JP2002212636A - Method for producing grain oriented silicon steel sheet having high magnetic flux density - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a grain oriented silicon steel sheet which has high magnetic flux density by a low temperature slab heating process. SOLUTION: A steel having a composition containing, by mass, 0.8 to 4.8% Si, <=0.08% C, 0.01 to 0.065% acid soluble Al and <=0.012% N, and the balance Fe with inevitable impurities is heated at <=1,280 deg.C, and is thereafter hot-rolled. Next, cold rolling is performed into a final sheet thickness. After decarburizing annealing, the steel sheet is coated with a separation agent for annealing essentially consisting of magnesia, and is subjected to finish annealing into a grain oriented silicon steel sheet. In the production method, provided that the draft in the cold rolling is defied as R%, the ratio of I 111}/I 411} in the texture after the decarburizing annealing is controlled to (101n (100-R)/100)+44)/7 or lower. After that, nitriding treatment is performed to produce the grain oriented silicon steel sheet having high magnetic flux density.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a so-called "110"<001> orientation of crystal grains,
The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet. This steel sheet is used as an iron core of electric equipment such as a transformer as a soft magnetic material.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are {110} <001.
> A steel sheet containing 4.8% or less of Si constituted by crystal grains accumulated in an orientation (so-called Goss orientation). This steel sheet is required to have magnetic properties such as excitation properties and iron loss obtainability. As an index indicating the excitation characteristic, a magnetic flux density: B ₈ at a magnetic field strength of 800 A / m is usually used.

As an index indicating iron loss characteristics, iron loss per kg of steel sheet: W _17/50 when magnetized to 1.7 T at a frequency of 50 Hz is used. The magnetic flux density: B ₈ is the largest controlling factor of the iron loss characteristics, and the higher the magnetic flux density: B ₈ value, the better the iron loss characteristics. Flux density: in order to increase the B ₈ is important to align advanced crystal orientation. The control of the crystal orientation is achieved by utilizing a catastrophic grain growth phenomenon called secondary recrystallization.

In order to control the secondary recrystallization, it is necessary to adjust the primary recrystallization structure before the secondary recrystallization and to adjust a fine precipitate called an inhibitor. This inhibitor has a function of suppressing the growth of general grains in the primary recrystallized structure and preferentially growing only specific {110} <001> orientation grains. As typical examples of the precipitate, M.I. F. Littmann (Special Publication 30-36)
No. 51) and J.-A. E. FIG. May & D. Turnbul
1 (Trans. Met. Soc. AIM 212 (1
958) p769) et al. Used MnS and Taguchi et al.
No. 0-15644) discloses AlN and Imana et al.
Publication No. 1-13469) presents MnSe.

[0005] A method has been adopted in which these precipitates are completely dissolved in slab heating before hot rolling and then finely precipitated in hot rolling and a subsequent annealing step. In order to completely dissolve these precipitates, 135
It is necessary to heat at a high temperature of 0 ° C. to 1400 ° C. or more, which is about 200 times higher than the slab heating temperature of ordinary steel.
° C high and has the following problems.

(1) A dedicated heating furnace is required. (2) The energy intensity of the heating furnace is high. (3) The amount of the molten scale is large, and operation management such as so-called sticking out is required. Therefore, research and development by low-temperature slab heating have been advanced. As a manufacturing method by low-temperature slab heating, Komatsu et al. (Japanese Patent Publication No. 62-45285) use a method in which (Al, Si) N formed by nitriding treatment is used as an inhibitor. Disclosed. Kobayashi et al. Disclose a method of nitriding in strip form after decarburizing annealing (JP-A-2-77525), and Ushigami et al. Report the behavior of the nitrides. Materials Sci
ence Forum, 204-206 (1996), pp593-598).

In the method for producing a grain-oriented electrical steel sheet by low-temperature slab heating, since no inhibitor is formed during decarburization annealing, adjustment of the primary recrystallization structure in decarburization annealing is not sufficient for controlling secondary recrystallization. It becomes important. In research on a conventional method for manufacturing a grain-oriented electrical steel sheet by heating at a high temperature slab, there is almost no knowledge about the adjustment of the primary recrystallization structure before the secondary recrystallization.
The importance is disclosed in JP-A-32929 and JP-A-9-260551.

[0008] In Japanese Patent Publication No. 8-32929,
It has been disclosed that when the variation coefficient of the particle size distribution of the primary recrystallized grain structure becomes larger than 0.6 and the grain structure becomes non-uniform, the secondary recrystallization becomes unstable. Thereafter, Japanese Patent Application Laid-Open No. 9-2
In Japanese Patent No. 56051, as a result of a study on a primary recrystallized structure and an inhibitor, which are control factors of secondary recrystallization, as a primary recrystallized grain structure, the texture after decarburizing annealing shows that the goss-oriented grains have When I {111} / I {411} is adjusted to 3 or less, the ratio of grains having {111} orientation and {411} orientation, which is considered to promote growth,
It is disclosed that the magnetic flux density of the product is improved.

