JPH10298652A - Production of ultralow core loss grain-oriented silicon steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ultralow core loss grain-oriented steel sheet improved in core loss, an occupying volume rate and adhesion at a low cost by forming two or more layers of ceramic tension coating composed of nitride and/or carbide on the surface of a steel sheet after bright annealing. SOLUTION: This ultralow core loss silicon steel sheet is the one in which, on a thin TiN formed on the surface, two layers of thin nitride series ceramic coating on which Si3 N4 extremely small in a thermal expansion coefficient and having insulating properties is formed are applied. At the time of producing this, in the case of final finish annealing, as separation agent for annealing, forsterite generating suppression type one contg. inert MgO, Al2 O3 or the like is used. After the final finish annealing, bright annealing is executed at 900 to 1300 deg.C to clean the surface of the steel sheet. After that, on the surface of the steel sheet, two or more layers of ceramic tension coating composed of nitride and/or carbide are formed. In this way, the advantageous improvement of its core loss characteristics can be attained.

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 an ultra-low iron loss unidirectional silicon steel sheet, and more particularly to an effective cleaning treatment for a surface of a silicon steel sheet without a forsterite undercoating. By forming two or more layers of ceramic tension coatings made of nitride and / or carbide on the surface of the steel sheet, it is intended to improve the iron loss characteristics advantageously.

[0002]

BACKGROUND ART unidirectional silicon steel sheet is mainly being used as transformer cores and other electrical equipment, (represented by ₈ value B) flux density as the magnetization characteristic is high, the iron loss (W
_17/50 ) is required to be low.

In order to improve the magnetic properties of a grain-oriented silicon steel sheet, first, <001> of secondary recrystallized grains in the steel sheet is required.
The shaft needs to be highly aligned in the rolling direction, and second, it is necessary to minimize impurities and precipitates remaining in the final product.

[0004] For this reason, since NPGoss proposed a basic manufacturing technique by two-stage cold rolling of a unidirectional silicon steel sheet, a number of improvements were made to the manufacturing technique, and the magnetic flux of the unidirectional silicon steel sheet was increased. Density and core loss values have improved over the years. Particularly typical therein, a method described in JP-B-51-13469 utilizing a Sb and Se or S as inhibitors, B ₈ according to this method is 1.88
Products exceeding T have been obtained.

Further, in order to obtain a product having a high magnetic flux density, Mo is added to the material in a composite in Japanese Patent Publication No. 577-14737, and Mo is added to a material in a composite in Japanese Patent Publication No. 62-42968. after, adding improvements such as a quenching treatment after the intermediate annealing in the final cold rolling immediately before applying, B ₈ is at a high magnetic flux density of more than 1.90T, the iron loss W _17/50 is 1.05 W / kg (product thickness: 0.30 mm) It was disclosed to obtain the following ultra-low iron loss, but it was still necessary to improve the iron loss sufficiently.

[0006] In particular, the demand for minimizing power loss as much as possible since the energy crisis of more than ten years ago has been remarkably increased, and with this, further improvements in the use of iron core materials are desired. Therefore, in order to minimize eddy current loss, the product thickness was reduced to 0.23 mm (9
mill) Many of the following have come into use.

[0007] Apart from the above-described method for producing a silicon steel sheet,
As disclosed in JP-B-55-19976, JP-A-56-127749, and JP-A-2-3213, amorphous alloys have attracted attention as materials for ordinary power transformers and high-frequency transformers. Have been. In such an amorphous material, although extremely excellent iron loss characteristics are obtained as compared with a normal unidirectional silicon steel sheet, it lacks thermal stability, has a low space factor, and is not easily cut. However, since they are too thin and brittle, there are many practical disadvantages, such as a large increase in the cost of assembling transformers. Therefore, at present, they have not been used in large quantities.

[0008] In this regard, the present inventors have previously disclosed in Japanese Patent Publication No. 63-54767, etc.
Si, Mn, Cr, Ni, Mo, W, V, Ti, Nb, Ta, B, C on a grain-oriented silicon steel sheet smoothed by polishing by CVD, ion plating, and ion implantation.
It has been disclosed that an ultra-low loss can be obtained by forming one or more tension coatings selected from nitrides and carbides of u, Zr and B. This manufacturing method has made it possible to obtain extremely excellent iron loss characteristics as a material for power transformers and high frequency transformers, but nevertheless, it has sufficiently responded to recent demands for low iron loss. It was hard to be there.

