilibrium state is always achieved, in order to secure an appropriate amount of MnO, the transition will be as shown by the arrow in Fig. 5, for example, depending on the Mn activity. Just let it happen. Simply put, the oxygen partial pressure in the atmosphere should be gradually increased as the temperature rises. However, in the actual manufacturing process of grain-oriented electrical steel sheets, this does not apply from the initial stage. This is because the oxygen partial pressure during decarburization annealing is 1) to perform decarburization, and 2) to ensure the amount of SiO□ or oxygen necessary to form forsterite in a short time. ): set at about 0.3, and as can be seen from FIG. 5, this value is much higher than the oxygen partial pressure range that is a problem during final annealing. In order to form a good forsterite film starting from the oxide film thus formed, the method described in the present invention, that is, suppressing additional oxidation in the first half of the final annealing (P HzO/ P H□≦0
．． 015), especially in the actual coil, Mg (Of()
By limiting the amount of hydration components brought in as
This method (testing at 800-900°C) is effective. Once this state is reached, a certain amount of oxygen partial pressure is applied as the temperature increases and the MnO
Securing the necessary amount of this will work effectively.

Due to the technical advances mentioned above, S + 0.405S
e: 0.010 or less and Mn: {0.05+7(S
+ 0.405Se)) or more and 0.8% or less Mn@
It has now become possible to stably obtain a forsterite film on a material with a high content without causing any wrinkle defects.

Next, the limiting conditions of the constituent factors of the present invention will be described.

The regulations regarding Mn5S and Se in steel were determined mainly from the viewpoint of securing Mn activity in steel and improving the properties of the forsterite film. That is, as mentioned above, MnO produced by oxidation of Mn in steel improves the properties of the forsterite film of the finished product, but in order to secure the necessary amount of free Mn for this purpose, S should be 0.010. % or less. In terms of trapping Mn, Se also has a similar effect, so increasing Se is also not preferable. From the above points, the upper limit for S and Se was set to S + 0.405 Se, o, oio%.

If S is increased further than this, the material is called linear fine grain2.
Subsequently, defective recrystallization areas occur and the characteristics of the surface film also deteriorate.

The lower limit of Mn was set to 0.05+7 (S + 0.4055e) 1% with respect to the amount of S and Se from the viewpoint of obtaining the Mn activity necessary to obtain a good forsterite film. If Mn is less than this value, the film deteriorates and secondary recrystallization becomes unstable, which is not preferable.

The upper limit of Mn was set at 0.8%. If Mni increases more than this, the magnetic flux density of the finished product will deteriorate, which is not preferable.

The oxygen partial pressure in the atmosphere from the start of final annealing to 650℃ is P
I(□O/PI+□<0.015.

If it is more than this, a chirping defect will occur in the finished forsterite film. The amount of coating in the electrostatic coating method is limited as follows. First, the coating amount of the annealing separation material is 4 g/m or less on one side, which is applied as an undercoat in the form of a slurry and dried using the usual method. If it is more than this, the amount of hydration components brought into the space between the coil plates will be unnecessarily increased, and the original purpose of controlling the oxygen partial pressure in the atmosphere during final annealing will not be achieved. In addition, the amount of magnesia applied electrostatically to prevent burn-in is 3 to 6 g per side.
Let it be m. If the amount is less than 3 g/m, seizure of the coil may occur, and even if the amount exceeds 6 g/m, the effect of preventing seizure is the same and it is not economical.

When a steel plate is tested in a temperature range of 800°C to 900°C and the aim is to improve film properties, the testing time is limited to 10 to 30 hours. If the time is shorter than this, no significant effect on improving the film properties can be expected, and even if the time is longer than this, the effect is not much different from that of the 30-hour test. Therefore, it is not economical to hold the coil for more than 30 hours.

Next, the second half of finish annealing shown in claim (3) of the present invention 8
The reasons for limiting the atmospheric oxygen partial pressure in the temperature range from 00 to 900°C to 1100°C will be explained (Fig. 1). The purpose of this invention is to improve the characteristics of a forsterite film formed on the surface of a product, and the detailed content of the invention is the same as that of Japanese Patent Application No. 59-53819 filed by the present inventors. That is, the gist of the present invention is to secure a necessary amount of MnO, which has a catalytic function in the MgO-5iO□ solid phase reaction, which is a forsterite production reaction, in an oxide film mainly composed of SiO□. As a method, MgO-5iOz
11 from the temperature range of 800-900°C where solid phase reactions proceed.
The oxygen partial pressure in the final annealing atmosphere, specifically PI (□O/PH2), was limited to the range shown in FIG. 1 in the temperature range up to 00°C.

