JPS63259023A - Manufacture of grain-oriented silicon steel sheet mimimal in iron loss - Google Patents

Abstract

PURPOSE:To attain magnetic properties equal to those provided by a forsterite film- removing method, by carrying out secondary recrystallization annealing and purification annealing in a course of manufacturing stages by means of box annealing in a coiled state and continuous annealing at high temp. for a short period, period, respectively, and by forming an insulating film. CONSTITUTION:A silicon-containing steel slab is hot-rolled, cold-rolled once or two or more while process-annealed between the above cold rolling stages, and subjected to decarburizing and primary recrystallization annealing and successively to final finish annealing including secondary recrystallization annealing and purification annealing so as to be formed into a grain-oriented silicon steel sheet. In the above stages, final finish rolling is carried out by box annealing, and this box annealing is interrupted at the point of time when the secondary recrystallization annealing is finished, and the succeeding purification annealing of the steel sheet is carried out by continuous annealing at high temp. for a short period. Then an insulting film is formed on this steel sheet. By this method, the grain-oriented silicon steel sheet having magnetic properties equal to those provided by the method consisting of forming and then removing a forsterite film and requiring much labor and cost can obtained without adopting the above method.

Description

[Detailed Description of the Invention] (Field of Industrial Application) In recent years, remarkable efforts have been made to improve the electrical and magnetic properties of grain-oriented silicon steel sheets, and in particular to meet the extreme demands of reducing iron loss. Our development efforts are gradually bearing fruit, but one serious problem associated with their implementation is that when unidirectional silicon steel sheets are processed and assembled and then subjected to so-called strain relief annealing, their properties deteriorate. It has been pointed out that there are disadvantages in that this inevitably involves the use of treasury materials and restrictions on how they can be used.

In this specification, the following is related to the results of research and development that will lead to a new method that can advantageously meet the above requirements, regardless of whether or not it undergoes a high-temperature thermal history such as strain relief annealing. state

As is well known, grain-oriented silicon steel sheets are products in which secondary recrystallized grains are highly concentrated in the (110) <001>, or Goss, orientation, and are mainly used in transformers and other electrical equipment. It is used as an iron core, and the product's magnetic flux density (Bl.

) is high (, iron loss (W I ``I/''A O
(represented by the value) is required.

This grain-oriented silicon steel sheet is manufactured through a wide variety of complicated processes, but numerous inventions and improvements have been made so far, and today the magnetic properties of a product with a thickness of 0.30 mm have reached Bo
o 1.90T or more, 匈, wa 7. . 1. 0 koji 8g down,
In addition, the magnetic properties of a product with a plate thickness of 0.23 mm are 81°1.8
9T or more, WBzs. Unidirectional silicon steel sheets with ultra-low core loss of 0.90 匈/kg or less are being manufactured.

Particularly recently, there has been a marked increase in demand for power loss reduction features from an energy-saving perspective, and in Europe and the United States, when creating a transformer with low loss, the reduction in iron loss is converted into a monetary value and added to the transformer price.・The "evaluation" (iron loss evaluation) system is becoming widespread.

(Prior art) Under these circumstances, recently, the removal of the forsterite film on a grain-oriented silicon steel sheet or its formation has been prevented, the surface of the steel sheet has been smoothed, and a tensile strength film has been formed on the steel sheet, thereby making it extremely ferrous. Techniques have been developed to provide grain-oriented silicon steel sheets with low loss.

For example, Japanese Patent Application Laid-Open No. 1821/1983 discloses that the forsterite base film on the surface of a steel plate after finish annealing is removed, and then polished to a smooth surface of 0.4 μm or less, and further CV
A technique has been disclosed for providing a grain-oriented silicon steel sheet with extremely low core loss by forming a tension film of nitride, carbide, or oxide by method D.

In addition, in connection with this, in JP-A-62-1882, the composition of the annealing separator applied after decarburization and primary recrystallization annealing is limited, and forsterite is generated during final annealing. After suppressing the reaction and removing the non-metallic material layer on the surface of the directional silicon steel sheet, polishing is performed to create a smooth surface with an average roughness of 0.4 μm or less, followed by CVD and ion implantation. There is a disclosure of a technique for providing a grain-oriented silicon steel sheet with extremely low iron loss by depositing a tension coating of nitride, carbide, or oxide by a method.

Compared to the former method, the latter method does not cover the steel plate surface with a forsterite base film, so the Ra
: The pickling and polishing processes to make the surface smooth to 0.4 μm or less are greatly simplified and the cost can be reduced. The magnetic properties when a tension coating is applied by the above-mentioned method are inferior to those of the former method.

