JPH10102145A - Manufacture of extra thin silicon steel sheet and extra thin silicon steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an extra thin silicon steel sheet with high magnetic flux density by executing specific cold rolling and multistage annealing after specific annealing on a hot rolled steel plate with specific composition containing C, Si, Mn, P, S, Al, N and impurities. SOLUTION: A hot rolled steel plate containing, by weight, <=0.01% C, 2.5-7.0% Si, 0.005-0.12% Mn, <=0.02% P, 0.002-0.005% S, 0.0015-0.006% sol. Al, 0.001-0.008% N and <=0.003% Ti + Nb as impurities is annealed on condition indicated by a relation (T: annealing temp. in deg.C, t: holding time in min, R: temp. rising rate in deg.C/min). This steel plate is, after descaling, made into <=0.20mm thickness through two or three times cold rolling including intermediate annealing with >=0.1 deg.C/sec heating/cooling velocity and 0.5-10min holding time. This cold rolled steel sheet goes through primary and secondary annealing including heating and holding at 700-1000 deg.C under a reducing atmosphere of >=50vol.% N2 , and then tertiary annealing including heating and holding at 900-1300 deg.C under a reducing or nonoxidizing atmosphere without N2 or under vacuum.

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, and an improvement is made to the invention of Japanese Patent Application No. 08-089646 to manufacture an ultra-thin silicon steel sheet having a higher magnetic flux density. It is an object to provide a method 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: 0.005% or more and 0.12% or less, P: 0.02% or less, S: 0.002% or more and 0.005% or less,
sol. Al: 0.0015% or more and 0.006% or less, N: 0.001% or more and 0.008% or less, and Ti + Nb as an impurity is 0.1%.
(B) annealing temperature T (° C.), holding time t (min), and heating rate R (° C./min) of the following hot rolled steel sheet: ) Step of annealing under the condition satisfying the formula, 830 + 1000 / R ≦ T + 4.2t + 3000 / R ≦ 1040-1000 / R… (1) (However, T ≧ 500) (c) After descaling, the heating / cooling rate becomes 0.
2 or 3 times cold rolling including intermediate annealing with 1 ° C / sec or more and holding time of 0.5 to 10 minutes
(d) forming the cold-rolled steel sheet in a reducing atmosphere containing 50% by volume or more of nitrogen;
A first annealing step of heating to a predetermined temperature of 700 ° C. or more and 1000 ° C. or less at a temperature rising rate of at least 70 ° C./sec and maintaining the temperature at that temperature for 30 seconds or more; .
% In a reducing atmosphere containing at least 700% and not more than 1000 ° C for at least 3 hours in a reducing atmosphere containing at least
(f) Further, in a reducing atmosphere containing no nitrogen or a non-oxidizing atmosphere having an oxygen partial pressure of not more than 0.5 Pa and substantially no nitrogen or a vacuum having an oxygen partial pressure of not more than 0.5 Pa,
This is a method for producing an ultra-thin silicon steel sheet including a third annealing step of holding at a predetermined temperature in a range of 0 ° C. or more and 1300 ° C. or less for 30 seconds or more.

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-mentioned object, and as a result, the inventors have found that a high magnetic flux density of an ultra-thin silicon steel sheet is obtained by annealing a hot-rolled sheet. And found the following findings.

(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. However, the state of precipitation of the inhibitor in the hot-rolled sheet after hot rolling differs depending on the hot-rolled state, and if an appropriate control of the structure is performed by hot rolling, the inhibitor does not necessarily precipitate sufficiently finely.
It is difficult to produce ultra-thin oriented silicon steel sheets having high magnetic properties. Based on this idea, various hot-rolled sheet annealing was performed to change the state of the precipitates, and it was found that the secondary recrystallization behavior was different depending on the conditions.

(2) In consideration of the above, further detailed examination was conducted on the hot-rolled sheet annealing, and by maintaining the annealing temperature, the holding time, the heating rate and the relationship between them, an ultra-thin silicon having high magnetic properties was obtained. The present inventors have found that a raw steel sheet can be manufactured, and have completed the present invention.

(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, when it is contained in excess of 0.12 wt%, slab heating at a remarkably high temperature of 1250 ° C. or more is required for complete solid solution. On the other hand, if the content is less than 0.005 wt%, such a function is not recognized and secondary recrystallization is incomplete. For this reason, Mn needs to be 0.005 wt% or more and 0.12 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 0015% by weight, AlN as an inhibitor required for producing an ultra-thin silicon steel sheet having high magnetic properties is insufficient, and the matrix grains become coarse, so that secondary recrystallization becomes difficult. . 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 an inappropriate distribution is caused.
Although the secondary recrystallization does not occur or secondary recrystallized grains are partially formed, the coverage is extremely low. Furthermore, since such Al significantly reduces the grain growth at high temperatures, it becomes difficult to complete the secondary recrystallization within a predetermined time in the third annealing. Therefore, sol.Al in steel
Should be 0.0015 wt% or more and 0.006 wt% or less.

N: N is also very important for the formation of AlN which acts as an inhibitor. If N is less than 0.001 wt%, the amount of AlN as an inhibitor until the onset of nitrogen absorption is too small, so that the matrix grains become coarse, and as a result, secondary recrystallization becomes difficult. On the other hand, when the content exceeds 0.008 wt%, AlN precipitated during slab heating remains partially undissolved even during reheating during hot rolling. These coarsen during hot rolling,
As a result, the distribution form of AlN changes and secondary recrystallization hardly occurs. Therefore, N is 0.001wt% or more and 0.008wt%
% Or less.

