JP2003003215A - Method for producing grain-oriented silicon steel sheet having high magnetic flux density - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon steel sheet having high magnetic flux density by controlling a primary recrystallization texture and an inhibitor, in a production of a grain-oriented magnetic steel sheet with a low temperature slab heating process. SOLUTION: Ratio of I[111]/I[411] in the texture after decarburize-annealing is adjusted to 3.0 by regulating heating speed HR deg.C/sec from a zone having <=600 deg.C steel sheet temperature raising process of the decarburize-annealing operation to a prescribed temperature in the range of 750-900 deg.C to HR>=-650 [Al]+200.

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 a so-called grain-oriented electrical steel sheet in which crystal grains are integrated in {110} <001> orientation by Miller index. This steel sheet is used as a soft magnetic material as an iron core of electric equipment such as a transformer.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are {110} <001.
A steel plate containing 4.8% or less of Si composed of crystal grains accumulated in the> direction (so-called Goth direction). This steel plate is required to have magnetic properties such as excitation property and iron loss obtainability. Magnetic field strength of 800 A /
Magnetic flux density at m: B8 is commonly used. Further, as an index showing the iron loss characteristic, the iron loss per 1 kg of steel plate when magnetized to 1.7 T at a frequency of 50 Hz: W17 / 50 is used. The magnetic flux density: B8 is the most dominant factor of the iron loss characteristics, and the higher the magnetic flux density: B8 value, the better the iron loss characteristics. To increase the magnetic flux density: B8, it is important to align the crystal orientations at a high level. This control of the crystal orientation is achieved by utilizing a catastrophic grain growth phenomenon called secondary recrystallization.

In order to control this secondary recrystallization, it is necessary to adjust the primary recrystallization structure before the secondary recrystallization and to adjust the fine precipitates called inhibitors. This inhibitor has a function of suppressing the growth of general grains in the primary recrystallization structure and preferentially growing only specific {110} <001> oriented grains. Typical examples of the precipitate include M.I. F. Littmann (Japanese Patent Publication Sho 30-3
651) and J. E. May & D. Turnbu
ll (Trans.Met. Soc. AIM212
(1958) p769) and others present MnS, Taguchi et al. (Japanese Patent Publication No. 40-15644) AlN, and Imanaka et al. (Japanese Patent Publication No. 51-13469) MnSe.

A method is adopted in which these precipitates are completely solid-solved during heating of the slab before hot rolling and then finely precipitated in the hot rolling and subsequent annealing steps. In order to completely dissolve these precipitates, 1350 ° C to 1400 ° C
It is necessary to heat at a high temperature of ℃ or more, which is about 200 ℃ higher than the slab heating temperature of ordinary steel and has the following problems. (1) A dedicated heating furnace is required. (2) Energy intensity of heating furnace is high. (3) The amount of melt scale is large, and operation management such as so-called sticking out is necessary.

Therefore, research and development by low-temperature slab heating has been advanced, and as a manufacturing method by low-temperature slab heating, Komatsu et al. (Japanese Patent Publication No. 62-45285) uses a method of using (Al, Si) N formed by nitriding treatment as an inhibitor. Disclosure. As a method of this nitriding treatment, Kobayashi et al. Disclosed a method of nitriding in strip form after decarburization annealing (Japanese Patent Laid-Open No. 2-77525), and Ushigami et al. Reported the behavior of the nitride (Materials Science). Foru
m, 204-206 (1996), pp593-598).

In the method for producing a grain-oriented electrical steel sheet by low-temperature slab heating, an inhibitor is not formed during decarburization annealing, so that the primary recrystallization structure in decarburization annealing controls the secondary recrystallization. It becomes important. In the conventional research on the production method of the grain-oriented electrical steel sheet by the high temperature slab heating, there is almost no knowledge about the adjustment of the primary recrystallization structure before the secondary recrystallization.
The importance thereof is disclosed in Japanese Patent No. 32929, Japanese Patent Laid-Open No. 9-256051 and the like.

Japanese Patent Publication No. 8-32929 discloses that the secondary recrystallization becomes unstable when the variation coefficient of the grain size distribution of the primary recrystallized grain structure becomes larger than 0.6 and the grain structure becomes nonuniform. is doing. After that, further Japanese Patent Laid-Open No. 9-25
In the 6051 publication, as a result of research on a primary recrystallized structure and an inhibitor that are the control factors of secondary recrystallization, as a result, the growth of Goss-oriented grains in the texture after decarburization annealing was observed as the grain structure of the primary recrystallized grain structure. Ratio of grains in {111} and {411} orientations that are considered to promote; I
It was shown that the magnetic flux density of the product is improved by adjusting {111} / I {411} to 3 or less. Where I
{111} and I {411} are the proportions of grains whose {111} and {411} planes are parallel to the steel plate surface, respectively.
It shows the diffraction intensity value measured in the plate thickness 1/10 layer by X-ray diffraction measurement.

