JP2002129234A - Method for manufacturing grain oriented silicon steel sheet with high magnetic flux density - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold rolling method for obtaining a grain oriented silicon steel sheet using AlN as an inhibitor by which thinning can be combined with increase of magnetic flux density. SOLUTION: In the method for manufacturing the grain oriented silicon steel sheet: a slab having a composition containing 0.025-0.100% C, 2.5-4.5% Si and 0.007-0.040% Al is hot-rolled; the resultant plate is cold-rolled one or more times after hot rolled plate annealing or while process-annealed between the cold rolling stages; and the resultant sheet is subjected to primary recrystallization annealing and then to secondary recrystallization annealing. In the method of cold rolling for obtaining the grain oriented silicon steel sheet of <=0.23 mm product sheet thickness having high magnetic flux density, final cold rolling after the hot rolled plate annealing or the process annealing is performed using a reversing mill constituted of a housing splittable into the upper and the lower part in such a way that: at passes in the former stage of rolling, rolling is carried out using work rolls of 95-180 mmϕ diameter at least to <=0.40 mm intermediate sheet thickness; in the stage of sheet thickness midway through the rolling, the sheet is held at 100-350 deg.C at least for >=1 min; and subsequent rolling to Tf (mm) product sheet thickness is performed by replacing the above work rolls by work rolls of <=(Tf×520) mm diameter.

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 used for a core material of electric equipment such as a transformer and a generator.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet has a magnetization direction in a rolling direction.
Iron loss characteristics must be good. The quality of the magnetization characteristics is determined by the level of the magnetic flux density induced in the iron core in the applied constant magnetic field, and a product with a high magnetic flux density can reduce the size of the iron core. Iron loss is power loss that is consumed as heat energy when a predetermined AC magnetic field is applied to the iron core, and the quality is determined by the magnetic flux density, plate thickness, coating tension, impurity amount, specific resistance, crystal grain , The size of the magnetic domain width and the like have an effect. Among them, it is important that the magnetic flux density is high and the plate thickness is thin in order to reduce iron loss.

With today's manufacturing technology advances, for example,
Excellent steel sheet with 23mm thickness, magnetic flux density B8 (value at 800A / m magnetizing force) 1.92T, iron loss W17 / 50 (value at maximum magnetization of 1.7T at 50Hz) 0.85W / kg. Products have become available on an industrial scale. However, in order to respond to recent global warming, development of a thinner unidirectional magnetic steel sheet having a higher magnetic flux density, such as a sheet thickness of 0.20 or 0.18 mm, is required.

A grain-oriented electrical steel sheet having such excellent magnetic properties has a crystal structure in which the <001> orientation, which is the axis of easy magnetization of iron, is highly aligned with the rolling direction of the steel sheet. It is formed through a phenomenon called secondary recrystallization, in which crystal grains having a [110] <001> orientation, which is a so-called Goss orientation, are preferentially grown at the time of final finish annealing in a manufacturing process.

[0005] Basic requirements for sharply and sufficiently growing the Goss-oriented grains include the presence of an inhibitor that suppresses the growth of crystal grains having an undesired orientation other than the Goss orientation in the secondary recrystallization process. It is a well-known fact that it is essential to form a primary recrystallized structure in which goss grains are likely to develop preferentially. Here, as the inhibitor, a precipitate such as AlN, Mn (S, Se), Cu ₂ (S, Se) is generally used, and a component having a strong tendency to segregate at the grain boundaries such as Sn, Sb is used as an auxiliary. It is important that the primary recrystallized structure has a crystal grain size and its uniformity, and a texture in which the Goss-oriented grains and the oriented grains corresponding to the Goss-oriented grains are aligned in the rolling direction.

[0006] A method of obtaining a grain-oriented electrical steel sheet having a high magnetic flux density has been known for a long time, for example, Japanese Patent Publication No. 46-23820.
As disclosed in Japanese Patent Application Publication No.
Methods using N are widely known. In this method, an inhibitor component of AlN is once dissolved by high-temperature slab heating (≧ 1300 ° C.), and AlN is finely precipitated during annealing before final cold rolling to produce a grain-oriented electrical steel sheet.

