JP2659655B2 - Thick grain-oriented electrical steel sheet with excellent magnetic properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thick grain-oriented electrical steel sheet having excellent magnetic properties and used as an iron core of a transformer or the like.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are mainly used as core materials for transformers and other electric equipment, and are required to have excellent magnetic properties such as excitation properties and iron loss properties. Numerical values representing the excitation characteristics include a magnetic field strength of 800 A
/ Flux density B ₈ in m are usually used. In addition, as a numerical value representing the iron loss characteristic, the iron loss W _17/50 per kg when magnetized at a frequency of 50 Hz to 1.7 Tesla (T) is _used.
You are using

[0003] The magnetic flux density is the largest controlling factor of iron loss characteristics. Generally, the higher the magnetic flux density, the better the iron loss characteristics. In general, when the magnetic flux density is increased, the secondary recrystallized grains become large, and the iron loss characteristics may become poor.
In contrast, by controlling the magnetic domain, the iron loss characteristics can be improved regardless of the particle size of the secondary recrystallized grains.

This unidirectional electrical steel sheet undergoes secondary recrystallization in the final finish annealing step to develop a so-called Goss structure having {110} on the steel sheet surface and a <001> axis in the rolling direction. Being manufactured. In order to obtain good magnetic properties, it is necessary that <001>, which is the axis of easy magnetization, be highly aligned in the rolling direction.

[0005] As a typical production technique of such a high magnetic flux density unidirectional magnetic steel sheet, Satoru Taguchi et al.
No. 0-15644 and Japanese Patent Publication No. 51 by Takuichi Imanaka
There is a method described in JP-A-13469. In the former, MnS and AlN are used, and in the latter, MnS, MnSe, Sb are used.
Are used as the main inhibitors. Therefore, it is indispensable in the current technology to appropriately control the size, morphology, and dispersion state of the precipitates functioning as these inhibitors.

On the other hand, recent labor saving of transformer manufacturers,
From the viewpoint of cost reduction, especially in the field of laminated iron cores, the need for thick grain-oriented electrical steel sheets has increased in order to reduce the number of laminations. In the field of large-sized rotating machines, there has been a demand for using grain-oriented electrical steel sheets for some time. In this field, the need for thick grain-oriented electrical steel sheets is high in order to reduce the number of products.

[0007] On the other hand, increasing the sheet thickness generally leads to deterioration of iron loss characteristics. Therefore, there is an expectation for development of a thicker grain-oriented electrical steel sheet having excellent magnetic properties to solve this problem. I'm growing.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a grain-oriented electrical steel sheet having a large thickness and excellent magnetic properties.

[0009]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a thick grain-oriented electrical steel sheet having a thickness of 0.36 to 1.00 mm containing 2.5 to 4.5% by weight of Si. ,
The C of the steel sheet is 0.0050% or less by weight, the magnetic flux density B ₈ ≧ 1.83T, and the diameter of the steel sheet (diameter equivalent to a circle)
When the formula SF = (area of crystal grain × 4π) / (grain boundary length) ² is defined as an index representing the characteristics of the grain boundary shape for each crystal grain of more than 5 mm, SF ( Average value)
Is SF (average value) <0.80, and the steel plate diameter 5
For the crystal orientation at the center of gravity of the crystal grains larger than mm,
An azimuthal dispersion of 0.2 to 4 degrees exists, and the thickness of the product is t (m
m), the iron loss W _17/50 (w / kg) is W _17/50 ≦ 3.3.
× t + 0.35, which is a grain-oriented electrical steel sheet having a large thickness and excellent magnetic properties.

[0010]

The grain-oriented electrical steel sheet to which the present invention is directed is formed by casting a molten steel obtained by a conventional steelmaking method by a continuous casting method or an ingot-forming method, and interposing a slab with a lump-forming step as necessary. And subsequently hot-rolled to form a hot-rolled sheet, and then subjected to annealing as necessary, and if necessary, one or more times of cold rolling, decarburizing annealing, and final finish annealing with intermediate annealing sandwiched between them. It is manufactured by performing it sequentially.

The present inventors have studied a wide range of requirements for improving the magnetic properties in the process of manufacturing a grain-oriented electrical steel sheet having a large thickness, and have found requirements that the product should have.

