JPS60240108A - Superlow iron loss grain oriented silicon steel plate and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a hitherto unequaled superlow iron loss uni-directional silicon steel plate by using a final product plate of a specific value or less thickness containing specific quantity of Si, having a forsterite film coated on the surface and the interface between the forsterite film and the steel being smooth. CONSTITUTION:A uni-directional silicon steel plate containing 2.0-4.0wt% of Si, coated with a forsterite film on the surface, the interface between the forsterite film and the steel being smooth, the thickness of the final product being 0.18mm. or less and the iron loss at 50Hz being 0.83W/kg at 1.7T is used. A material slab for uni-directional silicon steel containing 2.0-4.0wt% of Si is made a final product plate of 0.18mm. or less thickness by hot rolling and then by cold rolling and an oxide layer is formed on the surface of the steel plate by decarburization annealing. Then, a separating agent of annealing containing 0.01- 1.0wt% Sb of Sb or an Sb compound and 1.0-20.0wt% Sr of Sr an Sr compound is coated and annealed for final annealing.

Description

[Detailed Description of the Invention] Technical Field The technical content described in this specification regarding an ultra-low iron loss grain-oriented silicon steel sheet and its manufacturing method is particularly applicable to the ultra-low iron loss grain-oriented silicon steel sheet, which has been difficult to obtain in the past. It relates to the advantageous improvement of iron loss characteristics of ultra-thin materials with a plate thickness of 0.18 mm or less by adding innovation to the method of forming an insulating film on the surface.

Background Technology Grain-oriented silicon steel sheets are mainly used as cores for transformers and other electrical and magnetic equipment, and their magnetization properties are excellent.
In particular, low iron loss (represented by W1~150) is required.

For this purpose, firstly, the secondary recrystallized grains in the steel sheet should be <001
> It is necessary to highly align the grain orientation in the rolling direction, and secondly, it is necessary to reduce as much as possible the impurities and precipitates present in the final product steel. The iron loss value of grain-oriented silicon steel sheets manufactured under these considerations has been improved over the years due to many improvement efforts to date, and recently, the value of -17150 has improved to 1 for products with plate thicknesses of 0 and 30 mm. ．．
05W/kg, and WI71 for 0 and 23mm products.
A low iron loss with a value of 50 of 0.90 W/kg has been obtained.

However, after the energy crisis a few years ago, there was a growing trend to use electrical equipment with lower power loss, and unidirectional silicon steel sheets with even lower iron loss were required as the iron core material for these devices. It looks like this.

Conventional technology and its problems By the way, ways to reduce the iron loss of grain-oriented silicon steel sheets include increasing the Si content, making the secondary recrystallized grains finer, etc.
reduce impurity content, and (110) C00L
), metallurgical methods are generally known, such as aligning the secondary recrystallized grains in the orientation to a higher degree, but these hand swords
Current production methods have already reached their limits, and further improvements are extremely difficult, and even if some improvement is recognized, the effect of improving iron loss will be small compared to the efforts made. It has been reached.

Recently, a method has been proposed to reduce eddy current loss by introducing minute strains on the surface of the product plate in a direction perpendicular to the rolling direction and subdividing the magnetic domains. Depending on the shape, average grain size, plate thickness, etc., the effect may not be fully demonstrated, and even if strain relief annealing, which is necessary during the manufacture of wound transformers, is applied, the This left a fatal flaw in that the iron loss value returned to its original value.

Furthermore, apart from the above-mentioned improvement measures, it is known that reducing the thickness of the product plate is effective in reducing iron loss. However, in reality, when the plate thickness is made thinner, the secondary recrystallized grains become coarser, and the inhibitor that is essential for secondary recrystallization becomes unstable, resulting in a deterioration of the magnetic properties. In this regard, as a measure to prevent the secondary particle size of the product from becoming coarse, a method using Gulurol was proposed in Japanese Patent Laid-Open No. 5
7-73127) and a method for improving iron loss by controlling the thickness of the forsterite film (Japanese Patent Laid-Open No. 57-4.
1326), etc. have been proposed.