On the other hand, Japanese Patent Application Laid-Open No. Sho 62-40315 discloses a method in which an AlN inhibitor is formed by a nitriding treatment in a later step to perform low-temperature slab heating (≦ 1250 ° C.). This method has been developed to avoid the equipment and operational disadvantages of high-temperature slab heating. It is well known that in a manufacturing method using these AlN inhibitors, a high magnetic flux density cannot be obtained without an appropriate primary recrystallization structure. The formation of the primary recrystallization structure is greatly affected by the cold rolling conditions, and it is generally preferable that the final cold rolling reduction is as high as 81% or more. Regarding other cold rolling, 1) Japanese Patent Publication No. 54-13846 discloses that 50
Aging treatment at ~ 350 ° C for 1 minute or more, and 2)
Japanese Patent Publication No. 54-29182 discloses a technique for holding at 300 to 600 ° C. for 1 to 30 seconds. The technique 1) is intended for reversal rolling, and the technique 2) is intended for tandem rolling.

[0008] High-temperature rolling using a tandem mill requires equipment and
It is difficult in terms of operation technology, and at present, high-temperature rolling is performed by utilizing the processing heat of reversal rolling, and the aging effect after the reel is wound up during rolling is used. In general, a reversing mill is a type in which rolls of a quadruple type, a six-type type, etc. are arranged in series. However, when the diameter of the work roll is reduced, roll deformation is likely to occur.

On the other hand, a Sendzimir mill or an NMS mill in which rolls of six, twelve, twenty, etc. are arranged in a cluster form enables the use of small-diameter work rolls in order to back up the work rolls from various angles. Since the grain-oriented electrical steel sheet contains a large amount of Si, the rolling reaction force is high, and it is more advantageous to use a small-diameter work roll to reduce the product sheet thickness. Therefore, a cluster type reversing mill is often used for high-temperature rolling of a grain-oriented electrical steel sheet.

On the other hand, regarding the work roll diameter of the cold rolling mill,
3) Japanese Patent Publication No. 50-37130 discloses a technique in which rolling is performed with a small-diameter roll having a diameter of 300 mm or less in all rolling passes or a subsequent pass. 4) Japanese Patent Application Laid-Open No. 02-282422 discloses a small roll having a diameter of 30 to 100 mm in a subsequent pass. Technology for warm rolling at 150-230 ° C with 5)
No. 05-33056, a technique of warm rolling at 150 to 350 ° C. with a small-diameter roll of 50 to 150 mmφ in the former pass, 6) JP-A-09-2
No. 87025 discloses a technique for increasing a rolling temperature (100 to 350 ° C.) with an increase in the diameter of a work roll (40 to 500 mmφ).

[0011]

As the cluster mill used for the conventional magnetic steel sheet, a Sendzimer mill represented by a 21 or 22 type is mainly used.
Mainly, small diameter work rolls of 95 mmφ or less were used.
For example, in the technique 5), the roll diameter is set to 50 to 150 mmφ, but in the embodiment, only examples of 80 and 90 mmφ are described.

In the production of an Al-containing grain-oriented electrical steel sheet, as disclosed in the item 3), the cold-rolled work roll is considered to have a small diameter, and a cluster mill that is advantageous for thinning meets this demand. Had matched. Also, as disclosed in the above 4) to 6), in rolling on the premise of aging treatment between passes, small-diameter rolls were considered to be advantageous from the viewpoint of magnetic properties.

The present inventors have studied in detail the effect of the work roll diameter on the magnetic properties when producing an Al-containing grain-oriented electrical steel sheet subjected to aging treatment between passes using a cluster type reversing mill. As a result, the magnetic flux density was low when rolling was performed with a conventional work roll diameter of 90 mmφ or less, but rather, the effect of improving the magnetic flux density was discovered by rolling with a work roll having a diameter of 95 to 170 mmφ, which was larger than before, and a patent application was filed. (Japanese Patent Application No. 2000-002944).

However, in the production of thin materials, large-diameter work rolls are disadvantageous from the viewpoint of the rolling reaction force. Therefore, it was investigated whether the effect of increasing the diameter of the work roll was effective in the first pass or the second pass of rolling. as a result,
It has been found that performing large-diameter work roll rolling in the previous pass of rolling has a greater effect of improving magnetic properties.
These results were inconsistent with the techniques 3) and 4). Therefore, in order to produce a thin material in the present invention, 95-
Perform cold rolling to an intermediate thickness with a cold rolling machine of a large diameter work roll of 170 mmφ, and then, in another cold rolling machine, for example, roll to a final thickness with a small diameter roll of 65 mmφ or less,
What is necessary is just to roll with two cold rolling mills. However, this method has the drawback that the fixed cost of cold rolling increases and productivity is poor.

