JPH10102146A - Method for producing ultra-thin silicon steel sheet and ultra-thin silicon steel sheet - Google Patents

Abstract

(57) Abstract: magnetic flux density B ₈ to produce a high ultrathin silicon steel sheet. SOLUTION: C, Si, Mn, P, S, sol.Al,
After heating a steel slab in which N, Ti + Nb is specified to a temperature of 1100 ° C or more and 1200 ° C or less, finish rolling is started at a temperature of 850 ° C or more and 1000 ° C or less and a hot rolling finish temperature of 750 ° C or more and 900 ° C or less. Hot rolling is performed at a temperature of 450 to 700 ° C. to obtain a hot-rolled steel sheet. And twice or three
Cold-rolled steel sheets having a thickness of 0.20 mm or less are obtained by cold rolling each time. Then, at a temperature rise rate of 1 ° C / sec or more, 700 ° C or more and 1000
Heating to a specified temperature below ℃ and holding for 30 seconds or more at the first stage, annealing at a predetermined temperature between 700 ℃ and 1000 ℃ for 3 hours or more Is performed at a predetermined temperature in the range of 30 seconds or more for the third stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an ultra-thin silicon steel sheet having excellent magnetic properties and an ultra-thin silicon steel sheet having excellent magnetic properties.

[0002]

2. Description of the Related Art Oriented silicon steel sheets used for iron cores of transformers and the like have conventionally been made of AlN or MnS for secondary recrystallization as shown in JP-B-46-23820.
It is manufactured using precipitates such as these as inhibitors. However, such a grain-oriented silicon steel sheet is made of Al
To completely complete the high-temperature slab heating step for solid solution of a large amount of inhibitors such as N and MnS, the decarburizing annealing step until the final annealing, and the secondary recrystallization, and to purify impurities affecting magnetic properties. The high temperature and long time annealing step is indispensable, and there is a problem from an economic viewpoint.

[0003] Among the magnetic properties required for such materials, the iron loss value, which is regarded as particularly important, is considered to increase as the sheet thickness becomes thinner. Due to problems, it has been said that it is difficult to produce ultra-thin materials of 0.2 mm or less.

To solve such a problem, Japanese Patent Application Laid-Open No. 62-8 / 1987
As disclosed in Japanese Patent No. 3421 and Japanese Patent Application Laid-Open No. 1-221721, on the assumption that it is a very low carbon system,
A method of avoiding the problem by devising a composition in which Al is added in a trace amount has been devised. Japanese Patent Laid-Open No. 5-1
A method for manufacturing an ultrathin oriented silicon steel sheet using surface energy as represented by JP 86829 is proposed.

[0005]

However, Japanese Patent Application Laid-Open No. 62-83421 and Japanese Patent Application Laid-Open No. 1-221721 are disclosed.
According to the method described in Japanese Patent Application Publication No. 2000-214, high-temperature slab heating and high-temperature long-time annealing process can be omitted, and economical effects can be obtained. There is a problem that the secondary recrystallization behavior cannot be obtained.

Further, the method disclosed in Japanese Patent Application Laid-Open No. 5-186829 is advantageous in principle for the production of ultra-thin steel sheets targeted by the present invention because no inhibitor is used. There has been a problem that crystal growth is affected by subtle changes and the like, and as a result, stability is lacking.

[0007] The present inventors have overcome these problems,
Without decarburizing annealing and annealing at high temperature for a long time, crystal grains having a {110} <001> plane orientation (hereinafter referred to as Goss grains) are stably secondary recrystallized at a plate thickness of 0.2 mm or less. Thus, a method for producing an ultra-thin silicon steel sheet having excellent magnetic properties, which was considered to be difficult in the past, and an ultra-thin silicon steel sheet having excellent magnetic properties were invented.
A patent application was previously filed as No. 6.

In this method, a cold rolled material having a thickness of 0.2 mm or less is produced by combining cold rolling and intermediate annealing on a hot rolled sheet, and recrystallization and a small amount of AlN.MnS precipitates are formed. One-stage or two-stage annealing for adjusting and developing and evolving the Goss grains, and annealing for causing the crystal grains other than the remaining Goss grains to be eaten by using the surface energy are performed. According to this method, an ultra-thin silicon steel sheet having a magnetic flux density B ₈ of more than 1.85 T could be obtained.

However, from the viewpoint of energy saving, it is desired to produce a product having better magnetic properties, that is, a product having a higher magnetic flux density.

