METHOD FOR PRODUCING A FORSTERITE INSULATING FILM ON A SURFACE OF GRAIN-ORIENTED ANISOTROPIC ELECTROTECHNICAL STEEL SHEETS

摘要

The invention relates to a method for producing a forsterite insulating film on the surface of grain-oriented anisotropic electrotechnical steel sheets, comprising the following steps: tempering-annealing a steel sheet in order to produce an SiO2-FeO-fayalite film on its surface; coating said steel sheet with MgO; spooling the MgO-coated steel sheet with its final thickness and annealing the spooled steel sheet with its final thickness at high temperatures in an atmosphere with a predetermined composition for forming a forsterite film. The inventive method is especially characterised in that the high-temperature annealing stage consists of the spooled steel sheet being heated at temperatures of 400 to 800 °C in an Fe- and Si-oxidising damp atmosphere containing hydrogen and/or inert gas. The saturation temperature is adjusted to a value of between -10 °C and +20 °C at least at the upper limit of said temperature range, depending on the ratio of hydrogen and inert gas.