Here, I {111} and I {411}
Are the proportions of grains in which the {111} and {411} planes are parallel to the steel plate surface, respectively, and represent the diffraction intensity values measured at a plate thickness of 1/10 by X-ray diffraction measurement. The primary recrystallized structure after this decarburizing annealing is affected not only by the annealing cycle of decarburizing annealing such as heating rate, soaking temperature and soaking time in the decarburizing annealing step, Manufacturing processes before decarburization annealing, such as the presence or absence of annealing and the reduction ratio of cold rolling (cold rolling reduction ratio), also have an effect.

[0010] Specifically, the effect of the cold rolling reduction is to increase the cold rolling reduction to 80% in order to develop crystal grains having {111} and {411} crystal orientations in the primary recrystallization structure. It is necessary to make the above, which is an index for obtaining a high magnetic flux density, I {111} / I ｛4
It is very important to make 11｝ 3 or less.

When the cold rolling reduction is increased, the magnetic flux density of the product basically increases. However, when the cold rolling reduction exceeds a certain level, I {111} / I {411} is exceeded. It was found that the secondary recrystallization became unstable and the magnetic flux density of the product was reduced despite the control at 3 or less.

[0012]

SUMMARY OF THE INVENTION The present invention avoids the above-mentioned secondary recrystallization instability by appropriately controlling the conditions of decarburization annealing, and is industrially stable and provides an excellent magnetic material having a high magnetic flux density. It discloses a method of manufacturing a grain-oriented electrical steel sheet having characteristics.

[0013]

The gist of the present invention is as follows. (1) In mass%, Si: 0.8 to 4.8%, C: 0.0
85% or less, acid-soluble Al: 0.01 to 0.065%,
N: steel containing 0.012% or less, the balance consisting of Fe and inevitable impurities is heated at a temperature of 1280 ° C. or less, then hot-rolled, and then cold-rolled to a final thickness,
After the decarburizing annealing, in the method for producing a grain-oriented electrical steel sheet in which an annealing separator containing magnesia as a main component is applied and subjected to finish annealing, when the cold rolling reduction ratio is R%, the texture after the decarburizing annealing Of {111} / I {411} at (10 In {(100−R) / 100} +44) / 7 or less, and then performing a nitriding treatment. Method.

(2) In the temperature raising step of the decarburizing annealing step, the temperature of the steel sheet is reduced from 750 to 900
The heating rate up to a predetermined temperature in the range of
0 ^{(( R-68) / 14]} <H
A method for producing a grain-oriented electrical steel sheet having a high magnetic flux density as described above. (3) The method according to (1) or (2) above, wherein the heating rate H ° C./sec in the temperature raising process in the decarburizing annealing step is 10 ^{[(R− 32) / 32]} <H <140. A) A method for producing a grain-oriented electrical steel sheet having a high magnetic flux density as described in the above.

(4) 900 hot rolled sheets obtained by the hot rolling
The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to any one of the above (1) to (3), wherein annealing is performed in a temperature range of up to 1200 ° C. for 30 seconds to 30 minutes. (5) In the decarburizing annealing step, 770 ° C to 900 ° C
Degree of oxidation of atmospheric gas (P _H2O / P _H2 ):
The oxygen content of the steel sheet is 2.3 g within a range of more than 15 and 1.1 or less.
The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to any one of the above (1) to (4), wherein the annealing is performed for a time period of not more than / m ² .

(6) Amount of acid-soluble Al in steel sheet: [Al]
(1) to (5), wherein the nitriding treatment is performed so that the amount of nitrogen [N] satisfies [N] / [Al] ≧ 0.67 according to. For manufacturing grain-oriented electrical steel sheets with high magnetic flux density. (7) In the steel, Sn is added in an amount of 0.02 to
The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to any one of the above (1) to (6), wherein 0.15% is added.

(8) In the steel, by mass%,
(3) The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to any one of the above (1) to (7), wherein 0.03 to 0.2% is added. The inventors of the present invention basically increased the magnetic flux density of the product as the rolling reduction was increased, but when the rolling reduction exceeded a certain level, the primary recrystallization structure I {111} / Despite controlling I {411} to be 3 or less, the secondary recrystallization became unstable, and the situation where the magnetic flux density of the product was reduced was investigated.
We examined the solution.

