Method for producing grain oriented electrical steel sheet

A method for producing a grain oriented electrical steel sheet,

• the method comprising:
• a hot rolling process of hot-rolling a steel piece to obtain a hot rolled steel sheet, the steel piece including, as a chemical composition, by mass %,
• 0.030 to 0.100% of C,
• 0.80 to 7.00% of Si,
• 0.01 to 1.00% of Mn,
• 0 to 0.060% in total of S and Se,
• 0.015 to 0.065% of acid soluble Al,
• 0.004 to 0.012% of N,
• 0 to 0.30% of Cr,
• 0 to 0.40% of Cu,
• 0 to 0.50% of P,
• 0 to 0.30% of Sn,
• 0 to 0.30% of Sb,
• 0 to 1.00% of Ni,
• 0 to 0.008% of B,
• 0 to 0.15% of V,
• 0 to 0.20% of Nb,
• 0 to 0.10% of Mo,
• 0 to 0.015% of Ti,
• 0 to 0.010% of Bi, and
• a balance consisting of Fe and impurities;
• a cold rolling process of cold-rolling the hot rolled steel sheet to obtain a cold rolled steel sheet;
• a decarburization annealing process of decarburization-annealing the cold rolled steel sheet to obtain a decarburization annealed sheet;
• an annealing separator applying process of applying and drying an annealing separator including MgO to the decarburization annealed sheet;
• a final annealing process of final-annealing the decarburization annealed sheet after applying the annealing separator to obtain a final annealed sheet;
• an annealing separator removing process of removing a redundant annealing separator from a surface of the final annealed sheet;
• a smoothing process of smoothing the surface of the final annealed sheet after removing the redundant annealing separator;
• and
• an insulation coating forming process of forming an insulation coating on the surface of the final annealed sheet after being smoothed,
• wherein, in the decarburization annealing process,
• PH2O/PH2 which is an oxidation degree of an atmosphere is 0.18 to 0.80, an annealing temperature is 750 to 900° C., and a holding is 10 to 600 seconds,
• wherein, in the final annealing process,
• the decarburization annealed sheet after applying the annealing separator is held at 1100 to 1200° C. for 10 hours or more in a mixed gas atmosphere including 50 volume % or more of a hydrogen,
• wherein, in the annealing separator removing process,
• the final annealed sheet is water-washed using a solution with an inhibitor which is at least one of a triethanolamine, a rosinamine, or a mercaptan in order to remove the redundant annealing separator from the surface thereof, and an amount of an iron hydroxide and an iron oxide on the surface thereof is controlled to 0.9 g/m2 or less per a side,
• wherein, in the smoothing process,
• the final annealed sheet after removing the redundant annealing separator is chemical-polished, and an average roughness Ra of the surface thereof is controlled to 0.10 μm or less, and
• wherein, in the insulation coating forming process,
• an insulation coating forming solution in which a phosphate, a colloidal silica, and a crystalline phosphide are included is applied and is baked at 350 to 1150° C., and after decreasing a temperature, an insulation coating forming solution in which the phosphate and the colloidal silica are included and in which the crystalline phosphide is not included is applied and is baked at 350 to 1150° C., in order to form the insulation coating.