JPH01147074A - Grain-oriented silicon steel sheet free from deterioration in property due to stress relief annealing - Google Patents

Abstract

PURPOSE:To reduce iron loss after stress relief annealing by forming a specific insulating film on the surface of a finish-annealed silicon steel sheet and then locally forming regions increased in crystallinity on the above insulating film. CONSTITUTION:A silicon slab is hot rolled and then subjected to finish annealing. At this time, a separation agent at annealing is selected, if necessary, and a forsterite film is formed on the steel sheet surface. An insulating film composed principally of phosphate and colloidal silica is formed on the above steel sheet surface. Subsequently, e.g., by applying electron beam in vacuum in a direction perpendicular to the rolling direction, regions having a crystallinity higher than that of the original surface can be locally formed on the above insulating film. By this method, a grain-oriented silicon steel sheet of low iron loss free from deterioration in properties due to stress relief annealing can be provided.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to grain-oriented silicon steel sheets that do not deteriorate in characteristics due to strain relief annealing, and in particular, devises a phosphate-based insulating coating formed on the surface of the steel sheets. By adding this, it is intended to advantageously improve the magnetic properties, especially the iron loss properties.

Remarkable development efforts in recent years to improve the electrical and magnetic properties of grain-oriented silicon steel sheets, particularly to meet the extreme demands of reducing iron loss, are gradually bearing fruit.

As is well known, unidirectional silicon steel sheets are products in which secondary recrystallized grains are highly concentrated in the (110) <OOb, or Goss orientation, and are mainly used in transformers and other electrical equipment. When used as an iron core, the product is required to have high electromagnetic characteristics such as high magnetic flux density (represented by the Boo value) and low iron loss (represented by the WIT/S value).

This unidirectional silicon steel sheet is manufactured through a wide variety of complicated processes, but numerous inventions and improvements have been made so far, and today products with a thickness of ff0.30mm have magnetic properties of B.
le value 1.90T or more, IL, zs. value 1.05/k
g or less, or the magnetic properties of the product with plate ff0.23mm are BIG value 1.89T or more, 1,7. . Value 0.90%17
Ultra-low core loss unidirectional silicon steel sheets weighing less than 1 kg are now being manufactured.

Particularly in recent years, demand for reducing power loss has become much stronger 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 surface of a unidirectional silicon steel sheet after final annealing is irradiated with a laser in a direction approximately perpendicular to the rolling direction to introduce local microstrain to subdivide the magnetic domains. It has been proposed to reduce iron loss by this method (see Japanese Patent Publication No. 57-2252, Japanese Patent Publication No. 57-53419, Japanese Patent Publication No. 5B-26405 and Japanese Patent Publication No. 58-26406).

This magnetic domain refining technology is effective for transformer materials for laminated core transformers that are not subjected to strain relief annealing, but for material for wound core transformers that are subjected to strain relief annealing,
There is a drawback that the local minute strain introduced by laser irradiation is released by annealing and the magnetic domain width becomes wider, so that the laser irradiation effect disappears.

On the other hand, earlier in Japanese Patent Publication No. 52-24499, the surface of a unidirectional silicon steel sheet after finish annealing was raised to a mirror finish, or the mirror finish surface was plated with metal or an insulating coating was applied thereon. By coating and baking,
A method for manufacturing ultra-low core loss unidirectional silicon steel sheets has been proposed.

However, this method of improving iron loss through mirror finishing cannot be adopted from a process perspective because it does not contribute enough to reducing iron loss, as it significantly increases costs. Due to problems with adhesion, it has not been adopted in current manufacturing processes. Japanese Patent Publication No. 56-4150 also proposes a method in which a steel plate surface is mirror-finished and then an oxide-based ceramic thin film is vapor-deposited. However, this method cannot be used in the actual manufacturing process because the steel plate and the ceramic layer will separate when subjected to high-temperature annealing at 600'C or higher.

