JPH0686631B2 - Method for manufacturing unidirectional electrical steel sheet with high magnetic flux density - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is applied to the expression of secondary recrystallization used as a basic metallurgical phenomenon in the production of a grain-oriented electrical steel sheet used as a core of an electric device. On the other hand, the present invention relates to a novel component composition as an effective precipitate (generally called an inhibitor) and a process premised on it.

[Conventional technology]

The unidirectional electrical steel sheet has a so-called Goss orientation ({110} in Miller index) with the {110} plane of the steel sheet and the <001> axis in the rolling direction.
It is composed of crystal grains having a <001> orientation) and is used as a soft magnetic material for iron cores for transformers and electric machines.

This steel sheet must have good magnetic properties and iron loss properties.

The quality of the magnetization characteristics is determined by the magnetic flux density induced in the iron core under a constant magnetic field applied, and the iron core can be miniaturized by using a product having a high magnetic flux density (unidirectional electrical steel sheet).

Steel plates with high magnetic flux density have a crystal grain orientation of {110} <001>
It is obtained by highly aligning with

Iron loss is the power loss consumed as thermal energy when a predetermined AC magnetic field is applied to the iron core. Depending on its quality, magnetic flux density, plate thickness, amount of impurities in steel, specific resistance, grain size And so on.

A steel sheet having a high magnetic flux density is desirable because it can reduce the iron core of an electric device and also reduce the iron loss. In the field, development of a method for manufacturing a product having a high magnetic flux density at a low cost is an issue.

By the way, the unidirectional electrical steel sheet is obtained by finishing annealing a hot rolled sheet obtained by hot rolling a slab to a final sheet thickness by a combination of appropriate cold rolling and annealing, and {110}
It is obtained by so-called secondary recrystallization in which primary recrystallized grains having a <001> orientation are selectively grown.

Secondary recrystallization is a fine precipitate in the steel sheet before secondary recrystallization,
For example, it is achieved by the presence of MnS, AlN, MnSe, (Al, Si) N, Cu ₂ S or the like or the presence of grain boundary existence type elements such as Sn and Sb. These precipitates and grain boundary type elements are
JEMay and D.Turnbull (Trans.Met.Soc.AIME 212 (1
958) As described in p769 / 781), the growth of primary recrystallized grains other than the {110} <001> orientation is suppressed and the {110} <001> oriented grains are selectively grown in the finish annealing step. With function.

Such a grain growth suppressing effect is generally called an inhibitor effect.

Therefore, the priority issue of research and development in this field is what kind of precipitate or grain boundary existing type element is used to stabilize the secondary recrystallization, and the existence of accurate {110} <001> oriented grains. How to achieve their proper state of existence, in order to increase the proportion.

Especially, recently, {110} <001> due to one kind of precipitate
From the point that there is a limit to the high degree of control of the orientation, by deeply elucidating the disadvantages and advantages of various precipitates, some precipitates can be organically combined to stabilize products with higher magnetic flux density and lower Development of technologies that can be manufactured at low cost is in progress.

As a type of deposits, NFLittmann uses Japanese Patent Publication No. 30-3651.
In addition, JEMay and D. Turnbull, Trans.Me.
t.Soc.AIME 212 (1958) p769 / 781 with MnS, Taguchi and Sakakura with Japanese Patent Publication No. 33-4710 AlN and MnS, Fiedler
Is Trans.Met.Soc.AIME 212 (1961) p.1201 to 1205 V
N., Imanaka et al., MnSe, Sb in JP-B-51-13469, J.
A. Salsgiver et al. Have proposed AlN and copper sulfide in Japanese Patent Publication No. 57-45818 and Komatsu et al. (Al, Si) N in Japanese Patent Publication No. 62-45285. In addition, TiS, CrS, CrC, NbC, SiO _{2 and the} like are also known.

