The effect of impurities on the tertiary recrystallization and magnetic properties of the thin (10 to 100 μm) silicon steels was investigated. For purification, the conventional grain oriented silicon steels, which were used as starting materials with a thickness of 0.30 mm were pre-annealed at 1200°C in a vacuum of 1×10-3 Pa before cold rolling. In sheets without pre-annealing, the tertiary recrystallization was observed after annealing for at least 3 h over 1200°C in a vacuum. On the other hand, in pre-annealed sheets, the tertiary recrystallization was completed within 10 min at an annealing temperature of 1150°C in a vacuum. Through recrystallization, B8 increased to 1.95 T. Even in sheets annealed at 1050°C, the B8 increased with increasing the annealing time, and became 1.95 T after anneals of 2 h. The pre-annealed sheets were also annealed in hydrogen atmosphere. In this case, at annealing temperatures over 1100°C, the tertiary recrystallization was completed in less than 1 h. Using the purified sheets, silicon steels with B8 over 1.9 T can be obtained by short time and low temperature annealing in either a vacuum or a hydrogen atmosphere.
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