METHOD OF PRODUCING FORSTERITE INSULATING FILM ON SURFACE OF ANISOTROPIC ELECTRICAL-SHEET STEEL Russian patent published in 1998 - IPC

FIELD: metallurgy. SUBSTANCE: method includes decarburizing annealing, high-temperature annealing of coiled strip of final thickness and coated with MgO in atmosphere of regulated composition, and provided for improvement of film quality with high magnetic properties, performance of heating in high-temperature annealing within the internal of 400-800 C in oxidizing atmosphere with respect to Fe and Si proceeding from attaining at the end of the said interval, the dew point temperature within minus 10 to plus 20 C depending on hydrogen-nitrogen ratio. Dew pointed temperature within minus 10 plus 5 C is attained by supplying of nitrogen to furnace atmosphere, and dew point temperature from puls 5 to plus 20 C is attained by moistening of hydrogen. Humidity of interturn atmosphere is regulated by varying the degree of hydration of MgO within the range of 5 to 20%. Humidity of interturn atmosphere is additionally regulated by addition to MgO of components dissociating within the interval of 600-900 C with separation of hydroxyl. End parts of strip coils are heat-insulated. EFFECT: higher efficiency. 6 cl, 2 tbl