The details will be described below based on the experimental results. FIG.
The effect of the C content and the magnetic flux density of the product on the iron loss characteristics of the product is shown below.

In this case, by weight, Si: 3.21 to 3.21.
30%, C: 0.025-0.085%, acid soluble A
l: 0.025 to 0.030%, N: 0.0075 to
0.0086%, Mn: 0.070 to 0.161%,
S: 0.005 to 0.029%, silicon steel slab consisting of Fe and unavoidable impurities with the balance being 1150 to 1380 ° C
For 1 hour and hot rolled into a hot rolled sheet of 2.8 mm thickness.
Next, treatment is performed under two conditions: (1) hot-rolled sheet annealing at 900 to 1100 ° C., and (2) hot-rolled sheet annealing, and then cold-rolled at a rolling reduction of about 83%. .48mm
A thick cold rolled sheet was used.

The cold rolled sheet is decarburized by annealing at a temperature of 810 to 860 ° C. for 250 seconds (atmosphere: 25% N ₂ -75% H).
₂ , dew point 65 ° C.), and then (a) NH ₃ gas during additional annealing at 750 ° C. × 30 seconds with N increase in N
A nitriding treatment of 102 to 0.0195% is performed. (B) No treatment, treatment under two types of conditions, and then applying an annealing separator containing MgO as a main component, and having an inner diameter of 200 to 1
A 500mm-shaped coil (5 tons), the N ₂ 10 to 10
In an annealing atmosphere containing 0% (remainder H ₂ ), the temperature was raised to 1200 ° C. at a heating rate of 15 ° C./hr, and final finishing annealing was performed at 1200 ° C. for 20 hours in an H ₂ annealing atmosphere. did.

After that, shape correction and tension coating
Then, it was cut into SST size, made into a plate shape, subjected to strain relief annealing kept at 850 ° C. for 4 hours, and subjected to magnetic measurement. The thickness of the final product was 0.50 mm.

As is apparent from FIG. 1, the C content of the product is 0.1.
Only under the conditions of 0050% or less and the magnetic flux density B ₈ ≧ 1.83 T, a product having good iron loss characteristics of W _17/50 ≦ 2.00 w / kg was obtained. However, even if this condition is satisfied, W _17/50 >
Since 2.00 w / kg sometimes occurred, the cause was examined in detail.

The result of this study will be described below. FIG. 2 shows that in the experiment shown in FIG.
Hereinafter, a grain boundary form factor (SF) of a crystal grain having a diameter (equivalent circle diameter) of more than 5 mm in a product having a magnetic flux density B ₈ ≧ 1.83T.
And orientation dispersion (Δθ) in crystal grains with a diameter of more than 5 mm
The relationship between (degree) and iron loss characteristics is shown.

In this case, the grain boundary shape factor (SF) was defined by the following formula: SF = (area of crystal grain × 4π) / (grain boundary length) ² , and the grain boundary shape was quantified. The value of SF is 1 when the crystal grain is circular, and when the irregularities of the grain boundary shape increase, the value of S
The value of F decreases.

The azimuthal dispersion (Δθ) (degree) in a crystal grain having a diameter of more than 5 mm indicates a difference in the azimuth in the crystal grain with respect to the position of the center of gravity of the crystal grain. When the product is produced and then flattened into a product, the orientation dispersion (Δθ) generally tends to increase as the rolling direction distance within the crystal grain increases from the center of gravity. Then, image analysis was used for measuring SF, and ECP was used for measuring Δθ. In addition, one point in FIG. 2 uses the SST of each experimental condition shown in FIG. 1, and SF shows an average value (SF (average value)) of 101 to 151 crystal grains having a diameter of more than 5 mm. Is a crystal grain with a diameter of more than 5 mm 8
Δ of maximum orientation variance (azimuth difference between the center of gravity position and the position farthest from the center of gravity position in the rolling direction) of each of 1 to 113 crystal grains
Indicates θ (average value).

As is apparent from FIG. 2, SF (average value)
Under the conditions of <0.80 and Δθ (average value) (degrees) = 0.2 to 4, good magnetic characteristics of W _17/50 ≦ 2.00 w / kg were obtained in all cases.

