JP2667110B2 - Method for manufacturing mirror-oriented silicon steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented silicon steel sheet (hereinafter referred to as grain-oriented electrical steel sheet) having a mirror-finished steel sheet surface and extremely low iron loss. In particular, complete the secondary recrystallization step (finish annealing step) without forming a forsterite (hereinafter, referred to as glass) film on the surface,
Thereafter, treatments such as magnetic domain refinement and tension coating are performed to improve iron loss characteristics.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are frequently used as magnetic iron cores for electrical equipment, and improvements have been repeatedly made to reduce energy loss. As a means for reducing iron loss of grain-oriented electrical steel sheets, a method of irradiating a laser beam to a material surface after finish annealing to impart local strain, thereby subdividing magnetic domains to reduce iron loss is disclosed in, for example, 26405. Means for preventing the magnetic domain refining effect from disappearing even by stress relief annealing is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-8 / 1987.
No. 617. These techniques have resulted in extremely good iron loss levels, but in order to further reduce iron loss values, it is necessary to remove irregularities on the surface of the ground iron that hinder the movement of magnetic domains near the steel sheet surface (smoothing ) Is important.

However, when a silicon steel sheet is processed in a normal manufacturing process, a glass film is formed on the surface of the steel sheet after the finish annealing, and it is necessary to remove the glass film in order to smooth the surface. As a method of removing the glass film, a technique such as pickling has been used for a long time. As a method of smoothing the surface thereafter, there are chemical polishing, electrolytic polishing and the like disclosed in JP-A-64-83620. In order to obtain a smooth surface, it is variously difficult to remove the glass coating once formed and further perform chemical polishing, mechanical polishing, or the like. Because the glass coating has its roots deepened in the ground iron, the amount that must be removed by pickling is 1 μm in steel plate thickness.
As mentioned above, productivity is extremely poor. Further, with the installation of the pickling facility, there are also environmental problems such as chemical concentration management and wastewater treatment.

On the other hand, as a method of not forming a glass film at the time of finish annealing without removing the glass film once formed, U.S. Pat. S. There is a method using an annealing separator which does not react with SiO ₂ , such as Al ₂ O ₃ disclosed in Patent No. 3785882, and a hydrous silicate mineral powder disclosed in Japanese Patent Publication No. 56-3414. This method is superior to the method of pickling and removing the formed glass film. However, also in this method, the Si formed during the decarburizing annealing
Since oxides such as O ₂ remain on the surface, a treatment such as chemical polishing or mechanical polishing is required to smooth the surface. In the chemical method, there are environmental problems such as chemical concentration control and wastewater treatment as in the above-mentioned pickling. In the physical method such as mechanical polishing, the surface with an industrially large area must be smoothed by the same standard. Have difficulty. Japanese Patent Laid-Open No. 64
No.-62417 and JP-A-2-228481, a chloride is added to an annealing separator, and MgO is added during finish annealing.
And a method of suppressing the reaction between SiO _2. This method is currently the most industrially superior, but the point that a thin oxide film remains and the obtained surface roughness is more impaired than when chemical polishing is used has hindered the reduction of iron loss.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide an industrial means for solving the above-mentioned problems in the conventional method and for smoothing the surface of an electromagnetic steel sheet to obtain a low iron loss. The present invention has reduced the iron loss to the utmost by removing the oxide film formed during the decarburizing annealing in the finish annealing of silicon steel, and applying a tension film or subdividing the magnetic domain after smoothing the steel sheet surface. The present invention provides a method for manufacturing a grain-oriented electrical steel sheet having an ultra-low iron loss.

[0006]

Means for Solving the Problems The present inventors have investigated in detail the process of adding various chlorine-containing compounds to an annealing separator to remove an oxide film on a steel sheet surface during finish annealing.
As a result, it was found that if the compound containing Bi and the chloride of the metal were added to the annealing separator, the steel sheet surface after the finish annealing was mirror-finished. It has also been found that when the addition amount is 0.2 parts by weight or more in terms of chlorine, the steel sheet surface after finish annealing is smoothened like a mirror surface. The iron loss characteristics of these grain-oriented electrical steel sheets are those obtained by removing the glass film by pickling, as disclosed in
The present invention was found to be lower than those obtained by removing an oxide film using a chloride disclosed in JP-A-62417 and JP-A-2-228481, and completed the present invention.

