JPH08319514A - Grain oriented silicon steel sheet having primary film extremely excellent in external appearance and its production - Google Patents

Abstract

PURPOSE: To produce a grain oriented silicon steel sheet having high magnetic flux density and low iron loss, which has a primary film extremely excellent in external appearance. CONSTITUTION: The grain oriented silicon steel sheet having a primary film extremely excellent in external appearance can be obtained by constituting the insulating primary film of the grain oriented silicon steel sheet of ceramics composed essentially of olivine type forsterite and regulating its grain size to 0.2-2μm and also regulating its relative density to 60-98%. Moreover, the grain size of MgO contained in a separation agent at annealing and the viscosity of slurry at the time of application of the separation agent at annealing are regulated to 0.1-5μm and >=50cps, respectively, and further, the coverage of the separation agent at annealing applied to the steel sheet is regulated to (1 to 10)g/m<2> per side. By this method, the grain oriented silicon steel sheet can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a primary coating of a grain-oriented electrical steel sheet having a high magnetic flux density and a low iron loss, and relates to a grain-oriented electrical steel sheet having a very good appearance and a method for producing the grain-oriented electrical steel sheet.

[0002]

2. Description of the Related Art A method of manufacturing a grain-oriented electrical steel sheet is Si:
A raw material slab containing 2.5 to 4.0 wt% is hot-rolled and annealed and cold-rolled once or twice with intermediate annealing to obtain a final plate thickness. Then, decarburization annealing is performed to form an oxide film containing SiO ₂ (amorphous silica and silicate such as firelite) as a main component on the surface. On top of that, M
An annealing separator containing gO as a main component is applied as a slurry, dried, wound on a coil for final finishing annealing, and usually an insulating film treatment and a heat flattening treatment are performed to obtain a final product.

SiO ₂ formed near the surface during decarburization annealing
The quality and the annealing separating agent containing MgO as a main component react during the final finishing annealing to form gray olivine-based ceramics. At that time, since it is held at about 1200 ° C. for several tens of hours, the appearance of the primary coating may be partially or wholly black, grayish brown, or grayish white, or a coating having bare spots may be formed. When such a defect occurs, there is no problem in performance, but the reliability of the customer who uses the electromagnetic steel sheet is often impaired.

Various studies have been carried out to reduce those defects. For example, Mg as disclosed in Japanese Patent Publication No. 2-5820 and Japanese Patent Laid-Open No. 3-120376.
It is a method of reducing defects by adding various additives to the annealing separator containing O as a main component. However, these methods inevitably increase costs associated with additives.

[0005]

As described above, the appearance of the primary coating is partially or wholly black, grayish brown,
The development of a magnetic steel sheet having a coating that does not show an off-white color and has no bare spots and a method for manufacturing the same is an issue.

[0006]

Means for Solving the Problems As a result of intensive investigations by the present inventors, the insulating primary coating is made of ceramics containing olivine as a main component and has a grain size of 0.
2 μm or more and 2 μm or less, and its relative density is 6
It was found that an electromagnetic steel sheet having an extremely good appearance can be obtained by setting it to 0% or more and 98% or less, and completed the present invention.

C: 0.03 to 0.1 wt%, Si:
A hot rolled sheet containing 2.5 to 4.0 wt% and at least one of sulfide and nitride as an inhibitor is
Times or two or more times of cold rolling sandwiching annealing to obtain the final plate thickness, decarburization annealing, forming an oxide film made of SiO _{2 on} the surface, finishing annealing after applying annealing separator, insulating film treatment In the method for manufacturing a grain-oriented electrical steel sheet comprising:
The grain size of MgO contained in the annealing separator is 0.1 μm or more 5
μm or less, the viscosity of the slurry when applying the annealing separator is 50 cps or more and 1000 cps or less, and the amount of the annealing separator applied to the steel sheet is 1 g / m ² or more and 10 g / m ² or more on one side.
It was found that this electrical steel sheet can be obtained by the method of manufacturing a grain-oriented electrical steel sheet of ² or less.

