PURPOSE: To obtain the steel sheet by a finish annealing stage and to industrially obtain a low-iron loss material by performing primary recrystallization annealing, applying an ASl2O3-type separation agent at annealing containing nitride and specific metal, and carrying out secondary recrystallization annealing while controlling orientation to high order.
CONSTITUTION: A hot rolled strip of a silicon steel having a composition consisting of, by weight, 2.0-4.8% Si, 0.008-0.05% acid-soluble Al, ≤0.010% N, and the balance Fe is subjected, if necessary, to annealing and cold-rolled once or cold-rolled twice or more while process-annealed between cold rolling stages to the prescribed sheet thickness. Subsequently, after primary recrystallization annealing, a separation agent at annealing composed essentially of Al2O3 and containing respective powders of a nitride and a metal having affinity for oxygen higher than that of silicon is applied. Then, the steel sheet is subjected to temp. rise up to 920-1150°C in a neutral or reducing atmosphere at ≥50°C/hr finish annealing rate and then to holding for ≥5hr. As the above nitride, respective nitrides of Al, Mn, Ti, V, Si, and Cr and mixtures thereof can be cited. Further, as the above metal powder, respective powders of Al, Ti, and V can be cited.
SUGA YOZO
USHIGAMI YOSHIYUKI
FUJII HIROYASU
