JP3271651B2 - Ultra-thin silicon steel sheet with excellent magnetic properties and manufacturing method - Google Patents

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 have conventionally been made of AlN or MnS for secondary recrystallization as shown in Japanese Patent Publication No. 46-23820. It is manufactured using the precipitate as an inhibitor. However, such oriented silicon steel sheets are made of AlN or M
A high-temperature slab heating step for solid solution of a large amount of inhibitors such as nS, a decarburizing annealing step until the final annealing and a secondary recrystallization are completely completed, and a high temperature for purifying impurities affecting magnetic properties. The long annealing step is essential, and has 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. 62-83421
As shown in Japanese Unexamined Patent Publication No.
Assuming that the composition is extremely low carbon, a method of avoiding the problem by devising a composition in which Al is added in a trace amount has been devised. Also, a method for producing an ultrathin oriented silicon steel sheet using surface energy as represented by Japanese Patent Application Laid-Open No. 5-186829 has been proposed.

[0005]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open
According to the method described in 62-83421 JP and JP-A 1-212721, although high-temperature slab heating and high-temperature long-time annealing process can be omitted, economic effects can be obtained,
When the thickness is 0.2 mm or less, there is a problem that the quality remarkably varies so that the industrially stable secondary recrystallization behavior cannot be obtained.

The method disclosed in Japanese Patent Application Laid-Open No. 5-186829 is
This method is advantageous in principle for the production of ultra-thin steel sheets targeted by the present invention because no inhibitor is used.However, the growth of crystal grains is affected by minute impurities and subtle changes in the atmosphere, resulting in stability. Had the problem of lacking.

[0007] The present invention overcomes such problems, and achieves stable {110} <001> plane orientation in a sheet thickness of 0.2 mm or less without performing decarburizing annealing and annealing at high temperature for a long time. Crystallize,
It is an object of the present invention to provide a method and a silicon steel sheet having excellent magnetic properties by which a silicon steel sheet having excellent magnetic properties can be manufactured.

[0008]

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%.
Preparing a hot-rolled steel sheet of 003% or less, (b) after descaling the hot-rolled steel sheet, performing cold rolling three times including intermediate annealing at an annealing temperature of 700 ° C. to 950 ° C. and a holding time of 30 seconds or more. A step of forming a cold-rolled steel sheet having a thickness of 0.20 mm or less, and (c) in a reducing atmosphere containing 50 vol.% Or more of nitrogen at a heating rate of 1 ° C./sec or more and 700 ° C. or more and 1000 ° C. or less. (D) heating to a predetermined temperature and maintaining the temperature for 30 seconds or more;
700 ° C or more in a reducing atmosphere containing 50vol.% Or more
(E) a nitrogen-free reducing atmosphere or a non-oxidizing material containing substantially no nitrogen and having an oxygen partial pressure of 0.5 Pa or less at a predetermined temperature of not more than 00 ° C for 3 hours or more. Ultra-thin silicon with excellent magnetic properties including a third annealing step of holding at a predetermined temperature in the range of 900 ° C to 1300 ° C for 30 seconds or more in an atmosphere or a vacuum with an oxygen partial pressure of 0.5 Pa or less This is a method for manufacturing a steel sheet.

[0009] A second means for solving the above-mentioned problems is as follows.
At least one of the intermediate annealings in the first means is performed.
This is a method for producing an ultra-thin silicon steel sheet having excellent magnetic properties, wherein the atmosphere of the intermediate annealing is a non-oxidizing atmosphere containing 50 vol.% Or more of nitrogen.

[0010] A third means for solving the above problems is as follows.
The step (b) in the first means is performed by (b′-1)
A step of subjecting the hot-rolled steel sheet to descaling and subjecting the cold-rolled steel sheet to primary cold-rolling at a rolling reduction of 70 to 90% to form a cold-rolled steel sheet; Performing a primary anneal under the conditions of an annealing temperature of 700 ° C. to 950 ° C., a holding time of 0.5 to 5 minutes, and a heating rate of 1 ° C./sec or more in a non-oxidizing atmosphere including (b′-3) A process of performing secondary cold rolling with a reduction ratio of 50 to 90% to produce a cold-rolled steel sheet having a thickness of 0.20 mm or less;
This is a method for manufacturing an ultra-thin silicon steel sheet having excellent magnetic properties.

