JPH1088240A - Method for evaluation of magnesium oxide for separation agent at annealing at manufacture of grain oriented silicon steel sheet, and manufacture of grain oriented silicon steel sheet excellent in film characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stable obtain a grain oriented silicon steel sheet excellent in mag netic properties as well as film characteristic by measuring gas adsorption isothermal line prior to the use of MgO for a separation agent at annealing and judging the feasibility of application. SOLUTION: A hot rolled silicon steel plate is cold-rolled while process- annealed between cold rolling stages and finished to final sheet thickness. Subsequently, after primary recrystallization annealing, a separation agent at annealing, prepared by using MgO as a main material agent and formed into slurry state, is applied to the surface of the resultant steel sheet and final finish annealing is performed. In this method, an MgO, having a powder characteristic where the N2 gas adsorption isothermal line up to 0.05-0.95 relative pressure satisfied the region enclosed with lines connecting point A (0.05, 2.7), point B (0.3, 4.0), point C (0.8, 7.7), point D (0.95, 13.6), point E (0.95, 40.9), point F (0.8, 15.9), point G (0.3, 7.1), and point H (0.05, 4.6) in the coordinates [relative pressure, amount of adsorption: (ml/g)], is used as MgO.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an annealing separator used for forming a forsterite film in a manufacturing process of a grain-oriented silicon steel sheet used for an iron core of a transformer or other electric equipment, particularly in a final finishing annealing process. With respect to MgO, which is the main agent of the agent, it is intended to provide a new index for judging the applicability of this MgO and to specify a suitable range thereof, thereby improving the film properties and magnetic properties advantageously. .

[0002]

2. Description of the Related Art As a method of manufacturing a grain-oriented silicon steel sheet,
After hot rolling of steel slabs, one or intermediate annealing 2
It is a common practice to perform cold rolling more than once, decarburize annealing, and then perform final finish annealing. Secondary recrystallization occurs during this final finish annealing, and coarse crystal grains having a uniform axis of easy magnetization in the rolling direction are generated.

[0003] Since the above-mentioned final finish annealing is a long-time treatment, an annealing separator mainly composed of MgO is usually applied before annealing in order to prevent seizure of the steel sheet during the treatment. This MgO has a function of forming a forsterite film by reacting with an oxide layer mainly composed of SiO ₂ formed on the surface of the steel sheet during decarburization annealing, in addition to the role of the annealing separator. This forsterite coating,
In addition to functioning as a kind of binder that makes the insulating coating adhere to the base iron part, it has functions such as increasing the insulation resistance and improving the magnetic properties by applying tension to the steel sheet. Therefore, it is extremely important to form a film having a uniform thickness and good adhesion to a steel sheet.

[0004] In addition to the above functions, the annealing separator has a function of affecting the magnetic properties by changing the growth and decomposition behavior of precipitates in the steel sheet and the growth behavior of crystal grains. For example, when MgO is slurried, if too much moisture is brought in, the steel sheet is oxidized and the magnetic properties are degraded, or point defects are generated in the coating. It is also known that secondary recrystallization behavior changes when impurities contained in MgO enter steel during annealing. Therefore,
The quality of the components and the powder properties of the annealing separator are important factors that influence the coating properties and magnetic properties of the grain-oriented silicon steel.

For this reason, various methods have conventionally been proposed for improving the quality of the annealing separator. For example, Japanese Patent Publication No. 57-14566 discloses a method for forming a good forsterite film by specifying the impurity concentration, hydration amount, and sieve permeability of magnesium fired in a muffle furnace at a high temperature. ing. Further, Japanese Patent Publication No. 57-45472 discloses that the powder characteristics such as the impurity concentration of SO ₃ , B, etc. and the specific surface area, particle size, etc. are within a specific range and the distribution of citric acid activity is within a predetermined range. There is disclosed a technique for forming a good film by containing the film. Furthermore, Japanese Patent Publication No. 57-8188 discloses that magnesium hydroxide is calcined,
Continued adsorption and surface area: 100 Å ²
Magnesium oxide with a BET specific surface area of 15 to 30 m ² / g in the range of 15 to 30: 70 to 90 wt% and a BET specific surface area of 1 to 10 m
MgO containing 10 / 30wt% of ² / g magnesium oxide
There is disclosed a method for improving film adhesion and magnetic properties by increasing the adhesive strength to a steel sheet by using the method.

