In order to clarify the difference of iron loss of single sheet and toroidal core and domain structure of TiN-coated very thin silicon steel sheets, TiN coating by the hollow cathode discharge (HCD) method was performed on polished very thin (0.10 mm) silicon steel sheets. Iron loss of single sheets and toroidal cores after domain refinig was measured. Also, domain structures of (011) [100] single crystals of silicon steel, which were chemical polished, TiN-coated and then domain refined by scribing with a knife at 4 mm widths perpendicular to the rolling direction, were observed by electron microscopy under (a) straight, (b) convex and (c) concave states.
0.10 mm TiN-coated very thin silicon steel showed ultra-low iron loss of W_13/50=0.12 W/kg with a single sheet measurement after the domain refining, whreas similar iron loss with a toroidal core showed minimun value of W_13/50=0.12 W/kg after 700°C annealing, being good value of building factor (B. F.) of 1.0.
The domain structures with (a) straight state obtained by TiN coating and inducement of a small local strain by scribing produced a drastic domain refinement, whereas that with (b) convex and (c) concave states showed further domain refinement. Also, the domain structure of (c) concave state could be observed after annealing above 873K.