The primary recrystallized structure after decarburization annealing is of course affected by the annealing cycle of decarburization annealing such as heating rate, soaking temperature, soaking time in the decarburization annealing step, The presence or absence of hot-rolled sheet annealing, cold rolling reduction (cold rolling reduction), and other manufacturing processes before decarburization annealing also have an effect. The preferential growth of grains having the [110] <001> orientation is enhanced during secondary recrystallization through the influence of the primary recrystallization texture controlled by these process control factors. The so-called precipitate also has an effect.

[0009]

DISCLOSURE OF THE INVENTION The present invention provides a grain-oriented electrical steel sheet having excellent magnetic properties, which is industrially stable and has a high magnetic flux density, by appropriately controlling the decarburization annealing conditions according to the inhibitor conditions. It discloses a method of manufacturing. Further, the present invention is a method for producing a thin grain-oriented electrical steel sheet by low-temperature slab heating.
It is intended to provide a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties with high magnetic flux density even by cold rolling only once by appropriately controlling the amount and decarburization annealing conditions.

[0010]

The gist of the present invention is as follows. (1) By mass, Si: 0.8 to 4.8%, C: 0.08
5% or less, acid-soluble Al: 0.01 to 0.065%,
N: 0.012% or less, the steel consisting of the balance Fe and unavoidable impurities is heated at a temperature of 1280 ° C. or less, and then hot-rolled, and then once or twice or more cold-rolled with intermediate annealing. The final plate thickness, after decarburization annealing, applied with an annealing separator containing magnesia as a main component, and subjected to finish annealing in the manufacturing method of grain-oriented electrical steel sheet, the amount of acid-soluble Al: [Al]% , 750 to 900 from the region where the steel plate temperature is 600 ° C. or less in the temperature rising process of the decarburization annealing process
Heating rate up to a predetermined temperature in the range of ℃: HR ℃
By adjusting ≧ −6250 [Al] +200, the ratio of I [111] / I [411] in the texture after decarburization annealing is adjusted to 3 or less,
A method for manufacturing a grain-oriented electrical steel sheet having a high magnetic flux density, characterized by performing nitriding treatment thereafter. (2) The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to (1), characterized in that a reduction rate is more than 90% in the cold rolling.

(3) The grain-oriented electrical steel sheet having a high magnetic flux density according to (1) or (2), characterized in that the hot rolled sheet is annealed in a temperature range of 900 to 1200 ° C. for 30 seconds to 30 minutes. Manufacturing method. (4) In the decarburization annealing step, the degree of oxidation of the atmospheric gas (PH ₂ O / PH ₂ ) in the temperature range of 770 ° C. to 900 ° C .: 0.
Within the range of more than 15 and 1.1 or less, the oxygen content of the steel sheet is 2.3 g /
The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to any one of (1) to (3), characterized in that the annealing is carried out for a time period of m ² or less.

(5) Amount of acid-soluble Al in the steel sheet: [A
Amount of nitrogen: [N] is [N] / [Al] ≧ 0.
The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to any one of (1) to (4), which is characterized by performing a nitriding treatment so that the amount satisfies 67. (6) Mass%, and Sn: 0.02 to 0.15%
The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to any one of (1) to (5), characterized in that:

(7)% by mass, Cr: 0.03
~ 0.2% is added, The manufacturing method of the grain-oriented electrical steel sheet with high magnetic flux density as described in any one of (1) to (6).

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have found that the value of B8 can be 1.88 T or more by controlling the I {111} / I {411} of the primary recrystallization structure to be 3 or less. As disclosed in Kaihei 9-256051,
By controlling the inhibitor, which is a major factor other than the primary recrystallized structure that affects the magnetic flux density of the product, we believe that the effect of primary recrystallized texture control can be exerted more remarkably. The relationship between the inhibitor of magnetic flux density B8 and the primary recrystallization texture control factor was investigated. Here, in particular, the correlation between the heating rate during decarburization annealing, which affects the primary recrystallization texture, and acid-soluble Al, which is related to inhibitor strength, was investigated in detail. As a result, it was found that the range of heating rate required to obtain high B8 was increased according to the amount of acid-soluble Al.

