JPS585969B2 - Manufacturing method of low core loss unidirectional silicon steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a grain-oriented silicon steel sheet with high magnetic flux density and low core loss.

Conventionally, grain-oriented silicon steel sheets have all crystal grains of 110.
001 It was said that the one in the ideal direction was the best.

Therefore, when manufacturing unidirectional silicon steel sheets, various methods are employed to bring all the crystal grains close to the ideal orientation of Iio, Oo1.

That is, great efforts have been made to increase the degree of integration of the 110,001 structure, since this improves the excitation characteristics and reduces iron loss accordingly.

As a result, today, unidirectional silicon steel plates with a thickness of 0.30 txm are industrially produced that exhibit iron loss values as low as W17150 t and IOWATTV imports.

However, it has become clear that in order to obtain a unidirectional silicon steel sheet with an even lower level of iron loss, there is a limit to simply bringing the crystal structure closer to the 110°001 orientation.

As one solution to this problem, on the surface of a unidirectional silicon steel plate,
Although a method of forming a special film and thereby applying tension to the steel plate to lower iron loss has been put into practical use as an effective means, this method also has the above-mentioned 110,001
It can be said that this is beyond the scope of manufacturing ideally oriented structures.

As a result of various studies regarding the correlation between the crystal structure and iron loss mentioned above, the present inventors have found that when the 001 axis has an angle with respect to the rolling surface rather than the ilo and ooi ideal orientations,
To obtain a lower core loss value that is even better than that of conventional unidirectional silicon steel sheets, that is, to align the 001 axis approximately ± with respect to the rolling surface.
It has been found that a magnetic domain structure effective for obtaining low core loss can be formed within crystal grains by forming a structure with an inclination in the range of 4.00 or less.

Note that the above symbols are used because the inclination of the 001 axis is both upward and F-directed with respect to the rolling part.

As a specific manufacturing method, secondary recrystallization is performed using a continuous strip annealing method, and before secondary recrystallization occurs, a wave shape extending in a direction crossing the rolling direction is given to the secondary recrystallization annealing, and the purification is carried out. The feature is that the above-mentioned wave shape is corrected in a step after annealing.

- This invention will be explained in detail below.

The basic basis for completing this invention is based on the following experimental facts discovered by the inventors.

In other words, 3%5i-
As a result of forming a deviation angle β of the Fe single crystal 001 axis from the ideal 110.001 direction and examining the relationship between this deviation angle β and iron loss, the fact shown in FIG. 1 was confirmed.

Here, the deviation angle β is the inclination angle from the rolling plane (crystal surface) of the 001 axis of the single crystal near the 1io, ooi orientation.

FIG. 1 shows the relationship between the deviation angle β and the iron loss at 50 Hz and 17 KG.

As is clear from Fig. 1, the iron loss value of a unidirectional silicon steel sheet strongly depends on the deviation angle β, and when the 001 axis is approximately 2 diagonal to the rolling surface, the iron loss value is It is the lowest.

As the deviation angle β approaches 00 when the deviation angle β is 2° or less, the iron loss value increases, and is maximum at the ideal iio, ooi orientation.

Further, as the deviation angle β becomes larger than 2°, the iron loss value increases.

Therefore, in order to obtain a steel plate with qualitatively excellent low core loss, the grain size should be β-0.5 to 4.0°, preferably 1 to 3°.
It can be seen that a tissue having a 001 axis inclination angle of 001 is formed.

The basic idea of this invention is as follows.

Low iron loss can be obtained by narrowing the 180° magnetic domain width and by minimizing the presence of return magnetic domains other than the 180° magnetic domain within the 1800 magnetic domains.

The iso° magnetic domain is subdivided in order to reduce the magnetostatic energy due to the surface magnetic poles caused by the 001 axis being inclined with respect to the rolling surface.

A reflux magnetic domain is also generated to lower the magnetostatic energy due to the surface magnetic pole, but this domain tends to disappear due to the tension along the 001 axis.

Therefore, the state in which the 001 axis is tilted with respect to the rolling surface and the reflux magnetic domain is almost eliminated due to further application of tension is 1.
The subdivision of 80° magnetic domains makes it possible to obtain the lowest core loss.

The surface film that is finally formed on the surface during the manufacturing process of grain-oriented silicon steel sheets provides surface tension to the steel sheet, which has the same effect as external tension, so 001 is inclined to the rolling surface because 180 ° is a necessary condition for subdivision of magnetic domains.

Figure 2 shows the 180° magnetic domain width and the supplementary domain with the surface film attached.
) shows the relationship between the density and the inclination angle of the 001 axis from the rolling surface.

When the inclination angle is 2° or less, there is almost no reflux magnetic domain, but the 180° magnetic domain width becomes wider, so the iron loss value increases (see Fig. 1).

When the inclination angle is 2° or more, although the magnetic domain width becomes very narrow, the iron loss value becomes large due to the existence of a reflux magnetic domain (see Fig. 1).

As is clear from FIG. 2, when the inclination angle of the 001 axis with respect to the rolling surface is approximately 2°, the optimum conditions are obtained in which the 180° magnetic domain width is narrow and the number of reflux magnetic domains is relatively small.

As mentioned above, the method of obtaining the optimal inclination angle of the 001 axis with respect to the rolling surface is to create a wave shape that extends in the direction that intersects the rolling direction, in most cases perpendicular to the rolling direction, on the steel plate that has reached its final thickness. It is characterized by two points: performing the secondary recrystallization annealing before the secondary recrystallization starts, and performing straightening after the secondary recrystallization annealing to erase the corrugation formed on the steel sheet. .

When performing secondary recrystallization by final high-temperature annealing of a Si-containing steel sheet that has been given a wave shape with a certain curvature extending in a direction crossing the rolling direction as shown in FIGS. 3A and B, secondary recrystallization nuclei Locally, the orientation is the 110°001 orientation, and when secondary recrystallization nuclei in this orientation grow within a steel plate having curvature, they grow while maintaining the same orientation regardless of the shape of the steel plate.

Such an aspect is schematically shown in FIG. 4a.

When a steel plate that has been subjected to secondary recrystallization annealing and has a corrugated shape extending in a direction crossing the rolling direction is flattened by straightening as shown in Fig. A portion where the 001 axis is inclined with respect to the rolling surface occurs.

In the portion where the 001 axis is inclined with respect to the rolling surface, a reflux magnetic domain is generated as shown in FIG. 4C.

Due to the existence of this reflux magnetic domain, the core loss value of the grain-oriented silicon steel sheet becomes large. removed, resulting in subdivision of the 180c domain as shown in Figure 4d.

As a result, iron loss is improved.In other words, using the same material steel sheet, it includes a unidirectional silicon steel sheet after secondary recrystallization annealing by the conventional process, and secondary recrystallization annealing and purification annealing by the manufacturing method of the present invention. When compared with the unidirectional silicon steel sheet obtained through the process, the grain size is approximately the same, but the one obtained by the manufacturing method of this invention is
For the reasons mentioned above, the 180° magnetic domain width is narrowed and iron loss is improved.

Next, a method for manufacturing a unidirectional silicon steel plate according to the present invention will be described.

This invention performs secondary recrystallization during the manufacturing process of unidirectional silicon steel sheets by the conventional method, which is completely different from the flat plate shape or the strip coil shape in the conventional method. After applying the wave shape extending in the intersecting directions, and performing the above-mentioned secondary recrystallization annealing,
Apply an annealing separator and perform purification annealing by box annealing.
The next step is to flatten a steel plate having a corrugated shape.

As mentioned above, this is close to the above-mentioned ideal structure of crystal grains consisting of a portion where the 001 axis is tilted at an angle of ±4.0° or less, preferably within a range of ±1 to 3°, relative to the rolling surface. structure, and the iron loss of the unidirectional silicon steel sheet can be brought to an extremely low level.

Conventionally, industrially produced unidirectional silicon steel sheets are obtained by obtaining a steel ingot with an appropriate composition by an electric furnace method, an open hearth method, or a converter method, soaking the steel in a soaking furnace, and then performing blooming rolling. Either by continuously casting the molten steel obtained by the above-mentioned steel manufacturing method and making it into slabs, or by adding preliminary pressure F processing after continuous casting to make slabs, these slabs can be made into intermediate plates. A hot rolled sheet is obtained by hot rolling to a thickness.

The hot-rolled sheet is pickled, and if the sheet is pickled, it is heat treated at this stage, and then it is usually cold rolled in two stages with intermediate annealing in between (two-stage cold rolling method), or it is cold rolled in only one stage. (-double cold rolling method) to obtain the final standard thickness.

It is manufactured by decarburizing it, annealing it, then finishing annealing (including purification annealing) at a high enough temperature to cause secondary recrystallization, and then going through a heat flat process.

Conventional final annealing, which is performed at a high enough temperature to cause secondary recrystallization, is usually done with MgO The so-called annealing separator, such as was.

On the other hand, there is also a method of secondary recrystallization by continuously heating a steel plate coated with the above-mentioned annealing separator to a high temperature for a predetermined time while it is still in the form of a band.

However, in either case, secondary recrystallization annealing was performed with the steel plate in a flat state.

In the manufacturing process of the unidirectional silicon steel sheet as described above, the present invention generates secondary recrystallization by continuous strip annealing, and at least during this secondary recrystallization, the steel sheet is formed in a direction intersecting the cold rolling direction. Its basic feature is that it has a wavy shape, and in subsequent steps, high-temperature purification annealing and straightening treatment to flatten the curvature of the wavy shape are performed.

As a result, it is possible to exhibit an iron loss value superior to that of unidirectional silicon steel sheets treated by conventional methods.

In this invention, the secondary recrystallization is performed by continuous strip annealing, which allows the desired secondary recrystallization to be applied to the steel plate in a corrugated shape (with a portion where the 001 axis is inclined at an angle of ±4° or less to the rolling surface). This is to make it easier to obtain

In conventional secondary recrystallization annealing in a coil shape, the curvature is different between the inside and outside of the coil, and especially as the inside diameter of the coil becomes smaller, bending deformation is added to the applied waveform, and in some cases, deformation occurs. , it may not be possible to obtain the appropriate inclination angle that is the objective of the present invention.

Therefore, the above-described continuous annealing method can prevent such a situation.

Continuous strip annealing may be performed in a separate process after decarburization annealing, but it must be performed in a continuous process with decarburization treatment, that is, decarburization annealing is usually performed continuously at 1000°C or less, followed by 1000°C. Continuous treatment for secondary recrystallization in a zone where the temperature can be raised above .degree. C., preferably around 1100.degree. C., eliminates the need for reheating from room temperature, which is extremely advantageous in terms of thermal efficiency.

In this case, means for adjusting the atmosphere is of course necessary.

In addition, purification annealing to remove impurities in steel has conventionally been performed in a coiled form in a process that includes secondary recrystallization annealing, but when considering the case where steel sheets with few impurities are targeted,
It is also possible to carry out the subsequent recrystallization annealing and this purification annealing in a continuous manner.

However, in the present invention, the 1200°C
In this invention, purification annealing is performed by coiled box annealing in the vicinity, secondary recrystallization is performed in a continuous manner by adopting this box annealing method, which is operationally advantageous in that the temperature can be raised rapidly.

In box annealing in coil form, in order to prevent seizure between steel plates,
It is necessary to apply an annealing separator mainly composed of MgO in advance.

After high temperature treatment, this annealing separator becomes a glass film,
Adds tension effect to steel plate.

As mentioned above, if the purification annealing is a continuous process, an annealing separator is not necessarily necessary, and a treatment that imparts tension to the steel sheet in a later step, such as forming an inorganic film, is sufficient.

The shape of the steel plate in secondary recrystallization annealing is shown in Figure 3A.
, H shows a typical example.

As shown in these figures, the shape of the steel plate needs to be wavy extending in a direction intersecting the rolling direction.

Generally, from the viewpoint of forming and ease of correction, the third
It is practical to give the steel plate the corrugated shape shown in Figure A.

In this case, θ is 0.5 to 4.0°, preferably 1 to 3°, and P is required to be smaller than the secondary recrystallized grains.

Even if θ is smaller than 0.5° or larger than 4°,
Alternatively, even if P is made larger than the secondary recrystallized grain size, iron loss will not be significantly improved.

The reason for this is clear from FIGS. 1 and 4 showing the principle of the invention.

To give a steel plate a wave shape extending in a direction crossing the rolling direction, rolling, pressing, etc. may be used.

For example, a method of imparting a corrugated shape to a steel plate using a pair of rolls carved with a corrugated shape extending in a direction intersecting the circumferential direction;
Alternatively, there is a method of applying it using a press having a die carved with a wave shape.

Regarding the timing of forming, as mentioned above, it may be formed at any stage after the final plate thickness until the secondary recrystallization begins to occur, but if cold corrugation is added after the primary recrystallization, In this case, the strain during processing tends to affect the secondary recrystallization growth, and crystal grains are generated from the strain-affected area, so it may not be suitable for the purpose of the present invention.

In this invention, after the secondary recrystallization annealing and the purification annealing, it is necessary to add a step of straightening the corrugated steel plate to make it flat.

The method for straightening the wave shape may be any conventional method (at room temperature) such as rolling, roller leveler, tension, or press.

The steel plate thus flattened may be used as is, but generally internal distortion due to shape correction processing exists in the steel plate and deteriorates magnetic properties, so it is usually 600 to 1
It is preferable to perform so-called strain relief annealing, which is heated to a temperature of 200°C.

Note that the above-described shape correction of the steel plate may be performed in a strain relief annealing furnace together with strain relief annealing, and it is practical to use a hot leveler in a continuous strain relief annealing furnace.

In this way, by giving a wave shape to a steel plate of the final thickness, performing secondary recrystallization annealing using a continuous strip method, and then performing purification annealing using a box type annealing, the wave shape of the steel plate is corrected and flattened. The core loss value of the unidirectional silicon steel plate can be lowered.

Industrially, the above-mentioned corrugations are applied to the steel plate using a roll having a corrugated surface.

The steel plate which has been given a corrugated shape in this way is subjected to secondary recrystallization annealing, then purification annealing, and then flattened.
The 01 axis is periodically tilted within a range of ±4° or less.

Below, reasons for limiting the constituent elements of this invention and modes of implementation will be explained.

First, the silicon content of the steel plate is limited to 0 to 4 Yu.

As is well known, silicon increases the electrical resistance of steel sheets and lowers iron loss, but it impairs workability.

From the viewpoint of workability, the content is usually 3 parts, with an upper limit of 4.0 parts.

In addition, unidirectional silicon steel sheets for specific uses may contain no silicon at all or have a very low silicon content, and the present invention reduces the silicon content of such conventional unidirectional silicon steel sheets. Since it can be applied in exactly the same way to the case, the lower limit is set to 0%.
And so.

Furthermore, there are no particular restrictions on other contained components in the present invention, as long as they contain appropriate amounts of the elements necessary for producing a normal grain-oriented silicon steel sheet.

For example, elements necessary to stably produce secondary recrystallized grains are not limited to Mn, S, C, Al, and N, but also include Ti, V, Nb, and Se.

It goes without saying that sb and the like may be contained singly or in combination.

Molten steel containing such components is subjected to the Nishinomiya industrial manufacturing process described above and then subjected to secondary recrystallization annealing material.

Example 1 C; o, 053%, Si: 2.93%, Mn: 0.07
Section 5, S; 0.026%, 5olAJl: 0.026%
, N; 0.0065% is bloomed and rolled to obtain a slab, and this slab is heated and hot rolled to obtain 2.311
11! A thick hot-rolled plate was obtained.

Hot-rolled plate annealed at 1150°C for 2 minutes, then pickled, 0.29y
Cold rolled to a

Next, the corrugated shape shown in FIG. 3Q was applied to the steel plate by a roll having a corrugated shape extending in the circumferential direction (crossing the circumferential direction) on the roll surface.

The wave shape on the steel plate at this time is h-25 as shown in Figure 3.
μm, P=5im.