On the other hand, as a grain boundary existence type element, the Journal of the Japan Institute of Metals 27 (19
63) P.186, Tatsuo Saito presents As, Sn, Sb, etc., but in industrial production, there are no cases where these elements are used alone, and all of these elements coexist with precipitates to assist them. It is used for the purpose of physical effect.

Furthermore, as a characteristic inhibitor, H. Grenoble
US Patent No. 3,905,842 (1975) by H. Fiedler and US Patent No. 3,905,843 (1975) by H. Fiedler. That is, the presence of S, B, and N in solid solution in appropriate amounts makes it possible to manufacture a unidirectional electrical steel sheet having a high magnetic flux density.

The criteria for selecting precipitates that are effective for secondary recrystallization have not always been clarified, but their representative views are described by Matsuoka in "Iron and Steel" 53 (1967) p.1007-1073. . In summary, (1) The size is about 0.1 μm (2) The required volume is 0.1 vol.% Or more (3) It can be completely melted or not melted in the secondary recrystallization temperature range. Yes, it is a solid solution to an appropriate degree.

Although the various precipitates described above are partially applicable to these conditions, not all phenomena are applicable to these conditions. In the process of nitriding the steel sheet after the cold rolling of the present invention, the above (1) has no significant meaning.

As described above, at present, the guiding principle for selecting a precipitate has not been established, and a new inhibitor control technique is being sought by repeating trial and error.

In any case, in order to obtain a high magnetic flux density (high degree of integration of {110} <001> orientation), it is necessary that fine precipitates are present in the steel sheet before finish annealing in a fine, uniform and large amount. Therefore, it is important to adjust the properties before secondary recrystallization by controlling the precipitates and by appropriately combining rolling and heat treatment that match the characteristics of the precipitates.

[Problems to be Solved by the Invention]

Currently, there are three types of typical industrially produced grain-oriented electrical steel sheet manufacturing methods, each of which has advantages and disadvantages.

The first manufacturing method is disclosed by MF Littmann in Japanese Examined Patent Publication Sho 30-3651.
It is a two-time cold rolling process using MnS as an inhibitor, which is presented in Japanese Patent Publication No. Although the secondary recrystallized grains grow stably, a high magnetic flux density cannot be obtained.

The second manufacturing method is Taguchi, Sakakura et al.
Although it is a one-time cold rolling process using AlN + MnS as an inhibitor and a final cold rolling with a high reduction of more than 80%, an extremely high magnetic flux density can be obtained.
In industrial production, the appropriate range of production conditions is narrow, and stable production of highly magnetic products is difficult.

The third production method is a two-time cold rolling process using MnS (and / or MnSe) + Sb as an inhibitor, which was proposed by Konaka et al. In Japanese Patent Publication No. 51-13469 and has a relatively high magnetic flux density. Although obtainable, harmful and expensive elements such as Sb and Se are used, and the manufacturing cost is high since the method is a double cold rolling method.

The above three types of manufacturing methods have the following problems in common.

That is, in any of these manufacturing methods, the precipitate is once solid-dissolved in order to finely and uniformly precipitate the precipitate. Therefore, the slab heating temperature is inevitably high.

Incidentally, in the first manufacturing method, the slab heating temperature is
The temperature is 1260 ° C. or higher.
As disclosed in Japanese Patent Publication No. 48-51852, it depends on the Si content of the material, but it is 1350 ° C. in the case of Si: 3%. Also in the third manufacturing method, as disclosed in JP-A-51-20716, the slab heating temperature is 1230 ° C. or higher, and according to the example in which a high magnetic flux density is obtained, it is extremely high at 1320 ° C. It is a high temperature.

In this way, the slab is heated to a high temperature to form a solid solution with precipitates, and the subsequent hot rolling middle region is precipitated during the heat treatment.

When the slab heating temperature rises, energy consumption for heating increases, and there is a problem that the yield decreases due to the generation of slag, and the cost of repairing the heating furnace increases and the operating rate of the equipment decreases. Furthermore,
As disclosed in Japanese Patent Laid-Open No. 57-41526, there is a problem that a continuous cast slab cannot be used because a linear secondary recrystallization defect portion occurs due to the high heating temperature of the slab.