This problem can be overcome if the diameter of the work roll can be changed by, for example, a single cold rolling mill. However, the Sendzimir mill represented by types 21 and 22 used in the production of conventional unidirectional magnetic steel sheets has the following problems. Since a monoblock type housing is used as a basic configuration, it is difficult to change the work roll diameter during a rolling pass. Therefore, the present inventors applied a cluster mill composed of a split-type housing to the production of unidirectional magnetic steel sheets for the first time, rolling the first pass of rolling with a work roll diameter of 95 mmφ or more, and thinning the second pass with thin rolling. We succeeded in rolling by changing to suitable small-diameter rolls, and established a technology to produce thin unidirectional magnetic steel sheets with high magnetic flux density with a single rolling mill at low fixed cost and high productivity.

The present invention organically combines the metallurgical discovery that the large-diameter work roll effect of the cluster mill is effective in the preceding stage of the rolling pass and the efficient cold rolling technology of the split-housing cluster mill. It is a thing.

[0017]

SUMMARY OF THE INVENTION The present invention has been made based on the above findings, and the gist thereof is as follows. (1) In mass%, C: 0.025 to 0.100%, S
i: 2.5 to 4.5%, Al: 0.007 to 0.040
% Of the electromagnetic steel slab containing the hot-rolled sheet, and then subjected to hot-rolled sheet annealing to perform one-time cold rolling or two or more times of cold-rolling through intermediate annealing. In the method for producing a grain-oriented electrical steel sheet to be subjected to recrystallization annealing and then to secondary recrystallization annealing, the final cold rolling is performed by a lever mill, and the work roll diameter is changed at a plate thickness stage during the rolling. Method for producing a thin magnetically unidirectional magnetic steel sheet having a high magnetic flux density. (2) The preceding pass of the final cold rolling in the cold rolling is cold-rolled to a thickness of at least 0.40 mm or less with a work roll having a diameter of 95 to 180 mmφ, and subsequently the thickness from the intermediate thickness to the final thickness T _f. (Mm), D ≦
The method for producing a high magnetic flux density thin unidirectional magnetic steel sheet according to the above (1), wherein the thin magnetic sheet is cold rolled with a work roll having a diameter D (mmφ) of T _f × 520. (3) In at least one of the final cold rolling passes in the cold rolling, the strip temperature is set at 100
The method for producing a thin magnetically unidirectional magnetic steel sheet having a high magnetic flux density according to the above (1) or (2), wherein the magnetic steel sheet is held in a temperature range of from about 350 ° C. to at least one minute or more. (4) The above (1) to the product plate thickness is 0.23 mm or less.
The method for producing a high magnetic flux density thin unidirectional magnetic steel sheet according to any one of the above items (3). (5) In the cold rolling, by using a cluster type reversing rolling mill composed of a housing that can be divided into upper and lower parts, the work rolls having different diameters are exchanged at a thickness stage in the middle of a plurality of passes. The method for producing a high magnetic flux density thin unidirectional magnetic steel sheet according to any one of the above (1) to (4), wherein the final cold rolling is performed by one rolling mill.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, test results on which the present invention is based will be described. [Experiment 1] In mass%, C: 0.005%, Si: 3.3
%, Mn: 0.1%, S: 0.07%, Al: 0.02
82%, N: 0.0070%, and Sn: 0.07
% Of the magnetic steel slab was heated at a low temperature of 1150 ° C., and then hot-rolled into a hot-rolled coil having a thickness of 1.8 mm.

After annealing this hot-rolled coil at 1100 ° C.,
Using a heavy-duty Sendzimir mill, cold-roll at a rolling reduction of 90%,
Finished to a thickness of 0.18mm. At this time, the work roll diameter of the rolling mill was changed in the range of 40 to 180 mmφ until the sheet thickness reached 0.26 mm, and rolling was performed under the same conditions as the pass schedule and the number of passes (5 times). Further, at the thickness stage in the second, third and fourth passes, aging treatment was performed at 200 ° C. for 5 minutes. Then, rolling from 0.26 mm to 0.18 mm was completed in one pass with a work roll diameter of 60 mmφ.

