| 摘要 |
PROBLEM TO BE SOLVED: To stably produce a grain-oriented silicon steel sheet excellent in magnetic properties by subjecting a cold rolled sheet of high silicon steel to surface treatment under specified conditions and thereafter executing decarburizing annealing and final finish annealing. SOLUTION: A high silicon steel slab is subjected to hot rolling and is subjected to cold rolling for one time of plural times including process annealing to form a thin steel sheet having a final sheet thickness. In this case, the amt. of oxide layer on the surface of the steel sheet before the cold rolling, the size of a work roll of a rolling mill or the like are adjusted to regulate the arithmetic average roughness of the surface of the cold rolled steel sheet to <=0.40μm. Next, decarburizing annealing is executed in such a manner that it is divided into the early period and latter period. As for the early period of the decarburizing annealing, the ratio of the partial pressure of steam to the partial pressure of hydrogen in the annealing atmosphere is regulated to 0.30 to 0.65, and as for the latter period of the decarburizing annealing, the partial pressure of steam in the annealing atmosphere is regulated to 0.05 to 3.0%, the annealing temp. is regulated to 850 to 950 deg.C, and decomposing reforming high densitifying treatment for fayalite is executed for 5 to 40 sec. After this decarburizing annealing composed of the early period and latter period, it is coated with a separation agent for annealing essentially consisting of MgO and is subjected to final finish annealing to produce the grain-oriented silicon steel sheet high in magnetic flux density. |
