JPH04154914A - Production of grain-oriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To stably produce a grain-oriented silicon steel sheet excellent in magnetic properties by subjecting a slab having a specific composition consisting of C, Si, Al, N, S, Se, Mn, and Fe to specific hot rolling and to coiling at low temp. and applying specific cold rolling to the resulting hot rolled plate. CONSTITUTION:A slab having a composition consisting of, by weight, <=0.020% C, 2.5-4.5% Si, 0.010-0.060% acid-soluble Al, 0.0030-0.0130% N, <=0.014% (S+0.405Se), 0.05-0.8% Mn, and the balance Fe with inevitable impurities is heated to <1280 deg.C and hot-rolled. Hot rolling finishing temp. is regulated to >900-<1150 deg.C, and the resulting plate is held at least for 1sec at >=800 deg.C and coiled at <700 deg.C. Moreover, in the above finish hot rolling, the cumulative reduction of area in the final three passes is regulated to >=50%, and further, it is preferable to regulate the reduction of area in the final pass to >=20%. This hot rolled plate is cold-rolled once at >80% reduction of area or is subjected to two or more cold rollings including final cold rolling at >80% reduction of area while process-annealed between the cold rolling stages, by which the final sheet thickness is reached. Then the resulting cold rolled sheet is subjected to decarburizing annealing and finish annealing, by which the grain- oriented silicon steel sheet excellent in magnetic properties can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a unidirectional electrical steel sheet with excellent magnetic properties, which is used as an iron core of a transformer or the like.

(Prior Art) Unidirectional electrical steel sheets are mainly used as iron core materials for transformers and other electrical equipment, and are required to have excellent magnetic properties such as excitation properties and iron loss properties.

The excitation characteristics are expressed by the magnetic flux density (B. value) at a magnetic field strength of 800 A/m. The iron loss characteristics are at frequency 50
1 in Hz. Energy loss per 1 kg of iron core when magnetizing the iron core up to 7 Tesla W+7/S.

Represented by The magnetic flux density of a grain-oriented electrical steel sheet is the most dominant factor in iron loss characteristics; - For boat fishing, the higher the magnetic flux density, the better the iron loss characteristics (lower iron loss value). Additionally, in general, when the magnetic flux density of the product is increased in the manufacturing process of grain-oriented electrical steel sheets, secondary recrystallized grains become larger and iron loss characteristics may deteriorate. For such unidirectional electrical steel sheets with high magnetic flux density and large secondary recrystallized grains, magnetic domain control that subdivides the magnetic domain width improves iron loss characteristics regardless of the size of secondary recrystallized grains. You can get used to it.

Unidirectional electrical steel sheets are manufactured by generating secondary recrystallization in the final finish annealing process and developing a so-called Goss structure that has a (11O) plane on the steel sheet surface and a <001> axis in the rolling direction. . In order to obtain a unidirectional electrical steel sheet with good magnetic properties, the axis of easy magnetization <001
>It is necessary to align the axes to a high degree in the rolling direction.

As a typical manufacturing technology for unidirectional electrical steel sheets with high magnetic flux density, Kawaguchi et al.
There is a technique disclosed in Japanese Patent Publication No. 44 or a technique disclosed by Imao et al. in Japanese Patent Publication No. 13469/1983. In the former case, A/! N and MnS, in the latter case M
nS, MnSe, and Sb function as the main inhibitors.

In the current industrial manufacturing process of grain-oriented electrical steel sheets, it is essential to appropriately control the size, morphology, and dispersion state of these precipitates that function as inhibitors.

Regarding MnS, a method has been adopted in which MnS is completely dissolved in solid solution in the slab heating stage prior to hot rolling, and then precipitated in the hot rolling stage. In order to completely dissolve the amount of MnS necessary to function as an inhibitor in the secondary recrystallization, the slab must be heated to a high temperature of about 1400°C.

This slab heating temperature is 200° C. or more higher than the heating temperature of ordinary steel slabs, and this causes the following problems.

1) Requires extra high-temperature slab heating exclusively for grain-oriented electrical steel.

2) The energy consumption rate of the heating furnace is high.

3) The amount of molten scale (slag) from the slab increases, forcing difficult operations such as slag scraping.

4) The heating furnace needs to be repaired more frequently, which not only increases maintenance costs but also lowers the equipment operating rate and equipment productivity.