Although the film properties and magnetic properties have been improved to some extent by the above techniques, it is still difficult to say that sufficient effects have been obtained. There is a demand for improved product characteristics.

[0007] Further, as described above, since MgO has a complicated function in the manufacturing process, it is still not completely understood how the change in each powder property of MgO affects the product properties. Not. Until now, as an index for evaluating MgO, powder characteristics such as impurity concentration of B, CaO, SO ₃ , Cl and the like, citric acid activity, BET specific surface area and particle size distribution have been used. However, the applicability of MgO cannot be sufficiently determined based on these characteristics, and in some cases, the influence of the product characteristics on the characteristics of each powder may be different from the tendencies conventionally known. Therefore, in studying the improvement of MgO, it has been strongly desired to find a more appropriate evaluation index.

[0008]

SUMMARY OF THE INVENTION The present invention has been developed in view of the above circumstances, and proposes a new method for evaluating MgO for an annealing separator in the production of a grain-oriented silicon steel sheet, and also provides an evaluation method for the same. It is an object of the present invention to stably obtain a grain-oriented silicon steel sheet having excellent coating properties and magnetic properties by using MgO whose characteristic value evaluated by the method is limited to a predetermined range.

[0009]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted various studies on the optimum MgO conditions for film formation. As a result, the quality of the film was determined by the profile of the gas adsorption isotherm of MgO. We have obtained new knowledge that we can judge accurately. The present invention is based on the above findings.

[0010] That is, the present invention relates to an Mg separation agent for annealing.
Prior to the use of O, a gas adsorption isotherm was measured, and the applicability was judged based on the obtained profile. 1 invention).

The present invention also provides a hot rolled silicon steel sheet comprising:
After finishing to the final sheet thickness by cold rolling multiple times including intermediate or intermediate annealing, primary recrystallization annealing is performed, and then MgO
In a method for producing a grain-oriented silicon steel sheet, comprising a series of steps of applying an annealing separator mainly containing water as a slurry with water and then applying it to the steel sheet surface, and then performing a final finish annealing,
As O, its powder properties are relative pressure: 0.05 to 0.95.
The N ₂ gas adsorption isotherms are points A, B, C, D, E, F,
A method for producing a grain-oriented silicon steel sheet having excellent coating properties, characterized by using a material satisfying a region surrounded by G and H (second invention). Here, the coordinates (relative pressure, adsorption amount: ml / g) of each point in FIG. 1 are as follows. Point A = (0.05, 2.7), Point B = (0.3, 4.0)
), Point C = (0.8, 7.7), point D = (0.95, 1)
3.6), point E = (0.95, 40.9), point F = (0.8
, 15.9), point G = (0.3, 7.1), point H = (
0.05, 4.6).

Further, the present invention provides a hot rolled silicon steel sheet,
After finishing to the final thickness by cold rolling once or multiple times with intermediate annealing, primary recrystallization annealing is performed, and then Mg
A method for producing a grain-oriented silicon steel sheet comprising a series of steps of applying an annealing separator mainly containing O as a slurry with water and then applying it to the steel sheet surface, and then performing a final finish annealing,
As the powder characteristic of MgO, its N ₂ gas adsorption isotherm at a relative pressure of 0.05 to 0.95 is indicated by points A, B, C, D, E,
Satisfies the area surrounded by F, G and H, and the relative pressure:
The water vapor adsorption isotherms from 0.05 to 0.90 correspond to points I, J,
A method for producing a grain-oriented silicon steel sheet having excellent coating properties, characterized by using a material that satisfies a region surrounded by K, L, M and N (third invention). Here, FIG.
The coordinates (relative pressure, adsorption amount: ml / g) of each point in are as follows. Point I = (0.05,1.8), Point J = (0.3,4.3)
), Point K = (0.9, 12.5), point L = (0.9, 3
3.2), point M = (0.3, 13.8), point N = (0.05,
8.4).