In order to further develop the above findings, the present inventors assumed that the slab used to explain FIG. 1 was used as a starting material, the thickness of the hot rolled sheet was 2.3 to 5.0 mm, and the thickness of the hot rolled sheet was 0 mm. .36-
A 1.00 mm thick product was made. Other process conditions were the same as those described in FIG.

FIG. 3 shows the experimental results. As is clear from FIG. 3, the product condition of the present invention is C ≦ 0.00.
50%, B ₈ ≧ 1.83T, SF (average value) <0.8
0, Δθ (average value) (degrees) = W _17/50 ≦ 3.3 × t + 0.35 (W _17/50 (w / kg), t : Excellent iron loss characteristics such as product thickness (mm).

Although the effect mechanism of the present invention is not always clear, the present inventors presume as follows. The higher the magnetic flux density, the better the iron loss characteristics,
Generally, the higher the magnetic flux density, the larger the crystal grain size, which is disadvantageous in that respect. However, as in the present invention,
When the plate thickness is large, there is a tendency that the crystal grain size of the product is unlikely to be excessively large, and in this sense, in the case of a thick material such as the present invention, the correlation between the magnetic flux density and iron loss becomes clearer. .

On the other hand, if C remains in the product, it forms carbides, hinders movement of the domain wall when magnetized, and causes deterioration of iron loss characteristics. In the case of a thick material as in the present invention, the decarburization in the decarburization annealing step is likely to be insufficient, so the regulation of the C content of this product is particularly important.

Further, the skeleton of the present invention is a combined effect of the shape of crystal grains and the orientation dispersion of the product. In the vicinity of the grain boundary, a segment of a magnetic domain, which is usually called a spike magnetic domain, tends to be generated. However, when there is azimuthal dispersion in a crystal grain, this tendency becomes more remarkable.

Further, as in the present invention, when the degree of irregularity of the shape of the crystal grain boundary is increased (the SF value is reduced), it means that the grain boundary area is increased, and the spike magnetic domain is increased. Occurs more frequently. The spike magnetic domain increased by the present invention causes magnetic domain segmentation under the tension applied to the steel sheet by the glass film and the coating, thereby improving iron loss characteristics.

In the case of a thick material as in the present invention, it is difficult to realize a magnetic domain refining effect only by a simple method (such as increasing the tension applied to a steel sheet). Performing a combination of controls is necessary to achieve good iron loss characteristics. Next, the reasons for limiting the constituent elements of the present invention will be described. The components of the slab used in the present invention are not particularly limited,
In order to stabilize the magnetic flux density of the product and facilitate decarburization to a required amount, 0.025 to 0.075% C by weight is desirable.

In order to improve the iron loss characteristics of the product, it is desirable to contain 2.5 to 4.5% of Si. In addition, Al, N,
Mn, S, Se, Sb, B, Cu, Nb, Cr, Sn,
Ti, Bi, etc. can be added.

The heating temperature of the slab is not particularly limited, but may be 130 ° C. from the viewpoint of energy cost and the like.
It is desirable to keep the temperature at 0 ° C. or lower. The heated slab is
Next, it is hot-rolled into a hot-rolled sheet. The hot-rolled sheet is annealed as necessary, and then is subjected to one or intermediate annealing.
The final thickness is obtained by cold rolling more than once.

The reduction ratio in the final cold rolling is, though not particularly limited, desirable for it to be 80% or more increase the product magnetic flux density ₍₈ value B). By setting the rolling reduction in the final cold rolling to 80% or more, sharp {110} <001> -oriented grains in the decarburized annealed sheet and corresponding oriented grains ({111}
<112> orientation grains) can be obtained in an appropriate amount. Thereby, it is possible to satisfy B ₈ ≧ 1.83T.

After the final cold rolling, the cold rolled sheet is 700 to 100
Decarburized annealing at 0 ° C. As in the present invention, the product thickness is 0.
If the thickness is as large as 36 to 1.00 mm, the decarburization annealing time required to decarburize to the required level tends to be long. It is advantageous to increase the temperature or increase the dew point of the annealing atmosphere.

If the inhibitor strength is not sufficient to cause secondary recrystallization for the decarburized steel sheet, NH ₃
It is desirable to use gas to perform an inhibitor strengthening measure such as nitriding treatment.