As a result, I {111} / I ｛4 which is an index of the primary recrystallized structure necessary for obtaining a high magnetic flux density.
It became clear that the threshold value of 11 ° changes with respect to the cold rolling reduction. Specifically, I ｛111｝ / I ｛4
It was found that the threshold value of 11 ° decreased with an increase in the cold rolling reduction. From this, I {111} / I ｛41
Regarding the effective control method to reduce the value of 1｝,
Further investigation result, it is possible to further increase the magnetic flux density of the product by adjusting the heating rate in the decarburization annealing step, by raising the decarburization annealing heating rate, cold rolled reduction ratio to be high B ₈ It has been found that the range extends to the high pressure reduction side.

The following is a description based on the experimental results. Figure 1
Is the true strain obtained from the cold rolling reduction R: ln ｛100 /
For (100-R)}, the texture of the primary recrystallized structure after decarburization annealing: I {111} / I {411} (surface layer; 1/10 layer thickness) was plotted and corresponded. FIG. 6 is a diagram showing a relationship between magnetic flux density of a product after secondary recrystallization annealing: B ₈ . The sample used here was Si: 3.2% by mass.
%, C: 0.05%, acid-soluble Al: 0.026%,
N: 0.008%, Mn: 0.1%, S: 0.007%
After heating the containing slab at a temperature of 1150 ° C.,
Hot-rolled to a thickness of 5 mm, 2.3 mm, 4.4 mm,
Thereafter, after annealing at 1120 ° C., cold rolling was performed to a thickness of 0.22 mm, and then 770 to 9 at a heating rate of 15 ° C./sec.
After decarburizing annealing at a temperature of 50 ° C., a part of the steel sheet is annealed, and a part of the steel sheet is annealed in an ammonia-containing atmosphere to reduce nitrogen in the steel sheet to 0.1%.
In this case, an annealing separator containing MgO as a main component was applied, and finish annealing was performed.

The points plotted in the figure indicate that the secondary recrystallization was performed stably.
As in 866 discloses, that the variation coefficient of the grain structure of primary recrystallization occurs a reduction in resulting from the B ₈ that is greater than 0.6 are excluded. As apparent from FIG. 1, the value and the magnetic flux density B ₈ of decarburization annealing after the I {111} / I {411 } is closely related, more high 1.88T with respect to cold rolling reduction rate It can be seen that the threshold for obtaining the magnetic flux density has changed.

[0021] In addition, I more than B ₈ 1.88T can be obtained
The boundary of the {111} / I {411} region is the true distortion ln
{100 / (100−R)} is almost linear, and its region is (10ln {(100−R) / 10
0 + 44) / 7 or less. Although the reason for the above result is not always clear, the present inventors think as follows. In the primary recrystallization texture, the {111} -oriented grains and the {411} -oriented grains that promote the growth of the {110} <001> secondary recrystallized grains increase at a high cold rolling reduction of 80% or more. At the same time, the {110} orientation grains including the [110] <001> orientation grains monotonously decrease.

When a thermally stable (strong) inhibitor such as a nitride such as (Al, Si) N in the present invention is used, the dependence of grain boundary movement on the grain boundary character increases. Therefore, rather than the number of Goss orientation grains, matrix grains having a {9} corresponding orientation relationship with the Goss orientation (specifically, {111} <
112>, {411} <148>) and the crystal orientation dispersion become more important, and promote the growth of [110] <001> orientation grains in the primary recrystallized structure, which becomes secondary recrystallized grains. It is considered that sufficient development of {orientation grains and {411} orientation grains is required, and in particular, development of {411} orientation grains having small crystal orientation dispersion is required.

Based on the above result, I {111} / I
The value of {411} was adjusted by the decarburization annealing heating rate and cold rolling reduction rate, we searched for additional high B ₈ conditions. FIG.
Is on graph plotting the cold rolling reduction ratio and decarburization annealing heating rate on the axis, the magnetic flux density of a good product: is a diagram showing a region B ₈ is obtained. This figure was created from the result of the product of B ₈ that it is possible to have obtained the following operation.

Si: 3.3% by mass%, C: 0.05
%, Acid-soluble Al: 0.027%, N: 0.007%,
Cr: 0.1%, Sn: 0.05%, Mn: 0.1%,
S: A slab containing 0.008% was heated at a temperature of 1150 ° C., and then hot-rolled to 2.0 mm and 2.3 m.
m, each having a thickness of 3.2 mm.
And then cold-rolled to a thickness of 0.22 mm. This cold-rolled sheet was heated to 800 ° C. at a heating rate of 20 to 600 ° C./sec. Fig. 1 shows the primary recrystallization texture after decarburizing annealing at 0.44.
Is adjusted to an area where a high B ₈ is obtained, and then 750
Annealing was performed in an ammonia-containing atmosphere at 30 ° C. for 30 seconds, an annealing separator containing magnesia as a main component was applied, and finish annealing was performed at 1200 ° C. for 20 hours.