The gist of the present invention is that Si: 2 to
After hot-rolling a silicon steel slab containing 7% by weight, annealing is performed as necessary, and one or two or more cold-rollings including intermediate annealing are performed. After decarburizing annealing, bismuth alone or a bismuth compound and In a method for producing a grain-oriented electrical steel sheet containing a chlorine compound of a metal, and applying and drying a substance mainly composed of a metal oxide and a metal hydroxide, a finish annealing is performed. The proportion of the metal hydroxide occupying is to be 1.0 to 25% by weight. As the metal oxide, magnesia, alumina, silica, zirconia, barrier, calcia, strontium oxide and forsterite are effective, and it is preferable to use one or a mixture of two or more thereof.

As the metal hydroxide, magnesium hydroxide, aluminum hydroxide, zirconium hydroxide, barium hydroxide, calcium hydroxide, strontium hydroxide, etc. are effective, and one or a mixture of two or more thereof may be used. Can be. Further, a water slurry of silica can be used as a substitute for metal oxide and metal hydroxide.
The grain-oriented electrical steel sheet after the finish annealing can achieve ultra-low iron loss by removing the annealing separating agent, applying magnetic domain refining treatment, and applying a tension coating.

The surface of the steel sheet after the finish annealing according to the present invention is
The glass coating shows the same smoothness as the steel plate surface after acid cleaning and chemical polishing. A magnetically ideal surface free of surface irregularities that would hinder the movement of the domain wall. Here, the substance mainly composed of a metal oxide and a metal hydroxide is a substance usually called an annealing separator,
It is a material that does not condense at temperatures up to 0 ° C and does not seize with iron. In addition, the metal hydroxide is usually about 1000 ° C.
By the time, it loses (decomposes) water (H ₂ O) and becomes a metal oxide, which plays a role of annealing separation. In the case of magnesium hydroxide, the following reaction occurs around 400 ° C., and the magnesium hydroxide becomes MgO (magnesia) and H ₂ O (water),
MgO serves as an annealing separator. Mg (OH) ₂ → MgO + H ₂ O

Hereinafter, the present invention will be described in detail. Silicon in silicon steel is extremely easily oxidized, and a normal finish annealing forms a glass coating on the surface of the steel sheet. The inventors have
Finishing No. First Sho 64-62417 during annealing in a way which does not form a glass film, is disclosed in JP-A-2-228481, and MgO upon addition to finish annealing chloride in annealing separator SiO ₂ A method for suppressing the reaction with lipase was studied. However, since this technique aims at improving the punching property by removing the glass coating on the steel sheet surface, sufficient surface smoothness and iron loss cannot be obtained.

The present inventors have added various metal chlorides to the annealing separator and investigated the steel sheet surface during the finish annealing in detail. As a result, only when the substance to be added is a chloride of bismuth and when the group A: bismuth alone or a compound of bismuth and the group B: a chlorine compound of a metal include both group A and group B, In addition, it has been found that when the addition amount is 0.2 parts by weight or more in terms of chlorine, the oxide film is removed together with its root and the surface is smoothed during the subsequent high-temperature annealing. Here, the case where the group A and the group B are the same substance is also included. For example, BiOCl (bismuth oxychloride) can be used for Group A, and bismuth oxychloride can also be used for Group B.

Further investigations have found that moisture in the annealing separator plays an important role. By weight, C: 0.05%, Si: 3.3%, Mn: 0.1
4%, S: 0.007%, Al: 0.028%, N:
A slab containing 0.007% was heated at 1150 ° C. and hot rolled to obtain a 1.8 mm hot rolled sheet. After annealing the hot-rolled sheet at 1120 ° C., it was cold-rolled to 0.16 mm, and decarburized annealing was performed at 830 ° C. Thereafter, as a group A, Bi ₂ O ₃ : 5 parts, as a group B, FeCl ₂ (iron chloride): 5 parts, and A as an annealing separator
l ₂ O ₃ (alumina) and Mg (OH) ₂ (magnesium hydroxide) were mixed and used as shown in Table 1.

