JPH05247538A - Manufacture of low iron loss grain-oriented electrical steel sheet - Google Patents

Abstract

PURPOSE:To manufacture a low iron loss grain-oriented electrical steel sheet by forming grooves to be imparted to the surface of a steel sheet in such a manner it is not executed after finish annealing, but it is directly formed on a cold rolled sheet by a simple method. CONSTITUTION:This method is characterized in that a grain oriented silicon steel sheet in which a slab contg., by weight, 2.0 to 4.5% Si is subjected to hot rolling, is annealed according to necessary and is subjected to cold rolling for one or two times including process annealing to regulate its sheet thickness into a final one, which is then subjected to decarburizing treatment including primary recrystallization annealing and is subjected to finish annealing, on the cold rolled steel sheet after the final cold rolling, by forming grooves which are not disappeared even after the following final treating stage in a direction cross to the rolling direction preferably at a depth of 5 to 50% of the sheet thickness in a linear or dotted shape.

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 having a high magnetic flux density and an extremely low iron loss value.

[0002]

2. Description of the Related Art Unidirectional electrical steel sheets are used as iron cores for transformers and other electric equipment to increase the magnetic flux density, but due to the recent trend of energy saving resulting from resource and environmental problems. Is required to further lower the iron loss value. As is well known, in order to improve magnetic flux density and iron loss, secondary recrystallized grains (110) [00
1] The texture of the orientation, that is, the so-called Goss orientation, should be increased in the degree of integration. The higher the degree of integration, the larger the crystal grains, and the larger the magnetic domain width. Will increase. Therefore, it has not been so much expected to improve the iron loss characteristics relatively.

Therefore, a method for subdividing magnetic domains has been developed and many proposals have been made in order to improve the iron loss of a high magnetic flux density unidirectional electrical steel sheet. For example, Japanese Patent Publication Sho 58-59
In Japanese Patent No. 68, a method of introducing a linear microstrain on the surface of a steel sheet that has been subjected to finish annealing in a direction crossing the cold rolling direction by a scoring method, and in Japanese Patent Publication No. 57-2252, a laser is applied to the surface of the steel sheet. A method of irradiating to introduce a linear strain, and Japanese Patent Publication No. 62-53579 discloses that a groove having a depth of more than 5 μm is formed in a base metal portion of a steel sheet subjected to an insulating film treatment after finish annealing and then heat treatment. ing. More recently, in Japanese Patent Laid-Open No. 63-76819, linear grooves are formed on the surface of a finish-annealed steel sheet having forsterite, and there is no strain around the grooves to generate fine recrystallized grains during strain relief annealing. And the linear grooves remove the forsterite coating linearly by a mechanical means such as a laser or a knife, or prevent the forsterite coating from being locally generated beforehand, and electrolytic or chemical etching is performed. It is disclosed that this is applied to form a base steel. Further, in Japanese Patent Application Laid-Open No. 2-50918, a finish-annealed steel sheet having a forsterite coating film is wound around a roll with protrusions in a state where bending stress is applied to locally remove the coating film on the surface of the steel sheet, and electrolytically etched to form a wire. A method of forming a groove is proposed.

In the above-mentioned Japanese Patent Laid-Open No. 63-76819, it is pointed out that in the scoring method and the laser method described above, the iron loss is deteriorated by the strain relief annealing after introducing the strain. Further, in the method of utilizing the fine recrystallized group generated at the time of annealing by locally introducing strain to the finish annealed steel sheet as in the above publication, the fine recrystallized grains grow at the time of high temperature annealing to cause iron loss deterioration. Therefore, it is described that the purpose is to solve this. In addition, JP-A-2-5091
No. 8 discloses that the method of the above publication has poor stability in industrial production, increases cost, and cannot obtain a stable iron loss value.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In, the problems of the conventional method are pointed out, and their solution methods are explained, but the invention described in any of the publications forms a linear strain or groove on the steel sheet surface after finish annealing, In the invention described in the gazette, since a complicated means step of locally removing or not forming the forsterite coating and forming a groove in this portion by etching is required, the production cost is increased. Further, these means are not always capable of stably forming a groove, and further, sufficient control is required for a stable etching method without affecting the coating film, which also complicates the treatment process. .. The present invention is to eliminate such conventional problems, rather than performing the grooves to be applied to the steel sheet surface after finish annealing, directly on the cold rolled sheet, by forming by a simple method,
An object is to provide a method for manufacturing a low iron loss unidirectional electrical steel sheet.