However, in all of the conventional improvement measures mentioned above, the plate thickness is 0.
．． The thickness is limited to a range of about 15 to 0.25 mm, and in reality, the best iron loss characteristics were obtained when the plate thickness was 0.18 mm, and as the thickness became thinner, the iron loss actually increased.

Such a phenomenon has been well known for a long time, for example, L
This has been confirmed by many researchers including Dr. Ittmann. In other words, iron loss (M) consists of hysteresis loss (Wh) and eddy current loss (l!le), but as shown in Figure 1, eddy current loss gradually decreases as the plate thickness decreases. Below a certain thickness, the decreasing tendency of hysteresis loss weakens, while below a certain thickness, hysteresis loss rapidly increases, resulting in iron loss (1'lT
) shows a minimum value at a plate thickness of about 0.18 mm to 0.20 mm, and it has been generally recognized that this phenomenon does not change.

In addition, good properties may be obtained if the thickness of comparator thick products is made thinner than the above range by mechanical or chemical polishing, but these products do not have a forsterite coating on the surface. However, the production method described above is not suitable for production on an industrial scale. Furthermore, if a forsterite film is formed after the material has been thinned by polishing, a significant deterioration in iron loss usually occurs.

Introduction to the Invention This invention was developed after careful study of the dependence of eddy current loss and hysteresis loss on plate thickness as described above, and as described below, it differs from what was previously believed. Based on completely different new knowledge and facts.

(1) The reason why eddy current loss hardly decreases below a certain plate thickness is that the width of the 180° magnetic domain, which plays a major role in determining eddy current loss, gradually increases.
In addition to this, it is also related that products with thinner plates generally have larger secondary particle sizes.

(2) As the plate thickness is further reduced, the eddy current loss decreases again (.

(3) The cause of the increase in hysteresis loss associated with reducing the plate thickness is not the inherent properties of silicon steel itself;
There is a strong correlation with the state of the interface between the forsterite film and the steel base. Figure 2 shows the relationship between the original iron loss and thickness of silicon steel sheets.

(4) Therefore, by appropriately controlling such interfaces, it is possible to further reduce the iron loss by further reducing the plate thickness.

This invention was developed based on the above knowledge,
In the ultra-thin plate thickness region, which was conventionally considered impossible with normal technology, the iron loss value is lower than the best level that can be obtained today, that is, W 1.7 / 50 ≦ 0.85 W
This paper proposes an ultra-low iron loss grain-oriented silicon steel sheet having an iron loss characteristic of /kg and a method for manufacturing the same.

The structure of the invention, that is, the present invention is based on Si: 2.0 to 4.0% by weight (
(hereinafter simply expressed in %) and has a forsterite coating on its surface, the interface between the forsterite coating and the base steel is smooth, and the final product has a thickness of 0. 18mm or less, 50Hzl,
0.83%/kg when the iron loss is 1.77
This is a super core loss grain-oriented silicon steel sheet with the following:

Here, it is more preferable that the smoothness of the interface between the forsterite coating and the base iron be 10 or less in terms of smoothness R, which will be described later, and that the average grain size of the secondary recrystallized grains be 3 mm or less.

In addition, the present invention provides a material slab of a unidirectional silicon steel sheet containing 2.0 to 4.0% Si, which is hot-rolled and then cool-rolled to obtain a final product thickness, and then subjected to decarburization annealing. In a method for producing a grain-oriented silicon steel sheet, the final product thickness is reduced to 0.1.
8 mm or less, and 0.01 to 1.0% of antimony or its compound as ↓b in the annealing separation material.
and strontium or its compound as Sr1.
0 to 20.0%, and in order to obtain particularly good iron loss properties in this invention method, decarburization annealing is required. The oxygen basis weight Os (g/m2) in the subsequent surface oxide layer is
It is more preferable to control the final product board thickness t (mm) within a range that satisfies the following relationship.

By adding antimony and strontium in combination to the annealing separator according to the method of this invention, the interface between the forsterite coating and the base steel was effectively smoothed, and unexpected results were obtained in terms of iron loss reduction. be.

This invention will be explained in detail below.

First, let's talk about the material of this invention.
It is necessary to use a unidirectional silicon steel material containing 2.0 to 4.0% of l.

