JPH0826398B2 - Method for producing unidirectional electrical steel sheet with extremely high magnetic flux density - Google Patents

Description

The present invention relates to a method for producing a high magnetic flux density unidirectional electrical steel sheet used for an iron core of a transformer or the like.

[Conventional technology]

The unidirectional electrical steel sheet is mainly used as a soft magnetic material for iron core materials of transformers and other electric devices, and it must have good magnetic excitation characteristics and iron loss characteristics.

Normally, B ₈ (magnetic field strength
Magnetic flux density at 800A / m) is used, and W17 / 50 (iron loss per 1kg when magnetized to 1.7T at 50Hz) is used as a numerical value to represent iron loss characteristics.

This unidirectional electrical steel sheet causes a secondary recrystallization phenomenon in the final finishing annealing step, causing the steel sheet surface to have a {110} plane and the rolling direction to have a <0.
It is obtained by developing a so-called Goth tissue with 01> axis. In order to obtain good magnetic properties, it is important to highly align the <001> axis, which is the easy axis of magnetization, in the rolling direction. In addition, plate thickness, grain size, specific resistance, surface coating,
The purity of the steel sheet also has a great influence on the magnetic properties.

The directionality has been significantly improved by the method characterized by final high-pressure cold rolling using MnS and AlN as inhibitors, and the iron loss characteristics have also been significantly improved.

On the other hand, in recent years, against the backdrop of soaring energy prices, transformer manufacturers are increasingly focusing on materials for low iron loss transformers. Amorphous alloy or 6.5% S as low iron loss material
Although the development of i-steel and the like is in progress, there are still problems to be solved for industrial use as a transformer material.
On the other hand, magnetic domain control technology using laser etc. has been recently developed,
As a result, the iron loss characteristics were significantly improved. Further, the higher the magnetic flux density of the product, the greater the effect of the magnetic domain control technology, so that it is necessary to develop a product having an extremely high magnetic flux density.

As a method for producing an Al-containing grain-oriented electrical steel sheet, a method has been proposed in which the magnetic flux density is increased by decreasing the temperature rising rate in final finishing annealing (Japanese Patent Publication No. 56-334).
50), there are still problems to be solved, such as difficulty in film formation.

[Problems to be solved by the invention]

It is intended to provide a method for solving the problem that it is difficult to stably obtain a product having an extremely high magnetic flux density when producing a grain-oriented electrical steel sheet.

[Means for solving problems]

The present invention uses AlN as a main inhibitor, anneales a hot-rolled silicon steel sheet as required, and performs one or more cold rolling processes including a final cold rolling process with a deep reduction of 80 to 95% in rolling reduction, and in between. In a method for producing a grain-oriented electrical steel sheet by performing decarburization annealing after intermediate annealing, final cold rolling, and final finishing annealing, when performing the final finishing annealing, the temperature range from 700 ° C to 900 to 1050 ° C is 2 Raises the temperature at ~ 50 ° C / hr and continues for 700-1000
A method for producing a grain-oriented electrical steel sheet having an extremely high magnetic flux density by lowering the temperature to a temperature range of 0 ° C and then raising the temperature to a finishing annealing temperature of 1100 to 1300 ° C at 2 to 50 ° C / hr is provided. .

That is, the present inventors, in the manufacturing method of the above-described grain-oriented electrical steel sheet using AlN as the main inhibitor, various examination results of methods for solving the problem that it is difficult to stably obtain a product with extremely high magnetic flux density. , 2 to 50 ℃ / hr from 700 ℃ to 900 to 1050 ℃ in the final finish annealing
At a temperature of 700 to 1000 ° C and then to a finish annealing temperature of 1100 to 1300 ° C at 2 to 50 ° C.
We discovered a phenomenon in which the magnetic flux density becomes extremely high by raising the temperature at / hr.

 The present invention will be described in detail below.

Regarding the components of the silicon steel hot-rolled sheet which is the starting material of the present invention, Si: 2.5-4.0%, C: 0.03-0.10%, acid-soluble Al: 0.010
~ 0.065%, N: 0.0010-0.0150%, Mn: 0.02-0.30%, S:
It is necessary to contain 0.005 to 0.040%.

If Si exceeds 4.0%, brittleness is severe and cold rolling becomes difficult, which is not preferable. On the other hand, if it is less than 2.5%, the electric resistance is low and it is difficult to obtain good iron loss characteristics.

If C is less than 0.03%, the amount of γ before the decarburization step becomes extremely small, and it is difficult to obtain a good primary recrystallization structure. on the other hand
If it exceeds 0.10%, decarburization becomes poor, which is not preferable.