To solve this problem, the slab heating temperature can be lowered to the same level as ordinary steel;
MnS functions as an inhibitor in secondary recrystallization
This means reducing the amount of or not using it at all, which inevitably leads to destabilization of secondary recrystallization. Therefore, in order to lower the slab heating temperature, MnS
It is necessary to strengthen the inhibitor with other precipitates to sufficiently suppress normal grain growth during final annealing. In addition to sulfides, such inhibitors can include nitrides, oxides, grain boundary precipitated elements, and the following are known.

In Japanese Patent Publication No. 54-24685, As, 5iSS
By incorporating grain boundary segregation elements such as n and Sb into the mesh, the slab heating temperature can be set to 1050 to 1350°C.

Disclosed. Furthermore, in JP-A-52-24116, in addition to Al, ZrXTi, B, Nb, Ta
, V.

By incorporating nitride-forming elements such as Cr and Mo into the slab, the slab heating temperature can be increased from 1100 to 1260°C.
It is disclosed that. Furthermore, JP-A-57-1
Publication No. 58322 discloses that the Mn content is lowered and the Mn content is lowered.
It is disclosed that by setting /S to 2.5 or less, the slab heating temperature can be lowered, and further, secondary recrystallization can be stabilized by adding Cu. On the other hand, a technique has also been disclosed in which improvements are made from the metal structure side in combination with reinforcement of these inhibitors. That is, in JP-A-57-89433, in addition to Mn, S, se, sb, Bi, Pb,
By adding elements such as B and combining this with the columnar crystallinity of the slab and the secondary cold rolling reduction rate,
This enables low-temperature slab heating.

Furthermore, in JP-A-59-190324, in addition to S or Se, A! A technique is disclosed in which the inhibitor is composed mainly of B and nitrogen, and the secondary recrystallization is stabilized by subjecting the material to pulse annealing during the primary recrystallization annealing after cold rolling. As described above, great efforts have been made to lower the slab heating temperature in the manufacturing process of grain-oriented electrical steel sheets.

By the way, the present inventors previously reported in JP-A-59-56522 that Mn was 0.08 to 0.45% and S was 0.007%.
% or less, thereby making it possible to heat slabs at low temperatures. This technology has solved the problem of linear secondary recrystallization defects in products caused by coarsening of crystal grains during high-temperature slab heating.

The manufacturing process that lowers the slab heating temperature to that of ordinary steel is
Originally, the purpose was to reduce manufacturing costs, but it goes without saying that it cannot be industrialized unless the manufacturing process can stably produce products with good magnetic properties. On the other hand, lowering the slab heating temperature involves changing hot rolling conditions, such as lowering the hot rolling temperature. However, up to now, an integrated manufacturing process based on low-temperature slab heating that incorporates hot rolling conditions has not even been considered.

In the case of conventional manufacturing processes that require high-temperature slab heating (e.g., 1300'C or higher), the main metallurgical roles of the hot rolling process are: a) Segmentation of coarse grains by recrystallization; b) MnS , fine precipitation or precipitation suppression of AffiN, etc., and C) formation of (110) <Ool> orientation due to shear deformation of the material.

However, in the case of a manufacturing process based on low-temperature slab heating, the above function a) is not necessary, and as for b), as disclosed by the present inventors in Japanese Patent Application No. 1-1778, after decarburization annealing, Precipitate control at the hot rolling stage is not essential, as it is sufficient to have an appropriate metallographic structure. Therefore, it can be said that the restrictions on hot rolling conditions required in conventional manufacturing processes based on high-temperature slab heating are fewer in the case of manufacturing processes based on low-temperature slab heating.

In order to control secondary recrystallization, the present inventors have developed a method using heat to optimize the metallographic structure of hot-rolled sheets, which was impossible to achieve in conventional manufacturing processes based on high-temperature slab heating. The inter-rolling method was investigated. For example, regarding the metal physical phenomena after the final pass of the hot rolling process, MnS, A
Fine precipitation or suppression of precipitation of RN and the like is the most important control item in conventional manufacturing processes, and other phenomena have not been given much attention.

The present inventors focused on the recrystallization phenomenon after the final pass of finishing hot rolling, which had received little attention in the past, and utilized this phenomenon to control the metallographic structure of hot-rolled sheets, and to develop the method based on the premise of low-temperature slab heating. We investigated a manufacturing method that would make the magnetic properties of the product good and stable in a manufacturing process using final heavy reduction cold rolling that applies a rolling reduction of more than 80%.