The present invention has been made in order to meet such a demand. The present invention has been made by improving the invention according to Japanese Patent Application No. 8-089646 to provide an ultra-thin film having higher magnetic properties, that is, a higher magnetic flux density. An object of the present invention is to provide a method of manufacturing a silicon steel sheet and an ultra-thin silicon steel sheet.

[0011]

The first means for solving the above problems is as follows: (a) C: 0.01% or less by weight%;
i: 2.5% or more and 7% or less, Mn: 0.04% or more and 0.1% or less, P: 0.02% or less, S: 0.002% or more and 0.005% or less,
sol. Al: 0.003% or more and 0.006% or less, N: 0.004% or more and 0.006% or less.
Preparing a billet that is not more than 003%; (b) removing said billet;
After heating to a temperature of 1100 ° C or more and 1200 ° C or less, 850 ° C or more
Start finish rolling at a temperature of 1000 ° C or less, and
Perform hot rolling at a finish rolling end temperature of less than or equal to
Winding at a temperature of 450 ° C. or more and 700 ° C. or less to form a hot-rolled steel sheet; (c) after descaling the hot-rolled steel sheet, a heating / cooling rate of 0.1 ° C./sec or more, and a holding time of 0.5 to 10 minutes. A cold rolling steel sheet having a thickness of 0.20 mm or less by two or three times of cold rolling including intermediate annealing within (d) a reducing atmosphere containing at least 50 vol. At a heating rate of 1 ° C./sec or more to a predetermined temperature of 700 ° C. or more and 1000 ° C. or less, and hold the temperature for 30 seconds or more.
(E) Subsequently, the cold-rolled steel sheet is heated to 700 ° C. or more in a reducing atmosphere containing 50 vol.% Or more of nitrogen.
A second annealing step in which the temperature is kept at a predetermined temperature of 1000 ° C. or less for 3 hours or more; A method of manufacturing ultra-thin silicon steel sheet including a third annealing step of holding at a predetermined temperature in a range of 900 ° C. to 1300 ° C. for 30 seconds or more in an atmosphere or a vacuum having an oxygen partial pressure of 0.5 Pa or less. is there.

A second means for solving the above-mentioned problem is as follows.
An ultra-thin silicon steel sheet manufactured by the method of the first means.

(Circumstances leading to the invention) The present inventors have conducted detailed experiments and studies to achieve the above object, and as a result, the composition of the steel slab and the manufacturing conditions of the hot rolled sheet were extremely thin. They have found that they have a great effect on increasing the magnetic flux density of the base steel sheet, and have obtained the following knowledge.

(1) In an ultra-thin steel sheet having a thickness of 0.2 mm or less, when secondary crystals are formed using AlN · MnS as an inhibitor, the grain growth of crystal grains having an orientation other than the Goss orientation is sufficiently suppressed. It is very important that the inhibitor be controlled in an effective amount and in an appropriate form.
In particular, controlling the form of the precipitate in the hot-rolled sheet is extremely important because it leads to control of the state of the precipitate at the time of final annealing. In addition, since the texture of the hot-rolled sheet is closely related to the magnetic properties of the product after the final annealing, it is extremely important to control the texture of the hot-rolled sheet. Then, when hot rolled sheets of various compositions were manufactured under various conditions, it was found that the secondary recrystallization behavior was different depending on the conditions.

(2) Further, the composition and the hot rolling conditions were examined in detail, and by controlling the slab reheating temperature, the finish rolling start temperature, and the finish rolling end temperature,
It has been found that an ultra-thin silicon steel sheet having high magnetic properties can be manufactured, and that an ultra-thin silicon steel sheet having even higher magnetic properties can be manufactured by adjusting the amounts of Mn, S, Al, and N serving as inhibitors. The present invention has been completed.

(Reasons for Limiting Chemical Components) First, the reasons for limiting the chemical components of the hot-rolled steel sheet in the present invention will be described.

C: In the inhibitor method, the structure and texture are controlled by C. However, in the present invention described above, since such a control is not performed, it is not necessary to actively add C. Rather, if C exceeds 0.01% by weight, the magnetic properties and workability are significantly reduced. Therefore, C is 0.01 wt% or less,
Preferably, the content is 0.005% by weight or less.