[0008]

The outline of the present invention is as follows. In the method for producing a grain-oriented electrical steel sheet, a raw material slab containing Si: 2.5 to 4.0 wt% is hot-rolled and annealed and cold-rolled at least once with intermediate annealing to obtain the final sheet thickness. Then, decarburization annealing is performed to form an oxide film containing SiO ₂ as a main component on the surface. On top of that, an annealing separator containing MgO as a main component is applied as a slurry, dried and wound on a coil for final finishing annealing. At that time, the SiO ₂ substance and the separating agent containing MgO as a main component form a liquid phase. Through the reaction, and finally becomes a gray-colored olivine-based ceramics.

The olivine referred to here is (Mg _x , F
e _y ) SiO ₄ (x + y = 2), and ceramics containing olivine as the main component means other small amounts of other phases,
In particular, it is a ceramic containing a glass phase.
The relative density is the ratio of the density of the primary coating to the density of pure forsterite.

Since the final finish annealing is carried out at about 1200 ° C. for several tens of hours, the appearance of the primary coating is partially or wholly black, grey-brown, grey-white, or a bare spot is produced on the coating. There are cases. As a result of observing the primary coating with a scanning electron microscope or the like and investigating the relationship of colors and the like, it was found that the particle size of the olivine-based ceramics had an influence.

If the particle size is less than 0.2 μm, sintering of the olivine ceramics is insufficient, and the olivine-type ceramic exhibits a grayish white color and insufficient adhesion to the steel sheet, so that the primary appearance is very good. A grain-oriented electrical steel sheet having a coating cannot be obtained. Further, if it exceeds 2 μm, not only a color such as black or grayish brown is exhibited, but also a bare spot may be seen. That is, the particle size must be 0.2 μm or more and 2 μm or less.

However, the regulation of the grain size alone was not sufficient to obtain a grain-oriented electrical steel sheet having a primary coating with a very good appearance. As a result of further studies, it was possible to obtain a grain-oriented electrical steel sheet having a primary coating with an extremely good appearance only by defining both the grain size and the relative density.

When the relative density is less than 60%, bare spots are observed, and black or grayish brown is exhibited. If it exceeds 98%, the sintering of the forsterite will proceed too much, and the surface will look wavy under the scanning electron microscope observation.
It has an off-white color.

Further, due to the sintering of the forsterite, the difference in the coefficient of thermal expansion from the steel sheet is further increased, and although tension is applied to the steel sheet, the adhesion is deteriorated and the coating film is peeled off.
That is, the relative density needs to be 60% or more and 98% or less.

That is, by the synergistic action of setting the particle size of the ceramic insulating primary coating containing olivine as a main component to 0.2 μm or more and 2 μm or less and setting the relative density thereof to 60% or more and 98% or less, the appearance is improved. A grain-oriented electrical steel sheet having a very good primary coating is obtained.

A method of measuring the size of the particle size and the relative density will be described. The particle size can be measured by peeling off the coating and measuring with a particle size distribution meter, and various methods such as measurement by observing with a scanning electron microscope and a transmission electron microscope can be adopted.
It is desirable to use relatively simple scanning electron microscope observation. In the present invention, this method is defined.

The relative density is measured by cutting a magnetic steel sheet with a primary coating into fine pieces, and using a mercury injection method, a pore size distribution measurement by nitrogen adsorption, a scanning electron microscope observation, an Archimedes method based on the difference between before and after the peeling of the coating. can do. Among them, it is desirable to adopt the Archimedes method, which is the simplest method, which is based on the difference before and after peeling the coating film. In the present invention, it is defined by this method. However, the density of olivine ceramics is assumed to be equal to that of pure forsterite for calculation.

Next, a manufacturing method for obtaining a grain-oriented electrical steel sheet having a primary coating having an extremely good appearance will be described. C: 0.03 to 0.1 wt%, Si: 2.5 to 4.0
A hot-rolled sheet containing wt% and at least one of sulfide and / or nitride as an inhibitor is decarburized and annealed after it is decarburized and annealed once to a final sheet thickness by cold rolling once or twice or more with sandwiching annealing. In a grain-oriented electrical steel sheet comprising forming an oxide film made of SiO ₂ material, applying an annealing separating agent, finishing annealing, and then performing an insulating film treatment, Mg contained in the annealing separating agent.
The particle size of O is 0.1 μm or more and 5 μm or less, the viscosity of the slurry when applying the annealing separator is 50 cps or more, and the amount of the annealing separator applied to the steel sheet is 1 g / m on one side.
^By setting it to ² or more and 10 g / m ² or less, it is possible to obtain a grain-oriented electrical steel sheet having a primary coating having an extremely good appearance.