Hereinafter, description will be given based on the experimental results. Figure 1
Magnetic flux density B8 of steel sheet against sol-Al content and decarburization annealing heating rate
It is a figure showing distribution of. The sample used here is% by mass
Then, Si: 3.3%, C: 0.06%, acid-soluble Al:
0.020-0.038%, N: 0.008%, Mn:
Slab containing 0.1%, S: 0.007% 115
After heating at a temperature of 0 ° C., hot rolling to a thickness of 2.0 mm,
Then, after annealing at 1120 ° C., cold rolling to a thickness of 0.22 mm, heating at a heating rate of 15 to 100 ° C./sec, and 7
After decarburizing and annealing at a temperature of 70 to 950 ° C., part of it is annealed as it is, and part of it is annealed in an atmosphere containing ammonia to make nitrogen in the steel sheet 0.02 to 0.03%, and then MgO as a main component. After the annealing separating agent is applied, finish annealing is performed. As a result of analyzing the primary recrystallization textures of the decarburized and annealed sheets of these samples, I {11
It has been confirmed that the value of 1} / I {411} is 3 or less. Further, the same result as in FIG. 1 was obtained in the same experiment as in the cold rolling to a thickness of 0.18 mm.

As is clear from FIG. 1, the decarburization annealing heating rate threshold value at which a high magnetic flux density of 1.92 T or more can be obtained decreases as the amount of acid-soluble Al: [Al]% increases. Recognize. That is, the heating rate during decarburization annealing is the same,
Even if the primary recrystallization texture is adjusted in the same manner, the effect of increasing the magnetic flux density by controlling the primary recrystallization texture can be obtained by increasing the [Al] to strengthen the inhibitor. It means that you can.

Hitherto, decarburization annealing of grain-oriented electrical steel sheets by rapid heating is disclosed in, for example, Japanese Patent Laid-Open Nos. 1-290716 and 6-212262. However, these patents are applied to a method for producing 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.

Unlike the above results, the effect of the present invention on the product has a great influence on the improvement of the magnetic flux density (B8). Further, the effect of texture control is to lower the lower limit of the heating rate during decarburization annealing, which is necessary for obtaining a high magnetic flux density by controlling the inhibitor with the amount of acid-soluble Al or the amount of nitriding. The present inventors consider the reason for the above results as follows. When a thermally stable (strong) inhibitor such as a nitride such as (Al, Si) N in the present invention is used, the grain boundary character dependence of the grain boundary migration increases, Matrix grains that have a Σ9-corresponding orientation relationship with the Goth orientation rather than the number of Goth orientation grains (specifically, {111} <112>, {411}
It is said that the number of <148>) and the crystal orientation dispersion are more important, but by increasing the number of thermally stable (strong) inhibitors, high B8 can be easily obtained even with the similar crystal orientation dispersion. That is. In addition, increasing [Al] has an effect on the primary recrystallization texture in addition to the effect on the inhibitor, and this is also considered to have contributed synergistically to increasing the magnetic flux density. Specifically, when [Al] is increased as shown in Example 1, I {111}
The value of / I {411} is decreased, which means that {111} oriented grains and {411} oriented grains that promote the growth of [110] <001> oriented grains in the primary recrystallized structure that becomes the secondary recrystallized grains. } Of the oriented grains, it means that the development of {411} oriented grains having a small crystal orientation dispersion was promoted. As a result,
The orientation dispersion of the secondary recrystallized grains (goss grains) is also small, and high B8 can be obtained.

The components of the steel used in the present invention are Si:
0.8-4.8%, C: 0.085% or less, acid-soluble A
1: 0.01 to 0.065% and N: 0.012% or less are required. When Si is added in a large amount, the electric resistance becomes high and the iron loss characteristic is improved. However, 4.8%
If it exceeds the range, it tends to crack during rolling. Also,
If it is less than 0.8%, γ-transformation occurs during finish annealing and the crystal orientation is impaired.

C is an element effective in controlling the primary recrystallized structure, but it has an adverse effect on the magnetic properties, so it must be decarburized before finish annealing. When C is more than 0.085%, decarburization annealing time becomes long and productivity is impaired. The acid-soluble Al is an essential element in order to combine with N in the present invention to function as (Al, Si) N as an inhibitor. The limited range is 0.01 to 0.065% at which the secondary recrystallization is stable.

When N exceeds 0.012%, voids in the steel sheet called blister are generated during cold rolling. In addition, since S adversely affects the magnetic properties, S is preferably set to 0.015% or less. Sn improves the texture after decarburization annealing and stabilizes the secondary recrystallization, so 0.02 to 0.15%
It is desirable to add. Cr is an element that improves the oxide layer of decarburization annealing and is effective in forming a glass film.
It is desirable to add 0.2%. Other traces of C
The inclusion of u, Sb, Mo, Bi, Ti, etc. in the steel does not impair the gist of the present invention.

