JPH07110973B2 - 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 80
The magnetic flux density at 0 A / m) is used, and W _17/50 (iron loss per 1 kg when magnetized to 1.7 T at 50 Hz) is used as a numerical value representing the iron loss characteristics.

This unidirectional electrical steel sheet causes a secondary recrystallization phenomenon in the final finishing annealing process, causing the {110} plane on the steel sheet surface and <00} in the rolling direction.
It is obtained by developing a so-called Goss structure with a 1> axis. In order to obtain good magnetic properties, it is important to align the <001> axis, which is the easy axis of magnetization, with a high degree in the rolling direction. Also, plate pressure, 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, A1N as an inhibitor, and the iron loss characteristics have also been significantly improved accordingly.

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% Si as low iron loss material
Although steel and other materials are being developed, they still have problems to be solved before they can be used as a transformer material in a factory. On the other hand, magnetic domain control technology using a laser or the like has been developed in recent years, which has significantly improved iron loss characteristics. 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.

The present inventors, in the production of Al-containing unidirectional electrical steel sheet,
We proposed a method to increase the magnetic flux density by increasing the N ₂ partial pressure in the annealing atmosphere in the intermediate stage from the start to the completion of secondary recrystallization (Japanese Patent Application No. 61-61993). It left a problem to be solved.

[Problems to be solved by the invention]

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

[Means for solving problems]

In the final finishing annealing step, the present invention is performed in an annealing atmosphere at 800 ° C or less. To 0.1 or less and increasing the N ₂ partial pressure of the annealing atmosphere in the intermediate stage from the start of secondary recrystallization to the completion of the method for stably producing Al-containing unidirectional electrical steel sheet with extremely high magnetic flux density. It is provided. The present invention will be described in detail below.

In the production of the Al-containing unidirectional electrical steel sheet which is the subject of the present invention, the molten steel obtained by the conventionally used steelmaking method is cast by the continuous casting method or the ingot casting method, and if necessary, slabbing A slab is obtained by sandwiching the steps, followed by hot rolling, and if necessary hot-rolled sheet annealing, and then once or intermediate annealing 2
The final gauge cold rolled sheet is obtained by cold rolling more than once, and then decarburization annealing is performed by a conventional method.

The chemical composition of the hot-rolled sheet is Si: 2.5-4.0%, C: 0.03--0 by weight%.
10%, acid soluble Al: 0.010 to 0.065%, N: 0.0010 to 0.0150
%, Mn: 0.02 to 0.30%, S: 0.005 to 0.040%, Sn, Sb, Se, Te, Cu, Nb, C known as other inhibitor constituent elements
If necessary, r, Ni, B, V, As, Bi, etc. may be contained, and other elements are essentially Fe. The main inhibitor in the component system of the present invention is AlN, and annealing for precipitating AlN is performed as necessary in the step before final cold rolling. After decarburization annealing, an annealing separator containing MgO as a main component is applied to the steel sheet, and final finish annealing is performed. The feature of the present invention lies in this final finish annealing step.

That is, in the final finishing annealing step, in an annealing atmosphere at 800 ° C or less. Is 0.1 or less and the N ₂ partial pressure of the annealing atmosphere is increased in the middle of the process from the start to the completion of the secondary recrystallization, so that the grain-oriented electrical steel sheet having an extremely high magnetic flux density can be stabilized.

The present inventors have proposed a method of increasing the magnetic flux density by increasing the N ₂ partial pressure of the annealing atmosphere in the intermediate stage from the start to the completion of secondary recrystallization in the final finish annealing step (Japanese Patent Application No. 61-61). -61993). Although the magnetic flux density is certainly increased by this method, there remains a problem that the condition range (temperature range, annealing time range, etc.) in which the N ₂ partial pressure is increased is not necessarily wide. Normally, the final finish annealing is performed by
It is performed in the form of a coil of up to 20 Ton, and inhomogeneities such as temperature differences inevitably exist in the coil. In order to industrially stably manufacture products with extremely high magnetic flux density, it was necessary to expand the range of effective conditions.

