A METHOD FOR MANUFACTURING LOW TEMPERATURE REHEATED GRAIN-ORIENTED ELECTRICAL STEEL SHEET HAVING SUPERIOR PUNCHING PROPERTY

摘要

PURPOSE: A method for manufacturing a grain-oriented electrical steel sheet having superior punching property is provided which improves punching property as well as magnetic property during processing operation by coating an annealing separation agent composed of MgO, SiO2 and metallic chlorides on the steel sheet. CONSTITUTION: In a method for manufacturing a grain-oriented electrical steel sheet comprising the processes of hot rolling the low temperature reheated steel slab after low temperature reheating a steel slab at a temperature of 1150 to 1190 deg.C a steel slab composed of 2.9 to 3.4 wt.% of Si, 0.045 to 0.062 wt.% of C, 0.015 to 0.035 wt.% of P, 0.022 to 0.032 wt.% of dissolved Al, 0.006 to 0.009 wt.% of N, 0.004 to 0.010 wt.% of S, 0.008 to 0.012 wt.% of Mn, 0.012 to 0.021 wt.% of Cu and a balance of Fe and other inevitable impurities; annealing the hot rolled steel sheet at a temperature of 1100 deg.C or less; cold rolling the pickled steel sheet after pickling the annealed steel sheet; simultaneously decarburizing and nitriding the cold rolled steel sheet at around 840 to 890 deg.C in the wet atmosphere of an ammonia gas contained mixed gas of hydrogen and nitrogen; coiling the annealing separation agent dried steel sheet to a large coil after drying the coated steel sheet at a temperature of 700 deg.C or less by coating an annealing separation agent on the decarburized and nitrided steel sheet; carrying out finishing annealing on the coiled steel sheet in which the steel sheet is uniformly heated at a temperature of 1190 to 1210 deg.C for 20 hours or more as maintaining a temperature increase ratio in the range of 700 to 1200 deg.C to 15 deg.C/hr or more; and coating a tension coating material on the resulting steel sheet, the method for manufacturing a low temperature reheated grain-oriented electrical steel sheet having superior punching property is characterized in that one annealing separation agent selected from the group consisting of 5 to 20% based on a solid content of MgO and fine SiO2 powder or SiO2 in the colloidal state for Mg, CuCl2, MgCl2 and NiCl2 is coated on the steel sheet in an amount of 0.008xtotal oxygen amount on the surface of the decarburized steel sheet (ppm)2 in the coating of the annealing separation agent.