In addition, as a conventional method for preventing the formation of a forsterite film, there is a method that considers the components of an annealing separating agent used before final annealing. That is, JP-A-53-22
No. 113 discloses a method of applying an annealing separator consisting of hydrated silicate mineral powder and fine-grained alumina to a decarburized and primary recrystallized annealed plate with a thickness of 4 μm or less, as disclosed in JP-A-55-89423.
In the publication, A1□0. JP-A No. 59-96278 discloses a method of applying an annealing separator containing Sr as the main component and further containing Sr or Ba compound, and JP-A-59-96278 describes an annealing separation agent containing 8l,03 as the main component and blending inert MgO. Each method of applying the agent is disclosed. However, since all of these methods use A1□03 as the main component, AI and 01 stick locally to the surface of the steel sheet after final annealing, and their removal requires a lot of effort. However, the magnetic properties after smoothing the surface to an average roughness of 0.4 μm or less were the same as when a forsterite film was formed and then removed, but when a tension film was subsequently applied. The magnetic properties when worn are poor.

(Problems to be Solved by the Invention) Therefore, it is an object of the present invention to realize magnetic properties equivalent to a method in which a forsterite film is formed and then removed by a method that does not form a forsterite film. It is.

(Means for Solving the Problems) The inventors formed a forsterite film after smoothing the surface, then removed the film, and compared the sample with a smooth surface to Ra: 0.3 μm and the forsterite film. For the samples whose surfaces were smoothed to Ra: 0.3 μm by suppressing formation, the base steel on the surface layer of the steel plate of each sample was further polished in several stages by chemical polishing, and a tension coating was applied at each polishing stage. Changes in magnetic properties and average roughness were investigated when it was applied.

The results are shown as a function of the polishing thickness from the original steel base surface. As shown in Figure 1, in the forsterite film removal method, the better the magnetic properties become as the average roughness of the steel plate surface becomes 0.4 μm or less In contrast, in the forsterite film formation suppression method, the steel plate surface roughness is Ra
: Even if the thickness is 0.4 μm, the magnetic properties are not improved, and polishing to a thickness of 5 μm or more is required to obtain good magnetic properties. However, polishing the base iron requires a great deal of labor and cost, and is extremely difficult to implement on an industrial scale.

In a series of manufacturing processes for grain-oriented silicon steel sheets, the inventors performed final finish annealing by box annealing, interrupted the box annealing when the secondary recrystallization annealing was completed, and performed the subsequent purification annealing of the steel sheet at a high temperature. It has been found that continuous annealing for a short period of time can be carried out on an industrial scale without increasing costs, and that steel sheets with excellent magnetic properties can be manufactured by this method.

That is, even when box annealing performed at a temperature of 1050 ° C or less is applied to the secondary recrystallization annealing and an annealing separator is used, it is possible to suppress the formation of a forsterite film, and when no annealing separator is used. It was discovered that by avoiding fusion between the steel plates and then hydrogen annealing at high temperature for a short time, oxides on the surface layer of the steel plate quickly floated to the surface layer of the steel plate and impurities in the steel were also removed.

That is, this invention hot-rolls a silicon-containing steel slab, then cold-rolls it once or twice or more with intermediate annealing, and then decarburizes and primary recrystallization annealing, and then In manufacturing a grain-oriented silicon steel sheet through a series of final annealing processes including secondary recrystallization annealing and pure 4H annealing,
A directional steel with extremely low iron loss characterized by performing secondary recrystallization annealing by box annealing in a coiled state, purification annealing by continuous annealing at high temperature for a short time, and then forming an insulating coating. Method for producing raw steel plate and hot rolling of a silicon-containing steel slab, followed by cold rolling once or twice or more with intermediate annealing, followed by decarburization and primary recrystallization annealing, followed by In manufacturing grain-oriented silicon steel sheets through a series of final finishing annealing processes including secondary recrystallization annealing and purification annealing, the secondary recrystallization annealing is performed by box annealing in a coiled state, and the purification annealing is performed at high temperature. Then, the surface of the steel plate is finished to a smooth surface with an average roughness Ra of 0.4 μm or less, and metal or ceramic is coated on the surface by CVD, ion plating, and ion implantation. This is a method for producing a grain-oriented silicon steel sheet with extremely low core loss, which is characterized by forming a tension coating.

Further, in carrying out the invention, it is advantageous to finish the surface of the steel plate into a smooth surface by rolling.