The acid-soluble Al, N is a basic component for obtaining the main inhibitor AlN essential for obtaining a high magnetic flux density in the present invention, and if it deviates from the above range, secondary recrystallization becomes unstable, which is not preferable. , 0.010 to 0.065%, N is 0.00
10 to 0.0150%.

Further, Mn and S are elements necessary for forming the inhibitor MnS, and if it is out of the above range, secondary recrystallization becomes unstable, which is not preferable. Therefore, Mn is 0.02 to 0.30% and S is 0.
Specified as 005 to 0.040%.

Other known Sn, Sb, as inhibitor constituent elements,
If necessary, Se, Te, Cu, Nb, Cr, Ni, B, V, As, Bi, etc. may be contained.

The present invention uses a silicon steel hot-rolled sheet containing the above components as a starting material, annealed as necessary, and one or more cold rolling operations including a final cold rolling with a reduction ratio of more than 80 to 95%. It is premised on a manufacturing process in which intermediate annealing, decarburization annealing after final cold rolling, and final finishing annealing are performed during that time.

In the present invention, AlN is used as a main inhibitor, and hot-rolled sheet annealing at 700 to 1200 ° C is performed as necessary for the purpose of precipitation treatment of AlN.

The intermediate annealing performed during cold rolling when performing cold rolling twice or more is performed at a temperature of 700 to 1200 ° C.

The reduction ratio of the final strong cold rolling should be over 80-95%. If it is less than 80%, it is difficult to obtain a high magnetic flux density, and if it exceeds 95%, the texture after decarburization annealing becomes inadequate and secondary recrystallization becomes unstable.

After the final high-pressure cold rolling, the steel sheet is decarburized and annealed at a temperature of 700 to 900 ° C. An annealing separator is applied to the surface of the steel sheet after decarburization annealing, and then final finishing annealing is performed to obtain a product. The feature of the present invention lies in this final finish annealing step.

When performing the final finishing annealing, the temperature is raised at 2 to 50 ° C / hr from 700 ° C to 900 to 1050 ° C, and then 700
It is necessary to lower the temperature to a temperature range of up to 1000 ° C and then raise the temperature to a finishing annealing temperature of 1100 to 1300 ° C at 2 to 50 ° C / hr. The reasons for limiting the final finish annealing conditions will be described below.

As a result of detailed investigation of the secondary recrystallization behavior, the present inventors have obtained the following new findings. FIG. 1 shows an example of the orientation of secondary recrystallized grains in the initial stage of secondary recrystallization and the stage of completion of secondary recrystallization. The orientation of the secondary recrystallized grains at the beginning of the secondary recrystallization is very close to {110} <001>. As the secondary recrystallization progresses, the oriented grains dispersed from the {110} <001> orientation are secondary recrystallized. I can see it coming. The secondary recrystallization phenomenon is essentially a phenomenon due to iron diffusion, and is greatly affected by temperature. The present inventors have noticed that the secondary recrystallized grains in the initial stage of the secondary recrystallization are very close to {110} <001>. Extensive experiments were conducted assuming that it would be possible to suppress the diffusion and to recrystallize only the grains oriented very close to {110} <001>. The details will be described below based on the experimental results.

FIG. 2 shows the relationship between the temperature at which the temperature starts to be lowered during the final annealing and the magnetic flux density of the product. In this case Si: 3.27
%, C: 0.078%, acid-soluble Al: 0.026%, N: 0.0085%, Mn:
Starting material is a hot rolled sheet having a thickness of 2.3 mm containing 0.071% and S: 0.025%, and the hot rolled sheet is annealed at 1100 ° C. for 2 minutes and then rapidly cooled,
Cold rolled to a final thickness of 0.225 mm, then decarburized and annealed with MgO-based annealing separator,
After the temperature was raised to each temperature shown in FIG. 2 at a temperature rising rate of ° C / hr, the temperature was lowered to 800 ° C. 15 ℃ again when 800 ℃ is reached
The temperature was raised at a heating rate of / hr, the temperature was raised to 1200 ° C, and then the temperature was kept at 1200 ° C for 20 hours. The annealing atmosphere here is
From room temperature to 1200 ° C, 25% N ₂ + 75% H _{2 was used,} and during retention at 1200 ° C, 100% H ₂ was used. As is clear from FIG. 2, the effect of improving the magnetic flux density was observed in the temperature-fall start temperature range of 900 to 1050 ° C., and the temperature-fall start temperature was specified based on FIG.