Next, the cold-rolled sheet was made to have a primary recrystallization particle size of 23 μm.
After decarburizing annealing by adjusting the temperature so that
Nitriding annealing was performed so as to be ppm, and then a magnesia slurry was applied. After finish annealing this coil by a usual method, "insulating coating of Al phosphate + colloidal silica" was applied, and shape correction annealing combined with coating baking was performed to obtain a product. Then, the magnetic flux density B8 of this product was measured.

FIG. 1 shows the relationship between the work roll diameter and B8. FIG. 1 shows that the magnetic flux density B8 improves when the work roll diameter is in the range of 95 to 180 mmφ. [Experiment 2] An electromagnetic steel slab having the same components as in Experiment 1 was hot-rolled by low-temperature slab heating at 1150 ° C to produce a hot-rolled coil having a thickness of 2.0 mm. After annealing this hot-rolled coil at 1100 ° C, it was cold-rolled at a rolling reduction of 90% using a Sendzimir mill with 20 double rolls,
Finished to 0.20mm thickness. At this time, the work roll diameter of the rolling mill was set to two levels of i) 100 mmφ and ii) 60 mmφ, and 0.60 mm
It was rolled to multiple intermediate sheet thicknesses in the range of ~ 0.20 mm. At this time, aging treatment was performed at 200 ° C. for 5 minutes at the stage of the thickness in the middle of the second pass (1.00 mm) and the third pass (0.80 mm). Then 0.22mm
The above is based on i) and ii), and
Was recombined into a work roll having a diameter of 100 mmφ and ii) was rolled to 0.20 mm.

Thereafter, the cold-rolled sheet was subjected to a primary recrystallization grain size of 23 μm.
After decarburizing annealing by adjusting the temperature so that
Nitriding annealing was performed so as to be ppm, and then magnesia was applied. This coil is subjected to finish annealing by the usual method, and “insulating coating of Mg phosphate and colloidal silica”
, And shape-correcting annealing also serving as coating baking was performed to obtain a product. Then, the magnetic flux density B8 of this product was measured.

FIG. 2 shows the relationship between the minimum plate thickness (intermediate plate thickness) and the magnetic flux density B8 in the first-stage rolling when the work roll diameter is changed in the first and second passes. As a result, under the condition i) in which the first pass of the rolling is a large-diameter work roll, a high B8 can be secured if the large-diameter work roll is rolled to a sheet thickness of at least 0.40 mm. In ii), high B8 was not obtained under any conditions.

As described above, the magnetic flux density of the grain-oriented electrical steel sheet is affected by the inhibitor and the primary recrystallized structure. In [Experiment 1] and [Experiment 2], since [N] after nitriding annealing did not change the inhibitor under constant conditions, it is estimated that the rolling conditions affected the magnetic flux density through changes in the primary recrystallization structure. I do. Therefore, primary recrystallization samples corresponding to the work roll diameters of 50, 95, and 150 mm in [Experiment 1] were collected, and the primary recrystallization texture was investigated. X-ray analysis by sampling around 1 / 5t thickness, SGH method (Harase et al .: Bulletin of the Japan Institute of Metals No. 2
9 Vol. 7, No. P552).

FIG. 3 shows the intensity (I) of the Goss direction around the ND axis.
_N ) and the intensity of the azimuth corresponding to Σ9 (IcΣ9). Looking at Figure 3, it work roll diameter is large, I _N intensity of Goss orientation (° rotation angle 0) is increased, I _N intensity shifted about 25 ° from the ND axis decreases, around the ND axis It can be seen that the distribution of IcΣ9 sharpens. In order to obtain a grain-oriented electrical steel sheet having a high magnetic flux density, the conditions that the primary recrystallized texture should have are that the goss orientation is large and the # 9 corresponding orientation for preferential growth of goss is sharp. When the work roll diameter is controlled according to the present invention, a primary recrystallized texture suitable for increasing the degree of Gos accumulation of secondary recrystallization is obtained.

The above is the result of the low-temperature slab heating method using the AlN inhibitor.
As shown in the above, the MnS, AlN + MnS (MnSe) inhibitor and the high-temperature slab heating method supplemented with Sn, Sb, Cu and the like were also investigated. As a result, the effect of improving the magnetic flux density with the increase in the work roll diameter was confirmed for all component-based materials containing AlN as an inhibitor. On the other hand, no effect could be confirmed in the component system containing no AlN.