Regarding hot rolling of unidirectional electrical steel sheets, secondary recrystallization failure (occurrence of linear fine grains connected in the rolling direction) due to coarse growth of crystal grains during slab heating at high temperatures (e.g., 1300°C or higher) In order to prevent
For example, a method of dividing coarse grains by subjecting the material to recrystallization high reduction rolling applying a rolling reduction of 30% or more per pass in a temperature range of 190°C is disclosed in Japanese Patent Publication No. 60-37172.
It is disclosed in the publication No. It is true that this method reduces the generation of linear fine particles, but this method is used in a manufacturing process that assumes high-temperature slab heating.

In the case of a manufacturing process based on low-temperature slab heating (below 1280°C), coarsening of crystal grains due to the high-temperature slab heating does not occur, so recrystallization for the purpose of dividing coarse crystal grains is performed. High reduction rolling is not necessary.

On the other hand, in the manufacturing process of grain-oriented electrical steel sheets in which MnS, Mn5eXSb acts as an inhibitor, hot rolling of slabs is performed continuously at a rolling reduction of 10% or more in a temperature range of 950 to 1200°C. , then cool the material at a cooling rate of 3°C/S or more, and MnS,
A method for improving the magnetic properties of products by uniformly and finely precipitating MnSe is disclosed in, for example, JP-A No. 51-2.
It is disclosed in Publication No. 0716.

In addition, the slab is hot-rolled at a low temperature to suppress the progress of recrystallization, and the (110)<00
1> A method for improving the magnetic properties of a product by preventing the reduction of oriented grains due to subsequent recrystallization is disclosed, for example, in Japanese Patent Publication No. 59-32526 and Japanese Patent Publication No. 59
It is disclosed in the publication No.-35415. Even in these methods, a manufacturing process using final heavy reduction cold rolling applying a rolling reduction of more than 80%, which is based on low-temperature slab heating, has not even been considered. In addition, in hot rolling of silicon steel slabs containing C≦0.02% by weight, 900%
By setting the cumulative reduction rate to 40% or more in the temperature range below ℃, the material undergoes low-temperature, large-reduction rolling that accumulates strain in the hot-rolled sheet, followed by recrystallization during hot-rolled sheet annealing to produce ultra-low carbon steel. A method to compensate for the peculiar lack of hot rolling recrystallization was developed in 1983.
Although this method is disclosed in Japanese Patent No. 34212, low-temperature hot rolling places an excessive load on the rolling mill, and the shape (flatness) of the hot-rolled sheet tends to be poor, and it is difficult to obtain good magnetic properties. It is also not easy to stably obtain products that have the same properties.

(Problems to be Solved by the Invention) The present invention provides a unidirectional electromagnetic material with excellent magnetic properties, using a manufacturing process using final heavy reduction cold rolling applying a rolling reduction of more than 80%, which is based on low-temperature slab heating. The purpose of the present invention is to provide a method that can stably produce steel plates.

(Means for solving problems) The gist of the present invention is as follows.

(1) By weight, C≦0.020%, SAl: 2.5-4
．． 5%, acid soluble Af: 0.010-0.060%
, N: 0.0030-0.0130%, (S +0
．． 405Se) 50.014%, Mn: 0.05~
A slab containing 0.8% Fe and unavoidable impurities is heated to a temperature below 1280° C., hot rolled, and then a cold rolling step of more than 80% is applied. Alternatively, a unidirectional electrical steel sheet that is subjected to decarburization annealing and finish annealing after reaching the final thickness through two or more cold rolling processes sandwiching intermediate annealing including final cold rolling applying a rolling reduction of more than 80%. In the manufacturing method, the hot rolling end temperature is 900
℃ but less than 1150℃, and at least 1 after the end of hot rolling
A method for producing a unidirectional electrical steel sheet with excellent magnetic properties, which comprises maintaining the temperature in a temperature range of 800°C or more for seconds and winding it in a temperature range of less than 700°C.

(2) The method for producing a unidirectional electrical steel sheet with excellent magnetic properties according to item 1 above, wherein the hot rolling is performed at a rolling reduction rate of 50% or more in the final three passes of finish hot rolling.

(3) The method for producing a unidirectional electrical steel sheet with excellent magnetic properties according to item 1 or 2 above, wherein the hot rolling is carried out at a rolling reduction rate of 20% or more in the final pass of finish hot rolling.

The present invention will be explained in detail below.

