Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Patent
1994-01-07
1998-07-21
Ip, Sikyin
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
148111, C21D 812
Patent
active
057829985
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for producing a unidirectionally grain oriented silicon steel sheet that is utilized mainly as an iron core of transformers and other electrical equipment. In particular, the present invention aims at an improvement in the iron loss property through effective finishing of the surface of a unidirectionally grain oriented silicon steel sheet.
BACKGROUND ART
Unidirectionally grain oriented silicon steel sheets are used in magnetic iron core in many types of electrical equipment. The unidirectionally grain oriented silicon steel sheets are steel sheets having an Si content of 0.8 to 4.8% and, in the form of a product, a highly integrated {110}<001> grain orientation.
They are required to have a high magnetic flux density (a value represented by a B8 value) and a low iron loss (a value represented by a W.sub.17/50 value) as magnetic properties. Particularly, in recent years, there is an ever-increasing demand for a reduction in the power loss from the viewpoint of energy saving.
In order to comply with this demand, a technique for dividing magnetic domains has been developed as means for reducing the iron loss of unidirectionally grain oriented silicon steel sheets.
In the case of laminated cores, for example, Japanese Unexamined Patent Publication (Kokai) No. 58-26405 discloses a method of domain refinement wherein a steel sheet after finish annealing is irradiated with a laser beam to give a small local strain to the steel sheet, thereby dividing magnetic domains to reduce the iron loss. On the other hand, in the case of wound iron cores, for example, Japanese Unexamined Patent Publication (Kokai) No. 62-8617 discloses a method which enables the disappearance of the effect of division of magnetic domains to be prevented even when strain release annealing (stress release annealing) is effected after the steel sheet is fabricated into an iron core. The iron loss has been significantly reduced through division of magnetic domains by the above-described technical means.
However, observation of the migration of these magnetic domains has revealed that some magnetic domains do not migrate, and it has been found that, in addition to the division of magnetic domains, the elimination of the pinning effect, which inhibits the migration of the magnetic domains and is derived from a glass film present on the surface of the steel sheet, is important to a further reduction in the iron loss value of the unidirectionally grain oriented silicon steel sheet.
For this purpose, it is useful to prevent the formation of a glass film on the surface of the steel sheet which inhibits migration of the magnetic domain. For example, U.S. Pat. No. 3,785,882 discloses a method wherein a coarse high-purity alumina is used as an annealing separator to prevent the formation of a glass film. In this method, however, inclusions just under the surface cannot be eliminated, so that the improvement in the iron loss is 2% at the highest in terms of W.sub.15/60.
Further, an enhancement in the orientation integration of the material is useful for improving the iron loss. In this connection, Taguchi and Sakakura (Japanese Examined Patent Publication (Kokoku) No. 40-15644), Komatsu et al. (Japanese Examined Patent Publication (Kokoku) No. 62-45285), etc. disclose methods wherein a nitride of Al is used as an inhibitor. When the method disclosed in U.S. Pat. No. 3,785,882 wherein alumina is used as the annealing separator is applied to these methods wherein a nitride of Al is used as the inhibitor, the secondary recrystallization becomes so unstable that it is impossible to attain an improvement in the iron loss on a commercial scale.
On the other hand, in order to regulate the inclusion just under the surface and, at the same time, to attain a specular surface, for example, Japanese Unexamined Patent Publication (Kokai) No. 64-83620 discloses a method wherein chemical polishing or electropolishing is effected after the completion of finish annealing. Although chemical polishing, elec
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Fujii Hiroyasu
Kuroki Katsuro
Kurosaki Yosuke
Nagashima Takeo
Nakayama Tadashi
Ip Sikyin
Nippon Steel Corporation
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