JPH07138648A - Method for reducing iron loss of grain oriented silicon steel sheet and low iron loss grain oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To subdivide a magnetic domain and to reduce iron loss by providing certain-shaped grooves on the surface of a steel sheet. CONSTITUTION:Plural grooves which are extended in a direction crossing the rolling direction of a steel sheet are formed at constant intervals on the surface of a grain oriented silicon steel sheet. The shape of the groove is made so that the groove depth ratio d/d0 of parts (d) where the angle theta of inclination of side walls constituting the groove to the surface of the steel sheet becomes >=5 deg. to the whole side walls d0 is >=60%. The inside of the formed groove is filled up with Al or Al compound, after that, decarburization/primary recrystallization annealing is executed and the Al or Al compound is made into an Al2O3 base sintered compact. Successively, annealing separating agent is applied on the surface of the steel sheet and the final finish annealing is executed. It is preferable that the grooves which are formed on the surface of the steel sheet have an inclination angle of 0-30 deg. to the orthogonal axis to the rolling direction, intervals of 2-30mm, groove width of 30-1000mum and depth of 5-50mum.

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 having a low iron loss, and in particular, the results of research and development on a technique for providing a groove on the surface of the steel sheet to subdivide magnetic domains to reduce iron loss. Will be described below.

[0002]

2. Description of the Related Art Grain-oriented silicon steel sheets are mainly used for transformers,
It is used as an iron core for other electrical equipment and has excellent magnetization characteristics, especially iron loss (at the maximum magnetic flux density of 1.7T).
Iron loss when alternating magnetized at a frequency of 50 Hz W _17/50
In addition, it is required to have a low iron loss ( _typically W _15/60 ) when alternating magnetization is performed at a frequency of 60 Hz with a maximum magnetic flux density of 1.5 T). For this purpose, firstly, the secondary recrystallized grains in the steel sheet must be highly aligned with the (110) [001] orientation, the so-called Goss orientation, and secondly, it exists in the final product steel. It is necessary to reduce impurities and precipitates as much as possible. The grain-oriented silicon steel sheet manufactured under such consideration has improved its iron loss value year by year through a lot of improvement efforts to date.
The value of _17/50 is 0.83 W / Kg, the value of W _15/60 is 0.35 W /
A low iron loss of 1b is obtained.

As a technique for reducing iron loss, a technique has been developed in which nonuniformity is introduced into the surface of a steel sheet by physical means to subdivide the width of magnetic domains. For example, in Japanese Examined Patent Publication (Kokoku) No. 57-2252, a laser beam is formed on the surface of the final product plate at a right angle to the rolling direction.
A technique has been proposed in which a beam is irradiated at intervals of several mm and a high dislocation density region is introduced into the surface layer of a steel sheet to reduce the width of magnetic domains and reduce iron loss. Similarly, a technique has been proposed in which a plasma jet is locally introduced into the surface layer of a steel sheet to make the magnetic domain width finer and reduce iron loss. However, these techniques release the strain introduced by heat treatment such as punching of steel sheet, shearing, winding, etc. after stress relief annealing or coating bake treatment.
It has a drawback that the iron loss reducing effect is diminished.

On the other hand, JP-A 1-211903
No. 2,294,427 and No. 3-138318, press rolls with protrusions are provided on the surface of the steel sheet after the final finish annealing to form dents, or strain energy due to denting is used to directly under the dents. A heat-resistant magnetic domain subdivision technique has been proposed in which fine crystal grains are formed, and the effects of dents and fine grains do not diminish the effect even by strain relief annealing. However, in these technologies, the protrusions on the roll surface are extremely worn and damaged, and it is difficult to maintain a stable and stable effect.It is also difficult to control the pressing amount of the protrusions, the amount of dents and the amount of added strain. Is difficult to control,
That is, there is a problem in that the expression of fine crystal grains is not stable.

Further, in Japanese Patent Laid-Open No. 1-252728, the surface coating of the steel sheet after the final finish annealing is linearly removed by ultrasonic vibration, and then electrolytic etching is performed to form a groove to form a magnetic domain. A manufacturing technique of a low iron loss grain-oriented silicon steel sheet for subdividing is disclosed. This technology has a large effect of reducing iron loss and is stable, but since the surface coating is made of ceramic, it is difficult to remove the coating, and even if ultrasonic processing technology is used, it is inefficient. Since it requires a coating step, it has not been industrially implemented.