This annealing separator is applied in the form of a slurry,
Finish annealing was performed at 200 ° C. for 20 hours. Table 1 shows the surface condition after finish annealing, the magnetic domain control by laser, and the iron loss after applying the tension coating (phosphoric acid-chromic acid-colloidal silica system). The state in which the surface condition after finish annealing is expressed as rough indicates that an oxide exists on the metal surface and the metal (silicon steel) is not thermally etched,
The term "mirror surface" means that the surface is mirror-finished by thermal etching.

In general, the movement of metal atoms on the surface of a metal surface is activated at a high temperature and the surface is smoothed. However, if a foreign substance such as an oxide is present on the surface, the smoothing is hindered. As shown in Table 1, when the amount of hydroxide of the annealing separator is 3 parts or more and 25 parts or less, the surface after finish annealing becomes mirror-finished. A water slurry of only Al ₂ O ₃ (alumina) was applied to a steel sheet, dried, peeled off, heated to 1000 ° C., and the weight was measured before and after heating, but there was no change in weight. That is, Al ₂ O ₃ (alumina) did not hydrate (no hydroxide was formed).

[0015]

[Table 1]

A similar experiment was conducted on a magnesia (MgO) water slurry. Ordinary magnesia, electrofused magnesia, magnesium hydroxide in water slurry 1
It was stirred for 0 minutes, then applied to a steel plate, dried and peeled off. This is put in a crucible and baked at 1000 ° C for 2 hours.
When the weight difference before and after was determined, the commercial ordinary magnesia was reduced by 4%, the commercial electrofused magnesia was reduced by almost 0%, and the commercial magnesium hydroxide was reduced by about 30% by weight. When the peeled sample was identified by X-ray diffraction, MgO and Mg (OH) ₂ were found in commercial magnesia, and only MgO was found in commercially available fused magnesia. Is Mg (OH)
Only _two were found. This is because when commercially available magnesia is used in a water slurry, part of the magnesia is hydrated and Mg (OH) ₂
Is shown.

That is, the water slurry of MgO (magnesia) is a mixture of MgO and Mg (OH) ₂ . The inventors also investigated this point in detail. CaO (calcia) hydrates immediately upon contact with water to become Ca (OH) ₂ (heats to high temperature). Therefore, CaO and Ca (O
H) A water slurry of the mixture of ₂ cannot be made. C
In order to use a mixture of aO and Ca (OH) ₂ as an annealing separator, a non-aqueous slurry or dry coating such as electrostatic coating must be used. CaO as a metal oxide,
Even when Mg (OH) ₂ is used as the metal hydroxide, it cannot be used in a water slurry.

As described above, a substance which does not easily react with water, such as Al ₂ O ₃ (alumina), can be easily used as a water slurry. This is because the amount of hydroxide does not change at the time of addition and after coating and drying. Such materials include zirconia as well as alumina. When a substance which reacts relatively easily with water represented by MgO (magnesia) is a water slurry, the components of the annealing separator must be determined in consideration of the amount of hydrate (hydroxide) at the time of application. Must. Also,
The degree of hydration in water slurry differs depending on the manufacturer and brand of commercial magnesia, and its selection is important.

An annealing test similar to the above was conducted using commercially available magnesia. The hydrated water after applying and drying magnesia as a water slurry is 3.9% by weight, and the amount of the metal oxide in the metal oxide and the metal hydroxide is 9.1% by weight. Bi is added to such an annealing separator (100 parts of MgO).
As a result of adding 5 parts of ₂ O ₃ (bismuth oxide) and 5 parts of FeCl ₂ (iron chloride), applying and drying as an annealing separator, and performing finish annealing, an extremely good mirror surface was obtained.

From the viewpoint of the hydration water, the water absorption (adsorption water) of the silica powder is effective. This is because the feature that water is adsorbed on silica and maintained at a relatively high temperature can be used. It is generally considered that the silica surface is covered with SiOH groups (cinoral groups) when it encounters moisture. It is said that this sinoral group releases H ₂ O between adjacent sinoral groups at a high temperature. This is the same as the behavior of metal hydroxide, and an annealing separator using silica powder is also effective. However, since the sinoral group exists only on the surface of the solid, the water content affects the state of the silica particles, and the influence of the particle size greatly affects the silica particles. In the case of particles having a large surface area, that is, generally fine particles, the water content increases.