Sl is an extremely effective element for increasing the electrical resistance of steel and reducing iron loss, but if it is less than 2%, the effect is poor, while if it is more than 4%, the workability deteriorates significantly and it is not suitable for industrial use. Since large-scale processing becomes virtually impossible, the amount of Sl should be 2.
．． It was limited to a range of 0 to 4.0%.

In this invention, the components are 1. Other than the above-mentioned Sl, there are no particular limitations, and elements normally contained in grain-oriented silicon steel can be added as appropriate; however, for reference, the typical composition is as follows. .

Mouth ≦0.06%, Sb2.0-4.0%, M
n: 0.01-0.20%, S, Se: 0.005-0.1% singly or in combination
, Sb: 0.005-0.20%, remainder Re0 In addition, in this invention, the final product plate thickness was limited to 0.18 mm or less, and the reason for this is that the minimum value of iron loss in conventional grain-oriented silicon steel sheets This is because the thickness of the plate exhibiting this was 0.13 mm, and that the eddy current loss decreases again when the thickness becomes 0.18 mm or less.

Furthermore, the grain-oriented silicon steel sheet according to the present invention requires a top having a forsterite coating, and the reason for this is that the presence of such a forsterite coating causes the surface of the product to This is because eddy current loss is reduced at the same time as insulation is imparted, and in addition, impurities from the steel base steel are effectively removed during final annealing, which is the formation process. As a result, the hysteresis loss increases and the total iron loss W1
? 150 is 0. In order to prevent such characteristic deterioration, the interface between the base steel and the forsterite coating is controlled as described above.

Here, the definition of smoothness R and its measurement method will be described.

The smoothness R is determined by the cross section of the steel plate as shown in Figure 3.
The straight line distance between two points Δ and B on the forsterite/substrate interface that are 0.1 mm or more apart is set at 1°, while the forsterite that exists between AB (including forsterite that exists independently in the substructure) If the total length of the boundary line between and the subway is l, then l/β. Defined by

Conventionally, smoothness measurements have only been applicable to areas that can be mechanically contacted by a sensor such as a record stylus, such as in the measurement of surface roughness. Therefore, in this invention, it was extremely difficult to measure an interface that does not appear on the surface, such as the interface between forsterite and base iron, but this has been made possible by the development of image analysis equipment in recent years.

A standard method for measuring smoothness R will be described below.

First, a cross section of the steel plate after secondary recrystallization annealing is polished according to a conventional method and then subjected to a microscope. The obtained cross-sectional image is as shown in FIG. 3a, but it may be made into a photograph, or it may be directly input into an image analysis device.

Next, two points Δ and B are defined on the interface of this image. ΔB
The distance between! . can be easily measured, but! The measurement is performed as follows.

First, only the forsterite image is extracted, but at this time, it is also necessary to measure independent forsterite grains, as shown by D in Figure 3a, as well as connected forsterite grains, as shown by C. . And in order to obtain the entertainment surface length l, image processing i is called "line thinning processing".
However, in order to correctly evaluate things like independent forsterite grains, it is desirable to perform the "thinning process" after adding the "connection process" with the nearest interface. This is because independent grains become extremely fine dots due to the "thinning process." Third
The figure shows an image after connection and thinning processing.

By performing a series of processes such as extraction series processing and line thinning processing, the boundary line actual length β can be easily determined. It is preferable that this series of processes be performed automatically, and that measurements be taken at at least 10 locations to obtain the average value.

FIG. 4 shows the results of an investigation into the relationship between smoothness R and iron loss in a grain-oriented silicon steel plate with a thickness of 0.15 mm.

As is clear from the figure, the iron loss W17150 is 0.83
In order to be W/kg or less, the smoothness R needs to be 10 or less.

By the way, as is clear from Figure 4 above, the smoothness is 1.
Even if it is 0 or less, it does not necessarily mean that an iron loss value of 0.83 W/kg or less can be obtained. The reason for this is thought to be that as the plate thickness decreases, the secondary grain size increases, which increases eddy current loss and reduces the effect of smoothing the interface.