[0011] A fourth means for solving the above problems is as follows.
The step (b) in the first means, (b ''-
1) subjecting the hot-rolled steel sheet to a hot-rolled sheet annealing in a reducing atmosphere containing at least 50% or more of nitrogen at an annealing temperature of 700 ° C to 950 ° C and a holding time of 2 minutes or more; (b ''-2) This is a method for producing an ultra-thin silicon steel sheet having excellent magnetic properties, instead of the step of turning a rolled annealed sheet into a cold-rolled steel sheet having a sheet thickness of 0.20 mm or less by cold rolling at a cold rolling reduction of 80% or more.

A fifth means for solving the above-mentioned problem is as follows.
A slurry having a pH of 8 or more containing colloidal silica is applied between the steps (c) and (d) in any one of the first to fourth means so that 10 mg of the slurry is applied to the surface of the cold-rolled steel sheet. / is a manufacturing method excellent ultra-thin silicon steel sheet on the magnetic properties, characterized in that m ² or more 2 mg / m ² obtained by adding the step of depositing the following silicon oxide.

A sixth means for solving the above-mentioned problem is as follows.
An ultra-thin silicon steel sheet having excellent magnetic properties manufactured by any of the first to fifth means.

Hereinafter, the background of the invention and details of the invention will be described. The present inventors have found that the {110} <001> plane orientation can be stably secondary-recrystallized at a plate thickness of 0.2 mm or less without performing decarburizing annealing and annealing at a high temperature for a long time. Experiments and researches were conducted to find out the composition of steel sheets and the method of manufacturing them so that excellent silicon steel sheets can be manufactured. As a result, the following findings were obtained.

1) Japanese Patent Application Laid-Open No. 62-83421 and Japanese Patent Application Laid-Open
Compared with the case of ordinary recrystallization of a steel sheet having a thickness of 0.3 mm as shown in JP-A-212721, the primary and secondary steel sheets having a thickness of 0.2 mm or less which are the object of the present invention are compared with those of the present invention. The effect of nitriding from the atmosphere in the annealing step for developing secondary recrystallization is extremely large, causing a new problem.
For example, with the composition corresponding to steel Y in Table 2 in the examples of JP-A-62-83421, AlN as an inhibitor becomes too large, and its distribution becomes inappropriate. As a result, secondary recrystallization occurs. What does not happen.

2) In order to prevent the formation of such excessive AlN, studies were made to reduce the nitrogen partial pressure of the annealing atmosphere or to lower the annealing temperature with the same composition.
In the case of the following plate thickness, the escape of nitrogen from the surface also occurs at the same time, so that AlN which is the main inhibitor in steel
It is extremely difficult to control the amount and morphology effective for developing secondary recrystallization.

3) In order to develop secondary recrystallization, optimization of the composition taking into account changes in the form and amount of AlN during annealing and study of the manufacturing process were performed, and the composition was limited to a specific component range. AlN that becomes an inhibitor when
Work effectively for the next recrystallization.

4) Further, a hot-rolled steel sheet adjusted to a specific component range is cold-rolled to obtain a primary recrystallization.
A certain degree of secondary recrystallization occurs when the second-stage annealing is performed to promote the second-stage recrystallization and the second-stage recrystallization. Cold rolling can be performed by three times of rolling including intermediate annealing. However, if cold rolling is performed at a specific rolling reduction rate and intermediate annealing is performed under specific conditions including a specific amount of nitrogen, only two cold rolling operations are required.
In addition, before cold rolling, subjected to hot rolled sheet annealing under specific conditions,
By setting the rolling reduction in a specific range, only one cold rolling is sufficient.

5) However, 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 left behind by the secondary recrystallized grains. The grain size should be in the range of the sheet thickness. Since such fine grains are penetrating grains, the grain boundary energy, which is inversely proportional to the curvature of the crystal grains, is not sufficient. Inadequately.

6) In order to make such fine-grained portions invaginate the secondary recrystallized grains, the surface energy at which {110} planes grow preferentially does not depend on the crystal grain size, and the secondary recrystallized grains are advanced. The secondary recrystallization coverage must be greater than 90% when used as a driving force.

7) The silicon steel sheet thus obtained has extremely good magnetic properties.