FIG. 2 shows that when the decarburizing annealing heating rate is increased, the range of the cold rolling reduction rate at which high B ₈ is obtained is widened toward the high pressure reduction rate, and the high B ₈ region and the low B ₈ region are increased. It can be seen that the boundary for dividing is expressed by a linear relationship between the logarithm of the decarburizing annealing heating rate H and the cold rolling reduction. When the high B ₈ region is 1.92 T or more, the decarburizing annealing heating rate H ° C./sec is set to 10% for the cold rolling reduction R%.
^{[(R-68) / 14]} <H, and in a region where the decarburizing annealing heating rate is limited to 10 ^{[(R-32) / 32]} <H <140, B _{8 is set} to 1. It can be 94 T or more.

Hitherto, rapid heating of decarburizing annealing of grain-oriented electrical steel sheets has been disclosed, for example, in Japanese Patent Application Laid-Open No. 1-290716.
And JP-A-6-212262. However, these disclosed methods are applied to a method for manufacturing a grain-oriented electrical steel sheet by high-temperature slab heating, and the effect is that the secondary recrystallized grain size is reduced and the iron loss characteristics are improved.

The effect of the present invention on the product is different from these results and has a great effect on the improvement of the magnetic flux density (B ₈ ). The present inventors consider the following mechanism for improving the magnetic flux density as follows. The grain growth of the secondary recrystallized grains is determined by the balance between the grain boundary energy density of the matrix grains serving as a driving force and the inhibitor for suppressing grain growth. In general, it has been known that, when the heating rate of the decarburizing annealing is increased, grains near the Goss orientation (nuclei of secondary recrystallized grains) increase in the primary recrystallized structure.
It is considered that the secondary recrystallization structure becomes finer.

However, in the present invention, when a thermally stable (strong) inhibitor such as a nitride such as (Al, Si) N formed by nitriding is used, the grain boundary of the grain boundary shifts. Since the character dependence is increased, the number and distribution of matrix grains having a Σ9 correspondence orientation relationship with the Goss orientation become more important than the number of Goss orientation grains. As a result of examining the primary recrystallized texture from this viewpoint, the heating rate at which the magnetic flux density (B ₈ ) was maximized was 100 ° C./sec, corresponding to the result of FIG.
The Σ9 correspondence azimuth density with respect to the Goss azimuth of the matrix becomes maximum, and the azimuth dispersion is small (the azimuth distribution is sharp).
It was confirmed that it became.

Therefore, the primary recrystallized texture by the heating rate of the decarburization annealing, particularly the adjustment of the orientation grains having a Σ9 correspondence orientation with the Goss orientation, and the synergistic effect of the strong (Al, Si) N inhibitor, are not achieved until the first time. It is presumed that only a sharp Goss direction can be developed, and a product having a high magnetic flux density can be stably manufactured.

[0030]

Next, an embodiment of the present invention will be described. As a component of the steel of the present invention, S
i: 0.8 to 4.8%, C: 0.085% or less, acid-soluble Al: 0.01 to 0.065%, N: 0.012% or less.

When Si is added in a large amount, the electric resistance increases and the iron loss characteristics are improved. However, if it exceeds 4.8%, cracks are likely to occur during rolling. 0.8%
If the amount is smaller than that, γ transformation occurs at the time of finish annealing, and the crystal orientation is impaired. C is an element effective in controlling the primary recrystallization structure, but has an adverse effect on the magnetic properties, and therefore needs to be decarbonized before the finish annealing. C is 0.08
If it is more than 5%, the decarburization annealing time will be long, and the productivity will be impaired.

In the present invention, acid-soluble Al is an essential element for bonding with N and serving as (Al, Si) N as an inhibitor. The limited range is 0.01 to 0.065% at which the secondary recrystallization is stable. N is 0.
If it exceeds 012%, pores in the steel sheet called blisters are generated during cold rolling.

In addition, since S has an adverse effect on the magnetic properties, it is desirable that the content be 0.015% or less. Sn is preferably added in an amount of 0.02 to 0.15% in order to improve the texture after decarburization annealing and stabilize the secondary recrystallization.
Cr is an element that improves the oxide layer in decarburization annealing and is effective for forming a glass film, and is desirably added in an amount of 0.03 to 0.2%. In addition, trace amounts of Cu, Sb, Mo, Bi, Ti
Inclusion in steel does not impair the gist of the present invention.

The silicon steel slab having the above composition is produced by melting a steel in a converter or an electric furnace, etc., subjecting the molten steel to a vacuum degassing treatment as required, and then performing continuous casting or ingot-forming and ingot-rolling. It is obtained by doing. Thereafter, slab heating is performed prior to hot rolling. In the present invention,
The slab heating temperature is set to 1280 ° C. or less to avoid the above-described various problems of high-temperature slab heating.