In addition, a more important problem than the above cost problem is to increase the Si content in order to reduce the iron loss, and to take measures such as reducing the product plate thickness, the linear secondary recrystallization defect part is generated. In the process that is premised on the high temperature slab heating method, which frequently occurs, there is no hope for future improvement of the iron loss characteristics.

In order to solve such a problem, Japanese Patent Publication No. 61-60896 proposes a process in which secondary recrystallization is made extremely stable by reducing the S content in steel, and high Si and thinness are possible. Was done. However, this process also has a problem that it is difficult to stabilize the magnetic flux density at a high level in industrial production.

On the other hand, the method presented by H. Grenoble in US Pat. No. 3,905,842 or H. Fiedler in US Pat.
There is a method presented in No. 43, but these technologies have essential contradictions and are not manufactured industrially. That is, since solid solution S is mainly used as an inhibitor in this technique, it is essential to reduce the Mn content so as to secure the solid solution S and not form MnS. Specifically, Mn
/S≦2.1 is an essential requirement. Here, as is widely known, solid solution S has a very bad influence on the toughness of the material. Therefore, in a grain-oriented electrical steel sheet having a high Si content and easily cracked, it is extremely difficult in industrial production to cold-roll the material in the state of such a solid solution S.

As mentioned above, it is necessary to rebuild the inhibitor design in order to manufacture low-cost, high-flux density, high-Si, and thin products with high potential for low iron loss in the future. . Further, in order to stably obtain a product having a high magnetic flux density, it is necessary to eliminate instability due to manufacturing conditions.
That is, when one manufacturing condition, for example, a cold rolling reduction ratio is specified, other conditions for obtaining a product having a high magnetic flux density, for example, a cooling condition in hot rolled sheet annealing, a decarburization annealing temperature, etc. Narrowing is disadvantageous in the production of electromagnetic steel sheets and also leads to a decrease in yield. Widening the tolerance of these conditions is important for stable industrial production.

The present invention aims to solve these problems as a technical problem in the invention.

[Means for Solving the Problems]

The feature of the present invention is, by weight, Si: 1.5 to 4.8%, acid-soluble Al: 0.012 to 0.050%, one or two kinds of S or Se in a total amount of 0.012% or less, N: 0.0010 to 0.0120%. %, Mn / (S
+ Se) ≧ 4.0, B: 0.0005 to 0.0080%, balance: Fe and unavoidable impurities slabs are hot-rolled to obtain the final plate thickness by one or two or more cold rolling steps with intermediate annealing. Then, decarburization annealing is performed in a wet hydrogen atmosphere, an annealing separator is applied, and then secondary recrystallization and finishing annealing for the purpose of purifying the steel are performed.Furthermore, after the final cold rolling, secondary annealing in finishing annealing is performed. In the method for producing a unidirectional electrical steel sheet having a high magnetic flux density, which is characterized by performing nitriding treatment of the steel sheet before the start of crystallization, further, the slab is 1200 ° C. before hot rolling.
Heating to the following temperature, and the final thickness 0.10 ~ 0.23
It has a feature in specifying to mm.

The present invention will be described in detail below.

The present inventors hot-rolled a material containing appropriate amounts of Al, N, and B under the conditions of reducing S in molten steel to a certain amount or less and reducing solute S. After forming the rolled sheet, the process is to make the final sheet thickness in one or two cold rolling steps, and perform nitriding treatment of the steel sheet between the final cold rolling and the start of secondary recrystallization in finish annealing. By doing so, we succeeded in manufacturing a magnetic steel sheet with a high magnetic flux density stably over a wide cold rolling reduction range.

Next, constituent features that characterize the present invention will be described.