A silicon steel slab having the above composition is a converter,
Alternatively, it can be obtained by smelting steel in an electric furnace or the like, subjecting the molten steel to vacuum degassing treatment if necessary, and then continuously casting or ingoting and then slabbing. After that, slab heating is performed prior to hot rolling. In the present invention, the slab heating temperature is set to 1280 ° C. or lower to avoid the above-mentioned problems of high temperature slab heating.

The hot rolled sheet is usually annealed at 900 to 1200 ° C. for 30 seconds to 30 minutes for a short time in order to improve the magnetic properties. Then, the final plate thickness is obtained by cold rolling once or twice or more with annealing. For cold rolling, as disclosed in Japanese Patent Publication No. 40-15644, the final cold rolling reduction should be 80% or more {11.
It is necessary for developing primary recrystallization orientations such as 1} and {411}. In particular, it is desirable to set the final cold rolling reduction to 85% or more so that the development of the {411} orientation becomes remarkable. Furthermore, if the cold rolling reduction ratio becomes larger than 95%, the load in the cold rolling process becomes large, and it is practically 95% or less from the viewpoint of actual operation. Further, the point of the present invention is to control the decarburization annealing heating rate according to the strength of the inhibitor to control the primary recrystallization texture in order to obtain high B8. It has become possible to realize extremely good secondary recrystallization even under the condition of a high cold rolling reduction rate that causes deterioration of B8 in the cold rolling once method. Specifically, for example, in the paper by Nakajima et al. (Iron and Steel 77 (1991) p.1710), B8 is improved with an increase in cold rolling reduction ratio.
It has been reported that the reduction rate reaches a maximum at 88%, and when it reaches about 90%, the B8 rapidly deteriorates. However, in the present invention, a high B8 can be realized even at a reduction rate of more than 90%. This makes it possible to manufacture by the cold-rolling once method in the manufacture of the thin high B8 material of 0.20 mm or less, which can be conventionally manufactured only by the cold-rolling method twice. Fourth
The experimental results that led to this are shown in the figure. In the experiment, a cold-rolled sheet having a sheet thickness of 0.20 mm cold-rolled from a hot-rolled sheet having a sheet thickness of 1.6 to 2.8 mm containing [Al] of 0.030% and a heating rate of 60 ° C./sec. 800 ~ 8 after heating to ℃
Oxidation degree of atmospheric gas is 0.5 at a predetermined temperature of 50 ° C.
It was annealed at 5 for 120 seconds. After that, a nitrogen content was adjusted to 0.020 to 0.030% by nitriding treatment, and then an annealing separator having magnesia as a main component was applied to finish annealing. As is clear from FIG. 4, B8 is particularly high at a reduction rate of more than 90%.
Can be obtained.

The steel sheet after cold rolling is subjected to decarburization annealing in a wet atmosphere in order to remove C contained in the steel. At that time, by controlling the decarburization annealing heating rate and the decarburization annealing soaking temperature, I [111] / I [411] of the primary recrystallization texture after decarburization annealing
It is possible to adjust the value of to 3 or less to set the magnetic characteristic B8 to 1.88T.
First of all, it is necessary to obtain the above products. Further, the heating rate in the annealing cycle of the decarburizing annealing step, which is the point of the present invention, is set so that the heating rate: HR ° C./sec satisfies HR ≧ −6250 [Al] +200 with respect to the amount of acid-soluble Al: [Al]%. A product with B8 of 1.92T or more can be obtained by adjusting (that is, the lower limit of HR when increasing [Al] is HR.
≧ −6250 [Al] +200 and the heating rate necessary for the value of I [111] / I [411] to be 3 or less). Also, the temperature range that needs to be heated at this heating rate is at least 6
The temperature range is from 00 ° C to 750 to 900 ° C.

2 and 3 show the experimental results that led to the above conclusion. A cold-rolled sheet having [Al] of 0.026% was heated at a heating rate of 40 ° C./second from room temperature to a predetermined temperature in a temperature range of 600 ° C. to 1000 ° C., and then cooled to room temperature with nitrogen gas. Then, it was heated to 850 ° C. at a heating rate of 20 ° C./second, and annealed for 120 seconds at an oxidation degree of atmospheric gas of 0.33.
After that, the amount of nitrogen was adjusted to 0.021% by nitriding treatment, and then an annealing separator containing MgO as a main component was applied to finish annealing. As shown in FIG. 2, it is understood that the magnetic flux density is improved in the range where the reached temperature at the heating rate of 40 ° C./sec is 750 ° C. or higher and 900 ° C. or lower. The reason why the effect is not exhibited below 750 ° C is that the primary recrystallization is not sufficiently advanced below 750 ° C, and the recrystallization needs to be sufficiently advanced in order to change the primary recrystallization texture. .
It is also considered that when heated to a temperature higher than 900 ° C., a transformation structure is generated in a part of the sample, and the structure at the time of subsequent completion of decarburization annealing becomes a mixed grain structure.