The hot-rolled sheet obtained by the above-mentioned hot rolling is usually treated at 900 to 1200 ° C. for 3 hours in order to improve the magnetic properties.
A short annealing time of 0 seconds to 30 minutes is applied. Then, the final thickness is obtained by cold rolling once or twice or more with annealing. In the cold rolling, as disclosed in Japanese Patent Publication No. 40-15644, setting the final cold rolling reduction to 80% or more develops primary recrystallization orientations such as {111} and {411}. It is necessary above.

In particular, the point of the present invention, {411}
The final cold rolling reduction is 85 so that the development of
% Is desirable. Further, if the rolling reduction of the cold rolling is greater than 95%, the load in the cold rolling process is increased, and from the viewpoint of actual operation, 95% or less is realistic. The steel sheet after the cold rolling is subjected to decarburizing annealing in a humid atmosphere in order to remove C contained in the steel. At this time, the value of I {111} / I {411} of the primary recrystallization texture after decarburizing annealing was set to (10%) with respect to the cold rolling reduction R%.
It is important to adjust the value to be less than ln {(100-R) / 100} +44) / 7.
₈ can manufacture products of 1.88T or more.

The primary recrystallization structure after the decarburizing annealing can be controlled by adjusting the annealing cycle (heating rate, soaking temperature, soaking time, etc.) in the decarburizing annealing step. In particular, the value of I {111} / I {411} is (10
In order to adjust ln {(100-R) / 100} +44) / 7 or less, the decarburizing annealing heating rate H ° C /
By heating at a heating rate of 10 ^{[(R-68) / 14]} <H, a higher B ₈ can be obtained.

The temperature range in which heating is required at this heating rate is a temperature range of at least 600 ° C. to 750 to 900 ° C. FIGS. 3 and 4 show the experimental results that led to the above conclusions. The cold rolled sheet was heated from room temperature to a predetermined temperature in a temperature range of 600 ° C. to 1000 ° C. at a heating rate of 40 ° C./sec, and then cooled to room temperature with nitrogen gas. afterwards,
Heating was performed to 850 ° C. at a heating rate of 20 ° C./sec, and annealing was performed for 120 seconds at an atmosphere gas oxidation degree of 0.33. Then, after the amount of nitrogen was reduced to 0.021% by nitriding treatment, an annealing separator containing MgO as a main component was applied and finish annealing was performed.

As shown in FIG. 3, it can be seen that the magnetic flux density is improved when the temperature reached at a heating rate of 40 ° C./sec is 750 ° C. or more and 900 ° C. or less. The reason why the effect is not exhibited below 750 ° C. is that the primary recrystallization does not sufficiently proceed below 750 ° C. In order to change the primary recrystallization texture, recrystallization needs to proceed sufficiently. When heated to a temperature higher than 900 ° C., the magnetic flux density decreases. This is because a transformed structure occurs in a part of the sample,
This is considered to be because the structure at the time of completion of the subsequent decarburization annealing becomes a mixed grain structure.

Next, the cold-rolled sheet is heated at a heating rate of 20 ° C./second to a predetermined temperature in a temperature range of 300 ° C. to 750 ° C., and then heated to 850 ° C. at a heating rate of 40 ° C./second. And cooled to room temperature with nitrogen gas. Then 2
The sample was heated to 850 ° C. at a heating rate of 0 ° C./second, and annealed at an oxidation degree of the atmosphere gas of 0.33 for 120 seconds. Then, after the amount of nitrogen was reduced to 0.021% by nitriding treatment, an annealing separator containing MgO as a main component was applied and finish annealing was performed.

As shown in FIG. 4, when the heating start temperature at a heating rate of 40 ° C./sec is higher than 600 ° C., there is no effect of improving the magnetic flux density. From these results, a heating rate of 40 ° C. /
The temperature range that needs to be heated in seconds or more is at least 6
It can be seen that the temperature range is from 00 ° C to 750 ° C to 900 ° C. Therefore, in the temperature raising process of the decarburizing annealing process, it is necessary to heat the steel sheet at a temperature of 40 ° C./sec or more from a temperature range of 600 ° C. or less. Regarding the heating in the temperature raising process of the decarburizing annealing step as described above, even if the heating annealing is performed between the cold rolling step and the decarburizing annealing step, the purpose of the present invention is not spoiled.

