Grain oriented silicon steel annealing separator - based on magnesium oxide and contg. rare earth oxides or metal silicates

An annealing separator for grain oriented Si steel sheets based on MgO contains in addn. oxides of rare earth metals, cpds. of rare earth metals which thermally decompose to oxides, or silicates. The separator economically improves the annealing operation and also improves the magnetic and electrical properties of the sheet. The surface of the annealed sheet has cavities contg. a glass film which affects the roughness and the resistivity. Rates of denitriding and desulphurisation are increased. The adhesion of vitreous films to the sheet is also increased. By reducing the roughness the drawability is improved, leading to improved magnetic properties. The final annealing time is reduced. In certain cases the additional insulating glass can be eliminated. There is also fewer problems when mechanically treating the sheet.