Furthermore, Japanese Patent Application Laid-Open No. 59-229419 proposes a method of forming thermal strain regions by locally applying thermal energy to the surface of a silicon steel sheet.

However, the preferential formation of this local thermal strain region occurs at 600°C.
It has the disadvantage that the above-mentioned high-temperature annealing loses its effect.

(Problems to be Solved by the Invention) It is an object of the present invention to compensate for the above-mentioned disadvantages and achieve a significant reduction in iron loss.

(Means for Solving the Problems) That is, the present invention provides a grain-oriented silicon steel sheet having an insulating coating mainly composed of phosphate and colloidal silica on the surface of the finish-annealed steel sheet, This is a grain-oriented silicon steel sheet whose properties do not deteriorate due to strain relief annealing because the coating locally has Al regions with a higher degree of crystallinity than the base material.

In this invention, an insulating coating mainly composed of phosphate and colloidal silica is formed on i) a forsterite coating formed on the surface of a steel sheet after final annealing, or ii) a nonmetallic oxide on the surface after final annealing. Ti, Zr, Iff, V, deposited on the removed surface
Nb, Ta.

Cr I Mo * W + Mn HCo + N
t +^1, B, nitride and/or carbide of Si and Al, Nt.

It is particularly advantageous to deposit it on an ultra-thin tension coating consisting of at least one selected from oxides of Cu, W, St and Zn.

First, the explanation will proceed according to a specific experiment that led to the success of this invention.

C: 0.048% by weight (hereinafter simply expressed as %), Si
: 3.40%, Mn: 0.066%, Se: 0.
020%, Sb: 0.023% and Mo: 0.0
Continuously cast silicon steel slab containing 12% was heated at 1350''C for 4 hours and then hot rolled into a hot rolled sheet with a thickness of 2.0 mm.

Then, after homogenization annealing at 900"C for 3 minutes, 950°C
It was cold rolled twice with 3 minutes of intermediate annealing in between.
A final cold-rolled sheet having a thickness of 23 mm was obtained.

After that, after decarburization and second recrystallization annealing in a wet hydrogen atmosphere at 820°C, the surface of the steel sheet is coated with annealing separator A mainly composed of MgO or inert Al2O:I (75%) and Mg
Apply annealing separator B consisting of O (25%), then 8
Secondary recrystallization annealing at 50'C for 50 hours and 1200''
Purification annealing was performed at C for 5 hours in dry hydrogen.

Among the obtained finished annealed plates, those on which a forsterite film was formed on the surface using A as an annealing separation agent were subjected to the treatments shown in the following (a) to (d).

(a) Electron beam irradiation (EB pre-irradiation acceleration voltage:
65kV, acceleration current: 1. OmA, beam diameter 0.1
5 mmφ, beam scanning interval near).

(b) After applying an insulating coating film mainly composed of magnesium phosphate and colloidal silica on the surface of the final annealed plate, pre-EB irradiation was performed in a vacuum in the direction perpendicular to the rolling direction under the same conditions as in (a) above. .

For comparison, (C) a final annealed plate without EB irradiation and (d) a product plate with the above insulation coating applied after final annealing but without EB pre-irradiation were also prepared.

On the other hand, the surface of the finished annealed plate obtained using B as an annealing separation agent was lightly pickled (in 10% 11Cl solution), and then
The steel sheets were chemically polished in a solution of 1.02% IP and finished to a mirror-like state with an average surface roughness of 0.03 μm, and then divided into four groups of samples, each of which was treated under the following conditions.

(e) A thin film of TiN with a thickness of 1.0 μm was formed on a mirror-finished steel plate using a continuous ion brating device (HCD method).

(f) After forming a 1.0 μm thick TiN film on a mirror steel plate using a continuous ion brating device,
Subsequently, EB pre-irradiation was carried out in a vacuum in a direction perpendicular to the rolling direction. Acceleration voltage: 65 V, acceleration current: 1. OmA.

The beam diameter was 0.15mm, and the beam scanning interval was near mm).