Further, in order to stably exert the effect of the adjustment of the heating rate, as shown in Example 4 described later, after heating, in a temperature range of 770 to 900 ° C.
The oxidation degree of the atmosphere gas (P _H2O / P _H2 ) exceeds 0.15.
It is effective to set the oxygen content of the steel sheet to 2.3 g / m ² or less by setting it to 1 or less. If the degree of oxidation of the atmosphere gas is less than 0.15, the adhesion of the glass film formed on the surface of the steel sheet deteriorates, and if it exceeds 1.1, defects occur in the glass film. In particular, when the heating rate in the temperature raising step is increased to 40 ° C./s or more, oxidation at the time of soaking is promoted. Therefore, in order to control the oxygen amount within a certain range, the atmosphere oxidation degree is reduced. It is necessary to lower it or shorten the soaking time.

The method of rapid heating is not particularly limited. For a heating rate of about 40 to 100 ° C./sec, a conventional radiant tube using ordinary radiant heat or a decarburizing annealing facility using a heating element was modified. Equipment, 100 ℃ /
For a heating speed of seconds or more, a method using a new high-energy heat source such as a laser or plasma, induction heating, an electric heating device, or the like can be applied.

Also, a method of using a new high-energy heat source such as a laser or a plasma in a conventional decarburizing annealing facility using a radiant tube or a heating element using radiant heat,
It is also effective to combine a method using an induction heating, an electric heating device or the like. Regarding the soaking temperature, for example,
The setting is made in consideration of the adjustment of the primary recrystallized grain structure as disclosed in JP-A-2-182866. Usually 77
It is performed in the range of 0 to 900 ° C. It is also effective to increase the temperature of the subsequent stage of the soaking for the purpose of grain adjustment after the decarburization in the preceding stage of the soaking, or to extend the soaking time by lowering the degree of oxidation of the atmosphere gas in the subsequent stage.

As the nitriding treatment, a method of annealing in an atmosphere containing a gas having a nitriding ability such as ammonia, MnN
Or the like, which is added during the final annealing by adding a powder having a nitriding ability to the annealing separator. In order to stably perform the secondary recrystallization when the heating rate of the decarburization annealing is increased, (A
l, Si) It is necessary to adjust the composition ratio of N, and the nitrogen amount after the nitriding treatment is N / Al with respect to the Al amount in the steel.
(Mass ratio) must be 0.67 or more.

Thereafter, after applying an annealing separating agent mainly composed of magnesia, finish annealing is performed, and {110} <
001> Orientation grains are preferentially grown by secondary recrystallization.

[0047]

EXAMPLES Example 1 Si: 3.2%, C: 0.05%, acid-soluble A by mass%
l: 0.026%, N: 0.008%, Mn: 0.1
%, S: The slab containing 0.007% was heated at a temperature of 1150 ° C., and then hot-rolled to a thickness of 2.3 mm. Then, after annealing at 1120 ° C., cold-rolling to a thickness of 0.27 mm, then decarburizing annealing at a heating rate of 5 to 40 ° C./sec. Nitrogen in the steel plate by 0.02 to 0.03
%. Next, an annealing separator containing MgO as a main component was applied and finish annealing was performed.

Table 1 shows the characteristic values of the products. Regarding the primary recrystallized texture, the value of I {111} / I {411} is (10 ln} (100−R) / 10 with respect to the cold rolling reduction R%.
0｝ +44) / 7, B ₈ is 1.8
It can be seen that a high magnetic flux density of 8 T or more is obtained.

[0049]

[Table 1]

Example 2 Si: 3.3% by mass, C: 0.05%, acid-soluble A by mass%
l: 0.027%, N: 0.007%, Cr: 0.1
%, Sn: 0.05%, Mn: 0.1%, S: 0.00
After heating the slab containing 8% at a temperature of 1150 ° C,
By hot rolling to a thickness of 2.0 mm, 2.8 mm, the hot rolled sheet was annealed at 1120 ° C.
It was cold rolled to a thickness of mm.

After the cold rolled sheet was heated to 800 ° C. at a heating rate of 5 to 600 ° C./sec, it was decarburized and annealed at 800 to 890 ° C. for 120 seconds at an atmospheric oxidation degree of 0.44. At this time, the oxygen content of the steel sheet was 1.9 to 2.1 g / m ² . Thereafter, the steel sheet was annealed at 750 ° C. for 30 seconds in an ammonia-containing atmosphere, and the amount of nitrogen in the steel sheet was adjusted to 0.023 to 0.029% by changing the ammonia content. Thereafter, an annealing separator containing magnesia as a main component was applied, and finish annealing was performed at 1200 ° C. for 20 hours.

These samples were subjected to a tension coating treatment. Table 2 shows the properties of the obtained product. From Table 2, the value of the primary recrystallized texture: I {111} / I {411} is (10In {(100−R) /
100｝ +44) / 7 or less (△ mark),
B ₈ is 1.88 T or more, and the heating rate H ° C./sec is 10 ^{[(R-68) / 14]} <H or more with respect to the cold rolling reduction R% ^(Ｒ mark), more preferably. Is 10 ^{[(R-32) / 32]} <
In the case of H <140 (marked with ◎), it can be seen that the magnetic flux density (B ₈ ) increases.