In order to increase the N ₂ partial pressure and expand the range of effective conditions, the present inventors need to expand the range of conditions (temperature range, annealing time range, etc.) from the start to the completion of secondary recrystallization. As a result of various experiments from the viewpoint of We obtained new knowledge that it is extremely effective to make the value 0.1 or less.

Figure 1 shows the annealing atmosphere below 800 ° C in the final finish annealing process. And the secondary recrystallization behavior are shown. In this case Si: 3.25%,
C: 0.080%, acid soluble Al: 0.026%, N: 0.0080%, Mn: 0.074
%, S: 0.024% containing a 2.3 mm thick hot rolled sheet as a starting material, and the hot rolled sheet was annealed at 1100 ° C. for 2 minutes and then rapidly cooled to 0.22
Cold rolling was performed to a final thickness of 5 mm, and then decarburization annealing and an annealing separator containing MgO as a main component were sequentially applied by known methods to obtain a large number of samples. The temperature was raised to 1100 ° C. at a heating rate of 15 ° C. / hr in a mixed gas of thereafter _{75% H 2 + 25% N} 2, the sample was successively drawn out from the heating furnace every 20 ° C. at each temperature of 900 to 1100 ° C. . Pickling the extracted sample,
The area ratio (secondary recrystallization ratio) of secondary recrystallized grains occupying the surface was measured. In an annealing atmosphere below 800 ° C Was set to 3 levels of 2 × 10 ^-1 , 1 × 10 ^-1 , 2 × 10 ^-2 . As is clear from Fig. 1, the annealing atmosphere below 800 ° C As the value becomes lower, the progress of secondary recrystallization is delayed.

Fig. 2 shows the relationship between the temperature at which the partial pressure of N ₂ was increased during the heating and heating of the final finish annealing and the magnetic flux density of the product. In this case the ingredients,
The process conditions leading up to the application of the annealing separator are the same as those described in Fig. 1. After the application of the annealing separator, the temperature is raised to 1200 ° C at a heating rate of 15 ° C / hr, and the temperature is 1200 ° C. Final finish annealing was performed for 20 hours. Annealing atmosphere is 75% H ₂ + 25% N ₂
The temperature rise is started with the mixed gas of 10% at each temperature shown in Fig. 2.
The gas mixture was switched to H ₂ + 90% N ₂ gas, and when it reached 1200 ° C., it was switched to 100% H ₂ gas. In an annealing atmosphere below 800 ° C Was set to 3 levels of 2 × 10 ^-1 , 1 × 10 ^-1 , 2 × 10 ^-2 . As is clear from Fig. 2, the annealing atmosphere below 800 ° C The lower the value, the wider the temperature range in which the magnetic flux density of the product remarkably increases.

The mechanism of the effect of controlling the annealing atmosphere at 800 ° C. or less in the final finish annealing, which is a feature of the present invention, is not necessarily clear, but the present inventors consider it as follows. At a temperature of 800 ° C or less in the final finish annealing It is considered that when the value is increased, the oxidation on the surface is promoted and the inhibitor such as AlN directly under the surface is deteriorated. It is known that the nuclei of the secondary recrystallization are located immediately below the surface, and it is considered that when the inhibitors beneath the surface are deteriorated, the secondary recrystallized grains can be easily grown after the secondary recrystallized grains are generated. Therefore, in order to delay the progress of secondary recrystallization by suppressing the deterioration of the inhibitor accompanying the progress of oxidation on the surface,
In an annealing atmosphere below 800 ° C It is considered effective to reduce

In the present invention, the annealing atmosphere at 800 ° C or lower in the final finish annealing As shown in Fig. 1, it was defined that A delay effect of secondary recrystallization was observed at 0.1,
As shown in the figure, This is because at 0.1, the temperature range in which the magnetic flux density of the product is improved can be widened. The temperature range below 800 ℃ is defined as 800 ℃ or below. Lowering the temperature causes a delay in secondary recrystallization, and This is because if the ratio is excessively reduced, the film formation mainly of forsterite is adversely affected.

