Nippon Steel Corporation

Takaaki Yamamoto

Osamu Tanaka

Yozo Suga

Katsuro Kuroki

Tadashi Nakayama

Shozaburo Nakashima

Fumio Matsumoto

Tadao Nozawa

Satohiro Hayami

Hirotada Katoh

Yoshihiro Ohya

Kikuo Takashina

Masahiro Fukumoto

In the secondary recrystallization of a grain-oriented silicon steel sheet, a specific temperature gradient is generated, thereby developing the secondary recrystallized grains having a good (110) [001] orientation and increasing the magnetic flux density higher than that previousy obtained. The temperature gradient is established at the boundary region between the primary and secondary recrystallized regions, with the result that highly oriented (110) [001] secondary recrystallization nuclei preferentially are caused to develop.

Process for producing grain-oriented electromagnetic steel sheet

In the conventional stacking method of the laminated core of a transformer, grain-oriented silicon steel sheet pieces of an identical grade or the identical magnetic properties are used as legs and yokes of the core. In a highly oriented silicon steel sheet having a high B.sub.8 value due to excellent magnetic properties in the rolling direction of the sheet, the excellent magnetic properties cannot be fully utilized for the watt loss reduction in the conventional stacking method. In a laminated core of the present invention, the transformer core comprises a grain-oriented silicon steel sheet having a higher orientation used for a leg(s) and a grain-oriented silicon steel sheet having a lower orientation used for a yoke(s). The former steel has the B.sub.8 value of generally 1.88 Tesla or higher and preferably 1.89 Tesla or higher. The latter steel has the B.sub.8 value of generally 1.86 Tesla or lower. A low watt loss, particularly at a low or medium magnetic flux density, can be achieved by the present invention, while decreasing the cost of the transformer.

Laminated core of transformer

A method of producing a grain-oriented electromagnetic steel sheet comprising the step of subjecting a sheet of hot-rolled steel containing silicon less than 4.5% to more than one operation of cold rolling and more than one operation of annealing, so as to set the thickness of said sheet to that of a commercially standard sheet, and also subjecting the sheet to the step of final high-temperature annealing. Prior to said final high-temperature annealing, part of the surface of said sheet is worked for controlling the growth of secondary recrystallization grains by working the sheets such that lines of less than 3.0 mm wide are formed on the surface of the steel sheet spaced apart at intervals of more than 5.0 mm so that the total effect is to produce worked and unworked regions alternatively arranged in lines across the steel sheet. Such working is effected by mechanical plastic working, local thermal treatment and by chemical treatment. The worked regions serve to control the growth of secondary recrystallization.

Method of producing grain oriented electromagnetic steel sheet

Annealing separator for heat treatment of a silicon steel sheet comprising not more than 0.2% SO.sub.3, not more than 0.04% Cl with the balance being MgO and unavoidable impurities, and having a bulk density between 0.18 and 0.30 g/cm.sup.3, and a particle size distribution of 40 to 70% of particles not larger than 3.mu.m, 10 to 25% of particles not smaller than 10.mu.m, not more than 15% of coarse particles larger than 15.mu.m with the balance being intermediate particles between 3.mu.m and 10.mu.m.

Annealing separator for heat treatment of silicon steel sheets

Growing community of inventors

Kitakyushu, Japan

Takaaki Yamamoto