C has a value of 0.
03% or more is required. If it exceeds 0.1%, the load on decarburization annealing increases, so the content is made 0.1% or less. Si
Is required to be 2.5% or more in order to obtain good iron loss characteristics. If it exceeds 4.0%, the workability deteriorates, so 4.0%
Must be:

The grain size of MgO contained in the annealing separator is 0.
If it is less than 1 μm, handling becomes difficult, for example, it becomes difficult to prepare a slurry. If it is larger than 5 μm, the steel sheet is not covered with the slurry, or the reactivity is deteriorated, and the relative density is less than 60%. That is, MgO
Must have a particle size of 0.1 μm or more and 5 μm or less.

However, this alone was not sufficient to obtain a grain-oriented electrical steel sheet having a primary coating with a very good appearance. As a result of diligent study on this, it succeeded for the first time by setting the viscosity of the slurry and the coating amount of the annealing separator during the production within the specified range.

When the viscosity of the slurry is less than 50 cps, the primary coating becomes porous and the relative density is less than 60%, so it is necessary to be 50 cps or more. The upper limit is not particularly limited, but if it exceeds 1000 cps, the appearance tends to deteriorate, so 1000 cps or less is desirable.

Further, even if the viscosity of the slurry is 50 cps or more, the amount of the annealing separator applied to the steel sheet is out of the range of 1 g / m ² or more and 10 g / m ² or less. Grain-free electrical steel sheets cannot be obtained. this is,
If it is less than 1 g / m ^2, the absolute amount of MgO is small and the reaction does not occur sufficiently, resulting in a bare spot.
This is because if it exceeds g / m ² , peeling occurs.

From the above, M contained in the annealing separator
The particle size of gO is 0.1 μm or more and 5 μm or less, the viscosity of the slurry when applying the annealing separator is 50 cps or more, and the amount of the annealing separator applied to the steel sheet is 1 g / m ² or more and 10 g / m
It can be seen that by setting it to ² or less, it is possible to obtain a grain-oriented electrical steel sheet having a primary coating with an extremely good appearance.

[0025]

Example 1 C: 0.055%, Si: 3.28%, Mn: wt%
0.14%, Al: 0.035%, S: 0.025%,
N: 0.008%, Sn: 0.05%, the balance is a grain-oriented electrical steel sheet slab consisting of Fe and unavoidable impurities, which is heated at a low temperature of 1150 ° C. by a known method, then hot rolled, and annealed and cold rolled. The final plate thickness was 0.23 mm. _{N 2 25% + H 2 75} % in the coil continuous annealing line, a decarburization annealing of 830 ° C. × 110 seconds in a wet atmosphere having a dew point of 65 ° C., subsequently as N content in steel is 200 ppm N ₂
750 in a dry atmosphere of 25% + H ₂ 75% + NH ₃
A nitriding treatment was performed at 30 ° C. for 30 seconds.

With respect to 100 parts by weight of MgO having a particle size of 1.5 μm, TiO ₂ : 5 parts by weight, Na ₂ B ₄ O ₇ : 0.
An annealing separator with 3 parts by weight was prepared and the viscosity was 230 cps.
Was applied to a steel sheet at a coating amount of 6 g / m ² on one side.

Next, after final finishing annealing at 1200 ° C. for 20 hours, the appearance (color) of the primary coatings is visually inspected, and the grain size of the ceramic containing olivine as a main component is determined by a scanning electron microscope (SEM). Then, the relative density was investigated by the Archimedes method based on the difference before and after peeling of the film. The appearance of the coating was gray and good. The particle size of the olivine ceramics was 0.8 to 1.2 μm, and the relative density was 95%.