In the present invention, it is defined that the N ₂ partial pressure of the annealing atmosphere is increased in the intermediate stage from the start to the completion of the secondary recrystallization, because the dispersion from the {110} <001> orientation is generated in the intermediate stage of the secondary recrystallization. The magnetic flux of the product is promoted by suppressing the secondary recrystallization of the generated oriented grains and promoting the grain growth of the secondary recrystallized grains that are very close to the {110} <001> orientation generated in the initial stage of the secondary recrystallization. In order to increase the density, it is necessary to increase the N ₂ partial pressure in the annealing atmosphere in the intermediate stage from the start to the completion of secondary recrystallization to form an AlN-based inhibitor (nitride).
This is because there is no effect before the start of the secondary recrystallization and after the completion of the secondary recrystallization. Since the above effect is more significant in the stage where the secondary recrystallization rate is lower, It is considered that the effective condition range (temperature range, etc.) is widened by lowering the temperature and delaying the progress of secondary recrystallization.

The method of final finish annealing is not particularly limited. Any method may be used, such as a method of causing secondary recrystallization during heating and heating, a method of causing secondary recrystallization during isothermal holding. The temperature for increasing the N ₂ partial pressure in the annealing atmosphere and the time from the start of annealing are not particularly limited as long as secondary recrystallization has started. It is clear that the effect of the present invention can be obtained also by a method of performing secondary recrystallization by combining constant temperature holding and temperature increase.

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 1 Si: 3.25%, C: 0.080%, acid-soluble Al: 0.026%, N: 0.0080
%, Mn: 0.073%, S: 0.025%, Sn: 0.012%, including 2.3mm
After annealing at 1100 ℃ for 2 minutes, cold-rolled to a final thickness of 0.225mm, followed by decarburization annealing, and subsequently applying an annealing separating agent containing MgO as the main component, up to 1200 ℃ at 15 ℃ / The temperature was raised at hr and the final finishing annealing was performed at 1200 ° C for 20 hours. In an annealing atmosphere below 800 ° C (1) 2 × 10 ^-2 , (2) 2 × 10 ^-1 and the atmospheric gas conditions are (a) 75% H ₂ + 25% up to 1200 ° C
Treatment with N ₂ , (b) Temperature rising process Treated with 75% H ₂ + 25% N ₂ up to 980 ° C, treated with 10% H ₂ + 90% N ₂ from 980 ° C to 1200 ° C,
(C) Temperature rising process 10 Treated with 75% H ₂ + 25% N ₂ up to 10 ° C,
Treated with 10% H ₂ + 90% N ₂ from 10 ℃ to 1200 ℃, (d) Temperature rising process Treated with 75% H ₂ + 25% N ₂ up to 1040 ℃, from 1040 ℃ to 12 ℃
Four treatments of 10% H ₂ + 90% N ₂ were carried out up to 00 ° C., and when it reached 1200 ° C., 100% H ₂ was annealed. (1)
In the case of condition (a), secondary recrystallization started at about 970 ° C,
Secondary recrystallization was completed at 060 ° C, and (1) (b),
Under the conditions of (1) (c) and (1) (d), it means that the N ₂ partial pressure was increased in the intermediate stage from the start to the completion of the secondary recrystallization. In the case of the condition (2) (a), the secondary recrystallization started at about 970 ° C, and the secondary recrystallization was completed at about 1050 ° C.
Under the conditions of (2) (b), (2) (c), (2) (d), it means that the N ₂ partial pressure was increased in the intermediate stage from the start to the completion of the secondary recrystallization. The processing condition and the magnetic flux density of the product
Shown in the table.