In this regard, as shown in Figure 5, which shows the relationship between the average particle size of secondary particles and iron loss, the above-mentioned adverse effects can be effectively eliminated if the secondary particle size is 3 mm or less. found.

Next, a manufacturing method according to the present invention will be explained.

A unidirectional silicon steel sheet material containing Si: 2.0 to 4.0% is hot rolled and then cold rolled once or cold rolled two or more times with intermediate annealing in between according to conventional method 4. The finished product is finished with a thickness of 0.18 mm or less.

The cold-rolled steel sheet is then subjected to decarburization annealing in a hydrogen atmosphere containing water vapor to form a layer consisting of 8102 and iron oxide on its surface, and then an annealing separator mainly composed of MgO is applied. After that, finish annealing is performed to form a forsterite insulating film on the surface and to perform secondary recrystallization, but since antimony or its compound and strontium or its compound are added in combination to this annealing separation agent, be.

Figure 3 shows a strontium compound (Sr) in the annealing separator.
S, 0=) alone (x mark in the figure) or 0 in sb conversion
．． The relationship between the iron loss characteristic WIT150 and the Sr content in SrSO4 is shown when it is added in various proportions together with 2% 5b20s (marked in the figure).

As is clear from the figure, the addition of 5rSOs alone cannot be expected to significantly improve iron loss, but the addition of 5rSOs in combination with sb significantly reduces iron loss.

Although the reason why such a combined addition of Sr and sb achieves the above-mentioned remarkable iron loss reduction effect is not yet clearly elucidated, it is due to the smoothing of the interface between the forsterite coating and the base steel. It is thought that this is because the effect of Sr contributing to sb is suppressed by the coarsening of the secondary grain size due to the thinning of the product board, which is eliminated by the grain-refining effect of sb.

If the amount of strontium or strontium compound added is less than 1.0% as S, the effect of the addition will be poor as shown in Figure 3 above;
This is because, if it exceeds this value, the smoothness of the film will be lost and the iron loss characteristics will tend to deteriorate.

In addition, the amount of antimony or antimony compound added is s
b is limited to a range of 0.01% to 1.0%.
．． If it is less than 0.01%, the effect of its addition is poor; on the other hand, if it is less than 1.0%
This is because, if it exceeds, the entire surface of the steel sheet will become fine grained and the iron loss characteristics will deteriorate rapidly.

Note that as the strontium compound and antimony compound, oxides, sulfides, nitrides, etc. are all suitable, but the following are typical examples.

Strontium compound 5rSO<, Sr (Kano)2. SrCO3, Sr
Antimony compounds such as (NO3) 2 5b203.5b20S, 5bS2, 5bS3.5b
2(SO4)3 etc. during annealing separation as described above.
Although a grain-oriented silicon steel sheet with an initial low core loss can be obtained by the combined addition of sb and sb, it has been found that some variations in the characteristic values sometimes occur.

The reason for this is thought to be that the inhibitor becomes unstable due to thinning of the plate, but regarding this point, the oxygen basis weight Os in the surface oxide during decarburization annealing is
It has been found that this problem can be effectively solved by controlling (g/m2) according to the plate thickness t (mm) within a range that satisfies the following equation.

Figure 7 shows various thicknesses of H250%-N250.
%.

830 °C in an atmosphere with various dew points of 55-63 °C,
The results of an investigation into the relationship between oxygen basis weight and iron loss when annealing for 3 minutes are shown.

As is clear from the figure, the desired effect is stably obtained by making the oxygen basis weight Os satisfy the above-mentioned relationship with respect to the plate thickness t.

Examples Example I A grain-oriented silicon steel hot rolled sheet containing 3.2% Si was
After making the final plate thickness to 0.15mm by cold rolling method, ■25
0%, N250%, 830 in an atmosphere with a dew point of 61℃
Annealed at ℃ for 3 minutes to give an oxygen basis weight of 2.0g/m2.
An oxide layer was obtained. Next, on the surface of this decarburized annealed plate,
An annealing separator mainly composed of MgO containing 5rSOn and S b 2 U 3 or 5b2s in various proportions was applied in the form of a slurry, dried, and then heated at 1200°C.
Finish annealing was performed for 10 hours.