AB and DC in FIG. 1 are the limitations regarding the components (as mentioned above), and the reason for the limitations has been explained, but to repeat, Mn4.719 (
If S+ 0.405 Se) is less than 0.05 (AB), the necessary amount of MnO, which is effective in improving film properties, cannot be obtained, and if it is more than 0.8 (DC), the magnetic flux density of the product will deteriorate. Undesirable.

BC is MnO, which is necessary for improving the properties of the forsterite film.
Since this must be the oxygen partial pressure necessary to ensure that

If Pi1□0/Plh is less than this, the average grain size of forsterite crystals will exceed 0.5 μm, which is inappropriate. pH□O/P)1. The upper limit value DE is such that if the Mn activity is increased further or the atmosphere is made oxidizing, film defects will occur which are thought to be caused by an excessively generated liquid phase.
Since it deteriorates the interlayer resistance of the product, it was set as shown in the figure. Further, the upper limit value AE is limited due to problems in on-site operations. That is, P11□0/pH□ is 5X10
- In order to perform final annealing at a temperature higher than 100%, a large-capacity humidifier is required, and it becomes difficult to apply oxygen partial pressure evenly in the width and length directions of the coil, and the product yield decreases, so the upper limit is It is necessary to set it as AE.PHz above
Due to constraints on O/P II□ and a□, the oxygen partial pressure from the temperature range of 800 to 900°C to 1100°C during final annealing must be maintained within the range shown in the drawing ABCDE.

Example IC: 0.054%, Si: 3.3%, Mn: 0.15%
, P: o, o2%, S: 0.006%, Se: O,
0O06%, acid soluble 117! :0.030%, N:
Create slabs from molten steel containing 0.007% by continuous casting method,
After heating the slab to 1150° C., it was hot rolled into a hot rolled sheet with a thickness of 1.3 mm. This hot rolled sheet was annealed at 1100° C. for 2 minutes, then cold rolled to a thickness of 0.18 mm, and decarburized annealed in hot hydrogen at a temperature of 810° C. This board was coated using the usual method (coating amount, 6 g/m on one side) and the electrostatic coating method (undercoat 3 g/rrr on one side + electrostatic coating method (HO only) 4 g/% on one side.
) was applied with magnesia containing 5 parts by weight of TiO□. The 10 ton coil created in this way was heated to 25% nitrogen, 75% hydrogen, and a dew point of -20°C (P11□o/PHz=0
．． 002), 0°C (P11□0/PH2=0.008)
The temperature was raised to 650°C in an atmosphere of 20°C (Pl+,0 /Pl+□-0,032), and then the dew point was changed to -20°C and the temperature was raised to 1200°C at a heating rate of 10°C/hr.

Table 4 shows the occurrence rate of shingle-like film defects in the obtained steel sheets.

Table 11 shows Example 2 of the present invention, C: 0.058%, Si: 3.4%, Mn: 0. %,
P: 0.03%, S: 0.007%, acid soluble Aff
An ingot was made from molten steel containing N: 0.029% and N: 0.008%. After heating the slab to 1150°C, it was rolled into a hot-rolled sheet of 2.3 mm. This hot rolled plate is 1
After annealing at 120°CX 2.5m1n, 0.281m
The plate was cold-rolled to a temperature of 850"C and subjected to decarburization annealing in wet hydrogen.
and electrostatic coating method (undercoat 3g/M on one side) electrostatic coating method (M
MgO containing 3% TiO2 was coated with gO (4 g/m on one side). These steel plates were heated in an atmosphere of 25% nitrogen, 75% hydrogen, and a dew point of 5°C (PHzO/pHz"0.012), and the temperature was raised at a rate of 6°C/h from 600°C to 860°C.
The temperature was raised to 860°C as r, then the temperature was maintained at the same temperature and the same atmosphere for 0.10.20 hours, and then the temperature was further raised to 1200°C at a rate of 12°C/hr in the same atmosphere. Table 5 shows the rate of occurrence of shingle-like film defects in the obtained steel plates.

