To obtain desired magnetic characteristics by simultaneously executing a siliconizing treatment to penetrate Si into a steel sheet from its surface and a diffusing treatment to diffuse the penetrated Si into the steel sheet in the same atmosphere, thereby controlling siliconizing and diffusing rates and the Si concn. distribution in a thickness direction.
The steel sheet is heated to about 1200°C in a heating furnace 1 and gaseous SiCl4 is introduced at a prescribed flow rate from a suitable point into a siliconizing and diffusing treatment furnace 2. The siliconizing and diffusing rates to the steel sheet are controlled by regulating the moving speed of the steel sheet, by which the Si concn. distribution in the thickness direction of the steel sheet is controlled. The steel sheet is thereafter cooled in a cooling furnace and is taken up. As a result, the construction of the furnace may be simplified and the oxidation of the steel sheet may be suppressed. In addition, the control of the Si concn. distribution is made easy and the treatment at a high degree of freedom may be executed. The silicon steel sheet having the preferable characteristics relating to the iron loss at a high frequency, residual magnetic flux density and workability may be produced. Furthermore, the steel sheet, which is excellent in magnetostriction characteristics and workability at about 6.5 wt.% Si concn.,is obtd. by this control.
YAMAJI TSUNEHIRO
TAKADA YOSHIICHI
NINOMIYA HIRONORI
HIRATANI TATSUHIKO
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