Production method for grain-oriented electrical steel sheet and primary recrystallized steel sheet for production of grain-oriented electrical steel sheet

A production method for a grain-oriented electrical steel sheet, the method comprising:

• subjecting a steel slab to hot rolling, without re-heating or after re-heating, to obtain a hot rolled sheet, the steel slab having a composition consisting of, by mass % or mass ppm, C:
• 0.08% or less, Si:
• 2.0% to 4.5%, Mn:
• 0.5% or less, S:
• less than 50 ppm, Se:
• less than 50 ppm, O:
• less than 50 ppm, sol.Al:
• less than 100 ppm, N:
• 80 ppm or less, and the balance being Fe and incidental impurities, and satisfying the relation of sol.Al (ppm)−N (ppm)×(26.98/14.00)≦30 ppm;
• then subjecting the hot rolled sheet to annealing and rolling to obtain a cold rolled sheet of final sheet thickness;
• then subjecting the cold rolled sheet to nitriding treatment, with a nitrogen increase (ΔN) being specified by the following formula (1) or (2), before, during or after primary recrystallization annealing;
• then applying an annealing separator on the cold rolled sheet;
• and
• allowing N to diffuse into steel substrate, during or after the primary recrystallization annealing and before the start of secondary recrystallization, so as to precipitate silicon nitride with a precipitate size of 100 nm or more without containing Al, for use as inhibiting force for normal grain growth:
• when sol.Al−N×(26.98/14.00)≦0, 50 ppm≦ΔN≦1000 ppm (1)
• ,or
• when 0<sol.Al−N×(26.98/14.00)≦30, (N−sol.Al×14.00/26.98+100)≦ΔN≦(N−sol.Al×14.00/26.98+1000) (2).

A primary recrystallized steel sheet for production of a grain-oriented electrical steel sheet, wherein the composition thereof satisfies a composition range of, by mass % or mass ppm, C:

• 0.08% or less, Si:
• 2.0% to 4.5% and Mn:
• 0.5% or less, with S, Se and O:
• each less than 50 ppm, sol.Al:
• less than 100 ppm, N:
• 50 ppm or more and 1080 ppm or less, and the balance being Fe and incidental impurities.