Thickness dependence of magnetic properties in rapidly quenched 6.5 percent silicon iron thin ribbons

Ribbons of 6.5% Si-Fe alloy were prepared with a rapid quenching single roller method. The thickness was 10 to 90μm. After annealing these samples at 1100°C for one hour in pure hydrogen, the grain structure was observed using a 25 kV-SEM. Mechanical properties were measured with a tensile testing machine. Magnetic properties were measured using an open magnetic circuit apparatus. Thickness dependence of these results were examined. The grain size became abruptly larger with increasing thickness and reached 1.8 mm in diameter at a 90 μm thickness. The tensile strength was about 65 kg/mm²for ribbon with a 60 μm thickness. The coercive force measured at a maximum applied field of 10 Oe decreased with increasing thickness and was 0.27 Oe at a thickness of 90 μm. The coercive force was reduced to 0.24 Oe by a double heat tretment. Initial and maximum permeabilities increased with increasing thickness. The former was 700 and the latter 18000 at a 90 μm thickness. The core loss was much lower than for grain oriented 3% silicon iron steel. It was less than one third the value for the steel when measured at frequencies above 1 kHz.