METHOD FOR MANUFACTURING GRAIN ORIENTED ELECTRICAL STEEL SHEET HAVING SUPERIOR MAGNETIC PROPERTIES

摘要

PURPOSE: A method for manufacturing grain oriented electrical steel sheet having superior magnetic properties is provided to stably form secondary recrystallization by analogizing nitrogen content of the steel sheet when simultaneously performing decarbonitriding or performing nitriding after decarburization, thereby controlling flow rate of ammonia gas. CONSTITUTION: The method comprises a step of hot rolling the reheated slab after reheating a slab to a temperature of 1,300 deg.C or less; a step of annealing the hot rolled steel sheet; a step of performing cold rolling on the annealed steel sheet, or performing cold rolling on the annealed steel sheet twice with an intermediate annealing being performed between the cold rolling operations; a step of simultaneously decarbonitriding the cold rolled steel sheet or performing nitriding on the decarburized steel sheet after performing decarburization on the cold rolled steel sheet at an atmosphere consisting of a mixed gas of water and ammonia and having a temperature of 800 to 900 deg.C; a step of predicting size of grains of the steel sheet by calculating decarbonitriding temperature or nitriding temperature; a step of measuring iron loss of the steel sheet simultaneously decarbonitrided or the steel sheet decarburized and then nitrided; a step of predicting nitrogen content of the steel sheet from the predicted grain size and the measured iron loss of the steel sheet; a step of controlling an atmosphere of decarbonitriding or nitriding and determining decarbonitriding temperature or nitriding temperature by increasing or decreasing flow rate of ammonia gas to control nitrogen content of the steel sheet to 100 to 500 ppm after performing decarbonitriding or nitriding operation based on the predicted nitrogen content; a step of performing decarbonitriding operation, or performing nitriding operation after decarburization to the determined decarbonitriding temperature or nitriding temperature at the controlled decarbonitriding or nitriding atmosphere; and a step of performing final annealing on the annealing separator coated steel sheet by coating an annealing separator on the steel sheet.