[0006]

In order to achieve the above object, the present invention has the following structures. That is, 2.0
Hot rolling a slab containing ~ 4.5 wt% Si,
The hot-rolled sheet thus obtained is annealed if necessary, and then cold-rolled once or twice or more with intermediate annealing to obtain a final sheet thickness, and then subjected to decarburizing treatment including primary recrystallization annealing. After that, finish annealing is performed, and in a series of unidirectional electrical steel sheet manufacturing methods including these steps, in the cold rolled steel sheet after the final cold rolling, after the final treatment step in the direction intersecting the rolling direction. In the method of manufacturing a low iron loss unidirectional electrical steel sheet, the groove is formed so as not to be erased. Further, it is preferable that the groove has a continuous or discontinuous linear or dot shape, and the depth thereof is 2 to 30% of the plate thickness.

The present invention will be described in detail below. In the present invention, a slab containing 4.5% or less of Si cast by a usual method is hot-rolled into a hot-rolled sheet, and the hot-rolled sheet is annealed if necessary and then cold-rolled. Cold rolling is carried out once or by a double rolling method with intermediate annealing to obtain the final plate thickness. The steel sheet having the final thickness is subjected to decarburization in wet hydrogen and primary recrystallization annealing, and after applying an annealing separator, finishing high temperature annealing is performed.

The present invention adopts a conventional method for producing a grain-oriented electrical steel sheet including such main steps. The cold-rolled sheet having a product sheet thickness obtained by this cold rolling intersects the rolling direction. The direction, that is, the orthogonal direction is preferable, but the groove is formed within an allowable range of ± 45 degrees with reference to this direction.

FIG. 1 shows a cross section of a cold rolled steel sheet S having a groove G formed therein. As shown in FIG. 2, the groove depth d is preferably 1/3 or less of the plate thickness t. The formed groove is not erased in the subsequent steps.

FIG. 2 shows the relationship between groove depth and iron loss. That is, the slab containing Si: 3.25% is 1340 ° C.
After hot-rolling, the product is hot-rolled into a hot-rolled sheet of 2.5 mm, and the hot-rolled sheet is annealed and cold-rolled to give a product thickness of 0.23 mm. 0% (without groove), 1%,
The V-shaped groove was processed and formed with a grooved roll so as to be 2%, 5%, 30%, and 40%. Samples of 5 grooves each for each groove depth were prepared, decarburization annealed in wet hydrogen at 800 ° C. for 60 seconds, and subsequently subjected to primary recrystallization treatment, and then MgO was applied as a main component annealing separating agent. Dried. The subsequent high temperature finish annealing was performed at 1200 ° C. for 20 hours, and after the insulation coating treatment, strain relief annealing was performed at 800 ° C. for 2 hours, and then the iron loss value was measured. As is apparent from the figure, the grooved material having a depth of 2% exhibits an extremely excellent iron loss value and the 30% material is also good as compared with the conventional material having no groove (0%). However, no significant effect can be seen at 40%. It is considered that when the groove depth exceeds 30%, the iron loss value becomes abnormal due to the local increase of the magnetic flux density at the groove forming portion, and the overall iron loss value is deteriorated. From these results, it is understood that if the groove depth introduced into the cold rolled sheet of the present invention is 30% or less, the magnetic domains are subdivided even after the strain relief annealing, and the iron loss can be reduced. However, if the groove is too shallow, the effect of domain division is small. That is, if it is less than 2%, no significant improvement in iron loss value is observed, and if it exceeds 0.8 w / kg, at least 2% or more is necessary.