On the other hand, Japanese Patent Laid-Open No. 3-69968 discloses that
Prior to the decarburization / primary recrystallization annealing, a linear notch (groove) is introduced on the surface of the steel sheet, and decarburization / primary recrystallization annealing and final finishing annealing are performed to promote purification. 4-88
No. 121 discloses that after the final cold rolling, an etching resist is linearly applied by printing and then a linear groove is formed by etching, and then the resist is removed, followed by decarburization, primary recrystallization annealing and final Magnetic domain subdivision technology that performs finish annealing
Each has been proposed.

Since these techniques form grooves before final finishing annealing, they are excellent in terms of stabilizing magnetic properties against heat treatment such as strain relief annealing, but unstable in terms of iron loss reducing effect. In particular, in the iron loss reduction effect in the region of medium magnetic flux density such as W _15/60 , the desired target effect may not be obtained in some cases.

[0008]

DISCLOSURE OF THE INVENTION The present invention is often sufficient in reducing iron loss in a magnetic domain refining technique in which a groove is formed after final cold rolling to carry out decarburization / primary recrystallization annealing and final finishing annealing. The present invention proposes a method of manufacturing a low iron loss grain-oriented silicon steel sheet that solves the problems that cannot be obtained in particular, and obtains a stable and excellent iron loss reduction effect.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the inventors conducted the following experiments. That is, on a cold-rolled sheet of silicon steel, grooves having a width of 200 μm and a depth of 20 μm and extending at right angles to the rolling direction were repeatedly formed at intervals of 4 mm in the rolling direction, and after decarburization / primary recrystallization annealing, an annealing separator was used. Using a steel sheet that has been applied, laminated and subjected to final finish annealing, and the same cold-rolled sheet, decarburization and primary recrystallization annealing are performed prior to formation of grooves, and then an annealing separator is applied, After lamination and final finishing annealing, the width is increased by ultrasonic vibration and electrolytic etching.
Table 1 shows the results of measuring the magnetic properties of a steel sheet formed by repeatedly forming grooves having a depth of 200 μm and a depth of 20 μm and extending at right angles to the rolling direction at intervals of 4 mm in the rolling direction. As shown in the table, in the steel sheet in which the grooves were formed before the decarburization and the primary recrystallization annealing, the iron loss W _15/60 was remarkably reduced at the medium magnetic flux density.

[0010]

[Table 1]

As a result of repeated studies to investigate the cause of this, the cross-sectional shape of the groove is important in the reduction of iron loss, especially in the iron loss region of medium magnetic flux density. It was newly found that the shape of the initial groove provided was not preserved finally.

Here, the groove cross-sectional shape of the steel sheet after the final finish annealing obtained in the above-mentioned experiment is shown in FIGS. 1 (a) to 1 (c).
Shown in. The figure (a) shows the groove cross-sectional shape of a steel sheet having a groove with a width of 200 μm and a depth of 20 μm after the final finishing annealing, and the figure (b) shows the cold-rolled sheet before decarburization and primary recrystallization annealing. To the width
It is a groove cross-sectional shape of the steel sheet after final finishing annealing in which a groove having a depth of 200 μm and a depth of 20 μm is formed. In addition, FIG. 7C shows a cold-rolled sheet having a width of 200 μm and a depth of 20 μm in the above-mentioned experiment.
3 shows the groove cross-sectional shape of the steel sheet immediately after forming the groove. It can be seen that in the steel plate of FIG. 6B, the inclination of the side wall of the groove is gentler than that of the example of FIG. Further, it was found that the slower slope of the side wall occurred during the final finish annealing by comparing with FIG. This is because the forsterite film formation during high temperature annealing and the softening of the steel cause viscous flow on the surface of the steel sheet, and a groove smoothing phenomenon occurs in order to reduce the surface energy.

The reason why the iron loss reducing effect is lost due to the gradual inclination of the side wall of the groove is considered as follows. That is, the iron loss is reduced by forming the groove as shown in FIG. 2 (a), because the free magnetic pole (+ and + in the figure) caused by the discontinuity of the magnetic flux (arrow in the figure) on the side wall of the groove. −
This is because magnetostatic energy increases and the magnetic domains are subdivided in an attempt to reduce this energy.