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an experiment which led to the present invention will be described. C: 0.045 wt% (hereinafter expressed as%), Si: 3.25%, Al: 0.01%, N: 0.0080%, Mn:
A silicon steel slab containing 0.07%, Se: 0.02%, Sb: 0.03% and Cu: 0.08%, with the balance being substantially Fe
After heating at 1400 ° C for 30 minutes, hot-rolled to a thickness of 2.2 mm,
Then, after a norma annealing at 1000 ° C. for 1 minute, the sheet was cold-rolled to a thickness of 0.35 mm at 120 ° C. by a tandem rolling mill, and finished to a final thickness. Next, after decarburizing annealing, an annealing separator mainly composed of MgO was applied and dried to perform final finish annealing. At this time, Mg
As O, the properties shown in Table 1 and those shown in FIG.
Five powders with N ₂ gas adsorption profile (Nanba1～
5) was used.

[0014]

[Table 1]

[0015] In Table 1, CAA40, 80 (s) corresponds to Japanese Patent Publication No. 57-45472.
The hydration was measured at 20 ° C.
It was determined from the loss on ignition after dehydration. The cumulative 50% diameter was measured using a laser diffraction type particle size distribution meter after performing ultrasonic dispersion at 300 W for 3 minutes with a 3% aqueous solution of hexametaphosphoric acid. Furthermore, the N ₂ gas adsorption curve was measured by performing a heat treatment at 400 ° C. for 2 hours in a vacuum as a pretreatment, and then using a constant volume measuring instrument to set the adsorption gas to N ₂ and the adsorption temperature to -196 ° C. Pressure: Measured from 0 to 0.99. In addition, the measured values shown here used data on the adsorption side of the adsorption / desorption curve.

Further, TiO _{2 is} added to each 100 parts by weight of MgO.
Was added as an annealing separator by adding 6 parts by weight of SrSO ₄ and 2 parts by weight of SrSO ₄ . After that, finish annealing from 850 ° C to 1150 ° C for 15 minutes
Heating was carried out at a temperature rising rate of ° C./h, followed by annealing at 1200 ° C. for 5 hours. Table 2 shows the results obtained by examining the magnetic properties and the coating defect occurrence rate of each coil thus obtained. In addition, the coating defect occurrence rate was evaluated using a laser type surface inspection device.

[0017]

[Table 2] As is clear from the table, when the N ₂ gas adsorption curve satisfies the region surrounded by points A, B, C, D, E, F, G and H in FIG. The defect occurrence rate was reduced, and a good film could be obtained. Also, good values were obtained for the magnetic properties. However, even when the N ₂ gas adsorption isotherm satisfies the above range, the occurrence rate of film defects was slightly deteriorated.

Then, next, in order to investigate the cause, as a result of the above-mentioned experiment, the N ₂ gas adsorption isotherm is shown by AB in FIG.
The same experiment as described above was performed using MgO having various water vapor adsorption isotherms shown in FIG. 4 only for powders within the range of CDEFGH. The measurement temperature at the time of measuring the water vapor adsorption isotherm was 25 ° C., the relative pressure was 0 to 0.90, and the other measurement conditions were the same as described above. Table 3 shows the obtained results.

[0019]

[Table 3] As is clear from the table, the N ₂ gas adsorption isotherm is shown in FIG.
In particular, when using MgO that satisfies the range of BCDEFGH and the water vapor adsorption curve satisfies the range of IJKLMN in FIG. 2, particularly good film defect occurrence rates and film adhesion are obtained.

The detailed mechanism by which such a result is obtained has not yet been clearly elucidated, but the inventors consider as follows. MgO for oriented silicon steel sheet
Shows a so-called BET type profile. This is due to the rapid adsorption in the low relative pressure region,
This is a phenomenon that is observed in non-porous or powders with macropores of about 50 nm or more, after the amount of adsorption gradually increases in the medium relative pressure region and then increases rapidly in the high relative pressure region. It is.

Sudden adsorption at a low relative pressure indicates the presence of micropores of several nm or less. In the case of oriented silicon steel, if such micropores are present, they become a slurry before the slurry is formed.
CO ₂ adsorption occurs and is released during finish annealing, causing carburization in the steel and rapid adsorption of moisture.
This water does not desorb at low temperatures and is released at high temperatures, which is harmful and makes it impossible to obtain good magnetic properties. The present results correspond to the fact that the powder having a large amount of adsorption up to a relative pressure of 0.05 resulted in a coating failure.

The medium relative pressure region corresponds to multi-molecule adsorption on the outer surface. Normally, the BET specific surface area is calculated from the data in this region, but roughly speaking, the larger the slope, the larger the external specific surface area. If the specific surface area is too large, the film formation proceeds too much, while if it is too small, the reactivity decreases.