[0009]

SUMMARY OF THE INVENTION The present invention advantageously meets the above-mentioned demands, and advantageously produces an ultra-low iron loss unidirectional silicon steel sheet which realizes a further reduction in iron loss as compared with the prior art. The aim is to propose a method. In addition, the present invention
Regarding the smoothing of the surface of silicon steel sheet before coating with a tension coating, it is a revolutionary method that is different from the conventional methods such as pickling (including mechanical polishing in some cases) and electropolishing, which increase production costs. An object of the present invention is to enable an advantageous reduction in manufacturing cost by adopting a processing method.

[0010]

Means for Solving the Problems The inventor has made fundamental reexaminations from all viewpoints in order to respond to the above demands. That is, the inventor, various oxides, nitrides, on the surface of the unidirectional silicon steel sheet smoothed in a stable process,
In order to obtain a product with ultra-low iron loss by applying one or more kinds of tension coatings selected from carbides, it is necessary to apply the process from the raw material components of the unidirectional silicon steel sheet to the final processing step. Recognizing the need for fundamental reexamination, from tracking the texture of silicon steel sheets, to pretreatment methods for silicon steel sheets before coating with a tension coating, and finally to the final CVD and PVD processing steps We continued our studies until now. As a result, the following findings were obtained.

(1) Even if a thin film of a ceramic (a TiN film is used as a representative example) coated on a silicon steel sheet has a thickness of 1.5 μm or more, the degree of improvement in iron loss is reduced. That is, a TiN film having a thickness of 1.5 μm or more can be expected to reduce the space factor, reduce the magnetic flux density, and slightly improve the iron loss. (2) In this case, the role of TiN is more important in the role of adhesion to the silicon steel sheet, in addition to the application of tension specific to ceramics. In other words, transmission electron microscope observation of the cross section of TiN
(Ichio Iguchi: Journal of the Japan Institute of Metals, 60 (1996), P.781-786
10), horizontal stripes of 10 nm were observed, which corresponded to 5 atomic layers in the [011] direction of the silicon steel sheet. (3) Simultaneous measurement of texture of two layers by X-ray in TiN coating area and chemical polishing area (Y. Inokuti: ISIJ Internationala)
l, 36 (1996), pp. 347-352).
The {200} peak shape is circular. However, the {200} peak shape of Fe in the TiN coating region is elliptical, and the silicon steel plate is strongly tensioned in the [100] _si-steel direction. (4) Tension of TiN thin film (Ichio Iguchi, Kazuhiro Suzuki, Yasuhiro Kobayashi:
Journal of the Japan Institute of Metals, 60 (1996), p.674-678)
10 MPa, this is the magnetic flux density difference ΔB ₈ = 0.014 to 0.016 T
Can be expected to improve. (This is equivalent to increasing the degree of Goss orientation integration by about 1 °.)

(5) For smoothening the surface of a silicon steel sheet before coating with a tension coating, inert MgO or Al ₂ O ₃
By using a forsterite generation-suppressing type containing, for example, it is possible to obtain a sufficiently satisfactory clean surface only by performing bright annealing without performing pickling and electrolytic polishing treatments, which are accompanied by a cost increase. . The present invention is based on the above findings.

That is, according to the present invention, a slab for unidirectional silicon steel is hot-rolled, and then cold-rolled once or twice with intermediate annealing to a final sheet thickness, and then decarburized.・ For the first recrystallization annealing, and then the final finishing annealing consisting of the secondary recrystallization annealing and the purification annealing, the forsterite generation suppressing type annealing separator containing inert MgO, Al ₂ O ₃ etc. as the annealing separator After the above-mentioned final finish annealing, performing bright annealing at a temperature of 900 to 1300 ° C. to clean the steel sheet surface; after the above-described bright annealing, the steel sheet surface is made of nitride and / or carbide. A method for producing an ultra-low iron loss unidirectional silicon steel sheet, comprising forming at least one layer of a ceramic tension coating.

In the present invention, in order to suppress the formation of forsterite, it is preferable to limit the amount of subscale generated during decarburization / primary recrystallization annealing to 1.0 g / m ² or less.

