MANUFACTURE OF GRAIN-ORIENTED MAGNETIC STEEL SHEET HAVING EXTREMELY HIGH MAGNETIC FLUX DENSITY

PURPOSE:To stably manufacture a grain-oriented magnetic steel sheet having high magnetic flux density, by adding a temp.-fall stage to the final finish annealing of a silicon steel sheet and specifying the heat-cycle conditions of this final finish annealing. CONSTITUTION:A hot-rolled plate of silicon steel consisting of, by weight, 2.5-4.0% Si, 0.03-0.10% C, 0.010-0.065% solAl, 0.0010-0.0150% N, 0.02-0.30% Mn, 0.005-0.040% S, and the balance essentially Fe is used as a stock. This steel plate is subjected to a single cold rolling including forced final cold rolling at >80-95% draft or to two-time or more cold rollings, while subjected to process annealing between the cold rolling stages. Subsequently, the resulting cold-rolled sheet is subjected to carburizing annealing and further to application of annealing release agent to undergo final finish annealing. The final finish annealing is carried out by means of a heat cycle where the steel sheet is first heated from 700 to 900-1,050 deg.C at 2-50 deg.C/hr temp.-rise rate, subjected to temp. fall down to 700-1,000 deg.C next, and further heated to a finish-annealing temp. of 1,100-1,300 deg.C at 2-50 deg.C/hr temp.-rise rate.