Next, the explanation will proceed according to specific experiments that led to the success of each of the above inventions.

C0,055% (hereinafter simply expressed as %), Si 3
．． 35%, MnO, 075%, SO, 025%, A
A hot rolled sheet containing ffi O, 025% and NO, 0,062% was uniformly annealed at 1150°C for 3 minutes and then rapidly cooled, and then warm rolled at 300°C to obtain a
A final cold-rolled sheet with a thickness of 3 mm was obtained.

Thereafter, decarburization and primary recrystallization annealing were performed in a wet hydrogen atmosphere at 20°C. The annealed plate was divided into three parts, one part was coated with an annealing separator mainly composed of MgO, the other part was not coated with anything, and each part was further divided into eight parts and wound into a coil shape. . Then, insert each coil into the box annealing furnace and
At a heating rate of C/hr, the reached temperature was 850″C, respectively.
, 900°C, 950°C, 1000"C, 1050°
C, 1100°C, 1150°C, and 1200°C, and after reaching each temperature, the furnace was cooled.

Table 1 shows the properties of the obtained steel plate.

Furthermore, the iron loss value (W+7/So) when a coil in which a forsterite film was not formed and the steel plate was not fused was annealed for 2 minutes at 1100"C in an H2 atmosphere in a continuous annealing furnace. are shown in Table 2.

Furthermore, the conventional method was applied to the remaining part of the decarburized and primary recrystallized annealed plate, which was divided into three parts. That is, AhO+ (70
%) and MgO (30%), it is wound into a coil, inserted into a box annealing furnace, and lθ
The temperature was raised to 1200°C at a heating rate of °C/hr.
After being maintained at ℃ for 10 hours, the mixture was cooled in a furnace. There was no forsterite coating formed on the surface of the steel sheet obtained, and the magnetic properties of the steel sheet were W+? /S. =0.92w/kg.

As shown in Tables 1 and 2, for the samples in which secondary recrystallization has been completed, the steel plate obtained by the method of this invention is
It exhibits a lower iron loss value compared to steel sheets obtained by changing the components of the conventional annealing separator and not forming a forsterite film. Further, in the copper plate of the present invention, no oxides were observed in the base iron in the surface layer, and all oxides were present only on the surface, and the steel plate was well purified. In addition, steel plates manufactured using conventional methods and the attained temperature 100 shown in Table 2
The surface of the steel plate at 0'C and 1050°C was lightly pickled, and chemically polished in 3% HF and lhO□ solution to obtain Ra0.
Smooth surface finish to center line average roughness of 03μm, then C
An ultra-thin tension film of TiC was formed with a film thickness of 0.4 μm by the VD method. As shown in Table 3, the iron loss of the steel plate obtained by the method of this invention was found to be extremely excellent.

Table 3 (Function) The above-mentioned improvement in magnetic properties is achieved by final annealing.
By subjecting the steel plate that has been annealed at a temperature below 1050°C and completed secondary recrystallization to continuous annealing at high temperatures and short periods of time, oxides on the surface of the steel plate float to the surface and purification of the steel plate is also promoted. This is achieved by

Next, a more detailed explanation will be given including the general manufacturing process of the unidirectional silicon steel sheet.

The starting material is a conventionally known unidirectional silicon steel material composition, for example ■C70.01~0.060%, Si: 2.5
0-4.5%, Mn: 0.01-0.2%, Mo
: 0.003-0.1%, Sb: 0.005-0.
2%, one or two types of S or Se, 0.
Composition containing 005-0.05% ■C: Q, 01-0.08%, Si:2. O~4.0
%, Sol AL: 0.005 to 0.06%
, S: 0.005 to 0.05%, N: 0
．． 001-0.01%, Sn: 0.01-0.
5%, Cu: 0.01-0.3%, Mn: 0
．． Composition containing 01~0.2% ■c: o, oi~0.06%, St: 2°O~
4.0%, S: 0.005-0.05%, B:
0.0003~0.0040%, N: 0.001~
0.01%, Mn: 0.01~0.2%. Next, the hot rolled sheet is subjected to homogenization annealing at 800-1100'C and then cold rolled once. One-time cold-rolling to achieve the final plate thickness, or two-time cold-rolling that involves intermediate annealing at 850°C to 1050°C and further cold rolling, in the latter case the initial rolling reduction is 50%. The final reduction rate is from 50% to 80%.
The final cold-rolled plate thickness is 0.15 mm to 0.35 mm at about 5%.