However, when the side wall of the groove is slanted slowly,
The density of the free magnetic poles generated on the wall is low and the μ ^* effect (the effect of reducing the magnetostatic energy by making the direction of spins responsible for magnetism parallel to the wall surface) reduces the increase in magnetostatic energy. Therefore, the subdivision of the magnetic domain is not effectively realized, and the effect of reducing the iron loss cannot be expected so much.

The inventors of the present invention have studied the proper inclination of the side wall of the groove to obtain the effect of reducing the iron loss. As a result, the inclination of the side wall of the groove is preferably perpendicular to the surface of the steel sheet. It was found that if the angle θ of the side wall with respect to the steel plate surface shown in a) (hereinafter, referred to as side wall inclination angle) θ is 5 ° or more, the effect of reducing iron loss can be sufficiently obtained. However, in FIG. 3A, in order to show the entire groove, the magnification ratio in the depth direction and the horizontal direction is shown as 10: 1.

However, the actual groove shapes are very diverse, and it is difficult to control all sidewall inclination angles θ to 5 ° or more. Therefore, the relationship between the occupancy rate of the entire sidewall and the iron loss reduction effect in the portion where the sidewall inclination angle is 5 ° or more was examined. That is, as shown in FIG. 3B, the sidewall inclination angle θ
Is divided into a region of 25 ° and a region of θ <5 °, and the ratio of the length d of the region of θ ≧ 5 ° projected in the groove depth direction to the projected length d _o of the entire sidewall (d / d _o ) X 100%; hereinafter referred to as depth ratio). At this time, the side wall inclination angle θ ≧ 5
As the depth ratio of the ° region, the average value of the depth ratios of both side walls was taken. As a result, the depth ratio of the side wall where θ ≧ 5 ° is
It was found that if the content is 60% or more, a sufficient value can be obtained as the iron loss reduction effect.

Next, an intensive study was conducted on a method of maintaining the above-mentioned proper groove shape even after final finishing annealing. That is, the idea of filling the groove with a sintered body of oxide was attempted, and various oxides were tried to be filled, but no good result was obtained. This is because many oxides are reduced by Si in the steel during final finish annealing, and as a result, the initial groove shape cannot be retained. In addition, for the specific oxides that are not reduced by Si in the steel, except for the oxides described below, it is difficult to sinter after filling the groove, and after all, the shape of the steel plate surface base metal after the final finish annealing is retained. I can't do it again
When high-temperature heat treatment was performed in order to accelerate the sintering, the result was that the secondary recrystallization in the final finish annealing became defective.

Therefore, the present inventors have conceived a method of giving up the filling of the oxide with the groove, filling the groove with a metal or a compound, and forming an oxide sintered body during decarburization / primary recrystallization annealing. . As a result of various experiments, it was found that filling the groove with Al or an Al compound was extremely effective for this method, and completed the present invention.

That is, according to the present invention, the surface of the grain-oriented silicon steel cold-rolled sheet has a groove depth direction which occupies the entire side wall of the portion where the inclination angle of the side wall forming the groove is 5 ° or more with respect to the steel plate surface. A plurality of grooves having a ratio of 60% or more and extending in a direction crossing the rolling direction of the steel sheet are formed at intervals in the rolling direction, and Al or an Al compound is attached to the grooves, followed by decarburization /
Performed primary recrystallization annealing to remove Al or Al compound from Al ₂ O ₃
It is a method for reducing iron loss of grain-oriented silicon steel sheets, which is characterized by forming a system sintered body, and then applying an annealing separator to the surface of the steel sheet and performing final finish annealing.

Further, according to the present invention, a linear groove extending at an inclination of 0 to 30 ° with respect to a direction orthogonal to the rolling direction is formed at the interface between the metal phase and the oxide phase on the surface of the steel sheet in the rolling direction.
A plurality of grooves are provided at intervals of 30 mm, each groove has a width of 30 to 1000 μm and a depth of 5 to 50 μm, and further, the groove depth occupying the entire side wall of the part where the inclination angle of the side wall of the groove is 5 ° or more. A low iron loss grain-oriented silicon steel sheet having a shape having a ratio in the depth direction of 60% or more.

Next, the method for manufacturing the grain-oriented silicon steel sheet according to the present invention will be described in detail. The material of this invention is
A hot rolled coil obtained by hot rolling is used after making a slab (steel piece) by a known steel making method, for example, a converter, an electric furnace, etc., and further by an ingot-agglomeration method or a continuous casting method. The obtained hot-rolled sheet has a Si content of 2.0 to 4.5.
It is necessary that the composition contains about wt%. That is, if the Si content is less than 2.0 wt%, the iron loss is significantly deteriorated.
This is because if it exceeds 4.5 wt%, the cold workability deteriorates. As for the other components, any component can be applied as long as it is a material component of the grain-oriented silicon steel sheet.

