METHOD FOR ESTABLISH WORKING CONDITIONS BY CONTROLLING NITROGEN INJECTION AMOUNT, TEMPERATURE, PRESSURE AND RESIDUAL HYDROGEN AMOUNT OF ANNEALING FURNACE WHEN CRACKS ARE FORMED ON OUTER WALL OF HIGH TEMPERATURE ANNEALING FURNACE

摘要

PURPOSE: To provide a method for performing an operation in such a manner that flaws are not formed on an electric steel sheet that is being annealing at high temperature and preventing cracks of a cracking part of the high temperature annealing furnace from being further extended to reduce maintenance time when cracks are formed on the outer wall of a high temperature annealing furnace. CONSTITUTION: In a manufacturing method of grain-oriented magnetic steel sheet comprising hot rolling the reheated steel slab after reheating a steel slab; decarburization annealing the cold rolled steel sheet after cold rolling the hot rolled steel sheet; and finish annealing the decarburization annealed steel sheet at high temperature, the method for establish working conditions when cracks are formed on the outer wall of the high temperature annealing furnace comprises, in case that cracks are formed on the outer wall of the high temperature annealing furnace when the decarburization annealed steel sheet is finish annealed at high temperature, a step of controlling nitrogen injection time to 8 to 10 hours, and injecting nitrogen into the high temperature annealing furnace at a pressure of 150 to 170 Nm¬3 from the beginning to 1 to 3 hours in the nitrogen injection time, and injecting nitrogen into the high temperature annealing furnace at a pressure of 250 to 300 Nm¬3 for remaining nitrogen injection time; maintaining a charging part of the high temperature annealing furnace in a temperature range of 400 to 600 deg.C, maintaining an initial heating section of the high temperature annealing furnace in a temperature range of 650 to 750 deg.C, and maintaining first to third cooling sections of the high temperature annealing furnace in a temperature range of 300 to 500 deg.C; and controlling pressure of the high temperature annealing furnace in a range of 60 to 100 mmH2O and a residual hydrogen amount of the high temperature annealing furnace in a range of 0.5 to 2.0 vol.%.