After finishing the final cold rolling, the steel plate finished to the product thickness is subjected to decarburization and primary recrystallization annealing in wet hydrogen at 750"C to 850°C after surface degreasing.

Next, it is wound into a coil, and whether or not an annealing separator is applied at this time does not affect the effects of the present invention.

Box annealing is performed at a temperature higher than the temperature at which secondary recrystallization is completed and at 1
Carry out at a temperature of 0.050°C or less. If the temperature is lower than the temperature at which secondary recrystallization is completed, the initial magnetic properties cannot be obtained and the temperature is 1050'.
If it exceeds C, fusion of the steel plates or formation of a forsterite film will proceed. In the subsequent purification annealing, it is necessary to perform continuous annealing at high temperature and for a short time in hydrogen in order to avoid fusion of the steel sheets.

The annealing temperature is preferably 1000°C or higher.

After this annealing, the nonmetallic substances on the surface are removed by known chemical removal methods such as pickling, mechanical removal methods such as cutting and grinding, or a combination thereof.

After this removal treatment, the steel plate surface is made smooth by conventional methods such as chemical polishing such as chemical polishing and electrolytic polishing, mechanical polishing such as puff polishing, or a combination thereof. Can be easily finished.

Further, by further rolling, it is possible to finish the thickness to 0.4 μm or less. In this case, recrystallization annealing is performed after applying the tension coating in the next step, so the copper plate has a small crystal grain size and is suitable as a silicon steel plate for high frequency use. Therefore, the plate thickness in this rolling is preferably 0.020 to 0.150 mm. In other words, if it is less than 0.020 nun, rolling becomes difficult;
．． If it exceeds 150 clay, it will be disadvantageous in terms of high frequency magnetic properties.

Further, if the surface condition is rougher than average roughness Ra: 0.4 μm, the effect of the tension coating cannot be obtained.

Thereafter, it is necessary to form a tension coating on the smooth surface of the steel plate by CVD, ion plating, or ion implantation.

At this time, conventionally known devices may be used for CVD, ion plating, or ion implantation.

As ultra-thin tension coatings made by these methods, for example, T
i N , T i C, V N , V C, N
bN.

NbC, SiJ, SiC, CrzN, Cr5
Ct.

A42N, A1. C, BN, NiC, CoC.

CoN, MozC, WC, WzN, ZrC, HfC
.

Mnz C, Ta C, TaN, 81203 +
S iOz * Z n O+Ti1t,
ZrO2, SnO,, pe203, Nip,
Cub.

MgO etc. are suitable.

Furthermore, after forming an ultra-thin tensile coating by CVD, ion plating, and ion implantation, an insulating coating mainly composed of phosphate and colloidal silica is applied and baked on top of this.
Naturally, it is necessary for the use of the i-transformer, which has a VA of 10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,”
A conventionally known method may be used.

゛ In addition, by applying magnetic domain refining treatment and applying a tension coating after finishing the surface to a smooth surface state, and applying magnetic domain refining treatment after applying a tension coating, the magnetic properties can be improved. to improve. As for magnetic domain refining processing,
Known methods such as laser irradiation and ion implantation can be applied.

(Example) C: 0.048%, Si: 3.2%, Acid-soluble A
β: 0.025%, N: 0.008%, Mn:
0.060%, S: o, ots% and Sb: 0.0
A silicon steel slab containing 20% was hot rolled by a conventional method, followed by normalizing treatment at 1100°C for 1 minute including rapid cooling, and then cold rolled twice by a known method. The final plate thickness was 0.23 mm. Next, it was subjected to primary recrystallization annealing in a decarburizing atmosphere, and then divided into two parts.

After winding one end into a coil, it is heated to 800℃ in a box annealing furnace.
After secondary recrystallization annealing was performed at a heating rate of 10° C./hr from 100° C. to 100° C., continuous annealing was performed at 1100° C. for 2 minutes in a dry hydrogen atmosphere to obtain a compatible example.

The other is fine particle alumina (90%) with a particle size of 10 μm or less.
After applying an annealing separator consisting of crushed serpentine particles (10%), the coil was wound into a coil, and the temperature was raised from 800°C to 1000°C at a rate of 10°C/hr in box annealing, followed by 1200°C.
After raising the temperature to ℃, it was held for 20 hours, and then the temperature was lowered to obtain a comparative example.