If the Si content becomes excessively large, linear secondary recrystallization defects frequently occur in the length direction of the product (strip), which makes stable production impossible. This tendency becomes remarkable especially in the high Si range where the Si content exceeds 3.2% and in the thin products having the final plate thickness of 0.23 mm (9 mil) or less. The content of S + Se must be specified as one of the requirements for better solving such a problem.

That is, the upper limit of the amount of S + Se must be 0.012% in order to prevent the generation of linear secondary recrystallization defects. Even within this limited range, S + as low as possible
Better to say Se. In the process of the present invention, the magnetic flux density rather deteriorates with the S or Se content which has been conventionally considered to be effective, and a product having a better magnetic flux density can be obtained with a lower S or Se content. . However, the S content that can be lowered by the current industrial electric steel melting technology without making the cost excessively high is generally 0.0005% by weight.

On the other hand, in the present invention, in order to reduce the manufacturing cost, it is aimed to eliminate the cracking of the material during the hot rolling and cold rolling processes, and the cracking of the material caused by the deterioration of the toughness of the material due to the solid solution S. In order to prevent this, Mn / (S + Se) ≧ 4, so that a small amount of S and Se present in the steel are fixed as MnS and MnSe as much as possible.

In Fig. 1, C: 0.053%, Si: 3.35%, P: 0.030%, Al: 0.03
0%, N: 0.0075%, B: 0.0039%, and Mn:
S content was changed to molten steel containing 0.04% and 0.12%
The condition of cracks at the edges of hot-rolled sheet obtained by heating a 50 kg ingot at 1360 ° C and 1150 ° C and hot rolling is shown. Mn / S ≧
The number of cracks decreased sharply at 4, and MnS did not form a solid solution.
The material having a low heating temperature of ℃ has almost no cracks.

In addition, the Mn content is, as described above, Mn / (S + Se) ≧ 4.0 in relation to the S content, which is sufficient from the viewpoint of preventing edge cracking of the hot rolled sheet, but the Mn content The upper limit of is preferably 0.45%. If it exceeds 0.45%, the product will have forsterite film defects.

Next, the effect of adding B will be described.

C: 0.053%, Si: 3.27%, Mn: 0.15%, S: 0.007%, P: 0.02
5%, Al: 0.027%, N: 0.0080%, B: 0.0002% and 0.009
A 50 kg ingot consisting of 5% and the balance: Fe and inevitable impurities was heated to 1150 ° C. and then hot-rolled to form a 2.0 mm hot-rolled sheet. Then, hot-rolled sheet is annealed at 1120 ℃ for 3 minutes and cold-rolled to a final plate thickness of 0.2mm at 810 ℃, 830 ℃ and 850 ℃.
After carrying out decarburization annealing at each temperature of ℃, 870 ℃, 890 ℃ and 910 ℃, finish annealing was carried out after applying an annealing separating agent containing ferromanganese nitride and containing MgO as a main component. The result is
It is shown in FIG.

As is clear from FIG. 2, although the magnetic flux density of the product increases when the decarburization annealing temperature is increased, fine particles are easily generated and the maximum value of B ₈ is low in the case where the B content is small.

On the other hand, if the B content is too high, a product having a high B ₈ value cannot be obtained depending on the decarburization annealing temperature. The proper range of B content is 0.0005 to 0.0080%.

The effect of B is significant when N is contained in an appropriate amount. Probably effective as BN. N <0.
If it is 001%, there is no effect, and if N> 0.0120%, swelling of the steel sheet called blister occurs.

Next, Al combines with N to become AlN. In the present invention, it is essential to form a compound containing Al by nitriding the steel in the subsequent step, that is, the step after the final cold rolling. , A certain amount of free Al is required. For that, 0.012 to 0.050% is required.

Regarding the slab heating temperature, as in the prior art,
Secondary recrystallization occurs even in high temperature slab heating in which an inhibitor is dissolved in solid solution, or in low temperature slab heating similar to that of ordinary steel, which was conventionally thought to be impossible. However, as shown in Fig. 1, it is possible to reduce the cracks on the side edges of the hot-rolled sheet, to reduce the energy consumption for heating the slab, and to repair the furnace without the generation of slag (steel slag). 1200 because of the fact that the frequency and degree of
Low temperature slab heating below ℃ is preferred.