The present inventors focused on the recrystallization phenomenon of the material after the final pass of finish hot rolling, which had not received attention in the past, and utilized this phenomenon to improve the We have completed research to establish a method for stably manufacturing unidirectional electrical steel sheets with excellent magnetic properties through a manufacturing process using cold rolling with final heavy reduction applying a rolling reduction ratio, and we have now completed the present invention. be.

The unidirectional electrical steel sheet to which the present invention is directed is produced by continuous casting of molten steel obtained by conventional steel manufacturing methods to directly form a slab, or by pouring molten steel into a mold and solidifying it to form a steel ingot. , which is bloomed into a slab, then hot-rolled into a hot-rolled sheet, annealed if necessary, and then subjected to a single cold rolling step applying a rolling reduction of more than 80%, or is manufactured by a process in which the final thickness is achieved by cold rolling two or more times with intermediate annealing, including a final cold rolling process applying a rolling reduction of more than 80%, followed by decarburization annealing and final finish annealing. .

The present inventors focused on the recrystallization phenomenon of the material after the final pass of finishing hot rolling, and as a result of carrying out extensive research from various viewpoints, we found that the We found that the recrystallization phenomenon and the magnetic properties of the product are closely related.

The present invention will be explained in more detail below based on experimental results.

Figure 1 shows the temperature at the end of hot rolling and the temperature at 8
2 is a graph showing the influence of the time a material (steel plate) is kept in a temperature range of 00° C. or higher on the magnetic flux density of a product.

Here, by weight, C: 0.011%, SAl: 3.
28%, acid soluble f: 0.026%, N: 0
．． 0078%, S: 0.007%, Mn: 0.1
A slab with a thickness of 20 to 60 mm containing 4% Fe and unavoidable impurities was heated at 1100 to 1280°C.
The material was heated to 2.3 mm in thickness and hot-rolled in 6 passes to obtain a hot-rolled sheet with a thickness of 2.3 mm. The material was subjected to various types of cooling such as water cooling immediately after hot rolling, air cooling for a certain period of time after hot rolling, water cooling after hot rolling, and air cooling after hot rolling, and cooling was completed at 550°C. A winding simulation was performed in which the material was maintained at a temperature of 550° C. for 1 hour and then cooled in a furnace. Next, this hot-rolled sheet is subjected to hot-rolled sheet annealing by holding at a temperature of 1100°C for 30 seconds, slowly cooling to 900°C, and then rapidly cooling, and then subjected to a final strong reduction applying a reduction rate of about 88%. It was cold rolled to a final thickness of 0.285 mm. After that, the cold-rolled plate was heated to 830-1000℃.
After decarburization annealing in a temperature range of , an annealing separator containing .MgO as a main component was applied, followed by final finish annealing.

As is clear from Figure 1, the hot rolling end temperature is 900.
℃ and less than 1150'C, and when the hot-rolled sheet is held in a temperature range of 800℃ or higher for at least 1 second after hot rolling, a product with a high magnetic flux density of B6≧1.88T can be obtained. It will be done.

The present inventors investigated this new finding in more detail.

Figure 2 shows that the magnetic flux density was good in the experimental results shown in Figure 1, and the hot rolling end temperature was over 900°C and 1150°C.
℃ and for at least 1 second after the end of hot rolling.
When holding a hot rolled sheet in a temperature range of 00°C or higher,
It is a graph showing the relationship between the cumulative reduction ratio of the final three passes of finish hot rolling and the magnetic flux density of the product. As is clear from FIG. 2, when the cumulative reduction ratio of the final three passes of finish hot rolling is 50% or more, a product with a high magnetic flux density of BIl≧1.90 T can be obtained. The present inventors investigated this new finding in more detail.

Figure 3 shows that the magnetic flux density was good in the experimental results shown in Figure 2, and the hot rolling end temperature was over 900°C and 1150°C.
℃ and for at least 1 second after the end of hot rolling.
The rolling reduction ratio of the final pass of finish hot rolling and the magnetic flux of the product when the hot rolled sheet is held in a temperature range of 00°C or higher and the cumulative rolling reduction ratio of the final three passes of finishing hot rolling is 50% or more. It is a graph showing the relationship between densities. As is clear from FIG. 3, when the reduction ratio in the final pass of finish hot rolling is 20% or more, a product with a high magnetic flux density of B8≧1.92 T can be obtained.