Next, the cold-rolled sheet is heated at a heating rate of 20 ° C./sec to a predetermined temperature in the temperature range of 300 ° C. to 750 ° C., and from that temperature to 850 ° C. at a heating rate of 40 ° C./sec, It was cooled to room temperature with nitrogen gas. Then 20 ℃
It was heated to 850 ° C. at a heating rate of / sec and annealed for 120 seconds at an oxidation degree of atmospheric gas of 0.33. After that, the amount of nitrogen was adjusted to 0.021% by nitriding treatment, and then an annealing separator containing MgO as a main component was applied to finish annealing. As shown in FIG. 3, the heating start temperature at a heating rate of 40 ° C./sec is 600 ° C.
It can be seen that there is no effect of improving the magnetic flux density in the super range.

From these results, it is understood that the temperature range in which it is necessary to heat at a heating rate of 40 ° C./sec or more is at least 600 ° C. to 750 to 900 ° C.
Therefore, in the temperature rising process of the decarburization annealing process, the steel plate temperature is 6
It is necessary to heat from a temperature range of 00 ° C or lower at 40 ° C / sec or higher. Further, the heating in the temperature rising process of the decarburization annealing process as described above does not impair the gist of the present invention even if the heat annealing is performed between the cold rolling process and the decarburization annealing process.

Further, in order to stably exert the above effect of adjusting the heating rate, as shown in Example 4 to be described later, after the heating, the degree of oxidation of the atmospheric gas is maintained in the temperature range of 770 to 900 ° C. It is effective to set (PH ₂ O / PH ₂ ) to more than 0.15 and 1.1 or less so that the oxygen content of the steel sheet is 2.3 g / m ² or less. If the degree of oxidation of the atmospheric gas is less than 0.15, the adhesion of the glass film formed on the surface of the steel sheet deteriorates, and 1.1
Above the range, defects occur in the glass film. In particular, if the heating rate in the temperature raising stage is increased to 40 ° C / s or higher, the oxidation during soaking is promoted, so in order to control the oxygen content within a certain range, lower the atmospheric oxidation degree. Or the soaking time needs to be shortened.

The heating method is not particularly limited,
For a heating rate of about 40 to 100 ° C / sec, a conventional radiant tube utilizing normal radiant heat or a remodeled decarburization annealing facility with a heating element, or a heating rate of 100 ° C / sec or more is used. It is possible to apply a method using a high energy heat source such as a new laser or plasma, an induction heating apparatus, an electric heating apparatus, or the like. In addition, combining methods such as the use of high energy heat sources such as new laser and plasma in decarburization annealing equipment using conventional radiant tubes and heating elements that use conventional radiant heat, methods of applying induction heating, electric heating equipment, etc. Is also effective.

Regarding the soaking temperature, for example, Japanese Patent Laid-Open No. 2-1
It is set in consideration of the adjustment of the primary recrystallized grain structure as shown in Japanese Patent No. 82866. Usually, it is performed in the range of 770 to 900 ° C. It is also effective to elevate the temperature in the latter stage of soaking for grain adjustment after decarburization in the former stage of soaking, or lower the oxidation degree of the atmosphere gas in the latter stage to extend the soaking time.

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

After that, after applying an annealing separator containing magnesia as a main component, finish annealing is carried out {110} <0.
01> oriented grains are preferentially grown by secondary recrystallization.

[0033]

EXAMPLE <Example 1> Weight% Si: 3.3%,
C: 0.06%, acid-soluble Al: 0.020, 0.02
6, 0.031%, N: 0.008%, Mn: 0.1
%, S: 0.007%, was heated at a temperature of 1150 ° C., and then hot-rolled to a thickness of 2.0 mm. After that, after annealing at 1120 ° C., after cold rolling to a thickness of 0.22 mm, the heating rate for decarburizing annealing is set to 15 to 100 ° C./sec, and after decarburizing and annealing at a temperature of 830 to 860 ° C., an ammonia-containing atmosphere Nitrogen in the steel plate is annealed at 0.02-
It was set to 0.03%. Then, after applying an annealing separator containing MgO as a main component, finish annealing was performed. The characteristic values of the product are shown in Table 1. Regarding primary recrystallization texture I [111] / I [4
11] value is 3 or less, heating rate in decarburization annealing process: HR
Amount of acid-soluble Al: HR ≧ −6250 [Al] +200 for [Al]%
It is understood that when the above condition is satisfied, B8 achieves a high magnetic flux density of 1.92 T or more. In other words, when [Al] is increased, B8 for the same decarburization annealing rate is improved, and the decarburization annealing heating rate range where a high B8 can be obtained spreads to a small heating rate range.