The width of the groove (w in FIG. 1) is preferably 300 μm or less because if the width is made too wide, the magnetic flux density decreases. The distance between adjacent grooves is 1 to 20.
It may be in the range of mm, and particularly preferably 2.5 to 10 mm. Such a groove may be provided on the steel plate surface in a direction perpendicular to the rolling direction or in a range of 90 degrees centering on this vertical direction,
The groove may be formed by, for example, scoring with a sharp blade, mechanical means such as gears, grindstones or water jets, high-density energy such as ultrasonic waves, lasers, EB, plasma, or chemical means such as electrolytic etching. Etc. These methods can be performed, for example, between the uncoiler and the annealing furnace in the decarburizing annealing step, the groove formed in the cold rolled steel sheet becomes V-shaped or U-shaped, and the final product obtained through the subsequent steps is subjected to the above-mentioned process. The groove of the shape remains as it is. As a result, the magnetic domains are effectively subdivided, and the iron loss can be significantly improved.

[0012]

EXAMPLE C: 0.075% by weight, Si: 3.25 by weight
%, Mn: 0.07%, S: 0.025%, Al: 0.
027%, N: 0.008%, Sn: 0.10%, C
u: 0.05%, 1 slab consisting essentially of Fe
After heating to 380 ° C., hot rolling was performed to manufacture a hot rolled steel strip 5 coil having a thickness of 2.3 mm. After rolling each of these coils to 1.6 mm, they were annealed at 1120 ° C. for a short time and rapidly cooled from 800 ° C. to room temperature. Next, this annealed steel sheet was subjected to cold rolling to obtain a cold-rolled sheet having a final sheet thickness of 0.23 mm, and transferred to a decarburization annealing line. Immediately before the annealing furnace on the entry side of the decarburizing annealing line, a grooved roll having a groove width of 80 μm and a groove interval of 5 mm for the three coils A, B and C among the coils,
Continuous rolling was performed so that the groove depth (groove depth / plate thickness × 100) was 1%, 7%, and 25%, respectively, while the coil D was 35% and the coil E was 0%.
(No reduction), then each of these coils was subjected to decarburization annealing to treat the steel plate C to 30 ppm or less, and then MgO
Was applied as an annealing separator. Then, above 5
The coil is subjected to finish annealing at 1200 ° C for 20 hours, and then the surface is coated with an insulating film to obtain a product.
After performing stress relief annealing at 00 ° C. for 2 hours, the magnetic properties of the obtained steel sheet were measured. The measurement results are shown in Table 1.

[0013]

[Table 1] As is clear from Table 1, in the coils B and C which were subjected to the grooved treatment within the scope of the present invention, the iron loss value was significantly improved as compared with the other coils A, D and E.

[0014]

As described above, according to the present invention, by forming grooves in the steel sheet after cold rolling, the magnetic domains of the final product can be subdivided, and the core loss of the high magnetic flux density unidirectional electrical steel sheet can be further improved. Can be improved.

[Brief description of drawings]

FIG. 1 shows a cross section of a grooved cold-rolled steel sheet of the present invention.

FIG. 2 shows the relationship between the groove depth formed in the product of the present invention and iron loss.

Claims (2)

[Claims] 1. A slab containing Si in an amount of 2.0 to 4.5% by weight is hot-rolled, and the obtained hot-rolled sheet is annealed as required and then sandwiched once or by intermediate annealing. In a manufacturing method of a series of unidirectional electrical steel sheets including these steps, cold rolling is performed twice or more to obtain a final thickness, decarburization treatment including primary recrystallization annealing is performed, and then finish annealing is performed. A method for producing a low iron loss unidirectional electrical steel sheet, comprising forming grooves in a direction intersecting the rolling direction on the cold rolled steel sheet after the final cold rolling. 2. The low iron loss unidirectionality according to claim 1, wherein the shape of the groove is continuous or discontinuous linear or dot-like, and the depth is 2 to 30% of the plate thickness. Manufacturing method of electrical steel sheet.