(2) After forming a thin film of TiN with a thickness of 1°0 μm on a mirror-polished steel plate using a continuous ion blating device, an insulating coating film mainly composed of magnesium phosphate and colloidal silica was applied.

A thin film of TiN with a thickness of 1.0 μm was formed on a mirror-finished copper plate by continuous ion blating treatment, and then an insulating coating film mainly composed of magnesium phosphate and colloidal silica was applied, and then it was coated in a vacuum. Pre-EB irradiation was carried out under the same conditions as above) in the direction perpendicular to the rolling direction.

Table 1 summarizes the results of investigating the magnetic properties of each sample subjected to the above treatment and of the product after being subjected to strain relief annealing at 800°C for 2 hours.

As is clear from Table 1, EB irradiation was performed on ordinary unidirectional silicon steel finish annealed plates (a) and (
The magnetic properties in case b) are B. Value is 1.90-1.91
T s W+'? /30 value is 0.81~0.84W/k
In g, the magnetic properties are compared with those in cases (C) and (d) without EB irradiation. Value is 0.05~0.08W/
kg has improved. In addition, after polishing the finish annealed plate, a TiN film is formed by ion blating, and then EB irradiation is performed.) and (h), the magnetic properties are B10.
Value is 1.91-1.92T, W+tzs. value is 0.64
~0.67W/kg, without EB irradiation (e) and (
(up to) compared to the magnetic property values of 1,7. . value is 0
．． It has improved by 0.05 to 0.09 W/kg.

It is noteworthy that when EB is irradiated in this manner, the characteristics do not deteriorate even if strain relief annealing is performed at 800° C. for 2 hours.

Therefore, the inventors investigated the reason for this.

FIG. 1a shows the results of structural analysis using thin film X-rays of the surface coated with an insulating film containing magnesium phosphate and colloidal silica as main components after final annealing.

In addition, the same figure shows the surface after being coated with the above-mentioned insulating film and subjected to EB treatment (conditions (1) in Table 1), and the figure C shows the surface after being coated with the above-mentioned insulating film. After applying EB treatment to the top (condition (b) in Table 1), strain relief annealing was performed at 800°C for 12 hours in N2.
These are the results of an X-ray analysis of a specimen subjected to strain relief annealing at 800°C for 2 hours in No. 2.

In Figure 1 a, Mg2SiO4, a-Fe, CaT
In addition to the iO3 peak, weak (020) and (022)
A peak of MgzP207 on the surface was observed. In addition, as shown in Figure 1, the Mg2SiO4+
In addition to the peaks of α-Fe, CaTiO3, a weak (
020) and strong (022) plane MgzhOt peaks were observed. Furthermore, the insulating film coating shown in Figure C was applied, and the strain relief annealing was performed after EB treatment.
In addition to the TiOs peak, weak (020) and very strong (022) plane MgzPzOt peaks were observed. Furthermore, the strain-relief annealed product after coating with an insulating film shown in Figure d shows weak (020) and strong ( 022) MgzP surface
A peak of zOt (the peak of MgzhOl on the (022) plane is weaker than that under the C condition) was observed.

Next, Table 2 shows the changes in (022) plane strength (strongest peak) of MgzPzOr in the insulating film under each treatment condition shown in Figure 1, as well as the I x 10
- MgzPzOl when subjected to laser and plasma treatment in a vacuum of 'torr and in air, respectively.
The results of the investigation regarding the change in strength of the (022) plane are summarized below.

As is clear from Table 2, EB, laser,
MgzPz0 when subjected to heat treatment such as plasma irradiation
The (022) plane strength of No. 7 is stronger than that of the coated material No. 2, but it becomes weaker when laser or plasma treatment is performed in the atmosphere. This tendency was observed even after strain relief annealing at 800°C for 2 hours, and when treated in vacuum, Mg in the conditions of
It is extremely stronger than the (022) plane strength of zhOt.

In contrast, MgzPzOy (022
) The surface strength is weaker than the condition (■), and crystallization does not proceed.