Example 2 Si: 3.25%, C: 0.079%, acid-soluble Al: 0.025%, N: 0.0081
%, Mn: 0.074%, S: 0.025%, Sn: 0.12%, Cu: 0.06%, a hot rolled sheet with a thickness of 2.3 mm was annealed at 1000 ° C for 3 minutes and then rapidly cooled to 1.3.
Cold rolled to a thickness of 5 mm, then intermediate-annealed at 1100 ° C for 2 minutes, then rapidly cooled, cold-rolled to a final thickness of 0.170 mm, then decarburized and annealed, followed by an MgO-based annealing separator. Then, increase the temperature up to 1200 ℃ at 15 ℃ / hr.
A final finish annealing of 0 hours was performed. In an annealing atmosphere below 800 ° C (1) 2 × 10 ^-2 , (2) 2 × 10 ^-1 and the atmospheric gas conditions are (a) 75% H ₂ + 25% up to 1200 ° C
Treatment with N ₂ , (b) Temperature raising process Treatment with 75% H ₂ + 25% N ₂ up to 960 ° C, treatment with 25% H ₂ + 75% N ₂ from 960 ° C to 1200 ° C, (c) Temperature raising process Treated with 75% H ₂ + 25% N ₂ up to 1000 ° C, treated with 25% H ₂ + 75% N ₂ from 1000 ° C to 1200 ° C,
(D) Temperature rising process Treated with 75% H ₂ + 25% N ₂ up to 1040 ° C.
From 40 ° C to 1200 ° C, four treatments of 25% H ₂ + 75% N ₂ were performed, and when the temperature reached 1200 ° C, 100% H ₂ was used for annealing. In the case of (1) (a), the secondary recrystallization started at about 950 ° C and completed at about 1050 ° C, and (1) (b),
Under the conditions of (1) (c) and (1) (d), it means that the N ₂ partial pressure was increased in the intermediate stage from the start to the completion of the secondary recrystallization. In the case of the conditions of (2) (a), the secondary recrystallization started at about 950 ° C, and the secondary recrystallization was completed at about 1040 ° C.
Under the conditions of (2) (b) and (2) (c), it means that the N ₂ partial pressure was increased in the intermediate stage from the start to the completion of the secondary recrystallization. Table 2 shows the processing conditions and the magnetic flux density of the product.

Example 3 Si: 3.28%, C: 0.077%, acid-soluble Al: 0.028%, N: 0.0083
%, Mn: 0.077%, S: 0.024% 11 mm
Hold at 20 ° C for 30 seconds, continue to hold at 900 ° C for 1 minute, quench, then cold-roll to a final thickness of 0.285mm, then decarburize and anneal, then apply an annealing separator containing MgO as the main component. Then, the temperature was raised to 1200 ° C at a rate of 20 ° C / hr, and final finishing annealing was performed at a temperature of 1200 ° C for 20 hours. In an annealing atmosphere below 800 ° C The ^{(1) 2 × 10 -4,} (2) 2 × 10 conditions of the atmosphere gas and two kinds of ^-1 to 1200 ° C. (a) heating process _{75% H 2 + 25% N} 2
(B) Temperature rising process Treated with 75% H ₂ + 25% N ₂ up to 990 ° C, treated with 10% H ₂ + 90% N ₂ from 990 ° C to 1200 ° C,
(C) Temperature rising process 10 Treated with 75% H ₂ + 25% N ₂ up to 10 ° C,
From 10 ℃ to 1200 ℃, treated with 10% H ₂ ＋ 90% N ₂ , (d) Temperature rising process 1030 ℃, treated with 75% H ₂ ＋ 25% N ₂
Four treatments of 10% H ₂ + 90% N ₂ up to 1200 ℃, 1200 ℃
When it became, it was annealed with 100% H ₂ .

