Patent ID: 8303730

Claim:
A manufacturing method of a grain-oriented electrical steel sheet, comprising: heating a slab containing: C: 0.04 mass % to 0.09 mass %; Si: 2.5 mass % to 4.0 mass %; acid-soluble Al: 0.022 mass % to 0.031 mass %; N: 0.003 mass % to 0.006 mass %; S and Se: 0.013 mass % to 0.022 mass % when converted into an S equivalent Seq represented by “[S]+0.405×[Se]” in which an S content is set as [S] and a Se content is set as [Se]; and Mn: 0.045 mass % to 0.065 mass %, a Ti content being 0.005 mass % or less, and a balance being composed of Fe and inevitable impurities, at 1280° C. to 1390° C., to make a substance functioning as an inhibitor to be solid-solved; next, hot-rolling the slab to obtain a steel strip; annealing the steel strip to form a primary inhibitor in the steel strip; next, cold-rolling the steel strip once or more; next, annealing the steel strip to perform decarburization and to cause primary recrystallization; next, performing nitriding treatment on the steel strip in a mixed gas of hydrogen, nitrogen and ammonia to form a secondary inhibitor in the steel strip; and next, annealing the steel strip to cause secondary recrystallization, wherein in said hot rolling, a ratio of N, contained in the slab, that is precipitated as AlN in the steel strip is set to 35% or less, and a ratio of S and Se, contained in the slab, that are precipitated as MnS or MnSe in the steel strip is set to 45% or less when converted into the S equivalent, said annealing to form the primary inhibitor in the steel strip is performed before a last-performed one of said cold rolling that is performed once or more, a rolling rate in the last-performed one of said cold rolling that is performed once or more is set to 84% to 92%, a circle-equivalent average grain diameter (diameter) of crystal grains obtained through the primary recrystallization is set to not less than 8 μm nor more than 15 μm, when a Mn content (mass %) in the slab is set as [Mn], a value A represented by an equation (1) satisfies an equation (2), [Mathematical Expression 1] A =([Mn]/54.9)/(Seq/32.1) equation (1) 1.6≦A≦2.3 equation (2), and when a N content (mass %) in the slab is set as [N], and an amount of N (mass %) in the steel strip that is increased by said nitriding treatment is set as ΔN, a value I represented by an equation (3) satisfies an equation (4) [Mathematical Expression 2] I= 1.3636×[Seq]/32.1+0.5337×[ N]/ 14.0+0.7131×Δ N/ 14.0 equation (3) 0.0011≦I≦0.0017 equation (4).