Next, after applying an annealing separating agent containing MgO as a main component to the steel sheet, the inner diameter of the coil is about 500 to 7 mm.
It is made into a 00 mm coil, and then subjected to final finish annealing. By setting the inner diameter of the coil during the finish annealing in such a range, it is possible to cause the crystal grain having a diameter of more than 5 mm of the steel sheet to have an orientation dispersion of 0.2 to 4 degrees with respect to the crystal orientation at the center of gravity. .

Next, the steel sheet is subjected to a process of removing strain and applying a tension coating, thereby obtaining a final product. Performing magnetic domain control using a laser or the like on this product is preferable from the viewpoint of improving iron loss characteristics.

The final product plate is Si: 2.5-4.
It must contain 5%. If it is less than 2.5%, it is difficult to improve iron loss properties, and if it exceeds 4.5%, a problem of brittleness during normal cold rolling occurs.

The thickness of the product is 0.36 to 1.00 mm in the case of a thick material as in the present invention. If it is less than 0.36 mm, the conditions for providing the product plate may not be essential for obtaining good iron loss characteristics. On the other hand, if the thickness of the product exceeds 1.00 mm, the C content level as in the present invention and the annealing time for decarburization become too long, which causes an increase in cost, which is not preferable.

The C content and the magnetic flux density of the product plate are each 0.00
It must be less than 50% and B ₈ ≧ 1.83T. This is because, as shown in FIG. 1, it is necessary to set the above range in order to obtain good iron loss characteristics. Preferably,
0.0030% or less.

On the other hand, the average value SF (average value) of the shape factor SF, which represents the characteristics of the grain boundary shape of crystal grains having a diameter (equivalent diameter of a circle) of more than 5 mm as a steel plate, is SF (average value) <0 .8
Must be 0.

The degree of orientation dispersion (Δθ) in crystal grains having a diameter of more than 5 mm must be Δθ = 0.2 to 4 degrees. This is because, as shown in FIG. 2, it is necessary to keep the content within this range in order to obtain good iron loss characteristics.

This SF value is determined by the Goss set at the onset of secondary recrystallization.
Competing grain growth in the other orientation
That is, it is increased by suppressing the growth of Goss tissue to some extent.
You. The method of controlling the SF value is not particularly limited, and controls the primary recrystallized particle size before secondary recrystallization is developed ,
For example, primary recrystallization by increasing the soaking temperature in decarburizing annealing
How to increase the particle size, a method of suppressing the Goss tissue growth, which utilizes Sn, grain boundary segregation elements, to inhibit the Goss tissue growth,
Adjust the inhibitor strength at the time of secondary recrystallization, Goss organization formed
How to suppress the length or the like may be any method.

On the other hand, the method for controlling the Δθ value
There is no particular limitation, as a coil diameter corresponding to the crystal grain size of the product, a method of performing a final finish annealing, a method of controlling a crystal grain size of a slab using a heat history from solidification to slab heating, etc. It may be a method. This effect of Δθ has an effect of improving iron loss even if one grain of the product plate has a predetermined orientation dispersion.

If the conditions for the above products are satisfied, W
_17/50 ≦ 3.3 × t + 0.35 (W _17/50 (w / k
g), t: The thickness of the grain-oriented electrical steel sheet having good iron loss characteristics of the product thickness (mm).

[0043]

【Example】

Example 1 C: 0.053%, Si: 3.26%, Mn:
0.15%, S: 0.006%, acid-soluble Al: 0.0
A slab containing 29% and N: 0.0076%
After heating to a temperature of 50 ° C., it was hot rolled into a 2.8 mm hot rolled sheet.

After subjecting the hot-rolled sheet to 1120 ° C. and subsequently to hot-rolled sheet annealing at 900 ° C., a rolling reduction of about 8
Cold rolled to a final thickness of 6% at 0.38mm,
Three levels of decarburizing annealing (25% N ₂ + 75% H ₂ , dew point 65 ° C.) were performed at 800 ° C. for 150 seconds, at 830 ° C. for 150 seconds, and at 860 ° C. for 200 seconds, and then at 750 ° C. for 30 seconds. NH ₃ gas was mixed into the annealing atmosphere during annealing for 2 seconds to cause nitriding of the steel sheet.

The N content after this nitriding is 0.0195-0.
It was 0211% by weight. After that, this steel sheet
Is applied to form a 5t coil with a coil inner diameter of 600 mm, and 1200 ° C. at 15 ° C./hr.
, And subjected to final finish annealing in which the temperature was maintained at 1200 ° C for 20 hours.