Table 5 Example 3 C: 0.055%, Si: 3.35%, Mn: 0.14
%, P: 0.025%, S: 0.006%, acid-soluble AN: 0.030%, N: 0.0078%, Cr:
Ingots were made from molten steel containing 0.12%. 1
After heating the slab to 150°C, it was rolled into a 1.811 hot rolled sheet. This hot rolled 1j.e is 1120°cx2mi
n After annealing, to 0.180) A, Weir, 830'C
Decarburization annealing was performed in wet hydrogen at a temperature of . This board was coated using the usual method (coating amount: 6 g/rr on one side) and the electrostatic coating method (undercoat 3 g/m on one side + electrostatic coating method (MgO only) 4 g on one side.
/rd) and coated with MgO containing 3% TiO2. At this time, for undercoating using the normal method and electrostatic coating method, ferromanganese nitride and Mn are added to the base MgO and TiO2.
A method including 4% o, as Feo, +s No, ts was also adopted. These steel plates were heated to 25% nitrogen, 75% hydrogen, and a dew point of -20°C (P(1□o/pH2=0.002).
The temperature was raised to 850°C at a heating rate of 8°C/hr from 650°C to 850°C, then kept at the same temperature and in the same atmosphere for 15 hours, and then heated to 1200°C for 15 hours.
The temperature was raised at 2°C/hr. At this time, 850℃~1200℃
The dew point of the atmosphere was set to -40°C +10°C. The magnetic properties and film properties of the obtained steel plate (forsterite crystal grain size and minimum extrusion radius (mm) of the film) are shown in Table 6. As is clear from this table, the magnetic flux density of steel plate is B for all materials, ≧1.92 (T), but 850
An atmosphere with a temperature of 1200°C to 1200°C and a dew point of +10°C exhibits better iron loss value and film properties.

B s: How many stocks density at 800 A/m 'A+
7yso: Iron 1-member value at 1.7 (T), 50 Hz Fo: Forsterite average grain size r: Minimum peeling radius Table 1 [Effects of the Invention] As detailed above, the present invention has a directionality The present invention provides a finish annealing method that does not involve the generation of flapping film defects in the forsterite film on the surface of an electrical steel sheet, and is particularly effective for materials with high Mn activity in the steel. This not only improves the appearance of the finished product, but also improves the mechanical properties such as the adhesion of the film, which is of great industrial benefit.

[Brief explanation of drawings]

Figure 1 shows 1 from the temperature range of 800 to 900℃ during final annealing.
Oxygen partial pressure PH□O/ in annealing atmosphere up to 100℃
PI+ is the amount of Mn, S and Se in the steel, that is, Mn-1
, 719 (S + 0.405 Se). FIG. 2 is a diagram showing the relationship between the oxygen partial pressure of the atmosphere and the amount of chimney-like film defects generated in the forsterite film from the start of final annealing to 650'C. FIG. 3 is a diagram showing the results of interfacial analysis using GDS after rapidly cooling the material for decomposing magnesium hydroxide at the temperature shown in the figure. FIG. 5 is a diagram showing the thermodynamic stability of MnO with respect to temperature and oxygen partial pressure using Mn activity as a parameter, and the region above the broken line is the region where MnO can exist stably.

Claims (1)

[Claims] 1. Si by weight: 3.0% or more and 4.5% or less, S+0.
405 Se: 0.010% or less, Mn: {0.05+
7(S+0.405 Se)}% to 0.8% is hot-rolled, cold-rolled, decarburized annealed in a wet hydrogen atmosphere, coated with an annealing separator mainly composed of magnesia, and finished annealed. In the method for manufacturing unidirectional electrical steel sheets, a slurry-like annealing separation material of 4 g/m^2 or less per side of the steel sheet is coated, dried, and then 3 g/m^2 or less per side of the steel sheet is applied.
Magnesia of g/m^2 or more and 6 g/m^2 or less is applied electrostatically, and the oxygen partial pressure (expressed as PH_2O/PH_2) of the atmosphere in the temperature range from the start of final annealing to 650°C is 0.015 or less. 1. A method for producing a unidirectional electrical steel sheet with a good forsterite film, characterized by annealing it as a unidirectional electrical steel sheet. 2. During final annealing, the steel plate is heated in the temperature range of 800 to 900℃
The method according to claim 1, characterized in that the assay is carried out for ~30 hours. 3. Temperature range from 800 to 900℃ during final annealing to 1100℃
Claim 1, characterized in that the oxygen partial pressure in the atmosphere when the temperature is raised to ℃ is set to a value in the region surrounded by ABCDE in FIG. 1 with respect to the amounts of Mn, Se, and S in the steel. or the method described in Section 2.