From the above experiments, it was found that EB in vacuum on an insulating film,
In areas that have been subjected to laser or plasma treatment, Mg2P2O
Crystallization of the (022) plane of No. 7 proceeds preferentially, causing non-uniform elastic tension in the insulating coating between the areas where these treatments are not applied, and as a result, such tension on the surface of the silicon steel sheet. The magnetic domain is subdivided to form non-uniform regions of
In turn, it is thought that it has become possible to achieve lower iron loss.

In other words, as mentioned above, conventional magnetic domain refining technology aims to reduce the iron content by applying localized thermal strain and plastic strain to the surface of the steel sheet, and as a result, strain relief annealing can reduce the strain. Characteristics (especially iron loss characteristics) deteriorated due to release. In contrast, in the present invention, only crystals having a specific (022) plane orientation are preferentially developed in the crystallization process of the insulating film by local heating treatment of the insulating film in vacuum and subsequent annealing. By locally forming regions of different tension, lower core loss is achieved.

Crystallization of Mg2P2O7 progresses through EB, laser, and plasma irradiation in vacuum, and subsequent strain relief annealing, whereby the (022) plane, which is the closest-packed plane, develops dominantly, and the steel plate is formed in this region. While tension is effectively applied, no tension is applied in the untreated area, so as a result, elastic tension is effectively applied to the steel plate,
It is considered that as a result, reduction in iron loss is realized.

FIG. 2 schematically shows a cross section of a steel plate according to the present invention.

As shown in the figure, by creating regions in the insulating coating that have a higher degree of crystallinity than the fabric, regions where different tensions act are divided, thereby achieving low iron loss.

In X-ray diffraction, the degree of crystallinity is determined by considering surface strength and half-width, but in this invention, it is mainly determined by M2PZO? of(
The surface intensity of X-ray diffraction of the 022) surface was used as an index. Note that M here refers to Mg or A1.

Next, the manufacturing process of a unidirectional silicon steel sheet according to the present invention will be explained.

The starting material has conventionally known unidirectional silicon steel material components, such as ■ C: 0.01 to 0.050%, 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: 0.01
~0.08%, Si: 2.0~4.0%, S:
0.005-0.05%, Al: 0.005
~0.06%, N: 0.001~0.01%,
Sn: 0.01-0.5%, Cu: 0.01
~0.3%.

Composition containing Mn: 0.01 to 0.2% ■C:
0.011-0.06%, Si: 2.0-4.0%
, S2 0.005~0.05%, B: 0.0003~
0.0040%, N: 0°001~0.01%, Mn
: Applicable to compositions containing 0.01 to 0.2%.

Next, the hot-rolled sheet is either uniformly annealed at 800-1100°C and then cold-rolled once to achieve the final thickness, or it is usually subjected to intermediate annealing at 850-1050"C. In the second cold rolling method, the initial rolling reduction is about 50% to 80%, and the final rolling reduction is about 50% to 8.
At about 5%, the final cold-rolled sheet thickness is from 0.15 mm to 0.35 mm.

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

After that, an annealing separation material containing MgO as a main component is usually applied to the surface of the steel plate.

At this time, - For boat fishing, if it is essential to form a forsterite film after finish annealing, an annealing separator containing MgO as the main component is applied, but if forsterite is not specifically formed, the steel plate is mirror-finished after that. Since it is effective in simplifying the processing, Aha, ZrO,
It is preferable to use an annealing separator containing 50% or more of MgO, such as TiO2.

After that, "secondary recrystallization annealing is performed, but this process is (110
) It is performed to sufficiently develop secondary recrystallized grains with <001> orientation, and is usually box annealed immediately after recrystallization.
This is done by raising the temperature to 0°C or higher and maintaining it at that temperature.

In this case, in order to develop highly aligned secondary recrystallized grains in the (110) <001> orientation, it is advantageous to perform retention annealing at a low temperature of 820°C to 900°C; Heat-removal annealing at a heating rate of .5 to 15°C/h may also be used.