As the metal oxide, magnesia, alumina, silica, zirconia, barrier, calcia, strontium oxide, forsterite and the like are effective, and a mixture of two or more kinds is also effective. The mechanism by which the oxide film is removed and the surface becomes a mirror surface is not yet clear, but is considered as follows.

Group A: bismuth simple substance or bismuth compound and group B: group A and B when chlorine metal compound is used
An annealing separator containing both groups forms Bi chloride: BiOCl at least above 183 ° C. This BiOCl
Decomposes while generating vapor of BiCl ₃ during the temperature rise in the finish annealing. Since BiCl ₃ has a high equilibrium dissociation chlorine partial pressure, Cl gas is easily generated between the coil plates. Cl gas diffuses the oxide layer on the steel sheet surface, and when it reaches the base iron, Fe + 2Cl →
Generating a vapor of FeCl ₂ according to the reaction of FeCl _2.

The volume of FeCl ₂ at the oxide film / base iron interface
When the gas is generated, the oxide layer and the ground iron are separated. It is presumed that the surface of the base iron is separated from the oxide layer, so that the movement of the surface Fe atoms is facilitated and the surface becomes a mirror surface at a high temperature of 1000 ° C. or higher. The same applies when Bi chloride is used.
Is mixed with water and dried to form BiOCl. Hereinafter, it is presumed that the mirror surface is formed by the same reaction as described above.

Group B: The metal chloride used for the metal chlorine compound must have a boiling point or sublimation point of 183 ° C. or higher. This is because at a low boiling point (114 ° C.) such as stannic chloride (SnCl ₄ ), the gas is gasified before reacting with group A, and the volume increases and disappears. Effective chlorides include iron chloride (FeCl ₂ , FeCl ₃ ),
There are cobalt chloride (CoCl ₂ , CoCl ₃ ), nickel chloride (NiCl ₂ ), antimony chloride and the like, and these may be used as a mixture.

Aluminum chloride (AlCl ₃ ) sublimation point: 183 ° C., antimony trichloride (SbCl ₃ ) boiling point: 221 ° C., nickel chloride (NiCl ₂ ) boiling point: 99
The boiling point is 3 ° C., the iron chloride (FeCl ₂ ) boiling point is 1024 ° C., and the cobalt chloride (CoCl ₂ ) boiling point is 1049 ° C., which is higher than the boiling point or sublimation point of aluminum chloride and is effective for mirror finishing.

Group A: Bismuth alone or a bismuth compound may contain Bi element. In particular, the bismuth compound is preferably Bi powder, bismuth oxide, bismuth hydroxide, bismuth sulfide, bismuth sulfate, bismuth phosphate, bismuth carbonate. , Bismuth nitrate, bismuth organic acid, and bismuth halide are effective.

Here, the reason why the metal hydroxide in the annealing separator is important is that when M is a metal element, H ₂ O (moisture) is released by the following reaction. M (OH) ₂ → MO + H ₂ O This H ₂ O (water) is considered to suppress the following reaction (shift to a higher temperature side). 2 ・ BiOCl + H ₂ → 2 ・ Bi + Cl ₂ +2 ・ H ₂ O

That is, it is considered that the generation of H ₂ O suppresses this reaction. It is presumed that releasing Cl ₂ at a high temperature will increase the reaction rate and lead to efficient utilization.
In addition to magnesium hydroxide, aluminum hydroxide, zirconium hydroxide, barium hydroxide, calcium hydroxide, strontium hydroxide, and the like were effective as metal hydroxides, and mixtures thereof were also effective. If the amount of the metal chlorine compound is less than 0.2 parts by weight of chlorine, the oxide film cannot be removed over the entire area in the coil width direction. Even if the amount of addition is increased, the volume of Cl gas that can be present between the plates is constant, so that BiCl ₃ added extra is added.
Escapes from between the coil plates and has no effect. Further, in order to prevent the steel sheet seizure from occurring during the finish annealing, it is necessary that the separating agent remains to some extent after the bismuth chloride is evaporated. Therefore, the upper limit of the amount of Bi chloride added was 15 parts by weight of chlorine.

