PURPOSE: To stably produce a grain oriented magnetic steel thick sheet having superior magnetic properties and film characteristics by subjecting a slab of specific composition to hot rolling, annealing, and cold rolling and further subjecting the resulting sheet to decarburizing annealing and final finish annealing.
CONSTITUTION: A steel slab, containing, by weight, 0.021-0.075% C, 2.5-4.5% Si, 0.01-0.06% acid soluble Al, 0.0010-0.0130% N, <0.014% S+0.405Se, and 0.05-0.8% Mn, is heated to <1280°C and hot-rolled into a plate of 2.8-5.0mm thickness. This hot rolled plate is annealed and cold-rolled at >80% draft. The resulting cold rolled sheet is further subjected to decarburizing annealing consisting of holding at 830°C for 400sec and then to heat treatment in a gaseous NH3 containing atmosphere at 750°C for 30sec to undergo nitriding. Finally, a separation agent at annealing, composed essentially of MgO, is applied and finish annealing is done at 1200°C and then an insulating film agent is applied, by which a finished goods of 0.36-1.00mm thickness can be produced. At this time, the relation in inequality is satisfied among the Al% and N% in the slab and the thickness (t)mm of the cold rolled sheet, by which the grain oriented magnetic steel sheet excellent in magnetic properties can be produced.
TANAKA OSAMU
MISHIMA YOUICHI
ISHIBASHI MAREMIZU