Purification annealing after secondary recrystallization annealing is performed at 1100°C in saturated hydrogen.
It is necessary to perform annealing for 1 to 20 hours to achieve purification of the steel sheet.

After that, an insulating film mainly composed of phosphate and colloidal silica is formed. Here, as the phosphate, magnesium phosphate, aluminum phosphate, etc. are suitable.

Then, local heat treatment, such as EB irradiation, is performed on this insulating coating in a direction transverse to the rolling direction, preferably in a direction of 60 to 90 degrees, at intervals of about 3 to 15 degrees. The EB irradiation conditions at this time are as follows: an accelerating voltage of 10 to 100 Kv, a current of 0.005 to 10 kW, a beam diameter of 0.005 to 1 cylinder, and it is effective to apply the beam in a dotted or linear manner. Note that the local heat treatment is not limited to the above-mentioned EB irradiation, but laser irradiation in a vacuum, plasma flame irradiation, etc. are also advantageously applicable. The preferred degree of vacuum at this time is about 10-2 to 10-'torr.

The steel plate of the present invention can be obtained as described above, but it can also be obtained as follows.

After purification annealing, the oxide film on the surface of the steel sheet is removed by pickling with a strong acid such as sulfuric acid, nitric acid, or hydrofluoric acid, or by mechanical grinding, cutting, etc., and further by conventionally known methods such as chemical polishing and/or electrolytic polishing. After finishing the steel plate surface to a mirror-like state, that is, to a center line average roughness Ra of 0.4 μm or less, using the method described above, CVD is performed.

Tit Zrt L Nb + Ta+ Cr by ion plating or ion implantation
, Mo+W.

Mn, Co+ Ni1^1. B, Si nitride and/or carbide and Al, Ni+Cu,
An extremely thin film of about 0.05 to 5 μm is formed, which is made of at least one selected from oxides of W, Si, and Zn.

Then, an insulating film containing phosphate and colloidal silica as main components is formed thereon.

Thereafter, the insulating coating is coated with 3 to 300 ml in a direction transverse to the rolling direction, preferably at an angle of 60 to 90°, in the same manner as described above.
Local heat treatment is performed at intervals of about 15 mm. Note that the heat treatment conditions at this time are the same as those described above.

In this way, a grain-oriented silicon steel sheet with low core loss according to the present invention can be obtained.

Furthermore, when the silicon steel sheet thus obtained is treated at a temperature of 600°C or higher, the degree of crystallinity in the heat-treated region becomes even higher, so when it is subsequently subjected to strain relief annealing or flattening heat treatment, The iron loss characteristics are further improved.

(Example) Example IC: 0.044%, Si: 3.45%, Mn:
0.068% + Mo: 0.021%, Se: 0
．． A hot rolled sheet containing Sb: 0.022% and Sb: 0.024% was uniformly annealed at 900°C for 3 minutes and then cold-rolled twice with intermediate annealing at 950°C in between. 23m
A final cold-rolled sheet with a thickness of m was obtained.

Then, after decarburization annealing in wet hydrogen at 820°C, M
850°C after applying an annealing separator mainly composed of gQ
Secondary recrystallization annealing was performed for 50 hours at 1200"C, and purification annealing was performed in saturated hydrogen for 8 hours at 1200"C.

After that, after forming an insulating film mainly composed of magnesium phosphate and colloidal silica, EB irradiation was applied linearly at seven intervals in a direction approximately perpendicular to the rolling direction (heating voltage: 65 kV,
Current: 1. OmA, spot diameter is 0.15mm
φ) was performed. MgzP20 by X-ray diffraction at this time
The (022) surface strength of B.7 is 56,000 cps, and that of the untreated portion is 40,000 cps. The value is 1.9
1T, W17ys. The value was 0.89 W/kg.

After that, strain relief annealing was performed at 800°C for 3 hours in a nitrogen atmosphere, and the magnetic properties of the product were B. The value is 1.91
T, Ltzs. The value was 0.80 W/kg.