Example 2 Decarburization annealing was carried out in the same manner as in Example 1 to obtain 0.1 μm and 7 μm.
m and particle sizes different two MgO: per 100 parts by weight, TiO _2: 5 parts by _{weight, Na 2 B 4 O 7:} 0.3 parts by weight to prepare an annealing separator agent used, the viscosity respectively 900
cps, 180cps slurry, coated on one side 5.5g
/ M ² was applied to the steel sheet.

Next, under the same conditions as in Example 1, 120
After the final finishing annealing at 0 ° C. for 20 hours, the appearance (color) of the primary coating is visually observed, and the particle diameter of the ceramic containing olivine as a main component is observed by a scanning electron microscope (SEM).
The relative density was investigated by the Archimedes method based on the difference before and after peeling of the coating. The appearance of the electrical steel sheet outside the scope of the present invention was not good.

Example 3 C: 0.077% by weight, Si: 3.29%, Mn:
0.065%, Al: 0.030%, S: 0.027
%, N: 0.009%, Sn: 0.01%, balance Fe
A grain-oriented electrical steel sheet slab consisting of unavoidable impurities was heated at a low temperature of 1150 ° C. by a known method, then hot rolled, and annealed and cold rolled to a final sheet thickness of 0.23 mm. This coil was continuously annealed at a line of N ₂ 25% + H ₂ 75% and a dew point of 65.
Decarburization annealing was performed at 830 ° C. for 110 seconds in a wet atmosphere at 750 ° C., and then nitriding treatment was performed at 750 ° C. for 30 seconds in a dry atmosphere of NH ₃ so that the N content in the steel was 200 ppm.

MgO having a particle size of 1.2 μm: 100 parts by weight, TiO ₂ : 5 parts by weight, Na ₂ B ₄ O ₇ : 0.3
By weight, a slurry having a viscosity of 290 cps is prepared, and the coating amount on one side is 0.8 g / m ² , 6.5 g / m ² , 12 g / m ^2.
Was applied to a steel plate and wound into a coil.

Next, final finishing annealing was carried out at 1200 ° C. for 20 hours. The appearance of these primary coatings and the particle size of ceramics containing olivine as a main component were calculated by a scanning electron microscope (SEM), and the relative density was calculated by measuring the pore size distribution by nitrogen adsorption. The results of Examples 1, 2 and 3 above are summarized in Table 1.

[0033]

[Table 1]

[0034]

According to the present invention, it is possible to obtain a grain-oriented electrical steel sheet having a very good appearance. As a result, it is possible to prevent a decrease in yield and obtain a great deal of credibility from customers, and the effect is enormous.

Front page continued (72) Inventor Go Hamaya 1-1 No. 1 Hibahata-cho, Tobata-ku, Kitakyushu City Inside Nippon Steel Co., Ltd. Yawata Works (72) Inventor Toru Tanaka, Tobata-ku, Kitakyushu 46-59 Nichihara Plastic Into Design Co., Ltd.

Claims (2)

[Claims] 1. An insulating primary coating is made of olivine-based ceramics and has a particle size of 0.2 μm or more and 2 μm or more.
m or less, and the relative density is 60% or more and 98%
A grain-oriented electrical steel sheet having a primary coating having an extremely good appearance characterized by being: 2. C: 0.03 to 0.1 wt%, Si: 2.
A hot-rolled sheet containing 5 to 4.0 wt% and at least one of sulfide and nitride as an inhibitor is cold-rolled once or two or more times with annealing to obtain a final sheet thickness, and then decarburized and annealed. In the method for producing a grain-oriented electrical steel sheet, which comprises forming an oxide film of SiO ₂ on the surface, applying an annealing separating agent, finishing annealing, and then performing an insulating film treatment, MgO particles contained in the annealing separating agent. Diameter is 0.1μm or more 5μ
m or less, the viscosity of the slurry when applying the annealing separator is 50 cps or more, and the amount of the annealing separator applied to the steel sheet is 1 g / m ² or more and 10 g / m ² or less on one side. A method for producing a grain-oriented electrical steel sheet having a primary coating having an extremely good appearance.