Further, in the present invention, it is more effective to reduce the iron loss by reducing the coefficient of thermal expansion of the ceramic tensile coating toward the outer layer side.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the process leading to the success of the present invention and the contents of the invention will be specifically described.
Figures 1 (a), (b) and (C) show (a) the current unidirectional silicon steel sheet, (b) the TiN-coated unidirectional silicon steel sheet, and (c) the ultra-low iron loss of the present invention, respectively. The cross section near the surface of the unidirectional silicon steel sheet is compared and shown schematically. The figures in parentheses in each figure show the space factor, and the numbers in each figure show the coefficient of thermal expansion (10 ^-6 / K). The current unidirectional silicon steel sheet shown in (a) is a silicon steel sheet with a coefficient of thermal expansion of 13 × 10 ^{-6 and} a forsterite undercoat with a coefficient of thermal expansion of 11 × 10 ^-6. ,
Further, an insulating film having a thermal expansion coefficient of 5 × 10 ⁻⁶ is formed thereon to reduce iron loss and improve magnetostriction characteristics. The space factor of the silicon steel sheet in this case is about 96.5%. In addition, the TiN-coated unidirectional silicon steel sheet of (b) is obtained by forming a thin TiN film having a thickness of about 1 μm on a silicon steel sheet and further forming an insulating coating thereon. In this case TiN
The thermal expansion coefficient of the coating is 8 × 10 ^-6, which is lower than the thermal expansion coefficient of the forsterite undercoating: 11 × 10 ^-6 , and it is possible to apply stronger tension to the silicon steel sheet, further reducing iron loss And the magnetostriction characteristics can be improved. In this case, the space factor of the silicon steel sheet is about 97.5%, which is improved by about 1%. On the other hand, the ultra-low iron loss silicon steel sheet of the present invention (c) has a thin TiN (0.01 to 0.5 μm) coated on the surface of the silicon steel sheet and further has a coefficient of thermal expansion of 3 × 10 ^{− This} is an ultra-low iron loss silicon steel sheet having two layers of thin nitride ceramic coating coated with Si ₃ N ₄ (0.3 to 1.5 μm) which is extremely small and has insulating properties. In this case, the space factor of the silicon steel sheet is about 99%, which can be said to be the ultimate silicon steel sheet.

However, the ultra-low iron loss silicon steel sheet described above
After removing the insulating film and the forsterite film of the current grain-oriented silicon steel sheet shown in FIG. 1 (a), pickling (in some cases, mechanical polishing for removing the forsterite undercoat) and electrolytic polishing or Ultra-low iron loss can be obtained, although ultra-low iron loss can be obtained because the silicon steel sheet is coated with two layers of TiN-Si ₃ N ₄ thin nitride ceramic after smoothing the surface of the silicon steel sheet by chemical polishing The problem is that it is not economical due to high costs.

However, the above disadvantages can be eliminated by a new surface cleaning method described below. Hereinafter, specific experimental examples will be described. C: 0.075 wt%
(Hereinafter simply shown as%), Si: 3.40%, Mn: 0.075%, S
e: 0.022%, Sb: 0.026%, Al: 0.025%, N: 0.007
A continuous cast slab for silicon steel containing 2% and Mo: 0.013% was heated at 1350 ° C. for 4 hours, and then hot-rolled into a hot-rolled sheet having a thickness of 2.0 mm. After subjecting this hot-rolled sheet to uniform annealing at 960 ° C for 3 minutes, intermediate annealing at 980 ° C is performed.
Cold rolling was performed twice to obtain a final cold rolled sheet having a sheet thickness of 0.23 mm.