Si: Si is extremely important for controlling the structure and texture through magnetic properties and phase transformation. If the Si content is less than 2.5 wt%, in the third annealing of the final annealing, the structure and the texture accompanying the phase transformation at a high temperature are remarkably changed, and it becomes difficult to produce a steel sheet having predetermined characteristics. On the other hand, if the content of Si is higher than 7% by weight, the workability is significantly reduced. Therefore, Si is 2.
5 wt% or more and 7 wt% or less. However, in terms of workability, S
The more preferable range of i is 4% by weight or less.

Mn: Mn is extremely important for the formation of MnS. This MnS acts as a nucleus for the precipitation of the AlN inhibitor and has a function of delaying the solid solution of AlN.
However, if it is contained in excess of 0.1 wt%, slab heating at a remarkably high temperature of 1250 ° C. or more is required for complete solid solution. On the other hand, if it is less than 0.04 wt%, such a function is not recognized, and the secondary recrystallization becomes incomplete. Therefore, Mn needs to be 0.04 wt% or more and 0.1 wt% or less.

P: P is harmful because it lowers the grain growth rate and workability. Therefore, the content is set to 0.02 wt% or less.

S: S is as important as Mn for the formation of MnS. For this, S is 0.002wt%
Must be contained. On the other hand, when the content exceeds 0.005 wt%, the grain growth rate is remarkably reduced, so that it is difficult to complete the secondary recrystallization within a predetermined time in the third annealing. Therefore, S is 0.002w
t% to 0.005 wt% or less.

Sol.Al: sol.Al is extremely important for the formation of AlN which acts as an inhibitor. sol.Al is 0.
If the content is less than 003% by weight, AlN as an inhibitor necessary for producing an ultrathin oriented silicon steel sheet having high magnetic properties is insufficient, and a Goss structure having a high degree of integration in the rolling direction is not obtained. On the other hand, when the content exceeds 0.006 wt%, AlN as an inhibitor becomes too large due to nitrogen absorption during annealing, and moreover,
Inappropriate distribution results in no secondary recrystallization or partial secondary recrystallized grains but very low coverage. Further, such Al
Since the grain growth at a high temperature is significantly reduced, it is difficult to complete the secondary recrystallization within a predetermined time in the third annealing. Therefore, the content of sol.Al in the steel should be not less than 0.003 wt% and not more than 0.006 wt%.

N: N is also very important for the formation of AlN which acts as an inhibitor. If N is less than 0.004 wt%, the amount of AlN as an inhibitor until the onset of nitriding becomes small, and a Goss structure having a high degree of integration in the rolling direction cannot be obtained. As a result, the magnetic properties deteriorate. On the other hand, 0.006wt
%, AlN precipitated during slab heating remains partially undissolved even during reheating during hot rolling. These coarsen during hot rolling, and as a result, the distribution form of AlN changes, resulting in a decrease in magnetic properties. Therefore, N is 0.004w
It must be at least t% and at most 0.006wt%.

Ti, Nb: Ti and Nb contained as impurities in steel form extremely stable nitrides.
Inhibits the secondary recrystallization behavior due to 1N. In order to avoid such effects, the amount of Ti + Nb is set to 0.003 wt% or less.

(Manufacturing Method) Next, a manufacturing method will be described.

(1) Hot rolling If the heating temperature (reheating temperature) exceeds 1200 ° C., firelite (2FeO.Si)
O ₂ ) is formed. Therefore, the removability of the scale is remarkably deteriorated, and the residue of the scale that is not removed remains, so that it is difficult to complete the secondary recrystallization at the time of final annealing. Further, if the heating temperature is less than 1100 ° C., Mn in steel
Since S and AlN are not completely dissolved and become coarse, 2
The next recrystallization is incomplete. For these reasons, the heating temperature is set between 1100 ° C and 1200 ° C.

The reason for setting the finish rolling start temperature at 850 ° C. to 1000 ° C. and the finish rolling end temperature at 750 ° C. to 900 ° C. is as follows.

It is important that the inhibitor after hot rolling is finely precipitated. When the precipitate is coarse, it is difficult to completely advance the secondary recrystallization,
Products having good magnetic properties cannot be manufactured.

When finish rolling is started in a high temperature range exceeding 1000 ° C., precipitation of inhibitors is promoted by strain induction.
In a high-temperature region, coarsening due to Ostwald growth of the precipitated inhibitor is remarkable, and it becomes difficult to precipitate the inhibitor finely at the end of hot rolling. Further, if the finish rolling is started at a temperature lower than 850 ° C., the inhibitor becomes coarse during cooling of the slab, so that the inhibitor cannot be finely precipitated at the end of hot rolling. When the temperature is 850 ° C. or higher, the thickness of the sheet is reduced, and the increase in the cooling rate can prevent the inhibitor from becoming coarse. For these reasons, the finish rolling start temperature is 850 ° C or more and 1000 ° C or less.