[0034]

[Table 1]

<Example 2> Mass%, Si: 3.3%,
C: 0.05%, acid-soluble Al: 0.027, 0.03
1%, N: 0.007%, Cr: 0.1%, Sn: 0.
A slab containing 05%, Mn: 0.1% and S: 0.008% is heated at a temperature of 1150 ° C., and then hot rolled to a thickness of 2.0 mm, and the hot rolled plate is annealed at 1120 ° C. Then, it was cold-rolled to a thickness of 0.22 mm. This cold-rolled sheet was heated to 800 ° C. at a heating rate of 10 to 600 ° C./sec, and then decarburized and annealed at 800 to 890 ° C. for 120 seconds at an atmospheric oxidation degree of 0.44. The oxygen content of the steel sheet at this time was 1.
It was 9 to 2.1 g / m ² .

After that, annealing was performed at 750 ° C. for 30 seconds in an atmosphere containing ammonia, and the amount of nitrogen was changed to 0.023 to 0.029% by changing the amount of ammonia. Then, after applying an annealing separator containing magnesia as a main component, finish annealing was performed at 1200 ° C. for 20 hours.
These samples were subjected to tension coating treatment. The characteristics of the obtained product are shown in Table 2. From Table 2, the value of I [111] / I [411] regarding the primary recrystallization texture is 3 or less, and the heating rate in the decarburization annealing step: HR is the amount of acid-soluble Al: [Al]% When HR ≧ −6250 [Al] +200 is satisfied, B8 is 1.9
It can be seen that a high magnetic flux density of 2T or more is obtained.
It is also found that B8 is particularly high when HR is 75 ° C./sec to 140 ° C./sec, and that region spreads to the lower limit side when [Al] increases.

[0037]

[Table 2]

<Example 3> Mass% of Si: 3.2%,
Mn: 0.1%, C: 0.05%, S: 0.008%,
Acid-soluble Al: 0.024%, N: 0.008%, S
A 2.0 mm thick hot-rolled silicon steel sheet containing n: 0.05% was cold-rolled to a final thickness of 0.22 mm. This cold-rolled sheet was heated to 840 ° C. at a heating rate (1) 20 ° C./second (2) 100 ° C./second and annealed at 840 ° C. for 150 seconds in a mixed gas of nitrogen and hydrogen with an oxidation degree of 0.33. It was recrystallized. Then, it was annealed at 750 ° C. for 30 seconds in an atmosphere containing ammonia, and the amount of nitrogen in the steel sheet was adjusted to 0.022 to 0.026% by changing the content of ammonia.

After applying an annealing separator containing magnesia as a main component to these steel sheets, finish annealing was performed. The finish annealing is performed up to 1200 ° C. in an atmosphere gas of N ₂ : 25% + H ₂ : 75% at a heating rate of 15 ° C./hr and 1200
It was annealed for 20 hours by switching to H2: 100% at ℃.
These samples were subjected to tension coating treatment. Table 3 shows the magnetic properties of the obtained product. Compared with Examples 1 and 2, since the annealing before cold rolling is not performed, the overall magnetic flux density is low, but the effect of improving the magnetic flux density of the present invention can be confirmed.

[0040]

[Table 3]

<Example 4> In mass%, Si: 3.2%,
C: 0.05%, acid-soluble Al: 0.029%, N:
0.008%, Mn: 0.1%, S: 0.007%, containing silicon steel slab heated to 1100 ° C., 2.0 mm
Made thick This hot rolled plate was annealed at 1100 ° C. and cold rolled to a final plate thickness of 0.2 mm. After that, heating rate 1
After heating to 850 ° C. at 00 ° C./sec, it was cooled to room temperature. After that, heat at a heating rate of 30 ° C./sec and at 830 ° C.,
After annealing for 90 seconds in an atmosphere gas with an oxidation degree of 0.12 to 0.72, it was annealed for 30 seconds at 750 ° C. in an atmosphere containing ammonia, and the nitrogen content in the steel sheet was set to 0.02 to 0.03%.
Then, after applying an annealing separator containing MgO as a main component, finish annealing was performed at 1200 ° C. for 20 hours.

The characteristics of the product are shown in Table 4. From Table 4, the glass of the product when the oxidation degree of the atmosphere specified by the present invention exceeds the range of 0.15 or more and 1.1 or less and the amount of oxygen after decarburization annealing of 2.3 g / m ² or less It can be seen that the film characteristics are deteriorated.