Next, the final target thickness is obtained by cold rolling, but the cold rolling is performed once or twice by sandwiching the intermediate annealing. At this time, if necessary, hot-rolled sheet annealing, warm rolling instead of cold rolling, or aging treatment between rolling passes can be performed.

Next, a groove is formed on the surface of the cold rolled plate having the final plate thickness. As a method of forming a groove, a method of pressing a linear protruding tooth disclosed in Japanese Patent Laid-Open No. 2-294427 and a laser beam, an electric discharge machining, a machine disclosed in Japanese Patent Publication No. 3-69968. However, in order to properly control the groove shape as in the present invention, for example, an etching resist is printed and a groove is formed by electrolytic etching as disclosed in JP-A-4-88121. The technique of forming is optimal.

Here, the region where the groove is provided on the surface of the cold rolled plate needs to be linear, and the linear shape may be any of a straight line, a wavy line, a broken line and a dotted line. Furthermore, it is necessary that the direction of the linear groove be 0 to 30 ° with respect to the direction orthogonal to the rolling direction, that is, the direction orthogonal to the rolling direction or an angle within ± 30 ° of deviation from this direction. However, if the deviation exceeds 30 °, the magnetic domain refining effect cannot be obtained. Further, it is necessary to repeatedly provide the grooves in the rolling direction, and the appropriate value of the interval is 2 to 30 mm. When the distance is less than 2 mm, the hysteresis loss is increased, and the iron loss is deteriorated. On the other hand, when the distance exceeds 30 mm, the sufficient iron loss reducing effect cannot be obtained.

The cross-sectional shape of the groove is one of the requirements of the present invention. The groove width is 30 to 1000 μm and the groove depth is 5 to 5.
It is necessary to set it to 50 μm. If the width of the groove is less than 30 μm, the effect of reducing iron loss is poor, and if it exceeds 1000 μm, the hysteresis loss increases and the iron loss deteriorates. Further, when the depth of the groove is less than 5 μm, the effect of reducing iron loss is poor, while when it exceeds 50 μm, hysteresis loss is increased and iron loss deteriorates.

Further, it is particularly necessary to strictly control the sidewall inclination angle of the groove. That is, a groove is formed in which the ratio of the portion having a sidewall inclination angle of 5 ° or more is 60% or more as the depth ratio with respect to the entire sidewall. If the inclination angle is less than 5 °, the effect of subdividing the magnetic domain hardly appears, and if the depth ratio of the side wall portion that is 5 ° or more is less than 60%, the subdivision of the magnetic domain is not effective, and the predetermined value is not obtained. Cannot obtain the effect of reducing iron loss.

Then, Al or Al compound is adhered to the groove portion of the cold rolled plate having the groove controlled on the steel plate surface as described above, and the Al or Al compound is decarburized / primary recrystallization annealing in the next step. The point of forming an Al ₂ O ₃ based sintered body is the most characteristic of the present invention.

The Al or Al compound may be any substance as long as it becomes an oxide in the oxidizing atmosphere in the next step and the sintering of the oxide proceeds, for example, Al plating, Al paste, active Al _{2 O 3, AlCl 3, Al (} OH) 3, Al (NO 3) 3, 9H 2 O,
AlN, AlPO ₄ ,, K ₂ Al ₂ (SO ₄ ) ₄ ,, Al (OH) ₂ CC ₁₇ H ₃₅ COO), Al ₂ (S
Al or Al compounds such as O ₄ ) ₃ nH ₂ O are advantageously suitable.

The adhesion of the substance to the groove may be carried out immediately after the formation of the groove or in a separate step, and the method of adhering to the groove is not limited. Further, the amount of adhesion to the groove is preferably such that the groove is filled and is simple, but it is not always necessary to fill the inside of the groove. That is, in the final finish annealing, it is sufficient that the groove shape is retained in an amount sufficient to maintain the groove shape.

The steel sheet having such a substance deposited in the groove is subjected to decarburization and primary recrystallization annealing in an oxidizing atmosphere.
Again, the usual decarburization and primary recrystallization annealing conditions are sufficient. A subscale is formed on the surface of the steel sheet, and the subscale and the annealing separator applied to the surface of the steel sheet undergo a solid phase reaction during final finishing annealing to form a forsterite coating.