In both cases, the secondary recrystallization was completely completed, and the base iron surface was exposed on the surface of the steel plate. 20 Sing particles were scattered on the surface of the base iron in the conforming example, and forsterite particles were scattered in the comparative example. The magnetic properties of the steel plate at this time are B, , = 1.947 and W,
,,,. =0.92 w/kg, and the comparative example is B1
o=1.947 and Wl? 15G =0.97w/kg
Met.

Next, 10%H for each compatible example! After removing oxides on the surface of this steel plate by light pickling with SO, it was finished to a smooth surface with an average roughness Ra of 0.35 μm by electrolytic polishing, and its magnetic properties were measured. =1.957 and W.I.
7yso=0.91w/kg.

Furthermore, by ion plating method, T
When a tension film of iN was applied, the magnetic properties were B+o=
1.957 and Wl'F15°=0.70w/kg.

1 Yutaka IC: 0.055%, Si: 3.2%, acid soluble A
l: 0.020%, N: 0.0070%, Mn
: 0.055%=S.

A silicon steel slab containing 0.015% and Sn: 0.020% was hot rolled by a conventional method, followed by pickling and cold rolling, followed by rapid cooling at 1050'C for 1 minute. After intermediate annealing, warm rolling is performed using a known method to reduce the temperature to 0.
．． The plate thickness was 23 mm. After decarburization and primary recrystallization annealing, the steel strip was wound into a coil, heated to 900°C in a box annealing furnace, held for 60 hours, and then cooled. After that, continuous annealing was performed at 1150'C for 30 seconds, and the secondary recrystallization was completely completed, and the steel plate surface was exposed, and SiO□ particles were scattered on the surface of the steel plate. The magnetic properties of the steel plate at this time are B1°=1.94T and W, □7. . -0.98w/kg.

Next, oxides on the surface of the steel plate were removed by light pickling with 10% H2SO4, and then electrolytic polishing was performed to obtain an average roughness Ra: 0.
When the magnetic properties were measured with a smooth surface of 30 μm, B, O = 1.95T and W, 5. =0.9
It was 2w/kg.

Next, the coil was divided into two parts, and one part was divided into 4 mm in the direction perpendicular to the longitudinal direction of the coil by the ion plantation method.
After embedding the pitch into the surface layer of the steel plate, a TiN tension film was deposited on the surface by ion plating, and the magnetic properties were as follows: B1° = 1.95T and W + 71
There were 5 + 1 = 0.65 W/kg 11'.

After a TiN tension coating was applied to the remaining coil surface by ion plating, B was embedded into the steel plate in a direction perpendicular to the longitudinal direction of the coil at a pitch of 411IITl by ion implantation, resulting in magnetic properties. is B, ,=1.95T and WH7y,.

=0.67w/kg.

Sharpness C: 0.052%, Si: 3.0%, Acid soluble A
l20, 020%, Mn: 0.070%, S:
A silicon steel slab containing 0.020% and N: 0.0045% was hot rolled by a conventional method, followed by normalizing treatment at 1050"C for 1 minute including rapid cooling, and then by a known method. It was cold rolled twice to have a thickness of 0.23 mm. After decarburization and primary recrystallization annealing, it was wound into a coil and heated at 800"C to 1oo in a box annealing furnace.
After secondary recrystallization annealing was performed at a heating rate of 15°C/hr to o'c, continuous annealing was performed at 1050°C for 13 minutes in a dry hydrogen atmosphere, and the secondary recrystallization was completely completed. , Particles of Sin were scattered on the bare steel surface of the steel plate. The magnetic properties of the steel plate at this time are B. =1
．． 94T and WI+7so =0.92w/kg"i:
'there were.

Next, oxides on the surface of the steel plate were removed by light pickling with 10% H2SO, and the final thickness of the steel plate was made 0.100 pm by cold rolling, and the surface was finished into a smooth surface with an average roughness Ra of 0.20 μm. . Furthermore, when a TtN tension film was applied to this surface by ion plating and annealed at 850°C for 1 minute, its high frequency magnetic properties were as follows.
B, o=1.86T, WS/1ooo=4.5W
/ kgs WI O/+ +100″20・OW/
kg-W I O/400 = 5.2 w/kg and N
V+5z4oo=10.4W/kg・Fu Niwata C: 0.065%, Si: 2.9%, acid soluble 〇: 0.020%, N: 0.0080%, Cu
: 0.05%, Sn 70, 10%, Mr+: 0.
A silicon steel slab containing 0.075% and S: 0.023% was hot rolled by a conventional method, then normalized at 1100°C for 2 minutes including rapid cooling, and then pickled and divided into two parts. , one was cold rolled with a reduction rate of 86% to a final thickness of 0.30 mm, and the other was cold rolled twice with a rapid cooling treatment and intermediate annealing for 2 minutes at 1050 °C (first reduction). The final plate thickness was 0.23 mm.