In the high relative pressure region, it is considered that rapid adsorption occurs due to capillary aggregation of the adsorbed molecules into macropores. From the adsorption data, the distribution of macropores can be determined. That is, it is considered that the larger the increase in the amount of adsorption is on the high relative pressure side, the more macropores are present. Micropores have the drawback that CO ₂ and H ₂ O are adsorbed preferentially and are difficult to dissociate. Therefore, they need to be minimized. However, macropores do not have such drawbacks. The macropores affect the filling rate of MgO, and cause shrinkage during finish annealing to adjust the MgO sinterability, thereby causing an effect of changing the coating reactivity. Therefore, the presence or absence of such pores greatly changes the product characteristics and variations thereof. Therefore, it is important that the pores be appropriately present in order to obtain good product characteristics.

Next, regarding the moisture adsorption, unlike the N ₂ gas adsorption, the activation and the chemical adsorption are measured at the same time. Further, the N ₂ gas adsorption, the polarity of the N ₂ gas is low, it is believed that uniformly adsorbed without selectivity for powder surface except for a portion of the micropores, the moisture adsorption, the polarity of the H ₂ O is Since it is strong, the degree of adsorption varies depending on the charged state of MgO, that is, the surface active state. Therefore, from these differences, it is considered that the adsorption of water molecules that occurs when MgO is slurried with water can be evaluated under conditions closer to the process conditions by water vapor adsorption than by N ₂ gas adsorption.

That is, the low relative pressure region indicates that water molecules are easily adsorbed by the micropores, and as in the case of N ₂ gas adsorption, if it is too high, the coating film will be adversely affected. The medium relative pressure region corresponds to adsorption at sites with high hydrophilicity on the outer surface,
If the inclination is large, the amount of water brought in during the finish annealing becomes too large, while if the inclination is small, the amount of water brought in becomes too small, and in any case, the coating deteriorates. The BET specific surface area for moisture adsorption calculated from the data in this region is
By comparing the specific surface area with the N ₂ gas adsorption, the strength of the hydrophilicity can also be evaluated. The amount of adsorption at a relative pressure of 1 extrapolating the high relative pressure region is considered to be equivalent to the hydration amount, but the adsorption at the high relative pressure region is due to capillary aggregation in macropores, and the slurry is dried. It dissociates quickly at low temperatures during medium and finish annealing, and does not significantly affect the steel sheet. Therefore, it is sufficient to measure the relative pressure before the amount of adsorption rapidly increases: about 0.9.

From the above points, the use of the gas adsorption isotherm makes it possible to accurately judge the quality of MgO for an annealing separator. Also, by keeping the N ₂ gas adsorption and water vapor adsorption isotherm in a predetermined range, it is possible to stably obtain a grain oriented silicon steel sheet having a good film quality.

Next, the preferred component composition of the silicon-containing steel which is the material of the present invention will be described. First, there is a method in which C is lowered at the tapping stage so that decarburization annealing is not performed, and a method in which a certain amount is secured to improve the structure and then removed by decarburization annealing. In the former case, the content needs to be 0.01% or less in order to avoid the adverse effect of C. On the other hand, in the latter, the preferable range for improving the structure is 0.01% or more and 0.10% or less.

The content of Si is preferably 2.0 to 4.5%. If less than 2.0%, the effect of reducing iron loss is weak, while 4.5%
%, The cold rolling property is impaired.

An inhibitor constituent element is added in addition to C and Si. AlN, MnS, MnSe and the like are well known as inhibitors, but any of these may be used. When MnS and / or MnSe is used for the inhibitor, M
n: 0.03 to 0.10%, S + Se: 0.01 to 0.03% is preferable. On the other hand, when AlN is used for the inhibitor, Al: 0.01-0.
04%, N: preferably about 50 to 120 ppm. This is because if each component is less than the above range, the effect as an inhibitor is poor, while if each component exceeds the above range, secondary recrystallization becomes unstable. In addition to these, Cu, Sn,
Cr, Sb, Ge, Mo, Te, Bi, P and V can also be used as appropriate. The effective amount of the inhibitor is 0.01% or more and 0.2% or less. In addition,
Each of these inhibitors can be used alone or in combination.