8) The method of abnormally growing Goss grains by only the surface energy method disclosed in Japanese Patent Application Laid-Open No. 5-186829 discloses a method in which S is contained in an amount of 0.0020 wt% or more like the steel of the present invention. In some steels, the grain growth is very poor,
The coverage of Goss grains after annealing at 900 ° C or more and 1300 ° C or less for 10 minutes is about 40% at the maximum, which is unsatisfactory.

Therefore, the present inventors have further studied based on the above findings and completed the present invention. First, in the present invention, the reasons for limiting the chemical components and the production method of a hot-rolled steel sheet will be described.

C: In the inhibitor method, the structure and texture are controlled by C. However, in the present invention described above, this is not performed, so that 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 wt%, AlN as an inhibitor becomes insufficient and the matrix grains become coarse.
The next recrystallization becomes difficult. On the other hand, if it exceeds 0.006 wt%, AlN as an inhibitor becomes too large due to nitrogen absorption during annealing, and the distribution becomes unsuitable. As a result, secondary recrystallization does not occur or the secondary recrystallization does not occur. Although recrystallized grains are formed, the coverage is extremely low. further,
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 is set to 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 is required.

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.

Next, the manufacturing method will be described. 1) Hot-rolled sheet annealing and cold rolling (a) In the first method, hot-rolled sheet annealing is not performed, and cold rolling is performed three times of cold rolling including intermediate annealing. Cold rolling is carried out according to a conventional method. However, unless a special method is employed as described later, less than three times is preferable for the growth of secondary recrystallized grains by selective grain growth during final annealing. Structure was not formed properly and grew sufficiently after final annealing 2
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, 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, the holding time is required to be 0.5 minutes or more to sufficiently generate recrystallization. Furthermore, in these intermediate annealings, it is preferable to set the heating rate to 0.5 ° C./sec or more and the holding time to 10 minutes or less in order to avoid coarsening of precipitates during the annealing process.

The annealing atmosphere may be a conventional method. However, a non-oxidizing atmosphere is used to prevent extreme oxidation. In particular
An inert gas such as Ar or He and a single or mixed atmosphere of nitrogen, hydrogen and the like are used. The oxygen partial pressure is not specified.
It suffices if extreme oxidation is prevented. In addition, at least one
The magnetic characteristics are improved by setting the atmosphere of the intermediate annealing in a non-oxidizing atmosphere containing 50 vol.% Or more of nitrogen. Although the reason is not clear, it seems to be related to the phenomenon of inhibitor formation. Therefore, it is more preferable that the atmosphere of at least one intermediate annealing be a non-oxidizing atmosphere containing 50 vol.% Or more of nitrogen.

(B) In the second method, hot rolling is not performed, but cold rolling is performed twice including intermediate annealing. In the case of performing the cold rolling twice, the cold rolling must be performed at a specific rolling reduction and the intermediate annealing must be performed under specific conditions including a specific amount of nitrogen.

The Goss grains that undergo secondary recrystallization during the final annealing are formed from a Goss structure originally formed at the time of hot rolling of a layer having a thickness of about 10% immediately below the surface of a hot-rolled steel sheet by cold rolling and intermediate annealing. It is inherited through the process.

If the rolling reduction exceeds 90%, the structure undergoes strong deformation by cold rolling, and a structure having a <110> orientation in the rolling direction is remarkably developed. A processed structure having such a <110> orientation forms coarse primary recrystallized grains. Therefore, crystal grains having a plane orientation other than coarse grains Goss are recrystallized in the primary recrystallization of the final annealing, and the driving force for the secondary recrystallized grains is reduced. As a result, the entire steel sheet cannot be covered with Goss grains, and high magnetic properties cannot be obtained. In order to further stably obtain a steel sheet having high magnetic properties, it is desirable that the rolling reduction in the secondary cold rolling be 80% or less from the viewpoint of not developing a worked structure having a <110> orientation.

If the rolling reduction of the first cold rolling is less than 70%, the elongated crystal grains having {100} <011> formed in the hot rolling at the center of the thickness of the hot-rolled steel sheet are deformed. It is inherited without being done. As a result, the rolling reduction is 90%
As in the case of exceeding the value, coarse grains other than Goss grains are formed at the time of final annealing, and hinder secondary recrystallization of Goss grains.