When the finish rolling end temperature is low, the hot rolling time becomes long, and the increase in cooling rate becomes small as compared with the case where finishing is performed at a high temperature due to the reduction in sheet thickness. For this reason, the inhibitor whose precipitation has been promoted by the induction of strain becomes coarse. Therefore, the finish rolling finish temperature is set to 750 ° C. or higher. Also, to make the finish rolling end temperature exceed 900 ° C,
Under the restriction that the finish rolling start temperature is 1000 ° C. or less, it is necessary to provide a special heating means or increase the thickness of the finished plate. Therefore, the finish rolling end temperature is set to 900 ° C. or less.

Further, setting the finish rolling start temperature and the finish rolling end temperature in the above ranges is advantageous from the viewpoint of texture, for improving magnetic properties.

Generally, as the degree of integration of a hot-rolled steel sheet in the Goss orientation increases, the magnetic properties after final annealing also improve. When the finish rolling start temperature is 1000 ° C or less and the finish rolling end temperature is 750 ° C or more, the shear deformation due to the rolls during hot rolling acts strongly, and extends from the surface layer of the steel sheet to a depth of about 1/5 of the thickness.
Unrecrystallized recovery grains having a Goss orientation are formed, the degree of integration of the hot-rolled steel sheet in the Goss orientation increases, and the magnetic properties are improved. When the finish rolling start temperature is higher than 1000 ° C., recrystallization occurs, and when the finish rolling end temperature is lower than 750 ° C., compression deformation is applied, so that the degree of integration in the Goss orientation is reduced and the magnetic properties are deteriorated.

If the winding temperature after hot rolling exceeds 700 ° C., the inhibitor becomes coarse, and recrystallization occurs in the surface layer, and the Goss integration degree of the hot-rolled steel sheet is reduced, so that the steel sheet has high magnetic properties. Products cannot be manufactured. On the other hand, if the winding temperature is lower than 450 ° C., the strength of the material is increased and the winding becomes impossible. For this reason, the winding temperature should be between 450 ° C and 700
It should be below ° C.

(2) Cold Rolling Cold rolling is performed twice or three times with intermediate annealing. Cold rolling is performed according to a conventional method, but if less than two times, a favorable texture for growth of secondary recrystallized grains by selective grain growth of crystal grains during final annealing is not appropriately formed, and sufficient rolling after final annealing is not performed. The grown secondary recrystallized grains cannot be obtained. The rolling reduction in each cold rolling is preferably 20% or more.

As conditions for the intermediate annealing, in order to completely cause softening, the recrystallization temperature is 700 ° C. or higher, and in order to avoid a shape defect of the cold-rolled steel sheet due to coarsening of crystal grains, 1000 ° C.
It should be below ° C. In addition, in these intermediate annealings, in order to avoid coarsening of precipitates during the annealing process, 0.1 ° C.
It is necessary to perform annealing for 0.5 to 10 minutes at a heating rate of / sec or more.

(3) Annealing after Cold Rolling In order for stable secondary recrystallization to be exhibited and for the coverage of the secondary recrystallized grains to be 90% or more, it is necessary to prevent the AlN serving as an inhibitor during annealing. The optimal form and quantity must be controlled. This is achieved by annealing three times after cold rolling.

First annealing: The first annealing is performed for recrystallization of the material and adjustment of the form of the precipitate. If the annealing temperature is lower than 700 ° C., the material does not completely recrystallize, and as a result, secondary recrystallization in the subsequent two-step annealing becomes unstable.
On the other hand, when the temperature is higher than 1000 ° C., the crystal grains that have grown normally begin to coarsen, and no secondary recrystallization occurs in the subsequent two-step annealing. Therefore, the annealing temperature is set to 700 to 1000 ° C.

When the heating rate is less than 1 ° C./sec,
Grain growth in plane orientations other than the {110} <001> plane cannot be sufficiently suppressed, and as a result, it is difficult to selectively cause secondary recrystallization in the {110} <001> plane. . Therefore, the heating rate is set to 1 ° C./sec or more.

Furthermore, the annealing atmosphere is a reducing atmosphere containing nitrogen such that nitrogen is not significantly desorbed from the steel and nitrogen is supplied more sufficiently than the atmosphere. However, in order to prevent oxidation of the steel sheet, it is preferable to contain hydrogen of 1 vol.% Or more. If the nitrogen content is less than 50 vol.%, The desorption of nitrogen from steel becomes remarkable. For this reason, the ratio of nitrogen is set to 50 vol.% Or more.