During cold rolling, the material is subjected to hot-rolled sheet annealing for a short time in order to obtain a product having the highest magnetic flux density. If the magnetic properties are tolerated, the hot-rolled sheet annealing can be omitted in order to reduce the cost.

Further, in order to reduce the crystal grains of the final product, it is possible to adopt two or more cold rolling steps with intermediate annealing sandwiched therebetween.

The reason why the final plate thickness is set to 0.10 to 0.23 mm in the third invention is as follows. For example, as disclosed in Japanese Unexamined Patent Publication No. 57-41326, when the plate thickness is reduced, the eddy current loss is reduced, but the hysteresis loss is increased. Range exists.
The range is 0.10 to 0.23 mm.

In the present invention, the cold rolling reduction ratio range in which the secondary recrystallization is stable and a product having a high magnetic flux density can be obtained up to the high reduction ratio side, and therefore, in producing such a thin product, it is extremely advantageous. Is.

For example, in order to obtain a thin, high magnetic flux density product with a plate thickness of 0.15 mm in a single cold rolling at low cost, the plate thickness of
Hot rolled sheet is required. However, on an industrial scale of 1.5 mm
Performing hot rolling to a thickness is extremely disadvantageous because of reduced productivity and difficulty in control.

As is clear from Example 3, with the B-added material, the final cold rolling rate was 93.
% Products can obtain high magnetic flux density, so the plate thickness is 2.0m
High magnetic flux density can be obtained by cold rolling once even from a hot rolled sheet of m, which is advantageous for stable industrial production.

The material after the final cold rolling is decarburized and annealed in wet hydrogen or a mixed atmosphere gas of wet hydrogen and nitrogen.

The temperature at this time is not particularly limited, but is preferably in the range of 800 to 900 ° C. The dew point of the atmosphere at that time depends on the mixing ratio of hydrogen and nitrogen, but is preferably + 30 ° C. or higher.

Then, apply an annealing separator, and apply high temperature (usually 1100-1200
(° C) Perform long-term finish annealing. The present invention is characterized in that an inhibitor necessary for secondary recrystallization is produced by nitriding the steel in the process after the final cold rolling and before the secondary recrystallization occurs in the finish annealing. In that case, the most preferable embodiment is a method of nitriding steel in the temperature rising process of finish annealing. To achieve this, it is necessary to add an appropriate amount of a compound having a nitriding ability, such as MnN, CrN, etc., to the annealing separator, or to add a gas having a nitriding ability, such as NH _3, to the atmospheric gas. .

In the process of the present invention, the slab heating temperature is 1200 ° C.
Because of the low temperature below, Al that was coarsely precipitated during casting
N and MnS are difficult to re-dissolve. Therefore, a strong inhibitor necessary for suppressing the growth of primary recrystallized grains as in the conventional process cannot be obtained.

Therefore, in the present invention, AlN, (Al, Si) N is formed by nitriding the steel sheet after the completion of cold rolling to function as an inhibitor.

Figure 3 shows the steel sheet after decarburization annealing (a) and the annealing separator with MnN added to the steel sheet after decarburization annealing to perform finish annealing (nitriding the steel sheet with MnN at the initial stage of finish annealing). )
This is an observation of the inhibitor of the steel plate (b) at 1000 ° C. during the temperature rising process.

It can be seen that the inhibitor is remarkably increased in the steel plate (b).

As another embodiment, after the soaking process of the decarburization annealing step, the steel sheet (strip) is treated with a gas containing a gas having a nitriding ability such as NH ₃ as an atmosphere, or after decarburization annealing, NH ₃ etc. There is a method of nitriding a steel sheet in a heat treatment furnace in which a gas containing a gas having a nitriding ability is used as an atmosphere.