When the rolling reduction of the secondary cold rolling is less than 50%, the nucleation sites for primary recrystallization decrease because the accumulation of strain energy is small. As a result, the primary recrystallized grains at the time of final annealing become large, and the grain boundary energy, which is the driving force for secondary recrystallization of Goss grains, is reduced. In order to more stably develop the secondary recrystallization, the rolling reduction is required from the viewpoint of grain refinement.
It is desirable to be 60% or more.

For the above reasons, the rolling reduction of the first cold rolling is
70-90%, that of secondary cold rolling is defined as 50-90%.
The more preferable range of the rolling reduction in the secondary cold rolling is 60 to 80%.

The intermediate annealing is performed in a non-oxidizing atmosphere containing 50 vol.% Or more of nitrogen. By setting the atmosphere to a nitrogen atmosphere, nitriding and denitrification of the steel sheet occur at the same time.
N is refined. If the nitrogen content is less than 50 vol.%, Denitrification proceeds more than nitriding of the steel sheet, AlN decreases from an appropriate amount, and sufficient secondary recrystallization does not progress. The oxygen partial pressure is not specified. That is enough if significant oxidation is prevented.

In order to avoid coarsening of precipitates during the annealing process, the temperature is maintained at a rate of 1 ° C./sec or more for 5 minutes or less. However, if the holding time is less than 0.5 minutes, a sufficient effect cannot be obtained, and the progress of the secondary recrystallization varies. For this reason, the heating rate is defined as 1 ° C./sec, and the holding time is defined as 0.5 to 5 minutes.

Further, the annealing temperature is specified at 700 to 950 ° C. If the annealing temperature is lower than 700 ° C., softening due to recrystallization, morphological control of precipitates, and texture control are insufficient. on the other hand
When the temperature exceeds 950 ° C., coarsening of precipitates starts, normal grain growth progresses, and recrystallized grains become larger than the sheet thickness. For this reason, secondary recrystallized grain growth during final annealing is suppressed.

(C) In the third method, after performing hot-rolled sheet annealing, one cold rolling is performed. Hot-rolled sheet annealing is extremely important for optimizing the amount of inhibitors by nitriding during annealing. For this reason, the annealing atmosphere is a reducing atmosphere containing nitrogen such that nitrogen is not significantly desorbed from the steel and N 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 temperature needs to be 700 ° C. or higher for effective absorption of N. However, when the temperature exceeds 950 ° C., the structural change of the hot-rolled sheet becomes remarkable, and as a result, a desired texture cannot be obtained, and secondary recrystallized grains sufficiently grown after the final annealing cannot be obtained. Therefore, it is desirable that the temperature be 700 ° C or more and 950 ° C or less.

Further, the holding time is required to be 2 minutes or more in order to generate absorption N for stably developing secondary recrystallization. Therefore, the holding time is set to 2 minutes or more. However, if the time exceeds 10 hours, the effect is saturated. Therefore, it is preferable to set the time within 10 hours from the economical point of view.

The cold rolling is a single cold rolling that does not sandwich intermediate annealing. Cold rolling is performed according to a conventional method, but if the cold rolling reduction is less than 80%, a texture preferable for growing secondary recrystallized grains by selective grain growth during final annealing is not appropriately formed, Secondary recrystallized grains that have grown sufficiently after the final annealing cannot be obtained. Therefore, the cold reduction ratio is set to 80% or more.

2) 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, it is necessary to optimize AlN serving as an inhibitor during annealing. The 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 N 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 at 700 ° C or more and 1000 ° C or less.

The heating rate is not particularly specified. 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 it exceeds 20 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 secondary recrystallization, and the fine-grained portion is used 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.

3) Slurry coating Of the annealing after the cold rolling, the second stage annealing is 700 to 10
It is necessary to perform the treatment at a high temperature of 00 ° C. for a long time of 3 hours or more. However, when the treatment is applied to the laminated cold rolled steel sheets, the steel sheets may be burned to each other. So 0.2mm
In the silicon steel sheet of the following thickness, under the annealing conditions,
An economical annealing separation method that can prevent seizure without hindering the nitriding of the steel sheet and that does not affect the abnormal grain growth using the surface energy as a driving force in the subsequent high-temperature annealing was studied. As a result, (a) as an annealing separation material, it is better to attach an oxide that reacts less with the steel sheet surface. (B) This oxide needs to have adhesion to the steel sheet to such an extent that it does not peel off by coiling. C) It has been found that this oxide needs to form a film having good air permeability for nitriding the steel sheet.