Further, the holding time is required to be 30 seconds or more in order to stably develop secondary recrystallization in the subsequent two-step annealing. Therefore, the holding time is set to 30 seconds or more. However, if the time exceeds 30 minutes, the effect is saturated. Therefore, it is preferable to set the time within 30 minutes from the economical point of view.

Second annealing: The second annealing is important for the appearance and progress of secondary recrystallization.

When the heating and holding temperature exceeds 1000 ° C., the crystal grains that are growing normally become coarse, and as a result, secondary recrystallization does not occur. On the other hand, when the temperature is lower than 700 ° C., the rate of growth of coarse grains serving as nuclei for secondary recrystallization is extremely slow, so that the secondary recrystallization does not progress even if the temperature is kept extremely long. Therefore, the heating and holding temperature is set to 700 ° C. or more and 1000 ° C. or less.

The heating rate is not particularly defined. Industrially available speeds are sufficient. Further, the annealing atmosphere is a reducing gas atmosphere containing nitrogen such that nitrogen is not remarkably desorbed from the steel and N is supplied more sufficiently than the atmosphere, similarly to the first annealing condition. However, to prevent oxidation of the steel sheet, 1vo
It preferably contains l.% or more hydrogen. In addition, nitrogen is 50
If the amount is less than vol.%, desorption of nitrogen from steel becomes remarkable.
Therefore, the ratio of nitrogen is set to 50 vol.% Or more.

The holding time requires a sufficient time for performing the secondary recrystallization, and is set to 3 hours or more. On the other hand, even if the time exceeds 10 hours, there is almost no change in the coverage of the secondary recrystallized grains.

Third annealing: The third annealing is necessary for covering the steel sheet surface by 90% or more with the secondary recrystallized grains.

In the annealing up to the second stage, the coverage of the secondary recrystallized grains is at most about 80%, and the remaining about 20% is
This is a region having a grain size of about the plate thickness left behind by the secondary recrystallized grains. Since such a fine grain portion is a through grain,
The grain boundary energy, which is inversely proportional to the curvature of the crystal grains, is insufficient, and is hardly consumed by the secondary recrystallized grains even after annealing for a long time.
The magnetic properties are also insufficient.

For this reason, in the third stage, the annealing is performed in a non-oxidizing atmosphere, and the surface energy at which the {110} plane grows preferentially is used as a driving force for secondary recrystallization. The aim is to feed the recrystallized grains on silkworms. However, in this case, the heating temperature needs to be 900 ° C. or higher to use the surface energy. In addition, when the steel sheet is heated to 1300 ° C. or more, it is difficult to stably anneal the steel sheet due to creep or the like of the steel sheet. At any temperature, the holding time is required to be 30 seconds or more, while the effect is saturated in 30 minutes. Therefore, the heating temperature range is 900 ° C. or more and 1300 ° C. or less, and the holding time is 30 seconds or more, preferably 30 minutes or less. The atmosphere is a reducing atmosphere, a non-oxidizing atmosphere having an oxygen partial pressure of 0.5 Pa or less and containing substantially no nitrogen, or a vacuum having an oxygen partial pressure of 0.5 Pa or less. This is because if nitrogen is contained in the atmosphere, nitrogen remains in the steel and deteriorates magnetic properties.

[0048]

【Example】

(Example 1) The steel types shown in Table 1 were melted in vacuum, slab-rolled to 30 mm, and then hot-rolled under the hot rolling conditions shown in Table 2 to obtain a hot-rolled steel sheet having a thickness of 2.5 mm. . Then,
Pickling, cold rolling and final annealing were performed.

The cold rolling was performed in the first cold rolling at 2.5 mm.
From 0.5mm to 0.3mm in the second cold rolling, from 0.5mm to 0.3mm in the second cold rolling, and from 0.3mm in the third cold rolling.
Rolled to 0.1 mm. 100% N between each cold rolling
_{In two} atmospheres, intermediate annealing was performed at an annealing temperature of 900 ° C. for a holding time of 2 minutes.

The final annealing was performed in three stages. In the first annealing step, the temperature was raised at a rate of 600 ° C./min and 95% N
_It was kept at 900 ° C. for 5 minutes in an atmosphere of 2-5% H ₂ . In the second stage annealing, 90% N ₂ -5% H ₂ atmosphere is used.
It was kept at 0 ° C. for 10 hours. In the third annealing, 100% H
_It was kept at 1200 ° C. for 10 minutes in the atmosphere of ₂ .