In addition, when the surface of the steel plate at that time was measured using thin film X-rays,
forsterite α-Pe, CaTiO3 and M
Peaks of gzhOl were observed, and among these peaks, the (022) plane of MgzPzOt had an intensity of 65'.
000CPS, half width: 0.90, it was recognized that the anisotropy was extremely strong and the degree of crystallinity was high.

Example 2 C: 0.055%, Si: 3.42%, Mn:
0.078%, ^l: 0.026%, S: 0.0
021%, Cu: 0.05%, Sn: 0.06
% was uniformly annealed at 1130° C. for 3 minutes and then rapidly cooled, and then warm rolled at 300″C to obtain a final cold rolled sheet with a thickness of 0.20 mm.

Then, after decarburization annealing in 850°C wet hydrogen, 81t
0.3 (80%), Mg0 (15%) and Zr0t (5%
) was applied as a main component, the temperature was raised from 850'C to 1150°C at a rate of 10°C/hr for secondary recrystallization, and then annealing was performed at 1200°C for 8 hours in soft hydrogen. Purification annealing was performed.

After that, after removing the oxide film by pickling, 3% IIP and 11
□0□After chemical polishing in liquid to a mirror finish, CVD,
By ion blating (IIcD method) and ion implantation, (1) BN, (2) Ti (CN
) , (3) Si+N4゜ (4) V N , (5) Z
r N, (6) Cr z N, (7) 8 IN,
(8) Nitride such as llfN, (9) ZrC, Oω!
IfC, (II) SiC, 02) TaC, (13) Zr
C, (14) carbides such as MnC and 05) ZnO,
OωNiO, (17)SiOz, Q8)Wo.

0981203. G! A thin film of lCuO oxide (0,5
~1.9 pm thick). Thereafter, an insulating film containing aluminum phosphate and colloidal silica as main components was formed.

Then, EB was applied linearly at 10 mm intervals in the direction perpendicular to the rolling direction.
Irradiation (EB irradiation conditions: acceleration voltage 70kV, current 0.8m
A.

beam diameter 0.05 mm). At this time, the (022) plane strength of MgzP207 in the irradiated part by X-ray diffraction was 50,000 cps, and that of the untreated part was 3,500 cps.
It was 0 cps. Then, strain relief annealing was performed at 800″C for 2 hours.

Table 3 shows the results of investigating the magnetic properties of the thus obtained products before and after strain relief annealing.

*) A: CVD treatment B: Ion plating treatment C: Ion implantation treatment *t) After forming an insulating film on BN, AlN, ZrC, and WO, and performing strain relief annealing after EB treatment,
As a result of thin film X-ray diffraction, peaks of α-Pe, CaTiOs, and A12P20° were observed in addition to the peaks of each base film. Among them, A12P207 (0
22) The peak of the plane was 5oooo to 75,000 cps, and the half-width was 0.65 to 0.74, and regions with extremely strong anisotropy and high crystallinity were formed.

Example 3 C: 0.066%, Si: 3.41%, Mn:
0.079%, Al: 0.021%, Se: 0
．． 022%, Sn: 0.1% and Cu: 0.03
A silicon steel slab having a composition containing 1390'
After heating at C for 8 hours, it was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.8M. After that, 2 minutes with intermediate annealing at 1100°C for 3 minutes.
The sample was cold-rolled twice to obtain a final cold-rolled sheet with a thickness of 0.20 mm. After decarburization and primary recrystallization annealing in wet hydrogen at 850°C, an annealing separator containing MgO as a main component is applied to the surface of the steel plate, and then the temperature is lowered from 850°C to lO°C/h.
After raising the temperature to develop secondary recrystallized grains with Goss orientation, a purification treatment was performed at 1200'C for 15 hours in dry H2.

After that, an insulating film mainly composed of aluminum phosphate and colloidal silica was formed on the surface of the steel plate, and then 4Xl
Laser irradiation in a vacuum of 0-'torr (spot diameter:
0.15 mmφ, spot interval: 300 gm: irradiation interval: 8 cylinders, energy per spot = 2.3 mJ
/cm2) in a direction perpendicular to the rolling direction.