Next, the obtained cold rolled sheet was treated under the following four conditions. In 840 ° C wet hydrogen ｛Amount of hydrogen in atmosphere: 55% (45 remaining
% Was N ₂ gas) and decarburization and primary recrystallization annealing were performed at a dew point of 60 ° C., and then an annealing separator containing MgO as a main component was slurry-coated on the steel sheet surface. At this time, the amount of subscale on the surface of the decarburized / primary recrystallization annealed sheet was 1.5 g / m ² . In wet hydrogen at 840 ° C (hydrogen content in atmosphere: 55%, dew point:
(25 ℃), after decarburization and primary recrystallization annealing
An annealing separator mainly composed of MgO was applied by slurry. At this time, the amount of subscale on the surface of the decarburized / primary recrystallization annealed sheet was 0.5 g / m ² . In wet hydrogen at 840 ° C (hydrogen content in atmosphere: 55%, dew point:
After decarburization and primary recrystallization annealing at 60 ° C.), inert MgO on the steel sheet _{surface: 25%, Al 2 O 3} : 70% and CaSiO _3: of 5% of the composition annealing separator slurry coating did. At this time, the amount of subscale on the surface of the decarburized / primary recrystallization annealed sheet was
1.5 g / m ² . In wet hydrogen at 840 ° C (hydrogen content in atmosphere: 55%, dew point:
After decarburization and primary recrystallization annealing at 25 ° C), the surface of the steel sheet is coated with an annealing separator which has a composition of inert MgO: 25%, Al ₂ O ₃ : 70% and CaSiO ₃ : 5%. did. At this time, the amount of subscale on the surface of the decarburized / primary recrystallization annealed sheet was
0.5 g / m ² .

Next, the silicon steel sheet subjected to the above processes (1) to (5) is annealed at 850 ° C. for 15 hours in N ₂ gas, and then the temperature is increased from that temperature to 1150 ° C. at a rate of 10 ° C./h to obtain a Goss orientation. After the secondary recrystallized grains that had accumulated strongly were developed, they were purified in dry hydrogen at 1220 ° C. After removing MgO and Al ₂ O ₃ from the surface of the product thus obtained, a ceramic coating was further formed under the following conditions.

(A) The surface of a silicon steel sheet was immersed in 10% HCl (80%
℃), and after smoothing the surface of the silicon steel sheet by chemical polishing in a mixed solution of 3% HF and H ₂ O ₂ , TiN (ion plating by HCD method) is applied on the silicon steel sheet surface. About 0.2μm
A thick coating was formed thereon, and a further 0.5 μm thick SiO ₃ N ₄ was further formed thereon. (B) TiN (ion plating by the HCD method) was formed on the surface of the silicon steel sheet by about 0.2 μm as it was, and then Si ₃ N ₄ was formed thereon by 0.5 μm. (C) The surface of a silicon steel sheet is subjected to bright annealing at 1100 ° C in a dry H ₂ atmosphere, and then TiN (ion plating by the HCD method) is formed to a thickness of about 0.2 μm. S
i ₃ N ₄ was formed to a thickness of 0.5 μm.

Table 1 shows the results obtained by examining the magnetic properties and the bending adhesion of the grain-oriented silicon steel sheet with the ceramic tension coating thus obtained.

[0023]

[Table 1]

As is clear from the table, it is noted that under + (C) conditions, excellent iron loss and adhesion can be obtained in the same manner as in the case of treatment under each (A) condition. .

By the way, the condition (A) is a step which involves an increase in cost because the steel sheet surface is smoothed by pickling and chemical polishing regardless of the presence or absence of a forsterite undercoat. On the other hand, under the condition of + (C), decarburization and primary recrystallization annealing were performed at a low dew point to reduce the subscale amount on the steel sheet surface to 0.5 g / m ^2, and then suppressed the formation of forsterite on the surface. Since the final annealing is performed after the slurry of the mold annealing separator is applied, there is almost no forsterite undercoat on the steel sheet surface after the final annealing. The steel sheet surface can be sufficiently cleaned only by performing bright annealing at about 1100 ° C. without performing complicated and complicated polishing treatment. As described above, according to the present invention, since complicated polishing processing as in the related art is not required, the manufacturing cost can be effectively reduced.

Here, the ceramic film formed on the surface of the silicon steel sheet is made of Si, Mn, Cr, Ni, Mo, W, V, Ti, Nb, Ta,
It is selected from B, Cu, Zr, and nitride or carbide of B. The important thing here is to make the thermal expansion coefficient smaller toward the outer layer, and to make the outermost ceramic coating have insulating properties. That is.

In this case, the total thickness of the ceramic coating is preferably about 0.3 to 2 μm. This is because if the film thickness is less than 0.3 μm, the effect of improving iron loss is small because the tensile effect is small, while if it exceeds 2 μm, the space factor and the magnetic flux density decrease.