Hot rolling end temperature, time to hold the material (steel plate) in a temperature range of 800°C or higher after hot rolling, cumulative reduction rate of the final three passes of finish hot rolling, rolling reduction rate of the final pass of finish hot rolling. Although the reason why the relationships shown in FIGS. 1, 2, and 3 exist between the magnetic flux densities of products is not necessarily clear, the inventors of the present invention speculate as follows.

Conventionally, it has been thought that the matrix of (1101<001> oriented secondary recrystallized grains) is formed by shear deformation at the surface layer of the material during hot rolling of a slab.
0) In order to enrich the <001> oriented grains after cold rolling recrystallization, the (110) <001> oriented grains of the hot rolled sheet should be coarse grains,
It is believed that it is effective to create a state with less distortion.

In the case of the present invention, the crystal grains of the hot rolled sheet are small due to recrystallization after the final pass of hot rolling, but the strain is small.
This is inherited even after hot-rolled sheet annealing, and (110)<001
>In enriching oriented grains after cold rolling and recrystallization,
Although it is disadvantageous in terms of particle size, it is advantageous in terms of distortion,
As a result, the (110)<oot> oriented grains are not affected in the state after decarburization annealing.

On the other hand, it is the main orientation of the decarburized annealed plate (1111<112>
, (1001<025> is known as an orientation that affects the grain growth of (110)<001> oriented secondary recrystallized grains, and the more (111)<112> oriented grains, the more (
The fewer 1001<025> oriented grains, the more (110)<
It is considered that grain growth of secondary recrystallized grains with 001> orientation becomes easier.

In the present invention, by performing rolling with a high reduction rate in the final three passes of hot rolling, the number of nucleation sites in the recrystallization that follows after the final pass increases, recrystallization progresses, and crystal grains are also refined. Ru.

Next, when the hot-rolled sheet is annealed, many grains that were in a nucleated state in the hot-rolled sheet become recrystallized grains, and the entire steel sheet together with the fine recrystallized grains in the hot-rolled sheet. As a result, the metal structure is dominated by fine crystal grains.

Next, the material (steel plate) after annealing this hot rolled plate is cold rolled,
When recrystallized, many nuclei in the (111)<112> orientation occur near the grain boundaries due to the small grain size before cold rolling, and the nuclei in the (100) <025> orientation generated from within the grains are relatively decrease.

As described above, in the present invention, the recrystallization that continues after the final pass of hot rolling produces a hot rolled sheet with low strain and a large number of recrystallized grains, resulting in a state where the grain size is small, and this effect is reduced. This is carried over to the subsequent hot-rolled sheet annealing, cold rolling, and decarburization annealing, and in the state of the decarburization annealing sheet, (110)
(110) without affecting <001> oriented grains
(111) <11 which is advantageous for grain growth of <001> oriented grains
2> Succeeded in increasing oriented grains and decreasing (100) <025> oriented grains, which hinder the growth of (110) <001> oriented grains. This has made it possible to stably obtain products with good magnetic properties.

Next, reasons for limiting the constituent elements of the present invention will be described.

First, the reason for limitations regarding the slab components and slab heating temperature will be explained in detail.

If the amount of C is too large, the decarburization annealing time becomes long and it is not economical, so it is set to 0.020% or less.

If St exceeds 4.5%, cracking during cold rolling becomes significant, so it was set to 4.5% or less. In addition, if it is less than 2.5%, the specific resistance of the material is too low and the low core loss necessary for a transformer core material cannot be obtained, so it is set at 2.5% or more. Preferably 3
．． It is 2% or more.

An and N are AffiN necessary for stabilizing secondary recrystallization.
Or, in order to ensure (A l + St) n1 trides, 0.010% or more of acid-soluble A2 is required. Acid soluble! If it exceeds 0.060%, the Ajl! of the hot rolled sheet! Since N would be inappropriate and secondary recrystallization would become unstable, the content was set at 0.060% or less.

Regarding N, it is difficult to reduce it to less than 0.0030% in normal steelmaking operations, and it is economically undesirable to reduce it to less than this, so it is set to 0.0030% or more.
If it exceeds 0.0130%, "bulging" on the surface of the steel sheet called blister occurs, so it was set to 0.0130% or less.

Even if MnS and MnSe are present in steel, it is possible to improve the magnetic properties by appropriately selecting manufacturing process conditions. However, when S and Se are high, secondary recrystallization defects called linear fine grains tend to occur.
In order to prevent the occurrence of this secondary recrystallization defective area (S
+0.405 Se) 50.014% is desirable. If S or Se exceeds the above value, no matter how the manufacturing conditions are changed, there is a high probability that secondary recrystallization defects will occur, which is not preferable.