It is known that AlN has a higher inhibitor strength than MnS (MnSe) and is thermally stable. When such an AlN inhibitor is used, it is presumed that the primary recrystallized texture obtained by the present invention effectively exerts a magnetic flux density improving effect. The mechanism of the relationship between work roll diameter control and primary recrystallization texture formation is not clear at present, but is hypothesized as follows. It is known that when the work roll diameter is small, the shear deformation component of the steel sheet surface increases during cold rolling, and after the primary recrystallization, the (110) plane increases and the (111) plane decreases. (Kono et al .: Iron and Steel, 68 (1982), p. 58). At this time, (1
On the 10) surface, it is estimated that the orientation group rotated around the ND axis from the Goss orientation increases, resulting in a broad texture that is undesirable for unidirectional electromagnetic steel sheets. Therefore, it is presumed that sharpening the texture by increasing the diameter of the work roll is an effect of increasing the magnetic flux density. In addition, the reason why the effect of increasing the work roll diameter is effective in the former pass of rolling is that the thicker the plate thickness, the larger the bite angle into the work roll material, and the greater the shear deformation component on the steel sheet surface. I think there is.

Next, the reasons for limitation of the composition of the grain-oriented electrical steel in the present invention and the preferred range of the components will be described. The unit of the composition content is mass%. C
Is an important element for austenite formation, and 0.02
More than 5% is necessary. If too much, decarburization becomes difficult, so the upper limit is set to 0.100%. If the content of Si is too small, the electric resistance becomes small and good iron loss characteristics cannot be obtained.
If too much, cold rolling becomes difficult, so its content is 2.
5% or more and 4.5% or less.

Mn has a lower limit of 0.03% as an unavoidable component.
On the other hand, if too much, assuming high-temperature slab heating, it becomes difficult to solutionize MnS and MnSe, so the upper limit is set to 0.
45%. S and Se are appropriately added depending on the type of the inhibitor to be used. These combine with the Mn to form MnS or MnSe which acts as an inhibitor. The component range of S and Se is preferably 0.01% or more and 0.04% or less in both cases of single use and combination use. However, MnS,
In order to precipitate MnSe finely, high-temperature slab heating is required. On the other hand, in the low-temperature slab heating method using the post-step nitriding method, since fine MnS and MnSe are unnecessary, 0.015%
The following is desirable. Therefore, the ranges of S and Se are not particularly limited.

In the present invention, in particular, it is indispensable to contain Al as an inhibitor component in order to obtain a high magnetic flux density, and it is necessary to add a certain amount or more. However, if the amount is too large, the heating time of the high-temperature slab for solution treatment becomes long, and the productivity deteriorates. Therefore, the Al content is set to 0.007% or more and 0.040% or less. If N is premised on high-temperature slab heating, AlN is used for annealing before final cold rolling.
Therefore, it is contained in the range of 0.003% or more and 0.020% or less. On the other hand, in the low-temperature slab heating method,
Since AlN is formed by a nitriding treatment after the primary recrystallization, it is not essential to contain N in the steelmaking stage. Therefore, the range of N is not particularly limited.

In addition to the above, in order to improve magnetism,
Components such as n, Sb, Cu, Ni, Cr, P, V, B, Bi, Mo, Nb, and Ge can also be appropriately added within a known range. Next, conditions related to the manufacturing process will be described. In the present invention, a known manufacturing method is applied to the manufacturing process of the steel material. The manufactured ingot or slab is processed as necessary, adjusted in size, heated, and hot-rolled. The slab heating temperature is set in the range of 1100 ° C. to 1450 ° C. as necessary, and a normal gas heating furnace or an induction / electric heating furnace is used for heating. The final strip thickness of the steel strip after hot rolling is obtained by a single cold rolling method after hot-rolled sheet annealing or a plurality of cold rolling methods sandwiching intermediate annealing.

Prior to the final cold rolling, annealing is performed under known conditions. When assuming high-temperature slab heating,
In securing insufficient AlN fine precipitation by hot rolling,
Annealing before the final cold rolling is essential. On the other hand, when premised on low-temperature slab heating, annealing before final cold rolling for control of AlN precipitation is not essential, but because of carbide and solid solution C control technology, rapid cooling after annealing and cooling process In order to further enhance the aging treatment between passes of the present invention, techniques such as processing strain addition and retention for carbide precipitation, even if annealing before final cold rolling is performed, the effect of the present invention is not impaired. .