[0053]

[Table 2]

Example 3 Si: 3.1%, Mn: 0.1%, C: 0.1% by mass.
05%, S: 0.008%, acid-soluble Al: 0.029
%, N: 0.008%, Sn: 0.1%
A 3 mm hot rolled silicon steel sheet was cold rolled to a final thickness of 0.25 mm. This cold-rolled sheet was heated in a mixed gas of nitrogen and hydrogen having a degree of oxidation of 0.33 at a heating rate of (1) 20 ° C./sec.
It was heated to 840 ° C. at 0 ° C./sec, and annealed at 840 ° C. for 150 seconds for primary recrystallization. Thereafter, the steel sheet is annealed at 750 ° C. for 30 seconds in an ammonia-containing atmosphere, and the nitrogen content in the steel sheet is changed from 0.022 to 0.02 by changing the ammonia content.
6%.

An annealing separator containing magnesia as a main component was applied to these steel sheets and finish annealing was performed. Finish annealing is performed at a heating rate of 15 ° C./hr in an atmosphere gas of N ₂ : 25% + H ₂ : 75% up to 1200 ° C.
At 0 ° C., the atmosphere was switched to H ₂ : 100% and annealed for 20 hours. These samples were subjected to a tension coating treatment. Table 3 shows the magnetic properties of the obtained products. Compared with Examples 1 and 2, although annealing before cold rolling was not performed, the overall magnetic flux density was low, but it could be confirmed that the effect of improving the magnetic flux density of the present invention was obtained.

[0056]

[Table 3]

Example 4 In terms of mass%, Si: 3.1%, C: 0.05%, acid-soluble Al: 0.027%, N: 0.008%, Mn: 0.1
%, S: 110% silicon steel slab containing 0.007%
Heated to 0 ° C. to a thickness of 2.0 mm. This hot-rolled sheet is annealed at 1100 ° C., cold-rolled, and has a final sheet thickness of 0.2 mm.
And Then, after heating to 850 ° C. at a heating rate of 100 ° C./sec, it was cooled to room temperature.

Thereafter, heating was performed at a heating rate of 30 ° C./sec.
At 30 ° C., an atmosphere gas having an oxidation degree of 0.12 to 0.72
Anneal for 0 seconds and then 750 in an ammonia-containing atmosphere.
C. for 30 seconds to reduce the amount of nitrogen in the steel sheet to 0.02 to 0.0
3%. Next, an annealing separator containing MgO as a main component was applied, and finish annealing was performed at 1200 ° C. for 20 hours.

Table 4 shows the characteristics of the product. According to Table 4, when the degree of oxidation in the atmosphere defined by the present invention is out of the range of more than 0.15 to 1.1 or less and the amount of oxygen after decarburizing annealing is 2.3 g / m ² or less, the product is obtained. It can be seen that the glass coating characteristics of the sample were deteriorated.

[0060]

[Table 4]

Example 5 Si: 3.2% by mass, C: 0.05%, acid-soluble A
l: 0.024%, N: 0.007%, Cr: 0.1
%, Sn: 0.05%, Mn: 0.1%, S: 0.00
A silicon steel slab containing 8% was heated at 1150 ° C. and hot-rolled to a thickness of 2.3 mm. This hot rolled plate is
And then cold rolled to a thickness of 0.22 mm.
After heating this cold rolled sheet to 800 ° C. at 100 ° C./sec,
Decarburizing annealing at 20 ° C. for 90 to 600 seconds at an atmospheric oxidation degree of 0.52 to reduce the value of I {111} / I {411} to 2.7 or less, and define the primary recrystallization texture in claim 1. Adjusted so that the inequality holds.

Thereafter, the steel sheet was annealed at 750 ° C. for 30 seconds in an ammonia-containing atmosphere to reduce the amount of nitrogen in the steel sheet to 0.023 to
0.029%. An annealing separator containing MgO as a main component was applied, and finish annealing was performed at 1200 ° C. for 20 hours.
Table 5 shows the characteristic values of the products. The oxygen content of the steel plate is 2.41 g
/ M ² , it can be seen that the magnetic properties have deteriorated.

[0063]

[Table 5]

Example 6 Si: 3.2% by mass, C: 0.05%, acid-soluble A
l: 0.024%, N: 0.007%, Cr: 0.1
%, Sn: 0.05%, Mn: 0.1%, S: 0.00
A silicon steel slab containing 8% was heated at 1150 ° C. and hot-rolled to a thickness of 2.3 mm. This hot rolled plate is
And then cold rolled to a thickness of 0.22 mm.
After heating this cold rolled sheet to 800 ° C. at 100 ° C./sec,
Decarburization annealing was performed at 20 ° C. for 110 seconds at an atmospheric oxidation degree of 0.44. Texture: The value of I {111} / I {411} was 1.7, and the oxygen content of the steel sheet was 1.9 g / m ² .

