The time decrease of permeability in transformer steel

The paper describes some measurements of time-decrease of permeability on three types of samples stamped out from 4%-silicon hot-rolled transformer steel. The first samples contained severe mechanical stresses. Secondly, samples annealed at 800°C were used, and the maximum time of permeability decrease of about 24 hours was reduced after annealing to about 8 hours. Finally samples annealed at 1250°C in hydrogen atmosphere were measured and the results showed that the time-decrease phenomenon as practically eliminated according to the theory of Snoek.