Next, it was subjected to decarburization and primary recrystallization annealing, then wound into a coil, and secondary recrystallization annealing was performed in a box annealing furnace from 850°C to 1050°C at a heating rate of 25°C/hr. rear,
When continuous annealing was performed at 1100'C for 13 minutes in a dry hydrogen atmosphere, the secondary recrystallization was completely completed, and particles of SiO□, at, and O were present on the exposed steel surface. were scattered. The magnetic properties of the steel plate at this time are as follows: Plate thickness: 0.30 mm: B+. =1.95T, WI
T/S. =1.01w/kg plate thickness 0.23mm: B
+o=1.94T, WIqyso=0.97w/
It was kg.

Next, oxides on the surface of the steel plate were removed by light pickling with 10% Hz SO4, and then electrolytic polishing was performed to obtain an average roughness Ra: 0.
Finished to a smooth surface of 24μm, and measured the magnetic properties, the plate thickness was 0.30mm: B + o = 1.96T, WI
T/S. =0.94w/kg plate thickness 0.23mm: B
to=1.957, Wl,/s. =0.91w/
It was kg.

Furthermore, Ti was deposited on this surface by ion plating method.
When a tension film of N was applied, the magnetic properties were as follows: Plate thickness 0.30 mm: B + o = 1.96 T, Wl
? 15゜=0.83w/kg plate thickness 0.23 body: B +
o””1.95T, W+? 15°=0.70w/kg
Met.

C: 0.040%, Si: 3.3%, Mn: 0
．． 06%, Se: 0.018% and Sb: 0.
A silicon steel slab containing 0.025% was hot rolled by a conventional method, and then cold rolled twice by a known method to obtain a plate thickness of 0.23 mm.

Next, after performing decarburization and primary recrystallization annealing, it was wound into a coil shape and subjected to secondary recrystallization annealing from 800°C to 1050°C at a heating rate of 15°C/hr in a box annealing furnace. When continuous annealing was performed at 1050"C for 13 minutes in a dry hydrogen atmosphere, secondary recrystallization was completely completed, and SiO□ particles were scattered on the bare steel surface. The magnetic properties of the steel plate at this time were B, , = 1.927
and Wl7/So =0.97w/kg.

Next, oxides on the steel plate surface were removed by light pickling with 10% thsO4, and then electrolytic polishing was performed to improve the average roughness Ra.
: When the finished magnetic properties were measured on a smooth surface of 0.18 μm, B = 1.93T and WIT/S. =0.
It became 91w/kg.

Furthermore, by ion plating method on this surface,
When a TiN tension film was applied, the magnetic properties were B+o.
=1.937 and W , , , . -0,77w/kg
It became.

(Effects of the Invention) According to the present invention, it is possible to establish a method for manufacturing a grain-oriented silicon steel sheet without a forsterite coating and having good magnetic properties.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between magnetic properties and polishing thickness. Drawing 1 by the same patent attorney, Ko Sugimura

Claims (1)

[Claims] 1. A silicon-containing steel slab is hot rolled, then cold rolled once or twice or more with intermediate annealing, and then subjected to decarburization and primary recrystallization annealing, In manufacturing a grain-oriented silicon steel sheet through a series of subsequent steps of final finish annealing including secondary recrystallization annealing and purification annealing, secondary recrystallization annealing is performed by box annealing in a coiled state and purification annealing. A method for producing grain-oriented silicon steel sheets with extremely low iron loss, characterized by performing continuous annealing at high temperatures and in a short period of time, and then forming an insulating film. 2. A silicon-containing steel slab is hot rolled, then cold rolled once or twice or more with intermediate annealing, then subjected to decarburization and primary recrystallization annealing, followed by secondary recrystallization annealing. In manufacturing grain-oriented silicon steel sheets through a series of final annealing processes including crystal annealing and purification annealing, secondary recrystallization annealing is performed by box annealing in a coiled state, and purification annealing is performed at high temperature and in a short time. Then, the steel plate surface is finished to a smooth surface with an average roughness Ra of 0.4 μm or less,
A method for producing a grain-oriented silicon steel sheet with extremely low iron loss, characterized in that a metal or ceramic tension coating is formed on the surface by a CVD method, an ion plating method, or an ion implantation method. 3. The manufacturing method according to claim 2, wherein the smooth surface finishing is performed by a rolling method.