Moreover, you may implement combining the method mentioned above.

The steel sheet that has completed the secondary recrystallization is purified and annealed in a hydrogen atmosphere.

〔Example〕

Example 1%: C: 0.055%, Si: 3.50%, P: 0.031%, Al: 0.02
6%, N: 0.0077%, B: (a) 0.0003%, (b) 0.0015
%, (C) 0.0060%, and (d) 0.0100% cast molten steel at 1195 ° C. and then hot rolled, 2.
A hot rolled plate of 3 mm was obtained. Then, hot-rolled sheet is annealed at 1150 ° C for 1 minute, then cold-rolled to a sheet thickness of 0.23 mm, at 830 ° C for 2 minutes
Decarburization annealing was performed in a wet hydrogen / nitrogen mixture. At this time, the atmospheric dew point was 55 ° C. Further, an annealing separator made of MgO containing 4% by weight of ferromanganese nitride is applied, and the temperature is 10 ° C /
Finish annealing was performed by heating to 1200 ° C at a heating rate of hr and holding for 20 hours. The atmosphere at this time was N ₂ : 75% during the temperature rising process up to 1200 ° C., and H ₂ : 25% H ₂ : 100% during the retention at 1200 ° C.

The magnetic flux density of the obtained product was as follows.

Clearly from this result, there is a proper B component range.

Example 2 By weight, C: 0.050%, Si: 3.30%, Mn: 0.150%, P: 0.025
%, S: 0.006%, Al: 0.028%, N: 0.0075%, Cr: 0.120
%, The balance: an electromagnetic steel slab (A) consisting of Fe and inevitable impurities, and an electromagnetic steel slab (B) containing 0.0030% of B added to the above component system were heated to 1150 ° C. and then hot rolled, respectively. Hot-rolled sheets with sheet thicknesses of 1.6, 2.0, 2.5, 2.8 and 3.5 mm were obtained.

These were annealed at 1120 ° C. for 2 minutes and cold-rolled once to give a final thickness of 0.29 mm. Next, 850 ℃ x 150
After performing decarburization annealing for 2 seconds in a mixed gas of wet hydrogen and nitrogen with a dew point of + 60 ° C., an annealing separator made by adding TiO ₂ : 3% by weight and ferromanganese ferronitride: 5% by weight to MgO was applied.

This material is heated to 1200 ° C at a heating rate of 10 ° C / hr,
Finish annealing was performed for holding for a time. The atmosphere at this time is
The gas mixture was N ₂ : 25% and H ₂ : 75% during heating, and H ₂ : 100% gas during holding at 1200 ° C.

The result at this time is shown in FIG.

As is clear from FIG. 4, in the material (A), only the hot-rolled sheet having a thickness of 2.5,2.8 mm showed a high magnetic flux density, whereas in the material (B), the thickness of the hot-rolled sheet was high. 2.0,2.5,2.8,3.5mm
Shows high magnetic flux density, and the magnetic characteristics of the product are stable at a high level even if the rolling reduction during cold rolling is changed.

Example 3 A hot-rolled sheet having the same composition and thickness as in Example 2 was obtained, annealed at 1120 ° C. for 2 minutes, and then cold-rolled once to give a final sheet having a thickness of 0.20 mm. Made thick

This material was subjected to decarburization annealing at 850 ° C. for 90 seconds in a wet hydrogen and nitrogen atmosphere, then applied with an annealing separator, and then subjected to finish annealing under the same conditions as in Example 2.

The results are shown in FIG.

As is clear from FIG. 5, in the material (A), only the hot-rolled sheet having a thickness of 1.6, 2.0 mm showed a high magnetic flux density, whereas in the material (B), the thickness of the hot-rolled sheet was high. 1.6, 2.0, 2.5, 2.8m
A high magnetic flux density was shown for m.

