Thick grain-oriented electrical steel sheet exhibiting excellent magnetic properties

A method for producing a thick grain-oriented electrical steel sheet with excellent properties, the method comprising;

• preparing a slab comprising, by weight, 0.025-0.075% of C, 2.5-4.5% of Si, optionally one or more elements selected from the group consisting of Al, N, Mn, S, Se, Sb, B, Cu, Nb, Cr, Sn, Ti and Bi as inhibitor-forming elements, and the balance being iron and unavoidable impurities,
• heating the slab to a temperature not higher than 1,300° C., hot rolling the slab to a hot-rolled sheet, optionally annealing the hot-rolled sheet,
• cold rolling the hot-rolled sheet to a cold rolled sheet with a final thickness of 0.36-1.00 mm by a reduction ratio of not less than 80% by using a one stage cold rolling or two or more stages of cold rolling with intermediate annealing,
• decarburization annealing the cold-rolled sheet for decarburization of the sheet at a temperature between 700-1,000° C.,
• treating the cold rolled sheet for nitriding by using NH3 gas,
• coating the cold rolled sheet with an annealing separation agent consisting essentially of MgO, and
• annealing the cold rolled sheet for final finishing,
• wherein the thick grain-oriented electrical steel sheet has a C-content of not greater than 0.0050% by weight,
• exhibits a magnetic flux density B8 of not less than 1.83 T and an average value of SF of less than 0.80, where SF is an index representing the boundary configuration characteristics of the individual sheet grains with the same area as the circle with diameter exceeding 5 mm has and is defined as
• SF=(grain area×4π)/(grain boundary length)2, the average value of SF being the average value of the individual SF values,
• its grains of a diameter exceeding 5 mm have a crystal orientation deviation of 0.2-4 degrees in relation to that at the grain center, and the thick grain-oriented electrical steel sheet exhibits a core loss W17/50 (w/kg) of not more that 3.3×t+0.35.