As described above, the present invention uses an epoch-making cleaning method completely different from the conventional method for smoothing a finish-annealed plate, which is accompanied by an increase in cost. Needless to say, it is possible to obtain an ultra-low iron loss unidirectional silicon steel sheet excellent in magnetostriction, heat resistance and insulation properties, not to mention being excellent in loss and space factor.

[0029]

The silicon-containing steel used as the material of the present invention is compatible with any of the conventionally known component compositions, but the typical compositions are as follows.

C: 0.01 to 0.08 If C is less than 0.01%, the suppression of hot rolled texture is insufficient and large elongated grains are formed, so that the magnetic properties are degraded. Since it is not economical because decarburization takes a long time, it is preferable to be about 0.01 to 0.08%.

Si: 2.0 to 4.0% If Si is less than 2.0%, sufficient electric resistance cannot be obtained, so that eddy current loss increases and iron loss deteriorates, while 4.0%
If more, brittle cracks tend to occur during cold rolling, so
It is preferable to be in the range of about 2.0 to 4.0%.

Mn: 0.01-0.2% Mn is an important component that determines MnS or MnSe as a dispersed precipitation phase which affects secondary recrystallization of a unidirectional silicon steel sheet. When the amount of Mn is less than 0.01%, the absolute amount of MnS or the like necessary for causing secondary recrystallization becomes insufficient, causing incomplete secondary recrystallization and increasing surface defects called blisters. On the other hand, if it exceeds 0.2%, even if dissociated solid solution such as MnS is performed during slab heating or the like, the analytical precipitate phase precipitated during hot rolling tends to become coarse, and the optimal size distribution desired as an inhibitor is impaired. Since the magnetic properties are degraded, it is preferable that Mn be about 0.01 to 0.2%.

Each of S and Se is 0.1% or less.
The content of 0.008 to 0.1% or Se is preferably in the range of 0.003 to 0.1%. This is because if these contents exceed 0.1%, the hot and cold workability deteriorates, and if they do not reach the lower limits, respectively, there is no particular effect on the primary grain growth suppressing function as MnS and MnSe. is there. In addition, even if Al, Sb, Cu, Sn, B and the like, which are conventionally known as inhibitors, are added in combination, the effect of the present invention is not prevented.

Next, the manufacturing process of the ultra-low iron loss unidirectional silicon steel sheet according to the present invention will be described. First, in order to melt the raw material, it is possible to use not only a LD converter, an electric furnace, an open hearth furnace, and other known steelmaking furnaces but also vacuum melting and RH degassing.

According to the present invention, S,
As a method for adding a small amount of Se or another primary grain growth inhibitor to molten steel, any conventionally known method may be used. For example, LD converter, RH degassing at the end of molten steel or at the time of ingot casting Can be added. In slab production, it is advantageous to use the continuous casting method because of economic and technical advantages such as cost reduction and uniformity of components or quality in the slab longitudinal direction. It does not hinder.

The continuous cast slab is heated to a temperature of 1300 ° C. or higher in order to dissociate and form a solid solution of the inhibitor in the slab. Thereafter, the slab is subjected to hot rough rolling and then hot finish rolling to form a hot rolled sheet having a thickness of usually about 1.3 to 3.3 mm.

Next, the hot-rolled sheet is subjected to two cold rolling steps with intermediate annealing in a temperature range of 850 to 1100 ° C. as necessary to obtain a final sheet thickness. It is necessary to pay attention to the final cold rolling rate (usually about 55 to 90%) to obtain a product having characteristics. At this time, the thickness of the product is preferably about 0.05 to 0.5 mm.

The steel sheet having finished the final cold rolling and having the product thickness is then subjected to decarburization annealing. This annealing reduces the cold rolled structure to 1
At the same time as the next recrystallized structure, {110}
The purpose is to remove harmful C when secondary recrystallized grains having the <001> orientation are developed, for example, in wet hydrogen at 750 to 880 ° C. In addition, during the decarburization treatment, a subscale mainly composed of SiO ₂ is formed on the surface of the silicon steel sheet, and usually, at a high temperature with MgO in the annealing separator applied to the steel sheet surface thereafter. solid-phase reaction, i.e. 2MgO + SiO ₂ → the Mg ₂ SiO ₄ to form a forsterite base coating, MnS in the subsequent purification annealing step to the forsterite base film directly below, MnSe, by concentrating the fine precipitates such as AlN , Has achieved the purification of silicon steel sheets.