The surface of the steel sheet obtained by the present invention maintains a mirror-like luster, and the surface smoothness of the steel sheet is improved and iron loss is reduced as compared with the conventional technology using alkali metal and alkaline earth metal chlorides. Reduced. The present invention aims to obtain a low iron loss, but for other purposes, for example, a compound other than chloride of bismuth, for example, to stabilize secondary recrystallization, such as nitride, sulfide Etc. may be added.

The method of applying the separating agent may be a known method and is not particularly limited. It may be added to water with stirring and applied, or may be applied electrostatically. However, when the metal oxide hydrates as described above, this must be considered. In addition,
The scope of the present invention is such that when the metal oxide is formed into a water slurry as in the case of MgO to form a hydroxide, the hydroxide falls within the scope of the invention to obtain a good mirror surface. Can be.

The grain-oriented electrical steel sheet used in the present invention is an electrical steel sheet subjected to casting, hot rolling, cold rolling and annealing by a known method. A slab to which Si is added in an amount of 2% or more and 7% or less is used for the purpose of obtaining low iron loss. The upper limit is the amount of Si that can be rolled industrially, and the lower limit is the amount of Si that does not undergo transformation during high-temperature finish annealing that can cause mirror finishing. In the state of the finish annealing, since the metal surface is exposed on the surface of the steel sheet, an insulating tension coating is applied by a known method in order to maintain insulation between the sheets when the sheets are laminated. In order to increase the space factor, a technique for forming a thin high-tensile film such as PVD, CVD, or ion plating may be used.

[0032]

【Example】

(Example 1) C: 0.05% by weight, Si: 3.3 by weight
%, Mn: 0.14%, S: 0.008%, Al: 0.
Slab containing 029% and N: 0.007%
After hot-rolling at ℃, it was hot-rolled 1.8 mm. 1120 ° C
After annealing, the hot rolled sheet was cold rolled to 0.15 mm and decarburized annealing was performed at 830 ° C. An annealing separator having the composition shown in Table 2 was applied in the form of a slurry, and finish annealing was performed at 1200 ° C. for 20 hours. After annealing, the surface of the steel sheet was washed with water, and the glass coating was removed with nitric acid to remove the glass coating. After annealing for strain relief, magnetic measurement was performed on a single plate. Table 2 shows the results. According to the technology of the present invention, it can be seen that iron loss lower than removing the oxide film by pickling after finish annealing can be obtained. This is thought to be because the domain wall movement was facilitated by the smooth surface as described above.

[0033]

[Table 2]

(Embodiment 2) 1 to No. A solution containing aluminum phosphate, chromic acid and colloidal silica as main components was applied to the test piece of No. 5 and dried to form a tension film. Table 3 shows the results of the magnetic measurement performed on the single plate. Although iron loss is improved by forming a tension film, the ultimate iron loss value is the lowest in the present invention. The effect of smoothing the surface and facilitating domain wall movement remains even after the formation of the tension film.

[0035]

[Table 3]

(Embodiment 3) 1 to No. The test piece No. 5 was irradiated with a laser beam in a direction perpendicular to the rolling direction at intervals of 5 mm. Table 3 shows the results of the magnetic measurement performed on the single plate.
Although the iron loss is further improved by laser irradiation after the formation of the tension film, the ultimate iron loss value is the lowest in the present invention.
The effect of smoothing the surface and facilitating the movement of the domain wall remains even after the formation of the tension film and the fragmentation of the magnetic domain by laser irradiation.

[0037]

[Table 4]

(Embodiment 4) No. 1 and No. After washing and removing the separating agent in No. 4, a concave portion in the form of a broken line was formed on the plate surface by a gear roll in a direction perpendicular to the rolling direction.
Subsequently, a solution containing aluminum phosphate, chromic acid and colloidal silica as main components was applied and annealed. The annealing temperature is 800 ° C. Table 5 shows the results of single-plate magnetism measurement. It can be seen that the effect of smoothing the surface and facilitating the movement of the domain wall remains even after the magnetic domain refinement by the different orientation fine particles introduced by annealing after the formation of the concave portion.

