Grain-oriented silicon steel sheet prodn - avoiding oxide inclusions to allow lower manganese and sulphur contents

摘要

In the prodn. of grain-oriented silicon steel sheet by hot rolling a slab to strip, two-stage cold rolling the strip with an intermediate anneal, subjecting the strip to a decarburising primary recrystallisation anneal and then box annealing to produce secondary recrystallisation, the improvements are that the Mn and S in the steel are controlled so that the solubility product, %Mn x %S, is 0.007-0.0012, that the steel is cast so that oxidation of constituents in the surface of the casting stream, which lead to insoluble oxides distributed within the steel, is reduced to a minimum, that the steel slab is reheated to 1166-1310 degrees C before hot rolling and that the sheet is reduced by 44-56% by the second cold rolling step. By restricting the amt. of oxides dispersed in the steel, the effectiveness of MnS as grain growth inhibitor is increased. Thus the amt. of MnS in the steel and hence the reheating temp., can be reduced. The degree of reduction in the final cold rolling step gives optimum grain orientation.