Thereafter, the steel sheet is subjected to final cold rolling by reversal rolling. At this time, in order to obtain a high magnetic flux density, a reduction rate of 81% or more is conventionally known. preferable. In the present invention, aging treatment during cold rolling and warm rolling are important for improving magnetic properties. In particular, in the case of high-temperature slab heating, it is known that it is more effective than the effect of improving magnetic properties from the viewpoint of preventing the generation of linear fine particles. And in the present invention,
As shown in Example 3, 100 to 350
It is important to keep the temperature in the temperature range of ° C. for 1 minute or more.

Another feature of the present invention is to produce a grain-oriented electrical steel sheet having excellent magnetic properties by increasing the diameter of the work roll in the first pass of cold rolling.
As shown in Fig. 1, the magnetic flux density is 90 mm
Below, it is remarkably inferior, improved above 95 mmφ, and 120 mmφ
The above tends to be almost saturated. Therefore, in the present invention,
The work roll diameter is 95 mmφ or more, preferably 120 mmφ or more. On the other hand, if the diameter of the work roll is too large, the effect is not only saturated, but also the cluster mill becomes large-scale and equipment cost increases, so the upper limit is 180 mmφ. In addition, the range of applying a large-diameter work roll having a diameter of 95 to 180 mmφ is effective when the plate thickness is large and in the preceding pass of rolling, and it is necessary to perform the process up to at least 0.40 mm or less, preferably 0.26 mm or less. It can be seen from FIG.

On the other hand, in the latter pass rolling, the smaller the finished plate thickness, the larger the rolling reaction force.
Rolling becomes difficult with a large diameter work roll of 95 to 180 mmφ. Therefore, it is necessary to select the work roll diameter according to the required product thickness. Thus, the present inventors
The relationship between the work roll diameter and the minimum rollable plate thickness was experimentally determined using a work roll diameter variable rolling mill.
As a result, when the work roll diameter was Dmm and the minimum plate thickness was _Tf mm, the relationship of _Tf = D / 520 was obtained. This relationship is
Although slightly higher than the theoretical formula of Stone (μ = 0.1), it is considered that this is due to an adverse effect such as thermal crown caused by high-temperature rolling.

In conclusion, as shown in FIG. 4, the relationship between the work roll diameter and the final rolling thickness can be illustrated. Hereinafter, the rolling method of the present invention will be described by dividing into a first pass and a second pass of rolling. The work roll diameter is 95 to 180 mmφ at least up to a plate thickness of 0.40 mm in the first pass of rolling. The rolling at this time is based on high-temperature rolling and aging treatment between passes.
Next, the rolling of the latter pass, when the finished plate thickness is T _f mm,
By rolling with a work roll diameter of (520 × T _f ) mm or less, a thin material can be stably obtained. For example, in the case of a work roll of 120 mmφ which is preferable for improving the magnetic flux density, 0.23 m
Since the thickness of m is the rolling limit, it is difficult to finish the product thickness of 0.23 mm or less by rolling. Further, when the product thickness is 0.20 mm, the lower limit of the former pass of the present invention is 95 mm.
Although it is possible to finish with a work roll of φ, it is difficult to obtain a stable high magnetic flux density. When the product plate thickness is 0.18 mm or less, rolling cannot be performed with a work roll of 95 mmφ, and therefore, it is necessary to change to a small diameter roll of, for example, 60 mmφ. For the above reasons, in order to obtain a stable magnetic flux density improvement effect, it is necessary to replace the work roll with a small-diameter work roll in a subsequent pass of rolling.

From the viewpoint of the stability of high-temperature rolling and thin rolling, cold rolling mills are limited to cluster-type reversing mills (Senzimir mill, NMS mill, etc.) such as 6-layer, 12-layer, and 20-layer. Further, it is a feature of claim 2 of the present invention that the housing is changed to a suitable work roll diameter in the middle rolling stage by using a split mold and the above-mentioned rolling is performed by one rolling mill. FIG. 5A shows a conceptual diagram of a conventional monoblock type housing, and FIG. 5B shows a conceptual diagram of a split type housing. In (a), it is possible to change the diameter of the work roll by changing the diameter of the intermediate roll, but the change range is as small as about 10 mm, and the reloading work burden is large, which is not practical. In (b), the work roll diameter can be changed by raising and lowering the upper and lower housings and adjusting the distance between the bores. Further, the cluster mill has no chocks in the work rolls, so that the work rolls can be quickly replaced during the rolling of the coil, and the productivity is not deteriorated.

