A grain-oriented electrical steel sheet has been used as a material for composing an iron core of electric appliances such as transformer. It is important for a grain-oriented electrical steel sheet to be excellent in magnetization characteristics and iron loss characteristics. In recent years, there has been a growing demand for a grain-oriented electrical steel sheet characterized by small energy loss and low iron loss. Since a steel sheet having a large magnetic flux density generally has low iron loss, and may be downsized when used as an iron core, so that development thereof has very strongly been targeted at.
In order to improve a magnetic flux density of a grain-oriented electrical steel sheet, it is important to highly integrate the crystal grains to {110}<001> orientation called Goss orientation. Orientation of crystal grains is controlled making use of catastrophic grain growth called secondary recrystallization. Management of a structure obtained by a primary recrystallization before the secondary recrystallization (primary recrystallization structure), and management of fine precipitate called inhibitor such as AlN, or element segregated in the grain boundary hold the key for control of the secondary recrystallization. The inhibitor allows crystal grains having {110}<001> orientation to grow predominantly in the primary recrystallization structure, so as to suppress growth of crystal grains with other orientations.
One of the known method of producing the inhibitor is such as allowing AlN to deposit by nitriding conducted before the secondary recrystallization (Patent Document 5, for example). Still another known method totally different in mechanism is such as allowing AlN to deposit during annealing (hot-rolled sheet annealing), which takes place in the duration from hot rolling and cold rolling, without relying upon the nitriding (Patent Document 6, for example).
It is, however, difficult to effectively improve the magnetic flux density even with these techniques.