[0039]

[Table 5]

Example 5 By weight, C: 0.06%, S
i: 3.3%, Mn: 0.14%, S: 0.007%,
A slab containing 0.029% of Al and 0.007% of N was heated at 1150 ° C and hot rolled to obtain a 1.8 mm hot rolled sheet. After annealing the hot-rolled sheet at 1120 ° C., it was cold-rolled to 0.16 mm, and decarburized annealing was performed at 830 ° C. An annealing separator having the composition shown in Table 6 was applied in the form of a water slurry, and was subjected to finish annealing at 1200 ° C. for 20 hours. Magnesia (Mg)
O): 100 parts by weight, Bi compound: 5 parts by weight, metal chlorine compound: 5 parts by weight, and when there are two kinds of metal chlorine compounds, 2.5 parts by weight. Magnesia (MgO) was a commercially available product of KY, stirred in a water slurry state for 10 minutes, applied to a steel plate, dried and peeled, and baked at 1000 ° C. for 1 hour.
Of magnesium hydroxide (Mg (OH) ₂ )
Of MgO + Mg (OH) ₂ was 9.1% by weight.

A solution containing aluminum phosphate and colloidal silica as main components was applied to the material after finish annealing and dried to form a tension film. Further, laser irradiation was carried out at intervals of 5 mm in the direction perpendicular to the rolling direction. Table 6 shows the results of the magnetic measurement performed on the single plate. In the technology of the present invention, the attained iron loss value is low. The effect of smoothing the surface and facilitating the movement of the domain wall remains even after the formation of the tension film and the fragmentation of the magnetic domain by laser irradiation.

[0042]

[Table 6]

[0043]

According to the present invention, there is no need to pickle the glass coating once formed, and a grain-oriented electrical steel sheet having no forsterite coating and having a mirror surface can be obtained by finish annealing. When a magnetic domain is controlled and a tension coating is applied to this material, a grain-oriented electrical steel sheet having extremely low iron loss is obtained. In addition, this material has an extremely high industrial value because it can provide an iron loss value superior to that obtained by pickling the glass coating.

Claims (7)

(57) [Claims] 1. After hot rolling a silicon steel slab containing 2 to 7% by weight of Si, annealing is performed as necessary, and one or two or more cold rollings including intermediate annealing are performed, and decarburizing annealing is performed. Later, in a method for producing a grain-oriented silicon steel sheet containing bismuth alone or a compound of bismuth and a chlorine compound of a metal, and applying and drying a substance mainly composed of a metal oxide and a metal hydroxide to perform finish annealing, A method for producing a mirror-oriented silicon steel sheet, wherein the proportion of a metal hydroxide in an oxide and a metal hydroxide is 1.0 to 25% by weight. 2. The mirror surface according to claim 1, wherein the metal oxide is mainly composed of one or a mixture of magnesia, alumina, silica, zirconia, barrier, calcia, strontium oxide and forsterite. A method for producing a grain-oriented silicon steel sheet. 3. The metal hydroxide is one of magnesium hydroxide, aluminum hydroxide, zirconium hydroxide, barium hydroxide, calcium hydroxide, and strontium hydroxide.
The method for producing a mirror-oriented silicon steel sheet according to claim 1, wherein the method mainly comprises a kind or a mixture of two or more kinds. 4. A silicon steel slab containing Si: 2 to 7% by weight is hot-rolled, then annealed as necessary, and subjected to one or two or more cold-rollings including intermediate annealing, and decarburizing annealing. Thereafter, in a method for producing a grain-oriented silicon steel sheet in which an annealing separator containing bismuth alone or a compound of bismuth and a chlorine compound of a metal is subjected to finish annealing by applying and drying, a water slurry of silica powder is used as the annealing separator. A method for producing a mirror-oriented silicon steel sheet. 5. The method for producing a mirror-oriented silicon steel sheet according to claim 1, wherein after the finish annealing, the annealing separating agent is removed and a tension coating is applied. 6. The method for producing a mirror-oriented silicon steel sheet according to claim 1, wherein after the finish annealing, the annealing separating agent is removed and the magnetic domain is refined. 7. The method for producing a mirror-oriented silicon steel sheet according to claim 1, wherein after the finish annealing, the annealing separating agent is removed, and a magnetic domain refinement treatment and a tension coating are applied. .