However, Al deposited in the groove or
Al compounds, except for active Al ₂ O ₃ , undergo oxidation to form Al ₂ O ₃
It becomes a sintered body of the system. Further, in active Al ₂ O ₃ , crystallization and sintering proceed.

The Al ₂ O ₃ system sintered body existing in these grooves reacts with the annealing separator in the final finishing annealing in the next step, and the MgO, Al ₂ O ₃ system oxide sintered body is processed into the groove. Generated in,
Unlike the subscale formed during decarburization and primary recrystallization annealing, it is possible to maintain a predetermined groove shape even after decarburization and primary recrystallization annealing. By this action,
The magnetic domain subdivision effect can be fully exhibited.

The steel sheet after the final finish annealing is used as a product as it is, as in the usual case, or is further used as a product after being coated with a top coat, and stably exhibits good magnetic properties.

Further, in the grain-oriented silicon steel sheet of the present invention, MgO, Al ₂ O ₃ -based oxide is present in the groove portion,
The interface between the base iron phase and the surface oxide phase of the steel sheet has the following characteristic shape.

That is, the interface between the base metal phase and the surface oxide phase has a linear groove shape, and the width of this groove is 30 to 1000 μm.
, The depth is 5 to 50 μm, and the side wall inclination angle of the groove is 5
Depth ratio of the part that is more than 60 ° is 60% or more, and the direction of the linear groove is 0 to 30 ° with respect to the direction orthogonal to the rolling direction, and the groove interval is rolled. It needs to be 2 to 30 mm in the direction.

Here, the groove at the interface between the base iron and the oxide is
If the width is less than 30 μm or the depth is less than 5 μm, the iron loss reducing effect is poor, and conversely, the width is 1000 μm or the depth is 50 μm.
If it exceeds, the hysteresis loss increases and the iron loss deteriorates. Further, when the depth ratio at which the inclination angle of the wall of the groove cross section is 5 ° or more is less than 60%, the free magnetic pole is not sufficiently formed on the wall surface, and the predetermined iron loss reducing effect cannot be obtained.

[0037]

【Example】

Example 1 A grain-oriented silicon steel material containing Si: 3.2 wt% was formed into a cold-rolled plate having a thickness of 0.23 mm according to a conventional method, and then a slit having a width of 200 μm was formed on the surface of the steel plate in a direction orthogonal to the rolling direction. An etching resist was printed so that the slit interval in the rolling direction was 4 mm pitch in the rolling direction, and the groove having a depth of 20 μm was etched by adjusting the current density and the electrolytic solution flow rate. At this time, the depth ratio of the portion where the sidewall inclination angle of the etching groove was 5 ° or more was 82%. This coil is divided into two, one is filled with Al paste in the groove (invention example), the other is left as it is (comparative example), the etching resist is removed,
Decarburization and primary recrystallization annealing were performed at 840 ° C for 2 minutes in a wet hydrogen atmosphere. Furthermore, both were coated with an annealing separator containing MgO as the main component, and then wound into a coil and subjected to secondary recrystallization and 1200
A final finishing anneal consisting of a refining anneal at 5 ° C. and 5 hours was performed. After that, the unreacted annealing separator was removed, and the tension coating was baked at 800 ° C. for 2 minutes also as the flattening annealing. Table 2 shows the magnetic properties of both.

[0038]

[Table 2]

Further, the surface coating and oxides of both product plates were removed with molten caustic soda, the base metal surface was exposed, and the groove cross-sectional shape was measured. The results are shown in FIG. As shown in the comparative example in b), a remarkable difference occurs between the two, and in the case of the embodiment, the depth ratio of the sidewall inclination angle of 5 ° or more is 79%, whereas in the case of the comparative example, the depth ratio is 52%. It had fallen to%.

Example 2 A grain-formed silicon steel material containing Si: 3.3 wt% was formed into a cold-rolled plate having a thickness of 0.23 mm by a conventional method, and then grooves were formed in the same manner as in Example 1. Grooves of various shapes were formed at each position in the longitudinal direction of the coil by changing the current density of electrolytic etching and the flow rate of the electrolytic solution. That is, the depth ratios of the portions where the side wall inclination angle of each groove was 5 ° or more were 18%, 26%, 43%, 64%, 78% and 94%, respectively. After filling the grooves of the coil with fine particles of activated alumina, an annealing separation agent containing MgO as a main component was applied, and the coil was wound into a coil and subjected to final finish annealing. After the final finish annealing, remove the unreacted separating agent, and also perform the flattening annealing at 800 ℃,
The tension coating was baked for 1 minute. Table 3 and FIG. 5 show the magnetic characteristics of each part of the coil and the depth ratio of the part where the sidewall inclination angle is 5 ° or more with the coating and oxides removed.