Table 1 shows the results of examining the iron loss characteristics of the obtained unidirectional silicon steel sheet with an insulating coating. For comparison, the same investigation was conducted on an annealing separator containing no Sr compound or sb compound and one containing only one of them, and the obtained results are also listed in Table 1.

As is clear from the table, the grain-oriented silicon steel sheet obtained according to the present invention exhibits a much lower core loss value than the control material.

Example 2 A grain-oriented silicon, raw steel hot-rolled plate containing 3.2% Si was
After making the final plate thickness 0.1On+m by cold rolling twice, ■
250%, N250%, 820 tons in an atmosphere with a dew point of 55 to 62°C.

Decarburization annealing was performed for 3 minutes. Thereafter, an annealing separator containing 0.2% of 5b2s3 as an sb pure content and 10% of 5rSL as an Sr pure content was applied, and then final annealing was performed.

The iron loss value of the obtained unidirectional silicon steel plate with insulation coating is
Table 2 shows the oxygen basis weight after decarburization annealing.

Table 2 As is clear from the results in Table 2, all of the grain-oriented silicon steel sheets obtained according to the method of this invention had l'117150 of 0.
．． It exhibited excellent iron loss characteristics of 83 or less, and especially good results were obtained when the relationship expressed by the above formula was satisfied.

Effects of the Invention Thus, according to the present invention, it is possible to obtain an ultra-low core loss that is unparalleled heretofore in a grain-oriented silicon steel sheet.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between plate thickness and iron loss value in conventional unidirectional silicon steel sheets, and Figure 52 is a graph showing the relationship between plate thickness and iron loss value, which is the original characteristic of silicon steel plates. A graph showing the relationship. Figure 3a is a cross-sectional view of a grain-oriented silicon steel plate with a forsterite coating, and the same figure is an image after the connection-thinning process. Figure 4 is a graph showing the smoothness of the interface and A graph showing the relationship between the iron loss value and Figure 5 is a graph showing the relationship between the average grain size of the steel plate and the iron loss. Figure 6 is a graph showing the relationship between the Sr addition amount and the iron loss value. Figure 7 is a graph showing the relationship between plate thickness and oxygen basis weight on iron loss value. Figure 1 Figure 2 Plate thickness (mps) Figure 3 (b) Figure 4! Honte Fusen R Figure 5 Average H Measurement Figure 6 Figure 7 Rice scraps - Guan

Claims (1)

[Claims] 1. A unidirectional silicon steel sheet containing 2.0 to 4.0% by weight of 3i and having a forsterite coating on its surface, wherein the forsterite coating and the base steel are bonded together. The interface is smooth, the thickness of the final product is 0.18mm or less, and the iron loss at 50Hz is 0.8 at 1.7T.
Ultra-low iron loss grain-oriented silicon steel sheet of 3W/kg or less. 2. The smoothness of the interface between the forsterite film and the base steel is determined by the arbitrary straight line distance β on the base steel/forsterite film interface in the cross section of the steel plate. The grain-oriented silicon steel sheet according to claim 1, wherein the smoothness R expressed as the ratio of the actual boundary line actual length β to the actual boundary line actual length β is less than or equal to IO. 3. The grain-oriented silicon steel sheet according to claim 1 or 2, wherein the average grain size of the secondary recrystallized grains of the steel sheet is 8 mm or less. 4,3i: A material slab for unidirectional silicon steel containing 2.0 to 4.0% by weight is hot-rolled and then cold-rolled to obtain the final product thickness, and then subjected to decarburization annealing. A method for producing a grain-oriented silicon steel sheet, which comprises applying an annealing separator to form an oxide layer on the surface of the steel sheet, and then applying a final annealing, in which the thickness of the final product is 0.18 mm or less. In addition, the annealing separator contains 0.01 to 1.0% by weight of antimony or its compound as sb, and 1.0 to 20.0% by weight of strontium or its compound as Sr. A method for producing grain-oriented silicon steel sheets with ultra-low iron loss. 5. Oxygen basis weight Is in the surface oxide after decarburization annealing (
3. The method according to claim 2, wherein the final product board thickness t (mm) satisfies the following relationship: g/m2).