Method of manufacturing grain-oriented electrical steel sheets

A method of manufacturing a grain-oriented electrical steel sheet not having an undercoating made of primarily forsterite (Mg2SiO4) and having a high magnetic flux density, said method comprising the steps of:

• hot-rolling a slab prepared using molten steel containing, by mass %, C of not more than about 0.08%, Si of about 2.0 to about 8.0% and Mn of about 0.005 to about 3.0%, in which Al and N are reduced to be not more than about 150 ppm and about 50 ppm, respectively;
• cold rolling the slab once, or twice or more with intermediate annealing therebetween to form a cold-rolled steel sheet;
• primary recrystallization annealing the cold-rolled steel sheet in an atmosphere with a dew point of not higher than about 40° C. and adjusting C content in a resulting primary-recrystallized steel sheet to be held in the range of about 0.005 to about 0.025 mass %;
• secondary recrystallization annealing the primary-recrystallized steel sheet in an atmosphere with a dew point of not higher than about 0°C. to form a secondary recrystallized steel sheet;
• and
• flattening annealing the secondary recrystallized steel sheet such that the flattening annealing serves also as decarburization annealing.

A method of manufacturing a grain-oriented electrical steel sheet not having an undercoating made of primarily forsterite (Mg2SiO4) and having a high magnetic flux density and a low iron loss, said method comprising the steps of:

• hot-rolling a slab prepared using molten steel containing, by mass %, C of not more than about 0.08%, Si of about 2.0 to about 8.0% and Mn of about 0.005 to about 3.0% to form a hot-rolled steel sheet;
• optionally annealing the hot-rolled steel sheet;
• cold rolling the hot-rolled steel sheet once, or twice or more with intermediate annealing therebetween to form a cold-rolled steel sheet;
• primary recrystallization annealing the cold-rolled steel sheet in an atmosphere with a dew point of not higher than about 40° C. and adjusting a C content in a resulting primary-recrystallized steel sheet to be held in the range of about 0.005 to about 0.025 mass %;
• optionally applying an annealing separator to the primary-recrystallized steel sheet;
• and
• secondary recrystallization annealing the primary-recrystallized steel sheet such that the C content is reduced to be less than about 50 ppm by introducing a hydrogen atmosphere with a partial pressure of not lower than about 10 volume % in a temperature range of not lower than about 900° C. during secondary recrystallization annealing.

A method of manufacturing a grain-oriented electrical steel sheet not having an undercoating made of primarily forsterite (Mg2SiO4) and having a high magnetic flux density and a low iron loss, said method comprising the steps of:

• hot-rolling a slab prepared using molten steel containing, by mass %, C of not more than about 0.08%, Si of about 2.0 to about 8.0% and Mn of about 0.005 to about 3.0% to form a hot-rolled steel sheet;
• optionally annealing the hot-rolled steel sheet;
• cold rolling the hot-rolled steel sheet once, or twice or more with intermediate annealing therebetween to form a cold-rolled steel sheet;
• primary recrystallization annealing the cold-rolled steel sheet in an atmosphere with a dew point of not higher than about 40° C. and adjusting a C content in a resulting primary-recrystallized steel sheet to be held in the range of about 0.005 to about 0.025 mass %;
• secondary recrystallization annealing the primary-recrystallized steel sheet to form a secondary-recrystallized steel sheet;
• decarburization annealing the secondary-recrystallized steel sheet in a humid atmosphere to form a decarburization annealed steel sheet;
• and
• performing additional continuous annealing on the decarburization annealed steel sheet by holding the steel sheet in a temperature range of not lower than about 800° C. for at least about 10 seconds in an atmosphere with a dew point of not higher than about 40° C.

A method of manufacturing a grain-oriented electrical steel sheet not having an undercoating made of primarily forsterite (Mg2SiO4) and having a high magnetic flux density and a low iron loss, said method comprising the steps of:

• hot-rolling a slab prepared using molten steel containing, by mass %, C of not more than about 0.08%, Si of about 2.0 to about 8.0% and Mn of about 0.005 to about 3.0% to form a hot-rolled steel sheet;
• optionally annealing the hot-rolled steel sheet;
• cold rolling the hot-rolled steel sheet once, or twice or more with intermediate annealing therebetween to form a cold-rolled steel sheet;
• primary recrystallization annealing the cold-rolled steel sheet in an atmosphere with a dew point of not higher than about 40° C. and adjusting a C content in a resulting primary-recrystallized steel sheet to be held in the range of about 0.005 to about 0.025 mass %;
• secondary recrystallization annealing the primary-recrystallized steel sheet to form a secondary-recrystallized steel sheet;
• decarburization annealing the secondary-recrystallized steel sheet in a humid atmosphere to form a decarburization annealed steel sheet;
• and
• performing additional batch annealing on the decarburization annealed steel sheet by holding the steel sheet in a temperature range of about 800 to about 1050° C. for at least about 5 hours in an atmosphere with a dew point of not higher than about 40° C.