Patent ID: 7857915

Claim:
A method of production of a grain-oriented electrical steel sheet extremely excellent in magnetic properties comprising the steps of: reheating a slab comprising, by mass %, C: 0.025 to 0.10%, Si: 2.5 to 4.0%, Mn: 0.04 to 0.15%, solAl: 0.020 to 0.035%, N: 0.002 to 0.007%, S and Se, as Seq (S equivalents)=S+0.406×Se, 0.010 to 0.035%, Ti 0.007%, and a balance of Fe and unavoidable impurities to 1280° C. or more for dissolving inhibitor substances, hot rolling the slab into a hot rolled steel strip, annealing the hot rolled steel strip, cold rolling the steel strip one or more times with a rolling reduction ratio of more than 80% and less than 92% while intermediate annealing the steel strip before the last rolling, or omitting the annealing of the hot rolled steel strip and cold rolling the steel strip two or more times while intermediate annealing the steel strip before the last rolling, decarburization annealing the cold rolled steel strip at a temperature range of 650° C. to 950° C. for 80 to 300 seconds in a mixed gas of hydrogen and nitrogen with a wet atmosphere for decarburizing carbon content and controlling primary recrystallized grains having a circle equivalent mean size (diameter) of more than 7 μm to less than 20 μm, applying nitridation to the decarburized steel strip in a mixed gas of hydrogen, nitrogen and ammonia for controlling the increased N content (ΔN %) within the range defined by Equation (1), and further controlling the increased N content (ΔN %) at one surface of the steel strip (σN 1 , mass %) and the increased N content (ΔN %) at the other surface of the steel strip (σN 2 , mass %) in a 20% thickness portion of the surface of the steel strip to within the range defined by Equation (2), coating an annealing separator mainly composed of MgO to the steel strip, and secondary recrystallization annealing the coated steel strip, 0.007−([N]−14/48×[Ti])≦ΔN≦[solAl]×14/27−([N]−14/48×[Ti])+0.0025 Equation (1) |σN1−σN2|/ΔN≦0.35 Equation (2) wherein in Equation (1), [N], [Ti] and [Sol Al] represent respectively N, Ti and Sol Al contents (mass %) in the steel strip.