Next, the steel plate was decarburized and annealed.

At this stage, the steel plate is divided into two parts to form steel plates 1 and 2.

Next, after applying MgO to the surfaces of steel plates 1 and 2, steel plate 1
11 in a dry H2 atmosphere while retaining the wave shape.
Strip-like secondary recrystallization annealing was performed at 00°C for 5 minutes, and then purification annealing was performed at 1200°C for 20 hours in a dry H2 atmosphere.

On the other hand, steel plate 2 was subjected to secondary recrystallization annealing in a state in which the steel plate was brought into close contact with a patch plate having a radius of curvature of 25 crrL in order to reproduce the coiled box annealing conditions.

After the secondary recrystallization annealing and the purification annealing, the steel plates 1 and 2 were washed with water, and then the steel plates were laminated and subjected to strain relief annealing without applying pressure to correct the wave shape.

The magnetic properties of the steel sheets produced in this manner are shown in the table below.

From the above results, it can be seen that even though the same wave shape was imparted, the magnetic property of the strip annealed material is better.

Example 2 C; 0.0571%, Si: 2.76%, Mn: o, o
s%, S: 0.027 ratio, 5olAl; 0.030 ratio,
A hot-rolled sheet with a thickness of 2.3 mm containing N: 0.0070 was annealed at 1150'CX for 2 minutes, pickled, and then cold rolled to 0.29.

Next, a corrugated shape was given to the steel plate in the same manner as in Example 1.

The wave shape in the steel plate at this time was almost the same as in Example 1.

Next, the steel plate was decarburized and annealed. At this stage, the steel plate was divided into two parts (referred to as steel plates 1 and 2).

Next, after applying MgO to the surfaces of the steel plates 1 and 2, the steel plate 1 was heated in a dry H2 atmosphere while maintaining its wave shape.
Strip-shaped secondary recrystallization annealing was performed at 00°C for 5 minutes, and then box-type purification annealing was performed at 1200°C for 20 hours in a dry H2 atmosphere.

On the other hand, steel plate 2 was subjected to secondary recrystallization annealing (coiled box annealing reproduction material) in a state where the steel plate was brought into close contact with a patch plate having a radius of curvature of 25 cIrL.

After completing the secondary recrystallization and purification annealing, the steel plates 1 and 2 were washed with water, and subsequent steel plates were laminated and strain relief annealed without applying pressure to correct the wave shape.

The magnetic properties of steel plates 1 and 2 are shown in the table below.

The sample used here has a longitudinal length of approximately 7 crr.
It has large crystal grains of L.

[Brief explanation of drawings]

Figure 1 shows the inclination angle β from the rolling surface (crystal surface) of the 001 axis.
Figure 2 is a diagram showing the relationship between the 1800 magnetic domain width, the reflux magnetic domain and the inclination angle β of the 001 axis, Figure 3 is a diagram showing the types of waveforms, and Figure 4 a is a diagram showing the relationship between Figure 4 shows the direction in which the 001 axis develops when the steel plate is given a wave shape and subjected to secondary recrystallization annealing.The steel plate shown in Figure 4a is flattened after secondary recrystallization annealing. Figure 4C is a photograph showing the reflux magnetic domain pattern when there is no surface coating on the steel plate. Figure 4d is a photograph showing the pattern of the inclination of the 001 axis when the steel plate shown in Figure 4C has no surface coating. This is a photograph showing the magnetic domain pattern when

Claims (1)

[Claims] A steel slab containing 4% or less of 1Si is hot-rolled, the resulting hot-rolled sheet is heat-treated as necessary, and then the hot-rolled sheet is cold-rolled in one step or in two steps with intermediate annealing. The final plate thickness is obtained, a corrugation is formed on the obtained cold rolled sheet in a direction crossing the cold rolling direction, and then the corrugated steel sheet is decarburized and annealed.1. Subsequently, secondary recrystallization annealing is performed using a continuous strip method, and then, after applying an annealing separator, blunting annealing is performed using box annealing, and then, straightening is performed to flatten the corrugated shape of the corrugated steel sheet. A method for producing a low core loss unidirectional silicon steel sheet.