As a result of an examination based on this finding, the first stage
After eye annealing, PH8 or more containing colloidal silica
The slurry is applied to the surface of the cold rolled steel
mg / m ^TwoMore than 2g / m^TwoThe following steps for attaching silicon oxide are added.
It has been found that the above object can be achieved by the addition.

If the amount of silicon oxide to be adhered is less than 10 mg / m ^2, it is insufficient, and partial burning occurs during annealing. On the other hand, when it exceeds ² g / m ² , although the annealing separation property is sufficient, the steel sheet is not sufficiently nitrided due to insufficient nitrogen permeability, and the entire surface cannot be covered with the secondary crystal grains. . Therefore, the amount of silicon oxide to be deposited is 10 mg / m
^{2 to 2} g / m ² or less.

As a method for attaching silicon oxide, it is necessary to apply a method of applying a slurry containing colloidal silica. As an example of the slurry application method, a known method such as a coater, a dip, and a spray method can be used. Although the reason why the method of applying the slurry containing colloidal silica is effective has not yet been sufficiently elucidated, the present inventors consider as follows.

That is, when such a method is used, since the cohesive force of silica is weak, the film has a structure in which silica clusters having a diameter of about 100 nanometers are scattered on the surface of the steel sheet. Therefore, the nitrogen gas can freely contact the steel plate through the region where no cluster exists. In addition, the clusters of silica play the role of spacers to prevent contact between the steel plates, thereby improving the separability of the steel plates.

The reason why the pH of the slurry is set to 8 or more is to prevent the cold-rolled sheet from being oxidized.

[0066]

【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, after this was pickled, the steps shown in Tables 2, 3 and 4, the steps shown in Tables 5, 6 and 7, and the steps shown in Tables 8, 9 and 10 were carried out. After the final annealing, the obtained thin steel sheet has the following structure: the coverage of crystal grains having a grain size of 10 times or more the sheet thickness, the magnetic flux density B8 [T] in the rolling direction, and the holding force Hc [A / m]. It was measured. The results are shown in Tables 2 to 10. As is clear from these tables, only when the production method according to the present invention is performed in the component range according to the present invention, 90% or more of the coarse grains having a crystal grain size of 10 times or more the plate thickness are covered. An ultra-thin silicon steel sheet with excellent characteristics was obtained.

[0067]

[Table 1]

[0068]

[Table 2]

[0069]

[Table 3]

[0070]

[Table 4]

[0071]

[Table 5]

[0072]

[Table 6]

[0073]

[Table 7]

[0074]

[Table 8]

[0075]

[Table 9]

[0076]

[Table 10]

(Example 2) The steel types shown in Table 11 were melted in vacuum, slab-rolled to 30 mm, and then hot-rolled to 2.5 mm by heating at 1150 ° C. Subsequently, this was pickled, and a cold-rolled plate was manufactured in the following steps.

First cold rolling: reduction from 2.5 mm to 0.3 mm Intermediate annealing: heating rate: 3 ° C./sec, 100% N ₂ atmosphere
Maintained at 900 ° C. for 2 minutes Second cold rolling: reduction from 0.3 mm to 0.1 mm Then, the cold rolled sheet was subjected to three-step annealing under the following conditions.

First Stage Annealing: Heating Rate 3 ° C./sec, 95
Maintain at 900 ° C. for 2 minutes in an atmosphere of% N ₂ -5% H _{2 Second} annealing: Maintain at 900 ° C. for 15 hours in an atmosphere of 95% N ₂ -5% H ₂ Third annealing: Ascending At a temperature rate of 3 ° C./sec and kept at 1200 ° C. for 10 minutes in an atmosphere of 100% H ₂ , colloidal silica was applied to the steel sheet surface by a roll coater under the conditions shown in Table 12 after the first annealing. After drying, the steel sheets were laminated and subjected to a second annealing step. Furthermore, the peelability was investigated after the second stage annealing. Furthermore, for those having good releasability, a third step of annealing is performed after performing alkali cleaning, and as a structure of the obtained thin steel sheet, the coverage of the crystal grains having a grain size of 10 times or more the sheet thickness and the rolling rate are determined. Magnetic flux density in direction B8
[T] and holding power Hc [A / m] were measured.