Example 4 C: 0.055%, Si: 3.28%, Mn: 0.15%, S: 0.006%, P: 0.02
5%, Al: 0.027%, N: 0.0077%, B: 0.0003% and 0.0020
%, The slab added with is heated to 1150 ° C., and then hot rolled,
A 2.6 mm hot rolled sheet was obtained. After the scale was removed, it was cold-rolled to 1.8 mm and then annealed at 1100 ° C. for 2 minutes. After that, it was pickled, cold rolled to a thickness of 0.15 mm, and decarburized and annealed at 840 ° C. for 70 seconds. This steel sheet was coated with an annealing separator containing 3% by weight of manganese ferro-nitride in MgO.
After heating to 00 ° C. at a temperature rising rate of 8 ° C./h, annealing was performed for 20 hours. A mixed gas of N ₂ 50% and H ₂ 50% was used as the atmosphere of this temperature rising process, and H ₂ 100% was set at the time of soaking at 1200 ° C.

The magnetic properties and crystal grain size of the obtained product are as follows.

Example 5 C: 0.052%, Si: 3.30%, Mn: 0.14%, P: 0.033 by weight%
%, Al: 0.027%, N: 0.0075%, B: 0.0020% S in the molten steel consisting of the balance Fe and unavoidable impurities (a) 0.004%,
11 slabs obtained by adding (b) 0.010% and (c) 0.018%
After heating to 95 ° C., hot rolling was performed to obtain a hot rolled sheet having a thickness of 2.0 mm. This was hot-rolled sheet annealed at 1120 ° C x 2 minutes + 900 ° C x 1 minute, pickled, and cold-rolled to a sheet thickness of 0.20 mm. Then 85
Decarburization annealing is performed at 0 ℃ for 100 seconds in wet hydrogen, and then an annealing separator containing 3% by weight of MnN added to MgO is applied.
× 20 hours of finish annealing. The atmosphere gas of this finish annealing is a mixed gas of N ₂ : 25% and H ₂ : 75% in the temperature rising process,
It was H ₂ : 100% at the time of soaking at 1200 ° C. The magnetic flux density was as shown in the table below.

Example 6 By weight, C: 0.045%, Si: 3.50%, Mn: 0.16%, P: 0.035
%, Al: 0.028%, N: 0.0080%, B: 0.0025%, the balance Fe and inevitable impurities in molten steel containing Se (a) 0.0050
%, (B) 0.0100%, (c) 0.0200% were added to the obtained steel slab, which was heated to 1150 ° C. and hot-rolled to obtain a hot-rolled sheet having a thickness of 2.0 mm. To this, 1150 ℃ × 2 minutes + 900 ℃ × 2
After hot-rolled sheet annealing for 1 minute, it was rapidly cooled, then pickled, and then cold-rolled to a final sheet thickness of 0.20 mm.

Subsequently, decarburization annealing at 830 ° C for 90 seconds was applied to the steel sheet and MgO
Then, an annealing separator containing 5% by weight of ferro-manganese nitride added thereto was applied.

Then, the steel sheet was subjected to finish annealing by heating it to 1200 ° C. at a temperature rising rate of 10 ° C./hr and holding it for 20 hours. The atmosphere at this time was a mixed gas of N ₂ : 25% and H ₂ : 75% in the temperature rising process up to 1200 ° C., and a gas of H ₂ : 100% at the time of soaking at 1200 ° C.

The magnetic properties of the resulting product were as follows.

As is clear from this result, if the Se content is too high, a product with a high magnetic flux density cannot be obtained.

Example 7 By weight, C: 0.048%, Si: 3.30%, Mn: 0.145%, S: 0.008
%, Al: 0.030%, N: 0.0075%, B: 0.0024%, and a slab consisting of the balance Fe and unavoidable impurities was heated at 1100 ° C. and hot-rolled to obtain a hot-rolled sheet having a thickness of 2.3 mm.

This hot rolled sheet has (1) no hot rolled sheet annealing, (2) 900 ° C x 6
Hot-rolled sheet annealing of (3) 1130 ° C. × 2 minutes + 900 ° C. × 1 minute, followed by rapid cooling.