However, in the present invention, it is necessary to prevent the formation of such a forsterite undercoat as much as possible. In this decarburization annealing, the subscale amount on the silicon steel sheet is set to 1.0 g / m ² or less. It is preferred to regulate to. The sub-scale amount can be easily adjusted by controlling the dew point during decarburization.

As the annealing separator, an annealing separator containing MgO as a main component is usually used.
Since it is necessary to suppress formation of forsterite by final annealing as much as possible, it is necessary to include a component for suppressing the formation reaction of forsterite in the annealing separator used. Here, as the forsterite production inhibiting component,
Al ₂ O ₃ , ZrO ₂ , SnO ₃ , Sb ₂ O _3, CaSiO _3, etc. are suitable, and at least one selected from these is mixed with MgO at a ratio of 50% or more, and silicon steel sheet Is desirably applied to the surface of the slurry.

The final annealing is {110} <001>
This is applied in order to sufficiently develop secondary recrystallized grains of the orientation. Usually, the temperature is immediately raised to 1000 ° C or more by box annealing.
This is done by maintaining that temperature. In the present invention, in order to develop a secondary recrystallized structure highly integrated in the {110} <001> orientation, it is advantageous to carry out annealing at a low temperature of 820 ° C. to 900 ° C.
Slow annealing at a heating rate of about 0.5 to 15 ° C./h may be used.

After removing the annealing separator from the steel sheet surface after the final annealing, in the present invention, bright annealing is performed in dry H ₂ at 900 to 1300 ° C. for about 1 to 30 minutes to further purify the silicon steel sheet. And it is important to achieve surface cleaning.
Here, the reason why the bright annealing temperature is limited to the range of 900 to 1300 ° C is that if the treatment temperature is less than 900 ° C, sufficient cleaning cannot be achieved, while if it exceeds 1300 ° C, the shape of the steel sheet due to creep is increased. This is because it cannot be maintained.

After that, PVD, CV
Using various methods such as D or sputtering, Si,
Mn, Cr, Ni, Mo, W, V, Ti, Nb, Ta, B, Cu, Zr, and at least two layers of a tensile coating composed of at least one selected from nitrides or carbides of B. To form a ceramic tension coating. In forming such a ceramic tension coating, it should be noted that the thermal expansion coefficient is reduced toward the outer layer side as described above, and the outermost ceramic coating is provided with insulating properties. Here, the total thickness of the ceramic tension coating is preferably about 0.3 to 2 μm as described above.

With respect to the formation of the above-described ceramic tension coating, FIG. 1 (c) shows a case where the formed ceramic coating is clearly divided into two layers. However, it is not always necessary to clarify in this manner, and the components of each layer may be in a state in which they are mutually diffused into other layers. It just needs to be smaller.

It is also effective to apply a conventionally known magnetic domain refining treatment, for example, a laser irradiation, a plasma irradiation, a groove forming treatment, etc. on the ceramic coating thus formed. Can be used.

[0046]

【Example】

Example 1 C: 0.044%, Si: 3.40%, Mn: 0.072%, Se: 0.022
%, Sb: 0.023% and Mo: 0.013%, with the balance being 1340.
After soaking at 4 ° C. for 4 hours, a hot-rolled sheet having a thickness of 1.8 mm was formed by hot rolling. Then, after performing uniform annealing at 900 ° C,
Cold rolled twice with intermediate annealing at 950 ° C and thickness:
The final cold-rolled sheet was 0.23 mm. Thereafter, decarburization and primary recrystallization annealing were performed in wet hydrogen at 820 ° C. At this time, the amount of subscale generated on the steel sheet surface was 0.7 g / m ² . After that, an annealing separator having a composition of MgO: 20%, Al ₂ O ₃ : 70%, Sb ₂ O ₃ : 10% was applied on the steel sheet surface by slurry, and then 850
After performing a secondary recrystallization annealing at 50 ° C. for 50 hours, a purification annealing was performed in dry hydrogen at 1220 ° C.

