Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1999-08-18
2001-09-11
Jones, Deborah (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C428S332000, C428S216000, C428S141000, C428S697000, C428S698000, C428S699000, C148S307000, C148S308000
Reexamination Certificate
active
06287703
ABSTRACT:
TECHNICAL FIELD
This invention relates to a ultra-low core loss grain oriented silicon steel sheet and a method of producing the same, and more particularly its object it is to realize more improvement of core loss property together with an improvement of compression stress in magnetostriction.
As will be detailed hereinafter, Applicants do this at low cost by forming an extremely thin Si-containing nitride-oxide layer on a surface of final annealed silicon steel sheet or a surface of final annealed silicon steel sheet having a linear concave region and forming a tension insulating film thereon.
BACKGROUND ART
The grain oriented silicon steel sheet is mainly used as a core of a transformer or other electrical apparatus and is required to have a high magnetic flux density (represented by B
8
value) and a low core loss (represented by W
17/50
) as a magnetic property.
In order to improve the magnetic properties of the grain oriented silicon steel sheet, it is required to highly align the <001> axis of secondary recrystallized grain in the steel sheet into the rolling direction on one hand, and it is required to decrease impurities and precipitates remaining in the final product as far as possible on the other hand.
For this end, after a basic production technique of the grain oriented silicon steel sheet through two-stage cold rolling has been proposed by N. P. Goss, many improvements for such a production technique have been repeated to improve the magnetic flux density and core loss value of the grain oriented silicon steel sheet every year.
Among them, there are typically a method described in JP-B-51-13469 using Sb and MnSe or MnS as an inhibitor and a method described in JP-B-33-4710, JP-B-40-15644, JP-B-46-23820 and the like using AlN and MnS as an inhibitor. According to these methods, there was obtained a product having a high magnetic flux density that B
8
exceeds 1.88T.
In order to obtain a product having a higher magnetic flux density, JP-B-57-14737 discloses the composite addition of Mo to a starting material or JP-B-62-42968 discloses the application of quenching treatment after the intermediate annealing just before final cold rolling after the composite addition of Mo to the starting material, whereby there are obtained a high magnetic flux density where B
8
is not less than 1.90T and a low core loss that core loss W
17/50
is not more than 1.05 W/kg (product thickness: 0.30 mm). However, there is left room to be further improved as to sufficient reduction of core loss.
Particularly, it is considerably demanded to reduce power loss as far as possible because of the energy crisis, and it is desired to more improve the loss even in the application as an iron core material accompanied therewith. For this end, many products thinning the product thickness to not more than 0.23 mm (9 mil) are used for decreasing eddy current loss as much as possible.
The aforementioned techniques are mainly metallurgical methods. Besides these methods, there is developed a method of reducing core loss (technique of finely dividing magnetic domain), in which the surface of the steel sheet after the final annealing is subjected to laser irradiation or plasma irradiation to artificially decrease the 180° magnetic domain width (B. Fukuda, K. Sato, T. Sugiyama, A. Honda and Y. Ito: Proc. of ASM Con. of Hard and Soft Magnetic Materials, 8710-008, (USA), (1987)). The core loss of the grain oriented silicon steel sheet is largely reduced by the development of such a technique.
However, this technique has a drawback that it is not durable to annealing at a higher temperature, so that there is a problem that the application is restricted to only a laminated core type transformer not requiring strain relief annealing.
In this connection, a method wherein linear grooves are introduced in a surface of a steel sheet after the final annealing of the grain oriented silicon steel sheet to finely divide magnetic domain through anti-magnetic field effect of such grooves is industrialized as a finely magnetic domain dividing technique durable to strain relief annealing (H. Kobayashi, E. Sasaki, M. Iwasaki and N. Takahashi: Proc. SMM-8., (1987), P.402).
Besides this technique, a method wherein the magnetic domain is divided by subjecting a final cold rolled sheet of the grain oriented silicon steel sheet to a local electrolytic etching to form grooves (JP-B-8-6140) is also developed and industrialized.
Apart from the aforementioned production methods of the silicon steel sheet, amorphous alloys are noticed as a material for the usual power transformer, high-frequency transformer or the like as disclosed in JP-B-55-19976, JP-A-56-127749 and JP-A-2-3213.
However, a very excellent core loss property is obtained in such amorphous materials as compared with the conventional grain oriented silicon steel sheet, but they have demerits in practical use because thermal stability is lacking, space factor is poor, cutting is not easy, and they are too thin and brittle, to bringing about a large cost up in the assembled step of the transformer, and hence it is not yet attained to use a greater amount of such materials at the present time.
In addition, JP-B-52-24499 proposes a method wherein a forsterite base film formed after the final annealing of the silicon steel sheet is removed and the surface of the steel sheet is polished and then the surface of the steel sheet is subjected to a metal plating.
In this method, however, a low core loss is obtained at a low temperature, but when it is subjected to a high temperature treatment, the metal diffuses into the silicon steel sheet and there is a drawback that the core loss property is rather degraded.
In order to solve the above problem, the inventors have disclosed in JP-B-63-54767 and the like that an ultra-low core loss is obtained by forming one or more tension films selected from the group consisting of nitrides and carbides of Si, Mn, Cr, Ni, Mo, W, V, Ti, Nb, Ta, Hf, Al, Cu, Zr and B on the grain oriented silicon steel sheet smoothened by polishing through CVD or a dry plating (PVD) such as ion plating, ion implantation or the like.
Although a very excellent core loss property as a material for a power transformer, high-frequency transformer or the like is obtained by such a production method, it can not be said to sufficiently respond to the recent demand for the attainment of low core loss.
Therefore, the inventors have made fundamental reexaminations from all viewpoints for more reducing the core loss as compared with the conventional one.
That is, in order to obtain product having a ultra-low core loss by forming one or more tension films selected from various nitrides and carbides on the smoothened surface of the grain oriented silicon steel sheet at a stabilized step, the inventors became aware that it is required to conduct fundamental reexamination from raw material components of the grain oriented silicon steel sheet to the final treating step, and have made various studies from a pursuit on texture of a silicon steel sheet to smoothness of steel sheet surface or a final CVD or PVD treating step.
As a result, we have found the following:
(1) A thin ceramic film covered on the silicon steel sheet (use TiN film as a typical example) lessens the degree of improving the core loss even when it is formed at a thickness of not less than 1.5 &mgr;m. That is, TiN film having a thickness of not less than 1.5 &mgr;m can expect a slight improvement to the core loss and rather brings about the degradation of space factor and magnetic flux density.
(2) In this case, TiN is more important to play a role of adhesion to the silicon steel sheet in addition to the application of tension inherent to the ceramic. That is, when a lateral section of TiN is observed by means of a transmission electron microscope (see Yukio Inokuti: Bulletin of The Japan Institute of Metals, 60(1996), P.781~786), a lateral stripe of 10 nm is observed, which corresponds to a 5 atom layer of Fe—Fe atom in [011] direction of the silicon steel sheet.
(3) When a two-layer texture of
Jones Deborah
Kawasaki Steel Corporation
Savage Jason
Schnader Harrison Segal & Lewis LLP
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