Then, the steel sheet was annealed at 750 ° C. for 30 seconds in an ammonia-containing atmosphere, and the amount of nitrogen in the steel sheet was adjusted to 0.012 to 0.026% by changing the ammonia content. Thereafter, an annealing separator containing magnesia as a main component was applied, and finish annealing was performed at 1200 ° C. for 20 hours. Table 6 shows the characteristic values of the products. Nitrogen content after nitriding is 0.01
It can be seen that the magnetic flux density becomes higher at 7% or more ([N] / [Al] ≧ 0.67).

[0066]

[Table 6]

[0067]

According to the present invention, based on a method for producing a grain-oriented electrical steel sheet by low-temperature slab heating which does not cause any problems caused by conventional high-temperature slab heating, decarburization annealing for primary recrystallization structure and cold rolling conditions is performed. By defining the conditions, the surface oxide layer, and the amount of nitriding, a grain-oriented electrical steel sheet having a high magnetic flux density and excellent magnetic properties can be industrially manufactured stably.

[Brief description of the drawings]

FIG. 1 is a diagram showing the influence of the cold rolling reduction and the primary recrystallization texture: I {111} / I {411} on the magnetic flux density (B ₈ ) of a product.

FIG. 2 is a graph showing the influence of the cold rolling reduction and the heating rate of decarburization annealing on the magnetic flux density.

FIG. 3 is a diagram showing the effect of the rapid heating completion temperature of decarburization annealing on magnetic flux density.

FIG. 4 is a diagram showing the effect of the rapid heating start temperature of decarburization annealing on the magnetic flux density.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Norihiro Yamamoto 1-1-Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka F-term in Nippon Steel Corporation Yawata Works (reference) 4K033 AA02 BA01 CA02 CA07 DA02 FA13 FA14 HA06 JA04 JA05 LA01 MA00 5E041 AA02 AA19 HB11 NN06 NN18

Claims (8)

[Claims] 1. A mass% of Si: 0.8 to 4.8%,
C: 0.085% or less, acid-soluble Al: 0.01-0.
065%, N: 0.012% or less, the balance consisting of Fe and unavoidable impurities is heated at a temperature of 1280 ° C. or less, then hot-rolled, then cold-rolled to a final thickness, In the method for producing a grain-oriented electrical steel sheet in which an annealing separator containing magnesia as a main component is applied after charcoal annealing and subjected to finish annealing, when the cold rolling reduction is set to R%, the texture after decarburizing annealing is reduced. I {111} / I {411}
Of (10ln {(100-R) / 100} +4
4) A method for producing a grain-oriented electrical steel sheet, which is adjusted to / 7 or less, and thereafter, a nitriding treatment is performed. 2. In the decarburizing annealing step, the temperature is raised during the decarburizing annealing step.
The heating rate H ° C./sec from the region where the steel plate temperature is 600 ° C. or lower to a predetermined temperature within the range of 750 to 900 ° C. is 10
^{2. The} method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to claim 1, wherein ^{[(R-68) / 14]} <H. 3. The heating rate H ° C./sec in the temperature raising step of the decarburizing annealing step is set to 10 ^{[(R−32) / 32]} <H <140. For manufacturing grain-oriented electrical steel sheets with high magnetic flux density. 4. The hot rolled sheet obtained by the hot rolling is 900 to 1
The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to any one of claims 1 to 3, wherein annealing is performed in a temperature range of 200 ° C for 30 seconds to 30 minutes. 5. In the decarburizing annealing step, 770 ° C.
At a temperature range of 900 ° C, the degree of oxidation of the atmospheric gas (P _H2O /
The steel sheet is annealed for a period of time such that the oxygen content of the steel sheet is 2.3 g / m ² or less within a range of P _H2 ): more than 0.15 and 1.1 or less. 2. The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to claim 1. 6. A nitriding treatment is carried out so that the amount of nitrogen: [N] becomes an amount satisfying [N] / [Al] ≧ 0.67 according to the amount of acid-soluble Al in the steel sheet: [Al]. The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to any one of claims 1 to 5, characterized in that: 7. The high magnetic flux density according to claim 1, wherein 0.02 to 0.15% of Sn is further added to the steel by mass%. Manufacturing method of grain-oriented electrical steel sheet. 8. The steel according to claim 1, wherein Cr is added in an amount of 0.03 to 0.2% by mass%.
8. The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to any one of items 7 to 7.