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 Rolled Sheet Annealing The conditions of the hot rolled sheet annealing characterize the present invention, and are necessary for sufficiently precipitating the inhibitor in the hot rolled sheet. It is important to control the rate of temperature rise and their relationship.

If the annealing temperature is low, the inhibitor does not precipitate, so that the effect of hot-rolled sheet annealing does not appear, and the magnetic properties are not improved as compared with those without hot-rolled sheet annealing. If the annealing temperature is high, the inhibitor coarsens.

If the holding time is short, the inhibitor is not sufficiently precipitated, so that the effect of the hot-rolled sheet annealing is weakened as in the case where the annealing temperature is low. If the retention time is long, the inhibitor becomes coarse.

Even if annealing is performed at the same annealing temperature and holding time,
The precipitation state of the inhibitor varies depending on the heating rate, and the optimal annealing temperature and the holding time vary depending on the heating rate. For example, even if the annealing temperature and the holding time are such that the inhibitor is sufficiently finely precipitated when the heating rate is high, if the heating rate is slow, the change in the precipitation form of the inhibitor during the heating and coarsening due to Ostwald ripening will occur. For this reason, the inhibitor may not be sufficiently finely precipitated.

Based on such knowledge, the annealing temperature T
(° C.), holding time t (minutes), and heating rate R (° C./minute) were variously changed, and the experiment was performed. As a result, when these are subjected to hot rolling annealing under the conditions satisfying the following formula (1), the inhibitor in the hot rolled sheet is sufficiently finely precipitated, and as a result, an ultrathin grain oriented silicon steel sheet having high magnetic properties is obtained. Can be manufactured.

830 + 1000 / R ≦ T + 4.2t + 3000 / R ≦ 1040-1000 / R (1) (However, T ≧ 500) (1) (T + 4.2t + 3000 / R) in the equation Is less than (830 + 1000 / R), the inhibitor is not sufficiently precipitated, and therefore, the effect of hot-rolled sheet annealing is not sufficient, and improvement in magnetic properties cannot be obtained. When (T + 4.2t + 3000 / R) is more than (1040-1000 / R), the precipitates become coarse, so that secondary recrystallization does not completely proceed during the final annealing, and the magnetic properties No improvement is obtained.

If the annealing temperature T is less than 500 ° C., no inhibitor is precipitated, and the effect of hot-rolled sheet annealing cannot be obtained. Therefore, T ≧ 500 ° C.

(2) Cold Rolling Cold rolling is cold rolling 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, a recrystallization temperature of 700 ° C. or higher is used, and in order to avoid a shape defect of a 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 the coverage of the secondary recrystallized grains to be 90% or more, the annealing during the annealing of AlN serving as an inhibitor is required. 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.

If 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 surface energy in which the {110} plane grows preferentially by annealing in a non-oxidizing atmosphere is used as a driving force for the secondary recrystallization, and the fine-grained portion is formed in the secondary stage. 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.

[0047]

【Example】

(Example 1) The steel types shown in Table 1 were melted in vacuum, slab-rolled to 30 mm, and then hot-rolled to 2.5 mm by heating at 1150 ° C. Subsequently, hot-rolled sheet annealing was performed under the conditions shown in Table 2, followed by pickling, cold rolling, and final annealing.

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 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 .

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.

[0051]

[Table 1]

[0052]

[Table 2]

(Example 2) Steel type No. 1 in Table 1 was melted in a vacuum, slab-rolled to 30 mm, and then hot-rolled to 2.5 mm by heating at 1150 ° C. Subsequently, hot-rolled sheet annealing was performed under the conditions shown in Table 3, and then pickling, cold rolling, and final annealing were performed.

The cold rolling is described in Table 3 as rolling three times.
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.

[0057]

[Table 3]

[0058]

As described above, according to the present invention, the inhibitor, the chemical composition of the hot-rolled steel sheet, the hot-rolling annealing conditions, the cold-rolling / intermediate annealing conditions, and the final annealing conditions are made specific. The surface energy can be utilized, and 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: 0.005% or more and 0.12% or less,
P: 0.02% or less, S: 0.002% to 0.005%, sol.
Al: 0.0015% to 0.006%, N: 0.001% to 0.
008% or less, and Ti + Nb as an impurity is 0.003% or less.
% (B) an annealing temperature T (° C.), a holding time t (minutes), and a heating rate R (° C./minute) are as follows: Annealing process under the condition satisfying the formula, 830 + 1000 / R ≦ T + 4.2t + 3000 / R ≦ 1040-1000 / R… (1) (However, T ≧ 500) (c) Remove the hot-rolled steel sheet After scaling, the heating / cooling rate is 0.
2 or 3 times cold rolling including intermediate annealing with 1 ° C / sec or more and holding time of 0.5 to 10 minutes
(d) forming the cold-rolled steel sheet in a reducing atmosphere containing 50% by volume or more of nitrogen;
A first annealing step of heating to a predetermined temperature of 700 ° C. or more and 1000 ° C. or less at a temperature rising rate of at least 70 ° C./sec and maintaining the temperature at that temperature for 30 seconds or more; .
% In a reducing atmosphere containing at least 700% and not more than 1000 ° C for at least 3 hours in a reducing atmosphere containing at least
(f) Further, in a reducing atmosphere containing no nitrogen or a non-oxidizing atmosphere having an oxygen partial pressure of not more than 0.5 Pa and substantially no nitrogen or a vacuum having an oxygen partial pressure of not more than 0.5 Pa,
A method for producing an ultra-thin silicon steel sheet including a third annealing step of holding at a predetermined temperature in a range of 0 ° C. or more and 1300 ° C. or less for 30 seconds or more. 2. An ultra-thin silicon steel sheet produced by the method according to claim 1.