[0043]

[Table 4]

<Example 5> In mass%, Si: 3.2%,
C: 0.05%, acid-soluble Al: 0.024%, N:
0.007%, Cr: 0.1%, Sn: 0.05%, M
A silicon steel slab containing n: 0.1% and S: 0.008% was heated at 1150 ° C and hot-rolled to a plate thickness of 2.3 mm. The hot-rolled sheet was annealed at 1120 ° C., then
Cold rolled to a thickness of 0.22 mm. This cold rolled sheet is at 100 ° C
90 ~ 600 at 820 ℃ after heating to 800 ℃ / sec
Decarburization annealing with an atmospheric oxidation degree of 0.52 for 1 second, I {11
The value of 1} / I {411} was set to 2.7 or less, and the primary recrystallization texture was adjusted so that the inequality of claim 1 holds.
Then, it was annealed at 750 ° C. for 30 seconds in an atmosphere containing ammonia to adjust the nitrogen content in the steel sheet to 0.023 to 0.029%. After applying an annealing separator containing MgO as a main component,
Finish annealing was performed at 1200 ° C. for 20 hours.

The characteristic values of the product are shown in Table 5. It can be seen that when the oxygen content of the steel sheet is as large as 2.41 g / m ² , the magnetic properties are deteriorated.

[0046]

[Table 5]

<Example 6> In mass%, Si: 3.2%,
C: 0.05%, acid-soluble Al: 0.024%, N:
0.007%, Cr: 0.1%, Sn: 0.05%, M
A silicon steel slab containing n: 0.1% and S: 0.008% was heated at 1150 ° C and hot-rolled to a plate thickness of 2.3 mm.
This hot-rolled sheet was annealed at 1120 ° C., then 0.2
Cold rolled to a thickness of 2 mm. This cold-rolled sheet was heated to 800 ° C. at 100 ° C./sec, and then decarburized and annealed at 820 ° C. for 110 seconds at an atmospheric oxidation degree of 0.44. Organization: I {11
The value of 1} / I {411} was 1.7, and the steel sheet oxygen content was 1.9.
It was g / m ² . Then, it is annealed in an atmosphere containing ammonia for 30 seconds at 750 ° C., and the amount of nitrogen in the steel sheet is 0.012 to 0.026% by changing the content of ammonia.
And Then, after applying an annealing separator containing magnesia as a main component, finish annealing was performed at 1200 ° C. for 20 hours.

The characteristic values of the product are shown in Table 6. Nitrogen content after nitriding is 0.017% or more ([N] / [Al] ≧ 0.6
It can be seen that the magnetic flux density increases in 7).

[0049]

[Table 6]

<Example 7> Mass% of Si: 3.3%,
C: 0.06%, acid-soluble Al: 0.020, 0.02
6, 0.031%, N: 0.008%, Mn: 0.1
%, S: 0.007%, was heated at a temperature of 1150 ° C., and then hot-rolled to a thickness of 2.0 mm. After annealing the hot rolled sheet at 1120 ° C in the first stage and 900 ° C in the second stage,
After cold rolling to a thickness of 0.15 mm, the heating rate of decarburization annealing was set to 15 to 100 ° C / sec, decarburization annealing was performed at a temperature of 810 to 860 ° C, and then annealing was performed in an ammonia-containing atmosphere to remove nitrogen in the steel sheet. It was set to 0.02 to 0.03%. Then, after applying an annealing separator containing magnesia as a main component, finish annealing was performed. The characteristic values of the product are shown in Table 7. Heating rate in decarburization annealing step: When HR is HR ≧ −6250 [Al] +200 with respect to the amount of acid-soluble Al: [Al]%, B8 can obtain a high magnetic flux density of 1.92 T or more. I understand that.

[0051]

[Table 7]

<Example 8> Mass% of Si: 3.3%,
C: 0.05%, acid-soluble Al: 0.025%, 0.0
35%, N: 0.007%, Cr: 0.1%, Sn:
A slab containing 0.05%, Mn: 0.1%, and S: 0.008% was heated at a temperature of 1150 ° C., and then hot-rolled to a thickness of 2.3 mm.
It was annealed at 0 ° C. and then cold rolled to a thickness of 0.18 mm.
This cold-rolled sheet was heated to 800 ° C. at a heating rate of 5 to 600 ° C./sec, and then decarburized and annealed at 800 to 890 ° C. for 120 seconds at an atmospheric oxidation degree of 0.52 to obtain a primary recrystallization texture.
It adjusted to the area | region where the high B8 shown by was obtained. Then 7
Annealing was performed at 50 ° C. for 30 seconds in an atmosphere containing ammonia, and the amount of nitrogen in the steel sheet was adjusted to 0.025 to 0.035% by changing the content of ammonia. Then, after applying an annealing separator containing magnesia as a main component, finish annealing was performed at 1200 ° C. for 20 hours. The characteristics of the obtained product are shown in Table 8. From Table 8, heating rate in decarburization annealing step: HR is HR ≧ −625 with respect to the amount of acid-soluble Al: [Al]%.
When it is 0 [Al] +200, B8 is 1.92.
It can be seen that a high magnetic flux density of T or higher is obtained. Especially, when [Al] is increased, high B obtained by the cold rolling once method
8 effect is more prominent, and a high B8 effect can be obtained and a higher B8 can be obtained even if the decarburization annealing heating rate is low.