Next, preferred manufacturing conditions will be described. The steel slab having the composition adjusted to the above preferable range is hot-rolled by a known method, and then cold-rolled once or a plurality of times including intermediate annealing to a final thickness. Moreover, it is also possible to perform hot-rolled sheet annealing as needed. Next, after performing primary recrystallization annealing, an annealing separator is applied, and then final finish annealing is performed. The atmosphere, temperature, and time in the primary recrystallization annealing are not particularly limited, but usually, the atmosphere is a steam / hydrogen partial pressure ratio P (H ₂ O) / P (H ₂ ) of 0.05 or more and 0.68 or less. This is for forming a good internal oxide layer.If it is less than 0.05, the oxide layer becomes too thin, while if it is higher than 0.68, the oxygen content in the oxide layer becomes too large, and in any case during the finish annealing Inhibitors become more oxidized,
This is because the magnetic properties often deteriorate. The annealing temperature is desirably 750 ° C or more and 900 ° C or less, and the annealing time is desirably 30 seconds or more and 180 seconds or less. This is because the primary recrystallized grain size falls within a specific range, and the magnetic properties are improved within this range. In addition, a method is known in which the atmosphere during the primary recrystallization annealing and the atmosphere during the soaking are separately controlled to improve the film properties, but this method can also be used in the present invention. Further, when AlN is used as an inhibitor, a method of performing a nitriding treatment before, during, or after the primary recrystallization annealing is known, but in the present invention, such a method may be performed simultaneously.

After the primary recrystallization annealing, an annealing separator mainly containing MgO, that is, containing at least 40% of MgO is used. At this time, as MgO, relative pressure: 0.05-0.
The N ₂ gas adsorption isotherms up to 95 correspond to points A, B, C, D,
Satisfies the area enclosed by E, F, G and H
Furthermore, it is essential to use a water vapor adsorption isotherm having a relative pressure of 0.05 to 0.90 that satisfies the region surrounded by points I, J, K, L, M and N in FIG. It optimizes the distribution and the outer distribution to improve the coating properties. Even if this profile is partially off, a good coating cannot be obtained.

Specifically, the case where the N ₂ gas adsorption isotherm is used as an index is as described above.
Since MgO shows a BET-type profile, the following seven types and combinations thereof may be considered as deviating from the suitable range. (1) The adsorption amount at a relative pressure of 0.05 is higher than that in FIG.
The gas adsorption amount in the low relative pressure section up to 0.05 is too large. (2) The adsorption amount at a relative pressure of 0.05 is lower than that in FIG.
The gas adsorption amount in the low relative pressure section up to 0.05 is too small. (3) Relative pressure: The amount of adsorption gradually increases in the range of 0.05 to 0.8, and is higher than the adsorption isotherm indicated by the line segments FG and GH in FIG. High adsorption amount. (4) Relative pressure: Since the increase in the amount of adsorption is slight in the range of 0.05 to 0.8, in the region on the high relative pressure side within this range, FIG.
The adsorption amount is lower than the adsorption isotherm indicated by the line segments AB and BC. (5) Relative pressure: The amount of adsorption in the range of 0.3 to 0.8 increases extremely sharply, and in the region on the high relative pressure side within this range, the amount of adsorption becomes higher than the line segment FG in FIG. (6) Relative pressure: The amount of adsorption in the range of 0.3 to 0.95 increases very sharply, and in the region on the high relative pressure side within this range, the amount of adsorption becomes higher than the line segment EF in FIG. (7) Relative pressure: The increase of the adsorption amount is delayed in the range of 0.8 to 0.95, and in the high relative pressure side region within this range, the line segment C in FIG.
The adsorption amount is lower than D.

As described above, when the N ₂ gas adsorption isotherm deviates from the preferred range, the following problems occur. In the case of (1), it corresponds to too many micropores,
Deterioration of the coating occurs for the reasons already described. In the case of (2), it is equivalent to too few micropores, and in order to produce such a powder, it is inevitable to make the primary particle size finer with high purity, and the workability during use is reduced. Not only does it have an adverse effect, but also increases manufacturing costs. In the case of (3), the external surface area is too large,
Deterioration of the coating occurs for the reasons already described. In the case of (4), the external surface area is too small,
Deterioration of the coating occurs for the reasons already described. In case (5), the macropores are too small, which means that the crystallite size is too fine, and the reactivity is too high to use. The case (6) corresponds to the macropore being too large or too large, and causes film deterioration for the reasons already described. In the case of (7), it is equivalent to too few macropores,
Deterioration of the coating occurs for the reasons already described.