This is cold rolled to a thickness of 0.30 mm at one time, and decarburized and annealed at 840 ° C for 180 seconds in a mixture of wet hydrogen and nitrogen, and MgO is added by 5 times by weight.
% Ferromanganese nitride was added. After the annealing separator was applied, finish annealing was performed at 1200 ° C for 20 hours. The temperature raising rate in this temperature raising process was 15 ° C / hr, and the atmosphere gas was nitrogen: 25
%, Hydrogen: A mixed gas of 75% was used. Also, the atmosphere gas at the time of soaking at 1200 ° C was water and 100%.

The magnetic properties were as follows:

[Advantages of the Invention] The present invention is configured and operated as described above, so that the manufacturing conditions are free, such as the cold rolling reduction ratio range in which the grain-oriented electrical steel sheet having extremely excellent magnetic properties can be adopted. Since it can increase the degree, it has a special effect that enables stable production.

[Brief description of drawings]

Figure 1 shows the relationship between Mn / S and crack depth at the edge of hot-rolled sheet. Figure 2 shows the relationship between the amount of B added and the decarburization annealing temperature on the magnetic flux density (B ₈ ) of the product. Fig. 3 shows the effect, and Fig. 3 shows the temperature rising process 1000 when the decarburization-annealed steel sheet (a) and the MnN-added annealing separator are applied to the decarburized-annealed steel sheet and finish annealing is performed. A photograph showing the distribution of precipitates in the metal structure of the steel sheet (b) at 0 ° C, and Fig. 4 is a grain-oriented electrical steel material (A) in which B is not added,
For the grain-oriented electrical steel material (B) containing 0.0030% B, the relationship between the hot-rolled sheet and the sheet thickness and the magnetic flux density (B ₈ (T)) of the product when the final sheet thickness is 0.29 mm, Figure 5 shows a grain-oriented electrical steel material (A) with no addition of B,
Relationship between the thickness (gauge) of the hot-rolled sheet and the magnetic flux density of the product (B ₈ (T)) when the final sheet thickness is 0.20 mm for the grain-oriented electrical steel material (B) containing 0.0030% B FIG.

Claims (2)

[Claims] 1. Si: 1.5 to 4.8% by weight, acid-soluble Al: 0.01
2 to 0.050%, 0.01% in total of 1 or 2 types of S or Se
2% or less, N: 0.0010 to 0.0120%, Mn / (S + Se) ≧ 4.0,
B: 0.0005 to 0.0080%, balance: Fe and unavoidable impurities are slab hot-rolled to obtain the final plate thickness by one or two or more cold rolling steps with intermediate annealing, and then wet hydrogen. After decarburization annealing in the atmosphere, applying an annealing separator, then performing secondary recrystallization and finishing annealing for the purpose of purifying the steel, and further, after the final cold rolling to the start of secondary recrystallization in finishing annealing. A method for manufacturing a grain-oriented electrical steel sheet having a high magnetic flux density, which comprises nitriding a steel sheet. 2. Si: 1.5-4.8% by weight, acid-soluble Al: 0.01
2 to 0.050%, one or two kinds of S or Se in a total amount of 0.
012% or less, N: 0.0010 to 0.0120%, Mn / (S + Se) ≧ 4.
0, B: 0.0005 to 0.0080%, balance: Fe and unavoidable impurities slabs are heated to a temperature of 1200 ° C or lower and then hot-rolled, and cold-rolled once or twice with intermediate annealing. The final plate thickness is set by the process, then decarburized and annealed in a wet hydrogen atmosphere, an annealing separator is applied, and then secondary recrystallization and finishing annealing for the purpose of purifying steel are performed, and further, after final cold rolling, A method for producing a grain-oriented electrical steel sheet having a high magnetic flux density, comprising nitriding a steel sheet before the start of secondary recrystallization in finish annealing.