[0053]

[Table 8]

[0054]

According to the present invention, based on the method for producing a grain-oriented electrical steel sheet by low-temperature slab heating, which has no problems caused by conventional high-temperature slab heating, a primary recrystallization structure, decarburizing annealing conditions for acid-soluble Al, By defining the surface oxide layer and the nitriding amount, it is possible to industrially and stably manufacture the grain-oriented electrical steel sheet having a high magnetic flux density and excellent magnetic characteristics.
In particular, in a manufacturing method based on the single cold rolling method, by prescribing decarburization annealing conditions and nitriding amount for acid-soluble Al, a thin grain-oriented electrical steel sheet having high magnetic flux density and excellent magnetic properties is industrially produced. It can be stably manufactured. This makes it possible to obtain a grain-oriented electrical steel sheet which has less load on hot rolling, omits intermediate annealing, and is cheaper than conventional ones and has excellent iron loss.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of acid-soluble Al and decarburization annealing heating rate on the magnetic flux density (B8) of a product.

FIG. 2 is a diagram showing an influence of a rapid heating completion temperature of decarburization annealing on a magnetic flux density.

FIG. 3 is a diagram showing an influence of a rapid heating start temperature of decarburization annealing on a magnetic flux density.

FIG. 4 is a diagram showing the effect of cold rolling reduction on magnetic flux density.

Front page continuation (51) Int.Cl. ⁷ identification code FI theme code (reference) C22C 38/18 C22C 38/18 (72) Inventor Kenichi Murakami 1-1 Hibatacho, Tobata-ku, Kitakyushu, Fukuoka F term in Yawata Works (reference) 4K033 AA02 CA02 CA07 DA02 FA01 FA13 FA14 HA02 HA04 JA05 LA01 RA04 SA02 SA03 TA02 5E041 AA02 CA02 HB11 NN01 NN18

Claims (7)

[Claims] 1. By mass, Si: 0.8 to 4.8%, C:
0.085% or less, acid-soluble Al: 0.01 to 0.06
Steel containing 5% and N: 0.012% or less and the balance Fe and unavoidable impurities is heated at a temperature of 1280 ° C. or less and then hot-rolled to form a hot-rolled sheet, and then a single or intermediate annealing is sandwiched. In the manufacturing method of the grain-oriented electrical steel sheet, the final plate thickness is obtained by cold rolling two or more times, the annealing separator having magnesia as a main component is applied after decarburization annealing, and finish annealing is performed. Corresponding to Al]%, heating rate in the decarburization annealing temperature rising process from the region where the steel plate temperature is 600 ° C. or less to a predetermined temperature within the range of 750 to 900 ° C .: HR ° C./sec is HR ≧ By setting −6250 [Al] +200, the ratio of I [111] / I [411] in the texture after decarburization annealing is adjusted to 3 or less, and then nitriding treatment is performed. Of high grain oriented electrical steel sheet. 2. The method for manufacturing a grain-oriented electrical steel sheet having a high magnetic flux density according to claim 1, wherein the rolling reduction is set to more than 90% in the cold rolling. 3. The production of a grain-oriented electrical steel sheet having a high magnetic flux density according to claim 1, wherein the hot rolled sheet is annealed in a temperature range of 900 to 1200 ° C. for 30 seconds to 30 minutes. Method. 4. In the decarburization annealing step, 770 ° C. to
Oxidation degree of atmosphere gas (PH ₂ O / P
H ₂ ): Annealing is performed for a time such that the oxygen content of the steel sheet is 2.3 g / m ² or less in the range of more than 0.15 and 1.1 or less. The method for manufacturing a grain-oriented electrical steel sheet having a high magnetic flux density according to 1. 5. The amount of acid-soluble Al in the steel sheet: [Al]
Amount of nitrogen: [N] is [N] / [Al] ≧ 0.67
The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to any one of claims 1 to 4, wherein the nitriding treatment is performed so that the amount satisfies the above condition. 6. In mass%, Sn: 0.02 to 0.02
6. The method according to claim 1, wherein 0.15% is added.
A method for manufacturing a grain-oriented electrical steel sheet having a high magnetic flux density according to any one of 1. 7. In mass%, further, Cr: 0.03 to.
7. The method for producing a grain-oriented electrical steel sheet having a high magnetic flux density according to claim 1, wherein 0.2% is added.