Similarly, in the case where the water vapor adsorption isotherm is used as an index, the following five types and combinations thereof may be considered as deviating from the preferable range. (1) The adsorption amount at a relative pressure of 0.05 is higher than that in FIG.
Moisture adsorption in low relative pressure area up to 0.05 is too large. (2) The adsorption amount at a relative pressure of 0.05 is lower than that in FIG.
Moisture adsorption in low relative pressure area up to 0.05 is too small. (3) Relative pressure: The adsorption amount gradually increases in the range of 0.05 to 0.9, and becomes higher than the line segments LM and MN in FIG. 2 in the high relative pressure region within this range. (4) Relative pressure: Since the increase in the amount of adsorption was slight in the range of 0.05 to 0.9, in the region on the high relative pressure side within this range, FIG.
Is lower than the line segments IJ and JK. (5) Relative pressure: The amount of adsorption in the range of 0.3 to 0.9 increases very sharply, and in the region on the high relative pressure side within this range, the amount of adsorption becomes higher than the line segment LM in FIG.

As described above, if the water vapor adsorption isotherm deviates from the preferred range, the following problems occur. The case (1) corresponds to an excessive number of micropores from the viewpoint of hydration, and causes film deterioration for the reasons already described. In the case of (2), it is equivalent to too few micropores from the viewpoint of hydration, and in order to produce such a powder, it is inevitably required to have a high purity and a fine primary particle size. Not only adversely affects workability during use but also increases manufacturing costs. The case (3) corresponds to an excessively large external surface area from the viewpoint of hydration, and the hydration proceeds excessively, and the finish annealing atmosphere becomes peroxidized, resulting in film deterioration. In case (4), the external surface area is too small from the viewpoint of hydration, and the amount of hydration is too small, so that the finish annealing atmosphere is over-reduced and the coating deteriorates. In the case of (5), the macropores from the viewpoint of hydration correspond to too small, and, similarly to (3), the hydration proceeds too much and the film deteriorates.

Therefore, the N ₂ gas adsorption isotherm is represented by the points A,
The region surrounded by B, C, D, E, F, G and H is satisfied, and the water vapor adsorption isotherm is shown in FIG.
It is important to satisfy the area enclosed by J, K, L, M and N.

Here, regarding the measurement of the gas adsorption isotherm, N ₂
It is better to measure at a liquid nitrogen temperature of -196 ° C. for gas adsorption because the amount of adsorption is larger at a low temperature and the tendency to read the tendency is easy. Deviations during measurement up to ± 1 ° C are allowed. In addition, in N ₂ gas adsorption, the quality of MgO is determined by a sudden increase in the amount of adsorption at a high relative pressure.
It is necessary to measure the range from 5 to 0.95, but in the case of water vapor adsorption, the reliability of the measurement data on the high relative pressure side and the relative pressure:
The determination of the quality of MgO based on the high relative pressure side data of 0.90 or more does not differ so much from the usual measurement of the amount of hydration. Therefore, it is sufficient to measure only the relative pressure range of 0.5 to 0.90.

The preferred production conditions for obtaining MgO having the above-mentioned adsorption characteristics are as follows. As a raw material of magnesium oxide, there are magnesium hydroxide, magnesium carbonate, magnesium chloride, basic magnesium carbonate, and the like. In order to keep the pore distribution within the range of the present invention, magnesium hydroxide is preferable as the raw material. This is because magnesium hydroxide is hexagonal and in the form of a hexagonal disk, and during firing, magnesium oxide undergoes a dehydration reaction preferentially from the thickness direction of the hexagonal disk,
This is because the distribution of pores can be easily controlled by adjusting the firing conditions. Raw materials for producing magnesium hydroxide include seawater and bittern, but are not particularly limited thereto. In addition, magnesium oxide is obtained by firing magnesium hydroxide, but if the original hexagonal plate is broken at this time, the state of the macropores changes and it becomes difficult to control it in a good range, so the hexagonal disk is removed. It is desirable to increase the thickness at the magnesium hydroxide stage to 200 mm or more to make it hard to break.