Table 12 shows the results. As is clear from Table 12, only when the amount of adhered silicon oxide and the PH value of the slurry are within the range of the present invention, the peelability after the second annealing is good, and the grain size is 10 times or more the sheet thickness. An ultra-thin silicon steel sheet having excellent magnetic properties and covering 90% or more of the coarse grains having the above characteristics was obtained.

[0081]

[Table 11]

[0082]

[Table 12]

[0083]

According to the present invention, by using an inhibitor and a surface energy together, an ultrathin silicon steel sheet whose secondary recrystallized grains have an area ratio of the steel sheet surface of 90% or more can be obtained industrially stably. It became.

──────────────────────────────────────────────────続 き Continued on the front page (31) Priority claim number Japanese Patent Application No. 7-256375 (32) Priority date October 3, 1995 (Oct. 3, 1995) (33) Priority claim country Japan (JP) (72) Inventor Yasushi Tanaka 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Yoshihito Uemoto 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56 References JP-A-10-121137 (JP, A) JP-A-7-197126 (JP, A) JP-A-6-207219 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) C21D 8/12 C22C 38/00 303 C22C 38/06

Claims (6)

(57) [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) after descaling the hot-rolled steel sheet, annealing temperature 700 ° C. to 950 ° C., holding time
Thickness by cold rolling three times including intermediate annealing for 30sec or more
A step of forming a cold-rolled steel sheet having a diameter of 0.20 mm or less, and (c) a cold-rolled steel sheet having a temperature of 700 ° C. or more and 1000 ° C. or less at a heating rate of 1 ° C./sec or more 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; (d) continuing the cold-rolled steel sheet with nitrogen 50
In a reducing atmosphere containing at least vol.
(E) a reducing atmosphere containing no nitrogen or a non-oxidizing atmosphere containing substantially no nitrogen and having a partial pressure of oxygen of 0.5 Pa or less. Or an ultra-thin silicon steel sheet having excellent magnetic properties including a third annealing step of holding at a predetermined temperature in the range of 900 ° C to 1300 ° C for 30 seconds or more in a vacuum with an oxygen partial pressure of 0.5 Pa or less Manufacturing method. 2. The ultra-thin silicon having excellent magnetic properties according to claim 1, wherein the atmosphere of at least one of the intermediate annealings is a non-oxidizing atmosphere containing at least 50 vol.% Of nitrogen. Steel plate manufacturing method. 3. The method for producing an ultra-thin silicon steel sheet having excellent magnetic properties according to claim 1, wherein the step (b) comprises:
(b'-1) a step of descaling the hot-rolled steel sheet, performing a primary cold rolling of a reduction rate of 70 to 90% to obtain a cold-rolled steel sheet, (b'-2)
The cold-rolled steel sheet is subjected to an annealing temperature of 700 ° C. to 950 ° C. and a holding time of 0.5 to 5 in a non-oxidizing atmosphere containing 50 vol.
Min, a step of performing primary annealing under a condition of a heating rate of 1 ° C./sec or more, (b′-3) performing a secondary cold rolling of the reduction rate of 50 to 90% on the annealed sheet to a sheet thickness of 0.20 mm. A method for producing an ultra-thin silicon steel sheet having excellent magnetic properties, in place of the following step of forming a cold-rolled steel sheet. 4. The method for producing an ultra-thin silicon steel sheet having excellent magnetic properties according to claim 1, wherein the step (b) comprises:
(b ″ -1) annealing the hot-rolled steel sheet in a reducing atmosphere containing at least 50% or more of nitrogen at an annealing temperature of 700 ° C. to 950 ° C. and a holding time of 2
Step of performing hot-rolled sheet annealing for at least a minute, (b ''-2) the hot-rolled annealed sheet, a sheet thickness of 0.20 mm by cold rolling at a cold rolling reduction of 80% or more.
A method for producing an ultra-thin silicon steel sheet having excellent magnetic properties, in place of the following step of forming a cold-rolled steel sheet. 5. The method for producing an ultra-thin silicon steel sheet having excellent magnetic properties according to claim 1, wherein colloidal silica is provided between the steps (c) and (d). Ultra thin with excellent magnetic properties characterized by adding a step of applying 10 mg / m ² or more and 2 g / m ² or less silicon oxide to the surface of a cold-rolled steel sheet by applying a slurry of PH 8 or more containing Manufacturing method of silicon steel sheet. 6. An ultra-thin silicon steel sheet having excellent magnetic properties manufactured by the method according to claim 1. Description: