JP2001152250A - Method for producing grain-oriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extremely stably produce a grain-oriented silicon steel sheet excellent in magnetic properties. SOLUTION: In the method for producing a grain-oriented silicon steel sheet in which a slab for a grain-oriented silicon steel sheet containing a prescribed amount of Al is heated at >=1200 deg.C and is thereafter hot-rolled to form into a hot rolled sheet, and this sheet is, if required, annealed, is subjected to cold rolling for one time or two or more times including process annealing, is subsequently subjected to decarburizing annealing, is next coated with a separation agent for annealing and is subjected to finish annealing, the heating for the slab is executed at a temperature higher than the perfect solid solution temperature of a material having inhibitor capacity, and, moreover, till the start of secondary recrystallization in the finish annealing after the decarburizing annealing, the steel sheet is subjected to nitriding treatment. At this time, preferably, the average grain size of primarily recrystallized grains after the dedecarburizing annealing is controlled to 7 to <18 μm, the increased amount of nitrogen by the nitriding treatment is controlled to 0.001 to 0.03 weight%, and the draft in the cold rolling is controlled to 80 to 95%.

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 grain-oriented electrical steel sheet mainly used as an iron core of a transformer or the like.

[0002]

2. Description of the Related Art Various techniques for stably producing a grain-oriented electrical steel sheet having excellent magnetic properties and having a magnetic flux density B ₈ (magnetic flux density in a magnetic field of 800 A / m) exceeding 1.9 T have been proposed. However, these can be roughly classified into the following three. The first technique is to raise the slab from 1350 ° C to 1
This is a method in which the slab is kept at the heating temperature for a sufficient time to heat it to an extremely high temperature of 450 ° C. and to uniformly heat (soak) the entire slab. This method uses M
The purpose is to completely solubilize a substance having inhibitory ability such as nS or AlN so as to function as an inhibitor required for secondary recrystallization. This complete solution treatment is performed simultaneously with the strength of the inhibitor due to the slab site. In this regard, the above method makes sense in achieving stable production, as it is also a means of overcoming the differences.

[0003] However, in the case of the above method, the heating temperature required for completely solidifying a substance having inhibitory ability, that is, the complete solution temperature becomes an extremely high temperature, and in actual production, it is necessary for secondary recrystallization. In order to ensure a sufficient amount of inhibitor, heating is performed at a temperature equal to or higher than the complete solution solution temperature (extremely high temperature), which involves various problems in actual production.

[0004] For example, in hot rolling, it is difficult to secure a required hot rolling temperature. If the temperature cannot be secured, a deviation in inhibitor strength occurs in a slab.
As a result, secondary recrystallization defects occur.Coarse grains are generated during hot rolling and the coarse grains cannot be recrystallized secondarily, resulting in linear secondary recrystallization defects. Therefore, a large amount of labor is required for maintenance of the heating furnace, or a huge edge crack is generated in the steel strip after hot rolling to lower the yield.

As an improvement technique of this technique, Japanese Patent Laid-Open Publication No. 1-1
A method of stabilizing the secondary recrystallization by performing a nitriding treatment after the primary recrystallization based on the above method as disclosed in Japanese Patent No. 68817 is known. The problems that can be solved are only the above-mentioned problems, and it is still difficult to solve the above problems in actual production.

The second technique is disclosed in JP-A-59-56522, JP-A-5-112827, and JP-A-9-11.
As disclosed in JP 8964 and the like, a method is used in which AlN is used as an inhibitor, slab heating is performed at less than 1280 ° C., and nitriding treatment is performed after decarburization annealing and before the start of secondary recrystallization. In such a method, for example, as shown in JP-A-2-182866, the average particle size of primary recrystallized grains after decarburization annealing is controlled to a certain range, usually to a range of 18 to 35 μm. This is very important for good secondary recrystallization.

Further, Japanese Patent Application Laid-Open No. Hei 5-295443 discloses that the amount of a solid solution of a substance having an inhibitory ability, such as nitrogen dissolved during hot rolling, in steel determines the grain growth of primary recrystallization. There is disclosed a method of adjusting the components in order to keep the size of the primary recrystallized grains uniform so as to keep the dissolved nitrogen and the like at the time of hot rolling heating low. However, in this method, no matter how strictly the components are adjusted, there is a deviation in the slab such as the amount of dissolved nitrogen, and the difference in the inhibitor capacity in the slab, that is, the difference in the primary recrystallization particle size in the slab. It is impossible to eliminate it exactly. As a result, there is a problem that it may be difficult to make the secondary recrystallization uniform in the slab, and the above method is not an industrially extremely stable production method. .

[0008] A third technique is to use a C-type inhibitor as disclosed in Japanese Patent Application Laid-Open No. 6-322443.
u _x S _(x = 1.8, or 2) using, as a slab heating temperature method of less Cu _x fully solution temperature of fully solution temperature above MnS of S. The feature of this method is that, after the slab heating temperature is lowered, an additional step such as a nitriding treatment employed in the second technique is not required.

However, the above-mentioned method has the same problem as the above-mentioned second technique because the slab heating temperature is set to be equal to or lower than the complete solution solution temperature of MnS.
After all, it is not a very stable industrial production method. Also,
Originally, although Cu _x S is known as an inhibitor for controlling secondary recrystallization, it is not particularly suitable for producing a high magnetic flux density unidirectional electrical steel sheet having a final cold rolling reduction of more than 80% ( Iron and steel p.2049, N0.15
Vol. 70, N 0.1984).

[0010]

Generally, whether secondary recrystallization having good magnetic properties can be realized depends mainly on the primary recrystallized grain size and the secondary inhibitor for controlling the secondary recrystallization. For example, while the primary recrystallization particle size in the first technique is about 10 μm,
In the second technique, it is possible to realize good secondary recrystallization by any method despite that the primary recrystallization particle diameters are greatly different, such as 18 to 35 μm. Indicates that the combination of the primary recrystallized particle size and the secondary inhibitor required for realizing secondary recrystallization with a well-aligned Goss orientation ({110} <001> orientation) is not necessarily unique. .

[0011] Therefore, the present inventors adjust the secondary inhibitor for any value of the primary crystal grain size to obtain G G.
Research has been repeated with the idea that it is possible to realize secondary recrystallization with well-aligned oss orientation. Then, based on the above idea, the present inventors, from the viewpoint of establishing a stable production method, perform the primary re-operation of the inhibitor, which is indispensable for the production of a grain-oriented electrical steel sheet, by exerting its function. The production of unidirectional electrical steel sheets with excellent magnetic properties was studied by classifying them into primary inhibitors that control the crystal grain size and secondary inhibitors that control the secondary recrystallization grain size.

By the way, although the combination of the primary recrystallized particle size and the secondary inhibitor required for realizing the secondary recrystallization with good Goss orientation is not unique,
For example, when the primary crystal grain size varies over the entire slab (coil), a good secondary recrystallization orientation cannot be obtained unless the secondary inhibitor strength is properly controlled for each slab site. Therefore, a manufacturing method in which the primary recrystallized grain size and the secondary recrystallized grain size do not vary over the entire slab is a stable manufacturing method.

Further, since the primary crystal grain size is determined by the primary inhibitor strength and the temperature of the decarburization annealing for performing the primary recrystallization, it is desired that the primary inhibitor strength does not fluctuate over the entire slab. That is, from the viewpoint of establishing a stable production method, the biggest problem is how to produce both the primary inhibitor and the secondary inhibitor without variation over the entire slab.

In this regard, the first to third techniques are:
Each has the following problems: In the first technique, it is necessary to heat the slab in an extremely narrow temperature range, which is equal to or higher than the complete solution solution temperature of the inhibitor and equal to or lower than the coarse-grain formation temperature during hot-rolling heating, which causes instability of secondary recrystallization. In addition, it is very difficult to ensure both inhibitor strength necessary for secondary recrystallization and industrially stable quality.

According to the second technique, it is easy to secure the secondary inhibitor strength by performing a nitriding treatment after the decarburizing annealing and before the secondary recrystallization during the finish annealing, but the uniformity of the primary inhibitor strength is high. In view of the above, a finite amount of solute nitrogen and the like are unevenly distributed in the slab (coil), and this causes a change in the primary recrystallized grain size. Also, in this case, the primary inhibitor also acts as a secondary inhibitor, so that a change in the primary inhibitor over the entire slab (coil) also leads to a change in the secondary inhibitor.

In the third technique, since MnS is not subjected to a complete solution treatment and AlN is precipitated by 60% or more after hot rolling, the slab (primary inhibitor) is used as in the second technique. Coil) is disadvantageous in terms of homogenization, and since the inhibitor reinforcement treatment is not performed in the middle of the process, the secondary inhibitor has not changed from the primary inhibitor, and the secondary inhibitor has fluctuated for each slab site. It is difficult to ensure industrially stable quality. Further, as described above, although Cu _x S is known as an inhibitor for controlling secondary recrystallization, it is particularly suitable for producing a high magnetic flux density unidirectional electrical steel sheet exceeding a final cold rolling reduction of 80%. Not.

That is, the present invention has been made in view of the above-mentioned circumstances, and is intended to more stably produce a unidirectional magnetic steel sheet having more excellent secondary magnetic recrystallization and excellent magnetic properties. The purpose is to provide a method that can do.

[0018]

The gist of the present invention is as follows (1) to (8). (1) A slab for a grain-oriented electrical steel sheet containing a predetermined amount of Al is heated at a temperature of 1200 ° C. or higher, and then hot-rolled into a hot-rolled sheet, and then subjected to annealing or not. In a method for producing a grain-oriented electrical steel sheet which is subjected to cold rolling once or twice or more with intermediate annealing, followed by decarburizing annealing, and then applying an annealing separating agent and performing finish annealing, the inhibitor capacity is reduced. The slab is heated at a temperature (slab heating temperature Ts (° C.)) higher than the complete solution heat-up temperature of the material, and after the decarburizing annealing, the steel is nitrided before the secondary recrystallization of the finish annealing starts. A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, characterized by performing a treatment.

(2) The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to (1), wherein the slab is heated at a temperature of 1350 ° C. or lower. (3) The slab is represented by mass%, C: 0.025 to 0.10%, Si: 2.5 to 4.0%, Acid-soluble Al (sAl): 0.01 to 0.10%, N : 0.0075% or less, Seq = S + 0.406 × Se: 0.003 to 0.05
%, Mn: 0.02 to 0.20%, the balance being Fe and unavoidable impurities, and heating the slab by the following formula ([] is the mass of the component elements in []). _{%), T 1 = 10062 /} (2.72-log ([sAl] *
[N])) - 273, T 2 = 14855 / (6.82-log ([Mn] *
[S])) - 273, _{and, T 3 = 10733 / (4.08} -log ([Mn] *
[Se]))-273, characterized by performing at a slab heating temperature Ts (° C.) higher than the maximum temperature among T ₁ (° C.), T ₂ (° C.), and T ₃ (° C.). The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to the above (1) or (2).

(4) The slab further comprises, by mass%, C
u: 0.01 to 0.30%, and the heating of the slab is performed by the following formula (where [] is the mass% of the component elements in []): T ₄ = 43091 / (25. 09-log ([Cu] *
[Cu] * [S])) Slab heating temperature Ts higher than T ₄ (° C.) defined by -273
(1) The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to any one of the above (1) to (3), which is performed at (° C).

(5) The slab further comprises, in mass%,
B: 0.0005 to 0.0060%, and the slab is heated by the following formula (where [] is the mass% of the component elements in []): T ₅ = 13680 / (4. 63-log ([B] *
[N])) Slab heating temperature Ts higher than T ₅ (° C.) defined by -273
The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to any one of the above (1) to (4), which is performed at (° C.).

(6) The magnetic properties as described in any of (1) to (5) above, wherein the primary recrystallized grains after the decarburizing annealing have an average particle diameter of 7 μm or more and less than 18 μm. Manufacturing method of unidirectional magnetic steel sheet. (7) The nitriding treatment is performed in a mixed gas of hydrogen, nitrogen, and ammonia in a strip running state, and a nitrogen increase of the steel sheet is set to 0.001 to 0.03 mass%. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to any one of (1) to (6).

(8) In any one of the above (1) to (7), in the final cold rolling before the decarburization annealing, the cold rolling reduction is 80% or more and 95% or less. A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties as described.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have found that when a slab is heated, a substance having an inhibitory ability is completely dissolved.
Starting from the starting point that this is the best method to homogenize the primary inhibitor in the slab (coil) to the utmost, if the concentration in the slab of a substance having inhibitor capacity is made lower than in the conventional method, the complete solution heat-up temperature will decrease. I paid attention. As a technique for achieving complete solution of the inhibitor during hot rolling heating,
Although there is the first technique, when the concentration of a substance having an inhibitory ability in a slab is reduced in this technique, secondary recrystallization is destabilized, and it has not been established as a stable industrial production technique.

Therefore, the present inventors have conducted intensive studies and experiments, and as a result, when the nitrogen concentration in the slab component is high, even if the slab heating is performed at a temperature equal to or higher than the complete solution solution temperature, the primary inhibitor is formed over the entire slab. Is difficult to equalize. That is, it has been found that lowering the nitrogen concentration in the slab component is a key point in minimizing the difference in primary inhibitor ability in the slab.

On the other hand, it has also been found that sulfide and selenide inhibitors do not have as much an effect as nitride inhibitors in making the inhibitors uniform in the hot-rolling process, and sulfide and selenide are mainly used as primary inhibitors.
It has been found that it is effective to use selenide inhibitors. The cause of the difference in the effect between the nitride inhibitor and the sulfide or selenide inhibitor is unclear, but the solubility of AlN is significantly different between the α phase and the γ phase, and during hot rolling, Mother is A
It is considered that when the transition from the γ phase in which 1N is easily dissolved to the α phase in which it is difficult to dissolve is caused, AlN is deposited unevenly.

By the above method (reduction of the nitrogen concentration in the slab component), the difference in the primary inhibitor ability (strength) between the slab (coil) portions can be extremely reduced. In order to obtain a sharpened Goss orientation with excellent magnetic properties, in addition to sulfide and selenide, an inhibitor that is stable up to high temperatures is necessary. In the present invention, this inhibitor is
This is ensured by forming AlN by nitriding.

That is, the present invention lowers the concentration of a substance having an inhibitor ability in a slab component as compared with the conventional method, thereby lowering the complete solution solution temperature of the inhibitor, and
By making the slab heating temperature higher than that temperature, the primary inhibitor strength is made uniform regardless of the slab part,
Insufficient strength of the secondary inhibitor caused by lowering the concentration of the inhibitor component is achieved by performing a nitriding treatment after decarburizing annealing and before the start of secondary recrystallization during finish annealing to obtain nitride (AlN, Si ₃ N). ₄ , a single or composite precipitate of Mn or the like) is formed and compensated by functioning as an inhibitor, thereby enabling stable production of a grain-oriented electrical steel sheet having good magnetic properties.

That is, an object of the present invention is to provide an inhibitor having a large role in the production of a grain-oriented electrical steel sheet by metallurgically separating its functioning stages and using a different substance for each functioning stage. An object of the present invention is to provide an extremely stable manufacturing method by performing a function. In addition, since the temperature of decarburization annealing at which primary recrystallization is performed in the production of a grain-oriented electrical steel sheet is generally as low as 930 ° C. or less, at this stage, strong carbon steel formed by conventional high-temperature hot rolling is used. No inhibitors are required. In the present invention, since sulfide or selenide is mainly used as the primary inhibitor, the temperature dependence of primary recrystallization grain growth is extremely small, and the primary recrystallization annealing (actually, decarburization annealing) temperature is greatly changed. No need. As a result, the constituent composition of the primary oxide layer and the amount of nitridation in the subsequent nitriding treatment are remarkably stabilized, and the effect of drastically reducing primary film defects can be obtained.

Next, the reasons for limiting the component composition of the slab in the present invention will be described. If the content of C is less than 0.025%, the primary recrystallization texture becomes inappropriate, and 0.10%
If it exceeds, decarburization becomes difficult and it is not suitable for industrial production. S
If i is less than 2.5%, good iron loss cannot be obtained,
If it exceeds 4.0%, cold rolling becomes extremely difficult and is not suitable for industrial production.

Al combines with N to form AlN, and mainly functions as a secondary inhibitor. This AlN includes both those formed before nitriding and those formed during high-temperature annealing after nitriding, and 0.01 to 0.10% is necessary in order to secure the amount of both AlN. When the content is less than 0.01%, the function as a secondary inhibitor becomes insufficient, so that secondary recrystallized grains having a good Goss orientation cannot be stably obtained. In this case, the amount of nitridation required in the post-process increases, and the film is seriously damaged.

If N exceeds 0.0075%, it causes non-uniform precipitation during hot rolling.
And More preferably, it is 0.0050% or less.
S and Se combine with Mn and Cu and mainly act as primary inhibitors. The content of S and Se is
It is limited by Seq = S + 0.406 × Se, but if Seq exceeds 0.05%, the time required for purification by final finish annealing is undesirably too long. Also, 0.
If it is less than 003%, the effect as a primary inhibitor is weakened, so the lower limit must be made 0.003%.

If the Mn content is less than 0.02%, cracks tend to occur in the hot-rolled steel strip, and the yield decreases. on the other hand,
If it exceeds 0.20%, MnS and MnSe become excessively large, the degree of solid solution becomes uneven at some places, and stable production becomes difficult. Therefore, the upper limit is made 0.2%. Cu
When hot-rolled under the conditions of the present invention in which the slab is heated at 1200 ° C. or higher, fine precipitates are formed together with S and Se,
Exhibits primary inhibitory effects. The precipitate also serves as a precipitation nucleus for making the dispersion of AlN more uniform, and also plays a role of a secondary inhibitor, and this effect makes secondary recrystallization favorable. If it is less than 0.01%, the above effect is reduced and stable production becomes difficult. If it exceeds 0.30%, the above effect is saturated, and a surface flaw such as "copper heap" occurs during hot rolling.

If B is less than 0.0005%, B
The inhibitory effect as N was not exhibited, and 0.006
%, When the inhibitor is formed by nitriding, the required amount of nitriding becomes too large, and as a result, primary coating defects in which the base iron is exposed frequently occur. Furthermore,
Each of the contents of Al, N, S, Se, Mn, Cu, and B is _{one of} T ₁ (° C.) to T ₅ (° C.) defined by the following formula, which is obtained from the concentration of the components in the slab. But one
If the temperature exceeds 400 ° C., it is necessary to make the slab heating temperature Ts (° C.) extremely high in order to completely dissolve these components, which is not preferable. There is a need.

T ₁ = 10062 / (2.72-log)
([SAl] * [N] )) - 273 T 2 = 14855 / (6.82-log ([Mn] *
[S])) - 273 T 3 = 10733 / (4.08-log ([Mn] *
[Se])) - 273 T 4 = 43091 / (25.09-log ([Cu] *
[Cu] * [S]) ) - 273 T 5 = 13680 / (4.63-log ([B] *
[N]))-273 Here, [] in the formula represents mass% of the component element in [].

As described above, in the present invention, sulfides and selenides are mainly used as primary inhibitors to control the primary recrystallized grains, and it is necessary to minimize N in the slab component. 0.0050% or less is desirable.
However, this alone is not enough to control the secondary recrystallization, so that a nitriding treatment described later is required. In addition, as the inhibitor-forming component, Al described above,
N, S, Se, Mn, Cu, B, Sn, Sb, P,
Cr, Mo, Cd, Ge, Te, Bi and the like are also advantageously adapted, and Ni has a remarkable effect on the uniform dispersion of precipitates as primary and secondary inhibitors. Can also.

The preferred range of addition of the above components is S
n, Sb, P and Cr: 0.02 to 0.3%, Mo and Cd: 0.008 to 0.3%, Ge, Te and Bi:
0.005 to 0.1%, and Ni: 0.03 to 0.
3%, and each of these components can be used alone or in combination. Next, the reasons for limiting the conditions relating to the manufacturing process in the present invention will be described.

Regarding the average particle size of the primary recrystallized grains after the completion of the decarburizing annealing, for example, in Japanese Patent Application Laid-Open No. 7-252532, the average particle size of the primary recrystallized grains is 18 to 35 μm, but in the present invention, By setting the average particle size of the primary recrystallized grains to 7 μm or more and less than 18 μm, magnetic properties (particularly, iron loss) can be further improved. That is, if the particle size of the primary recrystallized grains is small, it means that the number of primary recrystallized grains existing in a unit volume increases. Further, when the particle size of the primary recrystallized grains is small, the volume fraction of Goss-oriented grains serving as nuclei for secondary recrystallization at the stage of primary recrystallization increases from the viewpoint of grain growth (Materials Science Forum Vol. 204). -206, Pa
rt2: pp: 631).

As a result, the absolute number of Goss-oriented grains is, for example, that the average grain size of primary recrystallized grains is 18 to 35 μm.
Since it is about five times as large as that of m, the secondary recrystallized grain size also becomes relatively small, and as a result, a remarkable improvement in iron loss is obtained. In addition, when the average particle size of the primary recrystallized grains is small, the driving force of the secondary recrystallization is increased, and the secondary recrystallization should be started earlier (at a lower temperature) during the final finish annealing during the temperature raising stage. Can be. In the current situation where the final finish annealing is performed in a coil shape, the temperature difference (temperature history difference) at each point of the coil increases as the temperature increases, so the temperature history at each point of the coil is reduced by lowering the secondary recrystallization temperature. Can be secondary-recrystallized in a more uniform temperature range (where the rate of temperature rise at each coil point is constant), and the non-uniformity between coil portions is significantly reduced, and the magnetic characteristics are extremely stable.

However, if the average grain size of the primary recrystallized grains is less than 7 μm, it is considered that the secondary recrystallization temperature becomes too low due to the large grain growth driving force. Dispersion from the Goss orientation increases, leading to a decrease in magnetic flux density. It is essential in the present invention that the steel sheet is subjected to a nitriding treatment after the decarburizing annealing and before the start of the secondary recrystallization. The method uses nitride (CrN, CrN,
MnN) or a method of nitriding in an atmosphere containing ammonia while the strip is running after decarburizing annealing. Either method may be adopted, but the latter method is industrially stable.

The amount of nitrogen (increased nitrogen) increased by this nitriding treatment is limited to 0.001 to 0.03% by mass.
If it is less than 0.001%, the secondary recrystallization becomes unstable, while if it exceeds 0.03%, primary coating defects where the base iron is exposed frequently occur. The preferred nitrogen increase is from 0.003 to 0.
025%. The slab heating temperature prior to hot rolling is an important aspect of the present invention. When the slab heating temperature is lower than 1200 ° C., the primary inhibitor, which is a key point of the present invention, is not sufficiently generated, and a problem such as a large variation in the primary recrystallized grain size with respect to the decarburization annealing temperature is caused.

On the other hand, by making the slab heating temperature higher than the complete solution-solution temperature of the substance having inhibitor ability, the difference in the intensity of the primary inhibitor at each slab site can be extremely reduced. However, when the slab heating temperature is set immediately above the complete solution solution temperature of the inhibitor, the time required to maintain the heating temperature for the solution of the inhibitor becomes longer, so from the viewpoint of productivity, at least about 20 ° C. The above is preferably set high. It should be noted that heating at an extremely high temperature exceeding 1400 ° C. is extremely difficult in industrial production and should be avoided.

In actual production, the slab heating temperature is set such that hot rolling is easy, the shape of the hot-rolled steel strip (crown) is excellent, and there is no actual harm associated with melting of the slab surface layer and generation of slag.
00-1350 degreeC is preferable. In the method of the present invention, first, the initial thickness is 150 mm by a known continuous casting method.
To 300 mm, preferably 200 mm to 250 m
m slabs. Instead of this slab, a so-called thin slab having an initial thickness of about 30 mm to 70 mm may be used. In this case, when manufacturing a hot-rolled steel strip,
There is an advantage that it is not necessary to perform rough processing to an intermediate thickness.
Further, it is also possible to manufacture a unidirectional magnetic steel sheet by the method of the present invention using a slab or a steel strip having a smaller initial thickness manufactured by steel strip casting.

In industrial production, a normal gas heating method may be used as a heating method for hot rolling. In addition to this method, induction heating and direct electric heating are used to achieve uniform annealing. In these special heating methods, there is no problem even if slab rolling is performed on the cast slab in order to secure a required shape. When the heating temperature is 1
When the temperature is 300 ° C. or more, the texture may be improved by this bulk-rolling to reduce the C content. These are within the scope of the prior art.

The final cold rolling reduction in cold rolling is 80.
%, It is difficult to obtain a desired degree of orientation integration in the Goss orientation grains in the primary recrystallization texture, so that it is difficult to secure a high magnetic flux density. On the other hand, the final cold rolling reduction rate is 95%
If it exceeds, the number of Goss-oriented grains in the primary recrystallization texture becomes extremely small, and secondary recrystallization becomes unstable.

Annealing of the hot-rolled steel strip is mainly performed in order to remove the non-uniformity of the structure and the dispersion of the inhibitor in the steel strip generated at the time of hot rolling. Annealing in a hot-rolled steel strip or annealing before final cold rolling may be used. That is, it is desirable to perform one or more annealings before the final cold rolling in order to eliminate non-uniformity due to a difference in temperature history during hot rolling. The final cold rolling may be performed at room temperature, but at least one
When the pass is kept at a temperature of 100 to 300 ° C. for 1 minute or more, the primary recrystallization texture is improved and the magnetic properties are extremely improved.

[0047]

EXAMPLES Example 1 Slabs having the component compositions of (1) to (4) shown in Table 1 were prepared at a: 1150 ° C., b: 1200 ° C.
c: 1250 ° C, d: 1300 ° C, e: 1350 ° C
After soaking at a standard temperature for 60 minutes each, hot rolling was performed, and 2.0
mm hot rolled sheet. Next, 1120
Immediately after holding at 200 ° C. for 200 seconds, the steel sheet was annealed at 900 ° C. for rapid cooling, pickled, and cold-rolled to 0.23 mm. The cold rolled sheet was subjected to decarburizing annealing at 850 ° C. for 150 seconds. Thereafter, nitriding annealing was performed at 750 ° C. for 30 seconds in a mixed gas of hydrogen, nitrogen, and ammonia to adjust the total nitrogen content of the steel sheet after nitriding to about 200 ppm. Next, an annealing separator containing MgO and TiO ₂ as main components was applied, heated to 1200 ° C. at a rate of 15 ° C./hour, and then subjected to finish annealing at 1200 ° C. for 20 hours. After the steel sheet was subjected to strain relief annealing, a tension coating treatment containing colloidal silica and aluminum phosphate as main components was performed, and the magnetic properties were measured. Table 2 shows the magnetic measurement results and the like for each of the above test levels.
l and N content, slab heating temperature and B _{8 in} product coil
FIG. 1 shows the relationship between the deviations. It can be seen that when manufactured from a slab belonging to the component composition of the present invention in accordance with the process conditions of the present invention, excellent magnetic properties are stably obtained over the entire length of the product coil.

[0048]

[Table 1]

[0049]

[Table 2]

Example 2 A slab having the component compositions (5) to (8) shown in Table 3 was soaked at the same five levels of temperature as in Example 1 for 60 minutes each, and then hot-rolled. It was a hot-rolled sheet of 3 mm. Next, the hot-rolled sheet was annealed at 1120 ° C. for 180 seconds and then immediately maintained at 900 ° C. for rapid cooling, followed by pickling and cold rolling to 0.30 mm. The cold rolled sheet was subjected to decarburizing annealing at 850 ° C. for 150 seconds. Then, in a mixed gas of hydrogen, nitrogen and ammonia,
Nitriding annealing was performed at 750 ° C. for 30 seconds to adjust the total nitrogen content of the nitrided steel sheet to about 200 ppm. Then
Apply an annealing separator mainly composed of MgO and TiO ₂ ,
Heating was performed at 1200 ° C. at a rate of 15 ° C./hour, followed by finish annealing at 1200 ° C. for 20 hours. After the steel sheet was subjected to strain relief annealing, a tension coating treatment containing colloidal silica and aluminum phosphate as main components was performed, and the magnetic properties were measured. For each test level above, the magnetic measurement results and the like in Table 4 also shows the content and the relationship of the slab heating temperature and the product coils in the B ₈ deviation Mn and S in FIG. It can be seen that when manufactured from a slab belonging to the component composition of the present invention in accordance with the process conditions of the present invention, excellent magnetic properties are stably obtained over the entire length of the product coil. In particular, when the average primary recrystallization particle size is 7 to 18 μm, particularly excellent magnetic properties of B ₈ of 1.92 T or more are stably obtained over the entire length of the product coil.

[0051]

[Table 3]

[0052]

[Table 4]

[Embodiment 3] (9) to (12) shown in Table 5
The slab having the component composition described above was soaked at the same five levels of temperature as in Example 1 for 60 minutes each, and then hot-rolled to obtain a hot-rolled sheet of 2.5 mm. Next, the hot-rolled sheet was annealed at 900 ° C. immediately after holding at 1120 ° C. for 30 seconds and then rapidly cooled, pickled, and cold-rolled to 0.27 mm. This cold rolled sheet was subjected to decarburizing annealing at 850 ° C. for 90 seconds.
Thereafter, in a mixed gas of hydrogen, nitrogen and ammonia, 75
Nitriding annealing at 0 ° C. for 30 seconds was performed to adjust the total nitrogen content of the steel sheet after nitriding to about 200 ppm. Then, Mg
Apply an annealing separator mainly composed of O and TiO ₂ ,
Heat to 00 ° C at a heating rate of 15 ° C / hr.
Finish annealing was performed at 200 ° C. for 20 hours. After subjecting this steel sheet to strain relief annealing, a tension coating process containing colloidal silica and aluminum phosphate as main components is performed,
The magnetic properties were measured. For each test level above, the magnetic measurement results and the like in Table 6 also shows the content and the relationship of the slab heating temperature and the product coils in the B ₈ deviation Mn and Se in FIG. It can be seen that when manufactured from a slab belonging to the component composition of the present invention under the process conditions of the present invention, excellent magnetic properties are stably obtained over the entire length of the product coil.

[0054]

[Table 5]

[0055]

[Table 6]

Example 4 (13) to (1) shown in Table 7
The slab having the component composition of 6) was soaked at the same five levels of temperature as in Example 1 for 60 minutes each, and then hot-rolled to obtain a 2.3 mm hot-rolled sheet. Then, the hot rolled sheet was heated to
After hot-rolled sheet annealing of quenching after holding for 0 seconds, pickling was performed,
It was cold rolled to 35 mm. At 850 ° C, 1
Decarburization annealing was performed for 50 seconds. Then, MgO,
An annealing separator containing TiO ₂ as a main component and MnN added is applied and heated to 1200 ° C. at a rate of 10 ° C./hour,
Thereafter, finish annealing was performed at 1200 ° C. for 20 hours.
After the steel sheet was subjected to strain relief annealing, a tension coating treatment containing colloidal silica and aluminum phosphate as main components was performed, and the magnetic properties were measured. For each test level above, in Table 8 the magnetic measurement results, etc., also shows the content and the relationship of the slab heating temperature and the product coils in the B ₈ deviation of Cu and S in FIG. From the slab belonging to the composition of the present invention,
It can be seen that when manufactured according to the process conditions of the present invention, excellent magnetic properties are stably obtained over the entire length of the product coil.

[0057]

[Table 7]

[0058]

[Table 8]

[Example 5] (17) to (2) shown in Table 9
The slab having the component composition of 0) was soaked at the same five levels of temperature as in Example 1 for 60 minutes each, and then hot-rolled to obtain a 2.3 mm hot-rolled sheet. Then, the hot rolled sheet was heated to 1150 ° C. for 30 minutes.
Immediately after holding for 2 seconds, the sheet was annealed at 900 ° C. and rapidly cooled, followed by pickling and cold rolling to 0.30 mm. This cold rolled sheet was subjected to decarburizing annealing at 850 ° C. for 150 seconds. Thereafter, nitriding annealing was performed at 750 ° C. for 30 seconds in a mixed gas of hydrogen, nitrogen, and ammonia to adjust the total nitrogen content of the steel sheet after nitriding to about 200 ppm. Next, an annealing separator mainly composed of MgO and TiO ₂ was applied and heated to 1200 ° C. at a rate of 15 ° C./hour, and then finish annealing was performed at 1200 ° C. for 20 hours. After the steel sheet was subjected to strain relief annealing, a tension coating treatment containing colloidal silica and aluminum phosphate as main components was performed, and the magnetic properties were measured. For each test level above, in Table 10 the magnetic measurement results, etc., also shows B and N content and relationships of the slab heating temperature and the product coils in the B ₈ deviations in FIG. It can be seen that when manufactured from a slab belonging to the component composition of the present invention in accordance with the process conditions of the present invention, excellent magnetic properties are stably obtained over the entire length of the product coil. However, it can be seen that the slab having the highest N concentration has a large magnetic deviation in the product coil.