[0038] The steel sheet after the final rolling is subjected to a degreasing treatment, and thereafter subjected to an annealing for both decarburization and primary recrystallization. In the case of the low-temperature slab heating method in which the slab heating temperature is 1250 ° C. or less, it is effective to perform a nitriding treatment between the primary recrystallization and the secondary recrystallization to form an AlN inhibitor. As a method of nitriding treatment, a method performed during finish annealing disclosed in JP-A-60-179885 and the like, and a method disclosed in JP-A-1-82393.
There is a method in which annealing is performed in a mixed gas of "hydrogen + nitrogen + ammonia" while running a strip disclosed in Japanese Patent Application Laid-Open Publication No. H10-163,036. To stably develop good secondary recrystallized grains,
The nitrogen content needs to be 120 ppm or more, preferably 150 ppm or more. Further, when the control of the primary recrystallization particle size disclosed in Japanese Patent Application Laid-Open No. 1-82939 is used in combination, the magnetic characteristics are further improved.

Next, the steel sheet is coated with an annealing separator containing MgO slurry as a main component, and then wound in a coil shape and subjected to final finish annealing. After that, if necessary, an insulating coating is applied, but laser, plasma, mechanical method,
It is also effective to perform a magnetic domain refining process by etching or other methods.

[0040]

EXAMPLES (Example 1) An electromagnetic steel slab containing the components shown in Table 1 was produced under the manufacturing process conditions shown in Table 2 in the range of 1350 to 1350.
1400 ° C high-temperature slab heating a), b) and c), and 1150-1290
The steel sheet was hot-rolled by a method of low-temperature slab heating d), e), and f) to obtain a hot-rolled steel strip.

In a), c) and f), the cold rolling was performed twice with intermediate annealing, and in b), e) and d), the cold rolling was performed once after hot-rolled sheet annealing. The final cold rolling was performed using a reversing mill, and the rolling reduction was 75 to 92%. The intermediate plate thickness and final plate thickness are as shown in the table. In the cold rolling, the work roll diameter was changed as shown in Table 1, and rolling was performed in 2 to 5 passes until the plate thickness was 0.30 mm. Select at least 2 pass intermediate plate thickness during rolling, 200 ℃
Aging treatment for 5 minutes. Subsequently, it was rolled in one pass to a sheet thickness of 0.18 mm with a work roll diameter of 60 mm. The cold-rolled steel strip is subjected to decarburizing annealing by a usual method. Of these, for d) and e), nitriding annealing is added after decarburizing annealing, and the amount of nitriding shown in Table 1 (after nitriding-before nitriding) ) To reinforce the inhibitor. Thereafter, magnesia application, finish annealing, insulating coating, shape correction and baking annealing were performed by a usual method, and the magnetic flux density (B8) of the obtained product steel strip was measured. Thereafter, the magnetic domain was controlled by a mechanical method, and the iron loss (W17 / 50) of the obtained product steel strip was measured. As shown in Table 1, it is found that when the work roll diameter of the cold rolling is controlled within the range specified in the present invention with the Al-containing component, a product having excellent magnetic properties can be obtained.

[0042]

[Table 1]

[0043]

[Table 2]

(Example 2) As shown in Table 3, ten kinds of workpieces were prepared by annealing an annealed material having an intermediate thickness of 1.6 mm as shown in Table 1 a) and Table 2 a) using a reversing mill. Roll diameter
Cold rolling was performed to a final sheet thickness of 0.20 mm using a combination of 120 mmφ and 60 mmφ. The aging between passes was performed at 200 ° C. for 5 minutes at the plate thickness stages shown in Table 2. The cold rolled steel strip was subjected to decarburizing annealing, magnesia coating, finish annealing, insulating coating, shape correction and baking annealing in the usual manner, and the magnetic flux density (B8) of the obtained product steel strip was measured. Then, after performing magnetic domain control by a mechanical method, the iron loss (W1
7/50) was measured. As shown in Table 2, it is understood that a product having excellent magnetic flux density can be obtained by applying a large-diameter work roll having a diameter of 120 mm to a thickness of at least 0.4 mm or less in a pass before rolling.