Also, the time required for purification in final finish annealing is undesirable, and from this point of view, S or S
There is no point in increasing e unnecessarily.

The lower limit of Mn is 0.05%. If it is less than 0.05%, the shape (flatness) of the hot rolled sheet obtained by hot rolling,
In particular, the side edges of the strip become wavy, which causes a problem of lowering product yield. On the other hand, when the Mn content exceeds 0.8%, the magnetic flux density of the product decreases.

The slab heating temperature was limited to less than 1280°C for the purpose of reducing costs by making it comparable to ordinary steel.

Preferably it is 1200°C or less.

The heated slab is subsequently hot-rolled into a hot-rolled sheet. The feature of the present invention lies in this hot rolling process.

That is, the end temperature of hot rolling is set to be higher than 900°C and lower than 1150°C, the temperature is maintained at 800°C or higher for at least 1 second after the end of hot rolling, and the coiling temperature is set to lower than 700°C. Furthermore, in addition to this, it is more preferable to set the cumulative reduction ratio of the final three passes of finish hot rolling to 50% or more in order to obtain good magnetic properties. In addition, the reduction rate of the final pass of finish hot rolling is 2.
It is more preferable that the content is 0% or more in order to obtain good magnetic properties.

The hot rolling process usually consists of heating a slab with a thickness of 100 to 400 nm, and then rough rolling and finish rolling, both of which are performed in multiple passes. The rough rolling method is not particularly limited and may be carried out by a conventional method.

The feature of the present invention is the finish rolling that follows the rough rolling.

Finish rolling is usually performed by high-speed continuous rolling of 4 to 10 passes. Normally, the reduction ratio in finish rolling is such that the reduction rate is high in the earlier stage, and the reduction rate is lowered toward the later stage to obtain a good shape. The rolling speed is usually 100 to 3000 m/min, and the time between passes is 0.01 to 100 seconds. What is limited in the present invention is only the end temperature of hot rolling, the cooling and coiling temperature after hot rolling, the cumulative reduction rate of the final three passes of finishing rolling, and in addition, the rolling reduction rate of the final pass of finishing rolling. ,
Although other conditions are not particularly limited, if the inter-pass time of the final three passes is made abnormally long, such as 1000 seconds or more, the strain will be released by recovery and recrystallization between the passes, and the effect of accumulated strain will be obtained. This is not preferable because it becomes difficult.

In addition, regarding the rolling reduction ratio in several passes before finish rolling,
Since it is difficult to expect that the distortion applied up to the final pass remains, there is no particular limitation, and it is sufficient to focus only on the final three passes.

Next, the reason for limiting the above hot rolling conditions will be described.

The hot rolling end temperature is more than 900"C and less than 1150°C,
The reason why we stipulated that the temperature should be maintained at 800°C or higher for at least 1 second after the completion of hot rolling is that, as is clear from Figure 1, products with a good magnetic flux density B8 of B8 ≥ 1.88 (T) in this range are This is because it can be obtained. In addition, after hot rolling, the net plate is 8
There is no particular limitation on the upper limit of the time for which the temperature is maintained at 00°C or higher, but the time from the end of hot rolling to the time when it is wound up is usually about 0.1 to 1000 seconds, and the time required for stripping the steel sheet for more than 1000 seconds is usually about 0.1 to 1000 seconds. It is difficult to maintain the temperature above 800° C. in terms of equipment.

Regarding the coiling temperature after hot rolling, if the coiling temperature is 700°C or higher, there will be A in the coil due to the difference in thermal history within the coil during cooling.
The temperature must be lower than 700° C. because it causes variations in the precipitation state of J2N, etc., variations in the surface decarburization state, variations in the metal structure, etc., which causes variations in the magnetic properties of the product, which is undesirable.

Next, it is more preferable that the cumulative reduction ratio in the final three passes of finishing hot rolling be set to 50% or more, as is clear from Fig. 2. This is because a product having a magnetic flux density of B6 can be obtained. In addition,
The upper limit of the cumulative reduction rate of the final three passes is not particularly limited, but industrially it is difficult to apply a cumulative reduction of 99.9% or more. More preferably, the rolling reduction ratio in the final pass is set to 20% or more, as is clear from FIG.
) This is because a product having a good magnetic flux density B8 can be obtained. Although the upper limit of the rolling reduction rate in the final pass is not particularly limited, it is industrially difficult to apply a rolling reduction of 90% or more.