Mg2Pz by X-ray diffraction on the surface of the steel plate thus obtained
The (022) surface strength of 07 is 48,000 cps, or that of the untreated area is 35,000 cps, and the BIG is 1
．． 93 T.

W　I　7/S. was 0.86 W/kg.

Then, strain relief annealing was performed at 800''C for 5 hours, and the magnetic properties of the product were as follows.

Boo: 1.94T, Wtt/so: 0.
76 W/kg Example 4 C: 0.044%, Si: 3.38%, Mn:
0.073%, Se: 0.021%, Sb: 0
．． A silicon steel slab having a composition containing 0.026% and Mo: 0.016% was heated at 1340°C for 4 hours and then hot rolled. It was made into a hot-rolled sheet with a thickness of 100 yen. After that, it was cold-rolled twice with intermediate annealing at 950°C for 3 minutes to obtain a final cold-rolled sheet with a thickness of 0.20mm.
Decarburization and primary recrystallization annealing were performed in wet hydrogen at 0°C. After that, an annealing separator mainly composed of MgO was applied to the surface of the steel plate, and then secondary recrystallization annealing was performed at 850°C for 50 hours, followed by purification treatment at 1200"C for 18 hours in saturated hydrogen. .

After that, an insulating film mainly composed of magnesium phosphate and colloidal silica was formed on the surface of the steel plate, and then 3Xl
In a vacuum of 0-'torr, a plasma jet (beam diameter: 0.15 mmφ, scanning distance: 10 mm, plasma energy: 5 x 10' W/mm) was irradiated linearly in a direction perpendicular to the rolling direction.

MgZp2o? by X-ray diffraction of the heat-treated region on the surface of the steel sheet thus obtained. The (022) plane strength of is 49000cp
s, and that of the unprocessed area is 38000 ps, and B
1° is 1.91T, 1L7zs. is 0.88/k
It was g.

Then, when strain relief annealing was performed at 800°C for 5 hours, the magnetic properties of the product were Boo: 1.92T, W+tzs. : 0.7
It became 5 W/kg.

(Effects of the Invention) Thus, according to the present invention, it is possible to obtain a low iron loss grain-oriented silicon steel sheet that can actually improve the iron loss characteristics, which conventionally had to deteriorate after strain relief annealing.

[Brief explanation of the drawing]

Figure 1 a, b, c, and d respectively show a surface coated with a phosphate-based insulating film after final annealing, a surface subjected to EB treatment after coating with the insulating film, and a surface subjected to EB treatment after coating with the insulating film, followed by strain relief. FIG. 2 is a graph showing the results of structural analysis by thin film X-rays of an annealed surface and a surface subjected to strain relief annealing after being coated with the insulating film. FIG. 2 is a cross-sectional view of a silicon steel sheet according to the present invention. to O CPS CPS to
^σ
Tsutomu

Claims (1)

[Scope of Claims] 1. A grain-oriented silicon steel sheet having an insulating coating mainly composed of phosphate and colloidal silica on the surface of the finish-annealed steel sheet, wherein the insulating coating is locally separated from the fabric. A grain-oriented silicon steel sheet that is characterized by having a region with a high degree of crystallinity and which does not suffer from characteristic deterioration due to strain relief annealing. 2. The grain-oriented silicon steel sheet according to claim 1, wherein an insulating coating mainly composed of phosphate and colloidal silica is formed on a forsterite coating. 3. The insulating film mainly composed of phosphate and colloidal silica contains Ti, Zr, Hf, V, Nb, Ta, Mn, C.
r, Mo, W, Co, Ni, Al and Si nitrides and/or carbides and Al, Ni, Cu, W, S
The grain-oriented silicon steel sheet according to claim 1, which is formed on an ultra-thin tensile coating consisting of at least one selected from oxides of i and/or Zn.