The method for calcining magnesium hydroxide may be either a method using a muffle furnace or a method using a rotary kiln. The surface area and pore distribution vary greatly depending on the firing conditions. In order to keep the surface area and the pore diameter within the range of the present invention, the firing temperature is preferably from 700 ° C to 1200 ° C.
Also, the degree of firing varies depending on the processing amount. For example, in the case of a muffle furnace having a volume of about 0.5 m ^{3, the} amount of insertion at one time is desirably about 10 cm to 70 cm, and in the case of a rotary kiln, the processing amount is 30 kg / h and not more than 200 kg / h. In addition, as an effective method for keeping the gas adsorption isotherm within an appropriate range, several types of MgO having various pore distributions and surface areas are prepared by changing the firing conditions in various ways. Should be mixed.

In addition, as the MgO to be used,
Since the sinterability is enhanced when the impurities are present in an appropriate amount, a small amount is effective. However, if the content is too high, a coating defect will occur. CaO: 0.25~0.80%, B: 0.05~0.18 %, SO 3: 0.03~
1.0%, halogen: 0.005% to 0.08% in total. The hydration amount was 0.5 to 3.5 in a hydration test at 20 ° C for 60 minutes.
% And the same level as in the past. Further, regarding other powder properties, the CAA 40% is as good as before in the range of 30 to 190 seconds. The average particle size varies greatly depending on the measurement method.However, when using a laser diffraction particle size distribution meter, it is preferable that the average particle size is less than 4.5 μm so as not to impair the adhesion of the steel sheet. In order not to impair the thickness, a thickness of 0.2 μm or more is preferable.

The auxiliary used for improving the magnetic properties and the film may be a conventionally known one.
Oxides, hydroxides, sulfates and the like of Cu, Nb, Tl, Sr, Bi, Fe, Sn, Ti and Mg are known. When these compounds are added, the total amount is preferably about 0.5 to 15 parts by weight based on 100 parts by weight of MgO.

The final finish annealing after the application of the annealing separating agent as described above may be performed by a conventionally known method. After these series of treatments, an insulating tension coat is applied and flattening annealing is performed to finish the product. Thus, a grain-oriented silicon steel having excellent coating properties and magnetic properties can be obtained.

[0043]

EXAMPLES Example 1 C: 0.05%, Si: 3.28%, Al: 0.015%, N: 75 ppm,
Mn: 0.07% and Sb: 0.01%, the balance being substantially Fe
The steel slab is heated to 1200 ° C, hot-rolled to a thickness of 2.2 mm by hot rolling, then subjected to a 1-minute immersion annealing at 900 ° C, and then cold-rolled to a thickness of 0.35 mm using a tandem rolling mill. Finished thick. Then, after decarburizing annealing at 840 ° C for 2 minutes,
As an annealing separator, a mixture obtained by adding 6 parts by weight of TiO ₂ and 1 part by weight of SrSO ₄ to 100 parts by weight of MgO was applied.
Let dry. At this time, powder Nos. 1, 3, 5, 7, 9 shown in Table 1 above were used as MgO. afterwards,
Heating rate from 800 ° C to 1150 ° C as finish annealing: 20 ° C
, Followed by purification annealing at 1150 ° C. for 5 hours in a dry H ₂ atmosphere. Table 4 shows the results obtained by examining the coating properties and magnetic properties of the steel sheet thus obtained.

[0044]

[Table 4]

As is clear from the table, when MgO whose gas adsorption isotherm satisfies the proper range of the present invention, good values are obtained not only in the film properties but also in iron loss and magnetic flux density. Was completed.

Example 2 A steel slab containing 0.06% of C, 3.28% of Si, 0.07% of Mn, 0.02% of Se and 0.025% of Sb, and the balance being substantially Fe was heated to 1400 ° C. And hot-rolled to a thickness of 2.2mm by hot rolling, and then 0.23mm with intermediate annealing at 1050 ° C for 2 minutes
It was cold rolled to a thickness and finished to the final thickness. Then, 840 ℃,
After decarburizing annealing for 2 minutes, TiO ₂ : 2 parts by weight to MgO: 100 parts by weight and various auxiliaries shown in Table 5 as an annealing separator:
After adding 1 part by weight, it was dried after being applied. At this time, as the MgO powder, the powder No.
2, No. 3 and No. 9 were used. After that, it was kept at 820 ° C for 50 hours as finish annealing, and then dried at 1150 ° C in dry H ₂ atmosphere.
Purification annealing was performed for 5 hours. Table 5 shows the results obtained by examining the coating properties and magnetic properties of the steel sheet thus obtained.