Therefore, the temperature is lowered from 900 to 1050 ° C to 700 to 1000 ° C. Since it is necessary to raise the temperature of the steel sheet to 1100 ° C or higher for the purpose of purification, lowering the temperature to less than 700 ° C increases the manufacturing cost, which is not preferable, and if it exceeds 1000 ° C, it is difficult to obtain the effect because the progress of secondary recrystallization is fast. ~ 1000 ° C
It was specified that the temperature be lowered to the temperature range of.

Subsequently, the temperature is raised from the temperature range of 700 to 1000 ° C to the finishing annealing temperature of 1100 to 1300 ° C. Purification at less than 1100 ° C is not preferable because it takes too much time, and in terms of purification, it is not necessary to raise the temperature to more than 1300 ° C and the manufacturing cost increases.

The rate of temperature rise from 700 ℃ to 900-1050 ℃ is 2
It was set to 50 ° C./hr. If it is less than 2 ° C / hr, the secondary recrystallization becomes unstable, which is not preferable, and if it exceeds 50 ° C / hr, the nucleation of the secondary recrystallization becomes excessive, and the nuclei easily disperse from the {110} <001> orientation. As a result, the magnetic flux density is lowered, which is not preferable.

The heating rate from the temperature range of 700 to 1000 ° C to the finishing annealing temperature of 1100 to 1300 ° C was 2 to 50 ° C / hr. If it is less than 2 ° C / hr, secondary recrystallization becomes unstable, which is not preferable, and 50 ° C / hr
When it exceeds, the secondary recrystallization nuclei are likely to be excessively generated, and nuclei are easily generated from the {110} <001> orientation to dispersed ones, resulting in a decrease in magnetic flux density, which is not preferable.

From the temperature range of 900 to 1050 ° C, which is a feature of the present invention,
Although the mechanism of the effect of lowering the temperature to the temperature range of 00 ° C is not always clear, the present inventors consider as follows. As shown in FIG. 1, the orientation of the secondary recrystallized grains at the initial stage of the secondary recrystallization is very close to the {110} <001> orientation. This suggests that nucleation of grains oriented very close to {110} <001> occurs earlier than nucleation of grains dispersed from {110} <001>. There are some ideas regarding the generation of secondary recrystallization nuclei, but they are common in that they require diffusion of iron. It is known that the diffusion phenomenon itself strongly depends on the temperature, and if the temperature is lowered at the stage when nuclei of oriented grains very close to {110} <001> are generated, {11
It is considered that nucleation of dispersed oriented grains does not occur from 0} <001>. 1 from any temperature from 700 to 1000 ℃
It is easy to obtain oriented grains that are extremely close to {110} <001>, which has already nucleated during heating to any temperature between 100 and 1300 ℃.
Next recrystallized grains become grains and grow, whereas {110}
The oriented grains dispersed from <001> will finally reach the nucleation time when the temperature reaches or exceeds the temperature at which the temperature begins to drop.
At that time, secondary recrystallized grains very close to {110} <001> occupied a large part of the steel sheet {110}.
It is considered that the number of steel sheet parts where nuclei of oriented grains dispersed from <001> can be generated has decreased. Therefore, the effect of the present invention is to positively suppress the nucleation of oriented grains dispersed from {110} <001>, thereby increasing the proportion of secondary recrystallized grains extremely close to {110} <001> in the steel sheet. It is thought that this is due to what was done.

After the temperature is raised to the finishing annealing temperature of 1100 to 1300 ° C, the temperature is kept at 1100 to 1300 ° C for 5 hours or more to purify impurities such as S and N.

The atmosphere during the final finish annealing is not particularly limited, but the temperature raising process from room temperature to 900 to 1050 ° C, the temperature lowering process to 700 to 1000 ° C, and the subsequent 1
It is 2 that the annealing atmosphere contains 5% or more of nitrogen gas during the temperature rising process up to the finishing annealing temperature of 100 to 1300 ℃.
It is preferable from the viewpoint of stabilizing the subsequent recrystallization.

The iron loss characteristics are further improved by coating the steel sheet with tension after the final finish annealing. Since the magnetic flux density of the product manufactured by the present invention is extremely high, magnetic domain control using a laser or the like makes the product extremely excellent in iron loss characteristics.

Examples will be described below.