Subsequently, bright annealing was performed in dry hydrogen at 1050 ° C. for 3 minutes to achieve further purification and surface cleaning. Thereafter, TiN (0.3 μm) and Si ₃ N ₄ (0.5 μm) were formed on the steel sheet surface by PVD and magnetron sputtering.
) After two layers of the ceramic film were formed, a domain refining treatment was performed. Table 2 shows the results obtained by examining the iron loss characteristics and the bending adhesion of the product thus obtained.

[0048]

[Table 2]

As shown in Table 2, when a silicon steel sheet was coated with a ceramic tension coating according to the present invention, much better iron loss characteristics could be obtained as compared with the prior art. Further, prior to the formation of the ceramic coating, the surface of the steel sheet can be cleaned only by performing bright annealing, so that the cost can be significantly reduced as compared with the conventional complicated polishing treatment.

Example 2 C: 0.076%, Si: 3.45%, Mn: 0.078%, sol.
025%, N: 0.0070%, Se: 0.022%, Mo: 0.013%,
A continuously cast slab for silicon steel containing 0.18% of Cu and 0.023% of Sb with the balance being substantially Fe was prepared at 40 ° C at 1260 ° C.
%, Re-heated to 1360 ° C. at a rate of 1.5 ° C./min, and then maintained at this temperature for 4 hours, followed by hot rolling and hot rolling with a thickness of 2.0 mm. And Next, after uniform annealing at 1050 ° C., cold rolling was performed twice with intermediate annealing at 1000 ° C. to obtain a final cold-rolled sheet having a thickness of 0.23 mm. In the rolling, warm rolling at 300 ° C. was performed. Thereafter, decarburization and primary recrystallization annealing were performed in wet hydrogen at 840 ° C. At this time, the amount of subscale generated on the steel sheet surface was 0.3 g / m ² . Then, MgO:
A slurry of an annealing separator having a composition of 30%, Al ₂ O ₃ : 60%, and SnO ₃ : 10% was applied by slurry, and then subjected to secondary recrystallization annealing at 850 ° C. for 50 hours, and then at 10 ° C./h. After the temperature was raised to 1150 ° C. at a high speed for secondary recrystallization, purification annealing was performed in dry H ₂ at 1220 ° C.

Then, bright annealing was performed in dry hydrogen at 1150 ° C. for 3 minutes to achieve further purification and surface cleaning. After that, two layers of TiN + Si ₃ N ₄ (0.6 μm) were formed on the steel sheet surface by magnetron sputtering,
A magnetic domain refinement treatment was performed. The iron loss and bending adhesion of the product thus obtained were as follows. Iron loss of product (W _17/50 ) = 0.50 W / kg Product adhesion = 15 mmφ

[0052]

As described above, according to the present invention, it is possible to obtain an ultra-low iron loss unidirectional silicon steel sheet with significantly improved iron loss, space factor and adhesion at a low cost.

[Brief description of the drawings]

FIG. 1 shows (a) a current unidirectional silicon steel sheet, (b) a TiN-coated unidirectional silicon steel sheet, and (c) a cross section near the surface of the ultra-low iron loss unidirectional silicon steel sheet of the present invention. FIG. 3 is a schematic diagram showing a comparison.

Claims (3)

[Claims] 1. A slab for unidirectional silicon steel is hot-rolled, and then cold-rolled once or twice with intermediate annealing to a final sheet thickness, and then decarburized and re-carried. When performing the crystal annealing, and then performing the final finishing annealing consisting of the secondary recrystallization annealing and the purification annealing, inert MgO or Al is used as an annealing separator.
Using a forsterite generation suppressing type annealing separator containing ₂ O ₃ etc., after the final finish annealing, performing bright annealing at a temperature of 900 to 1300 ° C. to clean the steel sheet surface, and the above bright annealing Thereafter, a method for producing an ultra-low iron loss unidirectional silicon steel sheet, comprising forming two or more layers of a ceramic tension coating made of nitride and / or carbide on the surface of the steel sheet. 2. The method according to claim 1, wherein the amount of subscale generated during decarburization / primary recrystallization annealing is limited to 1.0 g / m ² or less to suppress generation of forsterite. Manufacturing method of iron loss unidirectional silicon steel sheet. 3. The method for producing an ultra-low iron loss unidirectional silicon steel sheet according to claim 1, wherein the thermal expansion coefficient of the ceramic tension coating is reduced toward the outer layer.