This hot-rolled sheet is subjected to hot-rolled sheet annealing as necessary, and then
Cold rolling is performed two or more times, including final cold rolling with a rolling reduction of more than 80%, and intermediate annealing as necessary.

The reason why the rolling reduction ratio in the final cold rolling was set to over 80% is that by setting the rolling reduction ratio in the above range, the sharp (11
0) <QQl> oriented grains and corresponding oriented grains ((111) <112> oriented grains etc.) which are easily eroded by grains can be included in appropriate amounts, which is preferable for increasing magnetic flux density.

After cold rolling, the steel plate is decarburized and annealed in the usual way, coated with an annealing separator,
Finish annealing is applied to the final product. Note that if the inhibitor strength required for secondary recrystallization is insufficient in the state after decarburization annealing, a treatment to strengthen the inhibitor in finish annealing or the like is required. As an example of an inhibitor strengthening method, a method is known in which the nitrogen partial pressure of the final annealing atmosphere gas is set to be high in steel containing 1.

Furthermore, as an example of an inhibitor strengthening method, it is also effective to perform a nitriding treatment in a strip shape using NFl, gas, plasma, etc. following decarburization annealing.

〔Example〕

Examples will be described below.

Example 1 - C: 0.011% by weight, SAl: 3.29% by weight, M
n2 0.15% by weight, S: 0.005% by weight, acid soluble! : 0.027% by weight, N: 0°0079% by weight, and the balance consists of Fe and inevitable impurities.
After heating a 0 mw 1 thick slab at a temperature of 1150°C, hot rolling was started at 1070°C, 40 → 15 → 7 → 3.5 →
A hot rolled sheet with a thickness of 2.3 mm was obtained by hot rolling with a pass schedule of 3 → 2.6 → 2.3 (mm). At this time, the hot rolling end temperature was 913°C, and after 00.2 seconds of air cooling (911"C), water cooling at a cooling rate of 200°C/second to 550°C, holding at 550°C for 1 hour, and then furnace cooling. Winding resimulation, after air cooling for 05 seconds (860'C)
A winding resimulation was performed in which the material was water-cooled to 550° C. at a cooling rate of ° C./second, held at 550° C. for 1 hour, and then cooled in a furnace.

This hot-rolled plate was held at 1080°C for 30 seconds, and then
The hot-rolled plate was annealed by holding it at 00°C for 30 seconds and rapidly cooling it, then it was made into a cold-rolled plate with a thickness of 0.285 mm at a rolling reduction of about 88%, and it was decarburized by holding it at 830°C for 150 seconds. The obtained decarburized annealed plate was held at 750° C. for 30 seconds in an atmosphere gas containing 25% N and 8275% NH3 gas to allow the steel plate to absorb nitrogen. The nitrogen content after nitrogen absorption was 0.0195% by weight. Next, an annealing separator containing MgO as the main component was applied to the steel plate, and 25% N2,
120 at a rate of 10°C/hour in an atmospheric gas of 8275%
Final annealing was performed by raising the temperature to 0'C and then holding it at 1200C for 20 hours in a 100% H2 atmosphere gas.

Annealing was performed.

Table 1 shows the hot rolling conditions and magnetic properties of the product.

Example 2 - C: 0.013% by weight, SAl: 3.30% by weight, M
n2 0.15% by weight, S: 0.007% by weight, acid-soluble Af: 0.034% by weight, N: 0.0083
A slab with a thickness of 26 mm, containing % by weight and the balance consisting of Fe and unavoidable impurities, was heated at a temperature of 1150° C. and then hot-rolled in 6 passes to obtain a hot-rolled plate with a thickness of 2.3 mm. At this time, the reduction distribution is 26 → 15 → 10 → 7 → 5 → 2.8 → 2.
3 (mm), and the hot rolling start temperature is 01050℃1■9
Two conditions were set: 00'C. After hot rolling, it was air cooled for 3 seconds and then water cooled to 550°C at a cooling rate of 100'C/sec.
A winding resimulation was performed in which the sample was kept at 1 hour at ℃ and then cooled in a furnace, and the process conditions up to the final final annealing were the same as in Example 1.

Table 2 shows the hot rolling conditions and magnetic properties of the product.

