Method of producing extra-low iron loss grain oriented silicon steel sheets

A method of producing an extra-low iron loss grain oriented silicon steel sheet, which comprises subjecting a silicon containing steel slab to a hot rolling, subjecting the resulting hot rolled steel sheet to one or two cold rollings with an intermediate annealing to form a cold rolled steel sheet having a given final gauge, subjecting the cold rolled steel sheet to decarburization and primary recrystallization annealing, applying an annealing separator onto the surface of the treated steel sheet, subjecting the coated steel sheet to a finish annealing and to secondary recrystallization annealing for developing secondary recrystallized grains in { 110}<001>

• orientation and a purification annealing, removing the resulting oxide from the surface of the steel sheet, and forming on the sheet surface a thin coat of at least one layer composed mainly of at least one nitride and/or carbide of Ti, Zr, Hf, V, Nb, Ta, Mn, Cr, Mo, W, Co, Ni, Al, B and Si and strongly adhered to the surface of the silicon steel sheet through a mixed layer of the silicon steel sheet and the thin coat.