As the structure of the obtained thin steel sheet, the coverage of crystal grains having a grain size of 10 times or more the sheet thickness, the magnetic flux density B ₈ (T) in the rolling direction, and the holding force H _C (A / m) were measured. did. Table 2 shows the results. As it is clear from Table 2, when subjected to the manufacturing method of yet present invention in composition range of the present invention only, the magnetic flux density B ₈ is not less than 1.90T, to obtain a very thin silicon steel sheet having excellent magnetic properties Was completed.

[0052]

[Table 1]

[0053]

[Table 2]

(Example 2) Steel type No. 1 in Table 1 was vacuum melted, slab-rolled to 30 mm, and then hot-rolled under hot rolling conditions shown in Table 3 to obtain a hot-rolled steel sheet having a thickness of 2.5 mm. A rolled steel sheet was obtained. Subsequently, pickling, cold rolling and final annealing were performed.

[0055] The cold rolling is described as three times rolling in Table 3.
Are performed under the same conditions as in Example 1.
Was. About what is described as double rolling in Table 3
Is pressed from 2.5mm to 0.3mm in the first cold rolling.
From 0.3mm to 0.1mm in the second cold rolling
Rolled. And between these cold rollings, 100% N
_TwoIn the atmosphere, annealing temperature 900 ° C, holding time 2 minutes
Intermediate annealing was performed.

The final annealing was performed over three stages. In the first annealing step, the temperature was raised at a rate of 600 ° C./min and 95% N
_It was kept at 900 ° C. for 5 minutes in an atmosphere of 2-5% H ₂ . In the second stage annealing, 90% N ₂ -5% H ₂ atmosphere is used.
It was kept at 0 ° C. for 10 hours. In the third annealing, 100% H
_It was kept at 1200 ° C. for 10 minutes in the atmosphere of ₂ .

The magnetic flux density B _{8 in} the rolling direction of the obtained thin steel sheet
(T), the holding force H _C (A / m) was measured. Table 3 shows the results. As apparent from Table 3, the hot-rolled sheet annealing condition only if the range of the manufacturing method of the present invention, the magnetic flux density B ₈ it was possible to obtain a very thin silicon steel sheets of more than 1.90T.

[0058]

[Table 3]

[0059]

As described above, in the present invention, the chemical composition of hot-rolled steel sheet, hot-rolling conditions, cold rolling / intermediate annealing conditions, and final annealing conditions are specified.
Inhibitors and surface energy can be used,
An ultra-thin silicon steel sheet having excellent magnetic properties can be obtained.

Claims (2)

[Claims] 1. (a) By weight%, C: 0.01% or less, Si:
2.5% or more and 7% or less, Mn: 0.04% or more and 0.1% or less,
P: 0.02% or less, S: 0.002% to 0.005%, sol.
Al: 0.003% to 0.006%, N: 0.004% to 0.
006% or less, and Ti + Nb as an impurity is 0.003%
%), A step of preparing a billet of not more than 1100%
After heating to a temperature between 1200 ° C and 1200 ° C,
Finish rolling at a temperature of 750 ° C or less, hot rolling at a finish rolling end temperature of 750 ° C or more and 900 ° C or less, and then 450 ° C
(C) after descaling the hot-rolled steel sheet, the heating / cooling rate is 0.1 ° C / sec or more, and the holding time is 0.5 minutes or more and 10 minutes or less. 2 or 3 times cold rolling including intermediate annealing
A step of forming a cold-rolled steel sheet having a diameter of 0.20 mm or less, (d) in a reducing atmosphere containing 50 vol. A first-step annealing step of heating to a predetermined temperature and maintaining the temperature for 30 seconds or more; (e) continuing the cold-rolled steel sheet with nitrogen
700 ° C or more in a reducing atmosphere containing 50vol.% Or more
A second annealing step of maintaining the temperature at a predetermined temperature of 00 ° C. or less for 3 hours or more; A method for producing an ultra-thin silicon steel sheet, comprising a third annealing step of holding at a predetermined temperature in a range of 900 ° C. to 1300 ° C. for 30 seconds or more in an atmosphere or a vacuum having an oxygen partial pressure of 0.5 Pa or less. 2. An ultra-thin silicon steel sheet produced by the method according to claim 1.