ULTRA−HIGH MAGNETIC FLUX DENSITY UNIDIRECTIONAL ELECTRICAL SHEET EXCELLENT IN HIGH MAGNETIC FIELD IRON LOSS AND COATING CHARACTERISTICS AND PRODUCTION METHOD THEREFOR

摘要

A unidirectional electrical sheet which comprises ferrite and at least 0.01 ppm and less than 1000 ppm of Bi in terms of mass % present on a primary coating interface, and which is produced by subjecting the sheet to preliminary annealing at at least 700°C for 1−20 sec before decarburization anealing and controlling an atmosphere in this temperature region, or controlling a maximum reaching temperature B (°C) before a final cold rolling to within a range represented by an expression, −10×ln(A)+1100≤B≤10×ln(A)+1220, according to Bi content A (ppm) and heating the steel sheet cold−rolled to a final sheet thickness, before being decarburization annealed, to at least 700°C within 10 sec or at a heating rate of at least 100°C/sec, or immediately subjecting it to preliminary annealing at at least 700°C for 1−20 sec before decarburization annealing, or controlling TiO2 amount B against 100 pts wt of MgO and MgO coating amount C (g/m2) that are used when applying and drying an anneal separating agent mainly containing MgO to within a range, A0.8≤B×C≤400, according to Bi content A (ppm).