[0045]

[Table 3]

(Example 3) An annealed material having an intermediate plate thickness of 1.6 mm shown in a) of Table 1 and a) of Table 2 was used with a work roll diameter of 1 mm.
Using a reversing mill having a diameter of 65 mm, rolling was performed to 0.30 mm under the 12 conditions of holding temperature and time between passes shown in Table 4, and then cold-rolled to a work roll diameter of 50 mm and a final thickness of 0.15 mm. Decarburization annealing, magnesia application, finish annealing, insulation coating, shape correction,
Baking annealing was performed, and the magnetic flux density (B8) of the obtained product steel strip was measured. Then, after performing magnetic domain control by etching, the iron loss (W17 / 50) of the obtained product steel strip was measured.
As shown in Table 4, a product having excellent magnetic properties was obtained by holding at a temperature range of 100 to 350 ° C. for 1 minute or more at the thickness stage during rolling.

[0047]

[Table 4]

[0048]

According to the present invention, in a thin unidirectional magnetic steel sheet containing Al and having a product thickness of 0.23 mm or less, the magnetic properties can be improved by improving the magnetic flux density. Therefore, the present invention contributes to low iron loss and miniaturization of transformers and the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a work roll diameter and a magnetic flux density.

FIG. 2 is a diagram showing the relationship between the minimum thickness of pre-rolling and the magnetic flux density.

FIG. 3 is a diagram showing an analysis result relating to a primary recrystallization texture of a steel sheet when a work roll diameter is changed.

FIG. 4 is a diagram showing a relationship between a work roll diameter and a minimum rollable plate thickness.

FIG. 5 is a schematic view of a 20-stage cluster mill having a monoblock type housing and a split type housing.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 38/60 C22C 38/60 (72) Inventor Masao Mukai 1-1 Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Inside Nippon Steel Corporation, Yawata Works (72) Inventor Shinya Hayashi 1-1, Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Inside Nippon Steel Corporation, Yawata Works (72) Inventor Toshiyuki Shiraishi Chiba 20-1 Shintomi, Futtsu Nippon Steel Corporation Technology Development Division F term (reference) 4K033 AA02 BA01 BA02 CA01 CA02 CA03 CA04 CA06 CA07 CA08 FA04 PA05 5E041 AA02 AA19 CA02 HB05 HB07 HB11 NN01 NN06 NN17 NN18

Claims (5)

[Claims] C: 0.025 to 0.100 by mass%
%, Si: 2.5-4.5%, Al: 0.007-0.
After subjecting the electromagnetic steel slab containing 040% to hot rolling, hot-rolled sheet annealing is performed, and one cold rolling is performed, or two or more times of cold rolling is performed through intermediate annealing, and then, Primary recrystallization annealing, and then, in a method for producing a unidirectional electrical steel sheet subjected to secondary recrystallization annealing, performing the final cold rolling with a lever mill, and changing the work roll diameter at the thickness stage during the rolling. A method for producing a thin magnetically unidirectional magnetic steel sheet with a high magnetic flux density. 2. The pre-pass of the final cold rolling in the cold rolling is cold-rolled with a work roll having a diameter of 95 to 180 mmφ to an intermediate plate thickness of at least 0.40 mm or less,
2. The rolling according to claim 1, wherein the rolling from the intermediate sheet thickness to the final sheet thickness T _f (mm) is cold-rolled with a work roll having a diameter D (mmφ) satisfying D ≦ T _f × 520. Manufacturing method of high magnetic flux density thin unidirectional magnetic steel sheet. 3. The strip temperature is maintained in a range of 100 to 350 ° C. for at least one minute during at least one of the last cold rolling passes in the cold rolling. 3. The method for producing a high magnetic flux density thin unidirectional magnetic steel sheet according to 1 or 2. 4. The method according to claim 1, wherein a product thickness of the product is 0.23 mm or less. 5. In the cold rolling, using a cluster-type reversing rolling mill composed of a housing that can be divided into upper and lower parts, the work rolls are exchanged for work rolls having different diameters at a thickness step in the middle of plural-pass rolling. 5. The method for producing a high magnetic flux density thin unidirectional magnetic steel sheet according to claim 1, wherein the final cold rolling is performed by one rolling mill.