Example 3 - C: 0.009% by weight, SAl: 3.27% by weight, M
n2 0.14% by weight, S: 0.006 weight, acid soluble: 0.028% by weight, N: 0.0082
A 40 mm thick slab containing Fe and unavoidable impurities was heated at a temperature of 1150°C, and then hot rolling was started at 1050°C, resulting in a rolling process of 40 → 30 → 20 → 10
→ 5 → 3 → 2 (mm), after hot rolling ■ After cooling in air for 2 seconds l
Water cooled at OO°C/sec to 550°C, held at 550°C for 1 hour, then cooled in the furnace.■ After air cooled for 2 seconds, water cooled at 50°C/sec to 750°C, held at 750°C for 1 hour, then furnace cooled.2 Cooled under conditions. This hot-rolled sheet was annealed by holding it at 1080° C. for 30 seconds, then holding it at 900° C. for 30 seconds, and rapidly cooling it, and the process conditions up to the final finish annealing were the same as in Example 1.

Table 3 shows the hot rolling conditions and magnetic properties of the product.

-Example 4- C: 0.002% by weight, SAl: 3.20% by weight, M
n=0.14% by weight, S: 0.006% by weight, acid soluble: 0.034% by weight, N: 0.0081
A slab with a thickness of 40 mm containing 50% by weight, the balance being Pe and unavoidable impurities was heated at a temperature of 1100° C., then hot rolling was started at 1050° C., and the slab was hot rolled in 6 passes.
It was made into a hot-rolled plate with a thickness of 3 mm. At this time, the pressure distribution is ■40 → 1
5 → 7 → 3.5 → 3 → 2.6 → 2.3 (mm), ■4
0→26→18→12→6→3.2→2.3 (mm)
,■40→28→20→16→9.2→4.6→2.3
(1 m).

Cooling after hot rolling was performed under the same conditions as in Example 2. This hot-rolled sheet was annealed by holding it at 1050°C for 30 seconds and at 900°C for 30 seconds, and the rolling reduction was approximately 85%.
A cold-rolled plate with a thickness of mm was prepared, and the process conditions up to final annealing were the same as in Example 1.

Table 4 shows the hot rolling conditions and magnetic properties of the product.

(Effects of the Invention) As explained above, in the present invention, the hot rolling end temperature, the time for holding the steel sheet at 800°C or higher after hot rolling, and the coiling temperature after hot rolling, more preferably the final three passes of hot rolling. By controlling the cumulative rolling reduction rate, and more preferably the rolling reduction rate of the final pass of hot rolling, it is possible to stably obtain good magnetic properties in a manufacturing method that assumes low-temperature slab heating using a low C material. Therefore, the industrial effect as a method for producing unidirectional electrical steel sheets is extremely large.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the end temperature of hot rolling, the time the steel plate was held at 800°C or higher after the end of hot rolling, and the magnetic flux density of the product, and Figure 2 is the cumulative result of the final three passes of finish hot rolling. This is a graph showing the relationship between rolling reduction and magnetic flux density, and FIG. 3 is a graph showing the relationship between rolling reduction and magnetic flux density in the final pass of finish hot rolling. 02θ 40 60 8θ

Claims (3)

[Claims] (1) By weight, C≦0.020%, Si: 2.5-4.
5%, acid-soluble Al: 0.010-0.060%, N:
0.0030~0.0130%, (S+0.405Se
)≦0.014%, Mn: 0.05 to 0.8%, the balance consisting of Fe and unavoidable impurities.
heated to a temperature below 280°C, hot rolled, then 80°C
One cold rolling process applying a rolling reduction of more than 80%
After achieving the final plate thickness by two or more cold rolling processes sandwiching intermediate annealing including final cold rolling applying a super reduction rate,
In a method for producing a unidirectional electrical steel sheet that undergoes decarburization annealing and finish annealing, the hot rolling end temperature is set to more than 900°C and less than 1150°C, and the temperature is maintained in a temperature range of 800°C or higher for at least 1 second after the end of hot rolling, A method for producing a unidirectional electrical steel sheet with excellent magnetic properties, characterized by winding in a temperature range of less than 700°C. (2) The method for producing a unidirectional electrical steel sheet with excellent magnetic properties according to claim 1, wherein the hot rolling is performed at a rolling reduction ratio of 50% or more in the final three passes of the final hot rolling. (3) Claim 1 or 2, wherein the hot rolling is performed at a rolling reduction rate of 20% or more in the final pass of finish hot rolling.
A method for producing a unidirectional electrical steel sheet having excellent magnetic properties as described above.