[0041]

[Table 3]

Example 3 A grain-oriented silicon steel material containing Si: 3.2 wt% was formed into a cold-rolled plate having a thickness of 0.20 mm according to a conventional method, and when an etching resist was printed, a part of the steel plate was Set the slit width to 10, 20, 30, 50, 100, 500, 1000, 1500, 20
Changed to 00 μm and the depth of electrolytic etching is 14 to 18 μm
m. The remaining steel plate has a slit width of 200 μm.
Then, the electric quantity of the electrolytic etching was changed and the etching depth was changed to 2, 3, 5, 15, 20, 50, 60, 100 μm. Each of these grooves had a linear shape extending in a direction inclined by 10 ° from the direction orthogonal to the rolling direction, and the interval in the rolling direction was 4 mm. Further, the current density of electrolytic etching and the flow rate of the electrolytic solution were controlled so that the depth ratio of the sidewall inclination angle of the groove was 5 ° or more was about 80% in all cases.

After removing the resist from these steel sheets, the groove was filled with AlN and subjected to decarburization and primary recrystallization annealing in a wet hydrogen atmosphere. After that, an annealing separating agent containing MgO as a main component was applied and wound into a coil, and then subjected to final finishing annealing. After the final finish annealing, the unreacted separating agent was removed, and then the tension coating was baked at 840 ° C. for 1 minute also for flattening annealing. The relationship between the groove shape and iron loss of these products is shown in FIGS. 6 and 7.

[0044]

According to the present invention, in a low iron loss grain-oriented silicon steel sheet having a groove at the interface between the steel base metal and the surface oxide, the sectional shape of the groove is regulated, and even after the final finish annealing, In order to maintain such a groove shape, by depositing a specific substance in the groove before decarburization and primary recrystallization annealing,
An extremely good iron loss characteristic can be stably obtained, which is industrially useful.

[Brief description of drawings]

FIG. 1 is a diagram showing a change in groove cross-sectional shape due to final finish annealing.

FIG. 2 is a diagram for explaining that the inclination of the wall of the groove cross section affects the density of free magnetic poles generated on the wall.

FIG. 3 is a diagram defining a wall inclination angle and a depth ratio of a portion having an inclination angle of 5 ° or more.

FIG. 4 is a view showing a result of measuring a groove cross-sectional shape at an interface between a base iron and a surface oxide of a product plate.

FIG. 5 is a diagram showing a relationship between a ratio of a portion of a groove wall having an inclination angle of 5 ° or more and magnetic characteristics.

FIG. 6 is a diagram showing a relationship between groove depth and iron loss of a product.

FIG. 7 is a diagram showing a relationship between groove width and iron loss of a product.

Claims (2)

[Claims] 1. A ratio in the groove depth direction of the portion of the side wall forming the groove where the inclination angle of the side wall forming the groove is 5 ° or more with respect to the surface of the steel plate in the groove depth direction is 60%. Grooves extending in a direction crossing the rolling direction of the steel plate in the above shape,
A plurality of Al or Al compounds are formed at intervals in the rolling direction, Al or Al compound is deposited in the grooves, and then decarburization / primary recrystallization annealing is performed to convert Al or Al compound into an Al ₂ O ₃ system sintered body. None, and then a method for reducing iron loss of grain-oriented silicon steel sheets, characterized by applying an annealing separator to the surface of the steel sheet and performing final finishing annealing. 2. A linear groove extending at an inclination of 0 to 30 ° with respect to a direction orthogonal to the rolling direction at the interface between the metal phase and the oxide phase on the surface of the steel sheet at intervals of 2 to 30 mm in the rolling direction. Multiple grooves are provided, each groove having a width of 30 to 1000 μm and a depth of 5 to 50 μm
Low iron loss, characterized in that the ratio of m is 60% or more in the groove depth direction occupying the entire side wall of the portion where the inclination angle of the side wall of the groove with respect to the steel plate surface is 5 ° or more. Grain-oriented silicon steel sheet.