To show the optimum instruction of manufacture according to application magnetic flux density and to manufacture a steel sheet from deterioration in core loss due to stress relief annealing by regulating B8 deterioration before and after the formation of grooves in a steel sheet to a specific value when the design magnetic flux density of a transformer for which the steel sheet is used is set at a specific value.
Core loss is improved by physically forming grooves in a finish annealed steel sheet to fractionize a magnetic domain. When the design magnetic flux density of a transformer is ≥1.7 T, B8 deterioration before and after the formation of the grooves in the steel is 0.03-0.06 T. It is preferable that B8 deterioration becomes 0.04-0.06 T when the design magnetic flux density of the transformer is 1.4-<1.7 T and that B8 deterioration becomes 0.04-0.06 T when the design magnetic flux density becomes <1.4 T. A fixed relationship is held between the amount of B8 deterioration and core loss after the magnetic domain fractionization, and the depth of the grooves is regulated as a means of regulating B8 deterioration. Core loss characteristic after stress relief annealing treatment is regulated so that most suitable core loss can be obtained according to the applied magnetic flux density, and the energy loss of the transformer can be reduced.
FUJII HIROYASU
MATSUO MASAO
SUGIYAMA KIMIHIKO