[0047]

[Table 5]

As is clear from the table, no matter which of the separating agent auxiliaries is used, when MgO whose powder properties satisfy the proper range of the present invention is used, excellent coating properties and magnetic properties are obtained. Has been obtained.

Example 3 Silicon steel slabs having various chemical components shown in Table 6 were
After heating at 80 ° C for 30 minutes, hot-rolled to a thickness of 2.2 mm,
Then, the sheet was finished to a final thickness of 0.22 mm by cold rolling twice at 1050 ° C. for 1 minute with intermediate annealing. Then 840
After decarburization annealing for 2 minutes at ℃, MgO: 10
A coating obtained by adding 6 parts by weight of TiO _{2 and} 1 part by weight of SrSO ₄ to 0 parts by weight was applied and dried. At this time,
As the MgO powder, the powders No. 2, No. 3, N
o.9 was used. After that, finish annealing at 820 ° C for 15 hours
After the retention, the temperature was raised from 850 ° C. to 1150 ° C. at a rate of 15 ° C./h, followed by purification annealing at 1150 ° C. for 5 hours in a dry H ₂ atmosphere. Table 7 shows the results obtained by examining the coating properties and magnetic properties of the steel sheet thus obtained.

[0050]

[Table 6]

[0051]

[Table 7]

As is clear from the table, regardless of the composition of the material steel sheet, when the MgO according to the present invention was used, excellent film properties and magnetic properties could be obtained.

[0053]

As described above, according to the present invention, if the gas adsorption isotherm is used as an evaluation index, it is possible to accurately judge whether or not MgO for an annealing separator can be applied from the obtained measurement profile. In addition, the use of the MgO of the annealing separator having the above-mentioned gas adsorption isotherm satisfying a predetermined region can stably improve the film characteristics, and furthermore, the direction in which the film characteristics and the magnetic characteristics are excellent. A stable silicon steel sheet can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an appropriate range of an N ₂ gas adsorption isotherm according to the present invention.

FIG. 2 is a diagram showing an appropriate range of a water vapor adsorption isotherm according to the present invention.

FIG. 3 is a graph showing N ₂ gas adsorption isotherms of powder Nos. 1 to 5 used in the experiment.

FIG. 4 is a graph showing water vapor adsorption isotherms of powder Nos. 6 to 10 used in the experiment.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Michio Komatsubara 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. (Without address) Inside the Mizushima Works, Kawasaki Steel Corporation (72) Inventor Atsuto Honda, Atsuto Honda 1-chome (without address) Inside Kawasaki Steel Corporation Mizushima Works

Claims (3)

[Claims] 1. A method for producing a grain-oriented silicon steel sheet, comprising: measuring a gas adsorption isotherm of MgO for an annealing separator prior to its use, and judging the applicability of the MgO based on an obtained profile. Evaluation method of MgO for annealing separator. 2. A hot rolled silicon steel sheet is finished to a final thickness by cold rolling once or a plurality of times with intermediate annealing, followed by primary recrystallization annealing, and then annealing separation using MgO as a main component. In a method for producing a grain-oriented silicon steel sheet, which comprises a series of steps in which a slurry is formed into a slurry with water and then applied to the surface of the steel sheet and then subjected to final finish annealing, the powder characteristic of MgO is set as a relative pressure: 0.05 The N ₂ gas adsorption isotherm from ~ 0.95 to points A, B, C, D, E,
A method for producing a grain-oriented silicon steel sheet having excellent coating characteristics, characterized by using a material satisfying a region surrounded by F, G and H. A method for producing directional silicon steel. 3. A hot-rolled silicon steel sheet is finished to a final thickness by cold rolling once or a plurality of times with intermediate annealing, followed by primary recrystallization annealing, and then annealing separation using MgO as a main component. In a method for producing a grain-oriented silicon steel sheet, which comprises a series of steps in which a slurry is formed into a slurry with water and then applied to the surface of the steel sheet and then subjected to final finish annealing, the powder characteristic of MgO is set as a relative pressure: 0.05 The N ₂ gas adsorption isotherm from ~ 0.95 to points A, B, C, D, E,
Satisfies the area surrounded by F, G and H, and the relative pressure:
The water vapor adsorption isotherms from 0.05 to 0.90 correspond to points I, J,
A method for producing a grain-oriented silicon steel sheet having excellent coating properties, characterized by using a material that satisfies a region surrounded by K, L, M and N.