〔Example〕

Example 1 Si: 3.25%, C: 0.078%, acid-soluble Al: 0.026%, N: 0.00
85%, Mn: 0.071%, S: 0.025%, Sn: 0.12%, Cu: 0.07%
0.225 after annealing at 1100 ℃ for 2 minutes on a hot rolled sheet with a thickness of 2.3mm
Cold rolled to a final thickness of mm, then decarburized and annealed, and subsequently annealed and separated with MgO as the main component and applied at 1200 ° C.
Up to 15 ° C / hr, up to 950 ° C at 15 ° C / hr, then 800 ° C
Then, the temperature is lowered to 15 ° C / hr to 1200 ° C again, the temperature is raised to 1000 ° C at 15 ° C / hr and then lowered to 800 ° C, and again at 15 ° C / hr to 1200 ° C.
After three kinds of treatments of raising the temperature to ℃, the temperature was continuously maintained at 1200 ℃ for 20 hours. The annealing atmosphere was 25% N ₂ + 75% H ₂ below 1200 ° C and 100% H ₂ at 1200 ° C. Table 1 shows the relationship between the processing conditions and the magnetic flux density of the product.

Example 2 Si: 3.51%, C: 0.084%, acid-soluble Al: 0.025%, N: 0.00
Plate thickness including 80%, Mn: 0.075%, S: 0.024%, Sn: 0.16% 2.
3mm hot rolled sheet was annealed at 1100 ℃ for 2 minutes, cold-rolled to a final thickness of 0.225mm, then decarburized and annealed with MgO-based annealing separator. / hr
Then, the temperature was raised to 950 ° C. at 15 ° C./hr, then lowered to 800 ° C., and again raised to 1200 ° C. at 15 ° C./hr. After two treatments, the temperature was kept at 1200 ° C. for 20 hours. The annealing atmosphere was 25% N ₂ + 75% H ₂ below 1200 ° C and 100% H ₂ at 1200 ° C. Table 2 shows the relationship between the processing conditions and the magnetic flux density of the product.

Example 3 Si: 3.29%, C: 0.075%, acid-soluble Al: 0.026%, N: 0.00
85%, Mn: 0.071%, S: 0.025%, Sn: 0.12%, Cu: 0.06%
0.225 after annealing at 1100 ℃ for 2 minutes on a hot rolled sheet with a thickness of 2.3mm
Cold rolled to a final thickness of mm, then decarburized and annealed, and subsequently annealed and separated with MgO as the main component and applied at 1200 ° C.
Up to 15 ° C / hr, up to 1000 ° C at 15 ° C / hr,
After holding at 00 ℃ for 15 hours, heat up to 1200 ℃ at 15 ℃ / hr, 1000
After increasing the temperature to 15 ℃ / hr at 15 ℃ / hr, decrease the temperature to 800 ℃ and then again at 15 ℃ / hr.
After the temperature is raised to 1200 ° C, the temperature is increased to 1200 ° C and the temperature is increased to 1200 ° C for 20
Held for hours. The annealing atmosphere is 25% N ₂ +75 below 1200 ° C.
When it reached 1200 ° C. as% H ₂ , it was set to 100% H ₂ . Table 3 shows the relationship between the processing conditions and the magnetic flux density of the product.

[Advantages of the Invention] As described above, according to the present invention, it is possible to stably produce a grain-oriented electrical steel sheet having an extremely high magnetic flux density by adding a temperature lowering section to the heat cycle of the final finishing annealing step. , Its industrial effect is great.

[Brief description of drawings]

FIG. 1 is a comparison diagram of the orientations of secondary recrystallized grains at the initial stage of secondary recrystallization and at the stage of completion of secondary recrystallization. FIG. 2 is a diagram showing the relationship between the temperature at which the temperature starts to be lowered during the final finish annealing step and the magnetic flux density of the product.

Claims (1)

[Claims] 1. By weight%, Si: 2.5-4.0%, C: 0.03-0.10
%, SolAl: 0.010 to 0.065%, N: 0.0010 to 0.0150%, Mn:
0.02-0.30%, S: 0.005-0.040% and the balance is substantially
Hot-rolled silicon steel sheet made of Fe is subjected to one or more cold rolling including a final cold rolling under a strong reduction with a rolling reduction ratio of over 80 to 95%, or two or more cold rolling steps followed by de-rolling. Charcoal annealing, a method for producing a unidirectional electrical steel sheet by applying final finishing annealing, further applying an annealing separator, in performing the final finishing annealing, the silicon steel sheet having the above components from 700 ℃ to 900 ~ 1050 ℃
Within a temperature range of 2 to 50 ° C / hr and then to a temperature range of 700 to 1000 ° C.
A method for producing a grain-oriented electrical steel sheet having an extremely high magnetic flux density, which comprises heating to a finishing annealing temperature of 0 to 1300 ° C at a temperature rising rate of 2 to 50 ° C / hr.