Grain-oriented electrical steel sheet, intermediate steel sheet for grain-oriented electrical steel sheet, and methods for manufacturing same

A method for manufacturing a grain-oriented electrical steel sheet comprising:

• a hot rolling process of heating a slab at 1280° C. or lower and then performing hot rolling to manufacture a hot-rolled steel sheet;
• a hot-band annealing process of performing hot band annealing on the hot-rolled steel sheet to manufacture an annealed steel sheet;
• a cold rolling process of performing cold rolling on the annealed steel sheet to manufacture a cold-rolled steel sheet;
• a decarburization annealing process of performing decarburization annealing on the cold-rolled steel sheet to manufacture a base steel sheet;
• an annealing separator applying process of applying an annealing separator having a composition containing 50 mass % or more of alumina and, as a remainder, 0 to 50 mass % of magnesia to the base steel sheet;
• a final annealing process of performing final annealing on the base steel sheet after the annealing separator applying process;
• a cooling process of cooling the base steel sheet after the final annealing process in an atmosphere having an oxidation degree PH2O/PH2, which is a ratio of a water vapor partial pressure to a hydrogen partial pressure, within a temperature range of 1100° C. to 500° C. set to 0.30 to 100000;
• an intermediate layer forming process of performing, a heat treatment on the base steel sheet after the cooling process to form an intermediate layer mainly containing silicon oxide on a surface of the base steel sheet;
• and
• an insulation coating forming process of forming an insulation coating on a surface of the intermediate layer after the intermediate layer forming process.

An intermediate steel sheet for a grain-oriented electrical steel sheet comprising:

• a base steel sheet;
• and
• a film-shaped oxide formed on a surface of the base steel sheet,
• wherein the film-shaped oxide is present so as to cover the surface of the base steel sheet in a film shape, and
• a number density of the oxide particles in a region from the surface of the base steel sheet to a depth of 10 μm toward an inside of the base steel sheet is 0.020 oxide particles/μm2 or less.

A method for manufacturing an intermediate steel sheet for a grain-oriented electrical steel sheet comprising:

• a hot rolling process of heating a slab at 1280° C. or lower and then performing hot rolling to manufacture a hot-rolled steel sheet;
• a hot-band annealing process of performing hot band annealing on the hot-rolled steel sheet to manufacture an annealed steel sheet;
• a cold rolling process of performing cold rolling on the annealed steel sheet to manufacture a cold-rolled steel sheet;
• a decarburization annealing process of performing decarburization annealing on the cold-rolled steel sheet to manufacture a base steel sheet;
• an annealing separator applying process of applying an annealing separator having a composition containing 50 mass % or more of alumina and, as a remainder, 0 to 50 mass % of magnesia to the base steel sheet;
• a final annealing process of performing final annealing on the base steel sheet after the annealing separator applying process;
• and
• a cooling process of cooling the base steel sheet after the final annealing process in an atmosphere having an oxidation degree PH2O/PH2, which is a ratio of a water vapor partial pressure to a hydrogen partial pressure, within a temperature range of 1100° C. to 500° C. set to 0.30 to 100000.