At this time, the atmosphere gas during the temperature rise was changed to 25% N _2.
+ 75% H _2, and the atmosphere gas kept at 1200 ° C. was 100% H ₂ . Next, shape correction and tension coating
Annealing for cutting, cutting to SST size , making into plate shape, and performing strain relief annealing at 850 ° C for 4 hours
Then, a magnetic measurement was performed. The thickness of the final product was 0.40 mm. Table 1 shows the process conditions and the characteristic values of the product plate.

[0047]

[Table 1]

Example 2 C: 0.045% by weight, Si: 3.01%, Mn:
0.14%, S: 0.008%, acid-soluble Al: 0.0
35%, N: 0.0061%, Sn: 0.05%,
A slab consisting of two levels of Sn, that is, Sn <0.01%, and the balance of Fe and unavoidable impurities was set at 1150 ° C.
To a hot rolled sheet having a thickness of 2.3 mm.

Without subjecting this hot-rolled sheet to annealing, it was cold-rolled to a final sheet thickness at a rolling reduction of about 79% to obtain a cold-rolled sheet of 0.48 mm. 830 ° C. × 300 seconds (25% N ₂
(+ 75% H ₂ , dew point: 62 ° C.), followed by decarburization annealing, and the subsequent steps were performed under the conditions described in Example 1. The thickness of the final product was 0.50 mm. Table 2 shows the process conditions and the characteristic values of the product plate.

[0050]

[Table 2]

Example 3 C in an amount of 0.078%, 0.053%, 0.0
Three levels of 39%, Si: 3.21%, Mn: 0.1
2%, S: 0.009%, acid-soluble Al: 0.034
%, N: 0.0060%, the balance consisting of Fe and unavoidable impurities was heated to a temperature of 1200 ° C.
A hot-rolled sheet having a thickness of mm was used.

Without subjecting this hot-rolled sheet to annealing, it was cold-rolled to a final sheet thickness at a rolling reduction of about 81% to obtain a cold-rolled sheet of 0.58 mm. 830 ° C. × 450 seconds (25% N ₂
(+ 75% H ₂ , dew point: 62 ° C.), followed by decarburization annealing, and the subsequent steps were performed under the conditions described in Example 1. The thickness of the final product was 0.60 mm. Table 3 shows the process conditions and the characteristic values of the product plate.

[0053]

[Table 3]

[0054]

According to the present invention, by using an effect obtained by combining the C amount control, the magnetic flux density control, the crystal grain shape control and the crystal grain orientation control of the product sheet, the direction of the thick sheet having excellent magnetic properties is obtained. Since industrial electrical steel sheets can be obtained, their industrial significance is extremely large.

[Brief description of the drawings]

FIG. 1 is a table showing the relationship between the C content and magnetic flux density of a product and iron loss characteristics.

FIG. 2 is a table showing the relationship between the grain boundary form factor of crystal grains of a product sheet, the orientation dispersion in crystal grains, and iron loss characteristics.

FIG. 3 is a table showing the relationship between product thickness and iron loss characteristics (materials of the present invention and comparative materials).

Claims (1)

(57) [Claims] 1. A thick grain-oriented electrical steel sheet having a thickness of 0.36 to 1.00 mm containing Si: 2.5 to 4.5% by weight, wherein the C of the steel sheet is 0.0050% or less by weight. The magnetic flux density B ₈ ≧ 1.83 T, and as an index representing the characteristics of the grain boundary shape for each crystal grain having a diameter (equivalent circle diameter) of more than 5 mm of the steel sheet, the expression SF = (area of crystal grain × 4π) / (Grain boundary length) ^{2 When} defining ² , SF (average value) as a steel sheet of each SF value
Is SF (average value) <0.80, and the steel plate diameter 5
For the crystal orientation at the center of gravity of the crystal grains larger than mm,
An azimuthal dispersion of 0.2 to 4 degrees exists, and the thickness of the product is t (m
m), the iron loss W _17/50 (w / kg) is W _17/50 ≦ 3.3.
× t + 0.35. A thick, grain-oriented electrical steel sheet having excellent magnetic properties, characterized by satisfying xt + 0.35.