[0060]

[Table 9]

[0061]

[Table 10]

[0062]

According to the present invention, it is possible to eliminate the non-uniformity of the secondary recrystallization and to produce a grain-oriented electrical steel sheet having excellent magnetic properties in an extremely stable and industrial manner. . Therefore, the present invention greatly contributes to industrial production of a grain-oriented electrical steel sheet.

[Brief description of the drawings]

1 is a diagram showing the relationship between sAl and N content and the slab heating temperature and the product coils B ₈ deviation.

FIG. 2 is a diagram showing the relationship between the contents of Mn and S, the slab heating temperature, and the B ₈ deviation in a product coil.

FIG. 3 is a diagram showing the relationship between the contents of Mn and Se, the slab heating temperature, and the B ₈ deviation in a product coil.

FIG. 4 is a diagram showing the relationship between the contents of Cu and S, the slab heating temperature, and the B ₈ deviation in the product coil.

FIG. 5 is a diagram showing the relationship between the contents of B and N, the slab heating temperature, and the B ₈ deviation in a product coil.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Noriyoshi Fujii 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Inside the Nippon Steel Corporation Yawata Works (72) Inventor Naoki Mogi 20 Shintomi, Futtsu-shi, Chiba -1 Inside the Technology Development Division of Nippon Steel Corporation (72) Inventor Hitoshi Yokouchi 1-1 Yawata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Inside Nippon Steel Corporation Yawata Works (72) Inventor Norihiro Yamamoto Fukuoka F-term (reference) in Yawata Works, Tobata-ku, Kitakyushu-shi 1-1 Nippon Steel Corporation 4K033 AA02 BA02 CA01 CA10 DA01 FA01 HA01 HA04 HA06 JA04 LA01 MA00 5E041 AA02 AA19 BC01 CA02 HB05 HB07 HB09 HB11 NN01 NN06 NN17 NN18

Claims (8)

[Claims] 1. A slab for a grain-oriented electrical steel sheet containing a predetermined amount of Al is heated at a temperature of 1200 ° C. or higher, then hot-rolled into a hot-rolled sheet, and then subjected to annealing or In a method for producing a grain-oriented electrical steel sheet, cold rolling is performed once or twice or more with intermediate annealing, followed by decarburizing annealing, then applying an annealing separator, and performing finish annealing. The slab is heated at a temperature (slab heating temperature Ts (° C.)) higher than the complete solution temperature of the material having the ability, and after decarburizing annealing, before the secondary recrystallization of finish annealing starts. A method for producing a unidirectional magnetic steel sheet having excellent magnetic properties, characterized by subjecting a steel sheet to a nitriding treatment. 2. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein the heating of the slab is performed at a temperature of 1350 ° C. or less. 3. The slab is, by mass%, C: 0.025 to 0.10%, Si: 2.5 to 4.0%, Acid-soluble Al (sAl): 0.01 to 0.10% N: 0.0075% or less, Seq = S + 0.406 × Se: 0.003 to 0.05
%, Mn: 0.02 to 0.20%, with the balance being Fe and unavoidable impurities, and heating the slab by the following formula (where [] is []
, T ₁ = 10062 / (2.72-log ([sAl] *)
[N])) - 273, T 2 = 14855 / (6.82-log ([Mn] *
[S])) - 273, _{and, T 3 = 10733 / (4.08} -log ([Mn] *
[Se]))-273, characterized by performing at a slab heating temperature Ts (° C.) higher than the maximum temperature among T ₁ (° C.), T ₂ (° C.), and T ₃ (° C.). The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1 or 2. 4. The slab further comprises, in mass%, Cu:
0.01 to 0.30%, and heating of the slab is performed by the following formula (where [] is the mass% of the component elements in []): T ₄ = 43091 / (25.09− log ([Cu] *
[Cu] * [S])) Slab heating temperature Ts higher than T ₄ (° C.) defined by -273
The method according to any one of claims 1 to 3, wherein the method is performed at (° C). 5. The slab further comprises, in mass%, B:
0.005 to 0.006%, and heating of the slab is performed by the following formula (where [] is the mass% of the component elements in []): T ₅ = 13680 / (4.63 − log ([B] *
[N])) Slab heating temperature Ts higher than T ₅ (° C.) defined by -273
The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to any one of claims 1 to 4, wherein the method is performed at (° C). 6. The magnetic material according to claim 1, wherein an average particle diameter of primary recrystallized grains after the decarburizing annealing is 7 μm or more and less than 18 μm. Manufacturing method of unidirectional magnetic steel sheet. 7. The method according to claim 1, wherein the nitriding treatment is performed in a mixed gas of hydrogen, nitrogen, and ammonia in a strip running state to increase the nitrogen content of the steel sheet to 0.001 to 0.03 mass%. Item 7. A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to any one of Items 1 to 6. 8. The method according to claim 1, wherein the cold rolling reduction in the final cold rolling before the decarburizing annealing is set to 80% or more and 95% or less. For producing unidirectional electrical steel sheets with excellent magnetic properties.