(1) In the case of (a), secondary recrystallization started at about 970 ° C and completed at about 1060 ° C, and (1) (b), (1)
Under the conditions of (c), (1), and (d), the N ₂ partial pressure was increased in the intermediate stage from the start to the completion of secondary recrystallization.
In the case of condition (2) (a), secondary recrystallization started at about 970 ° C and completed at about 1050 ° C, and (2) (b),
Under the conditions of (2) (c) and (2) (d), it means that the N ₂ partial pressure was increased in the intermediate stage from the start to the completion of the secondary recrystallization. Table 3 shows the treatment conditions and the magnetic flux density of the product.

Example 4 Si: 3.30%, C: 0.081%, acid-soluble Al: 0.027%, N: 0.0079
%, Mn: 0.076%, S: 0.024%, Sn: 0.13%, Cu: 0.06% hot rolled sheet having a thickness of 2.3 mm, annealed at 1100 ° C for 2 minutes, cold rolled to a final thickness of 0.225 mm, Then, decarburize and anneal and continue Mg
Applying an annealing separator containing O as the main component, up to 1200 ℃ at 15 ℃ /
The temperature was raised at hr and the final finishing annealing was performed at 1200 ° C for 20 hours. 2 × 10 P _H2O / P _H2 in the annealing atmosphere at 400 ℃ or less
^-2 and the annealing atmosphere in the temperature range from 400 ℃ to 800 ℃ (1) 2 × 10 ⁻² , (2) 2 × 10 ⁻¹ , and the atmospheric gas conditions are as follows: (a) 75% H ₂ +25 up to 1200 ℃
% N ₂ in the process, (b) 75% to heating process _{980 ℃ H 2 + 25% N} 2
Treated with 100% N ₂ from 980 ℃ to 1200 ℃, (c)
Heating process up to 1010 ° C, treated with 75% H ₂ + 25% N ₂ , and treated from 1010 ° C to 1200 ° C with 100% N ₂ , (d) Heating process up to 1040 ° C, treated with 75% H ₂ + 25% N ₂ . 100 from 1040 ℃ to 1200 ℃
Treatment with 4% N ₂ and 100% H ₂ at 1200 ℃
Was annealed. Under the conditions of (1) (a), about 96
Secondary recrystallization started at 0 ° C. and completed at about 1060 ° C. (1) (b), (1) (c), (1)
Under the condition of (d), the N ₂ partial pressure was increased in the intermediate stage from the start to the completion of secondary recrystallization. Also (2)
In the case of condition (a), secondary recrystallization starts at about 960 ° C,
Secondary recrystallization was completed at 050 ° C, and (2) (b),
Under the conditions of (2) (c) and (2) (d), it means that the N ₂ partial pressure was increased in the intermediate stage from the start to the completion of the secondary recrystallization. Table 4 shows the processing conditions and the magnetic flux density of the product.

[Effects of the Invention] As described above, according to the present invention, in the final finish annealing step, Is set to 0.1 or less, and by increasing the N ₂ partial pressure in the annealing atmosphere in the intermediate stage from the start to the completion of the secondary recrystallization, a directional electrical steel sheet with extremely high magnetic flux density can be obtained in a wide condition range (increase of N ₂ partial pressure Since it can be stably manufactured at temperature etc., its industrial effect is great.

[Brief description of drawings]

Figure 1 shows the annealing atmosphere below 800 ° C in the final finish annealing process. And FIG. 2 is a relational diagram between the secondary recrystallization behavior and FIG. 2 is a relational diagram between the temperature at which the N ₂ partial pressure is increased during the heating and heating of the final annealing and the magnetic flux density of the product.

Claims (1)

[Claims] 1. In the production of an Al-containing grain-oriented electrical steel sheet, a cold-rolled sheet obtained in a usual step is subjected to decarburization annealing and then subjected to final finish annealing, and an annealing atmosphere at 800 ° C. or lower is used. of Is 0.1 or less, and the N ₂ partial pressure of the annealing atmosphere is increased in the intermediate stage from the start to the completion of the secondary recrystallization.