Primary recrystallized Fe-3%Si specimens were nitrided and annealed with the heating rate of 15°C/h in 100% N
2 atmosphere. With an increase in the heating temperature by 10°C, the heating was interrupted and the specimen was rapidly cooled and the magnetic induction
B8 was measured and rapidly heated again to the heating temperature. Onset of secondary recrystallization was detected by the rapid rise of
B8.
B8 after secondary recrystallization was closely related with the onset temperature of secondary recrystallization (
Tcr). The maximum
B8 obtained was about 1.94 T when the
Tcr was around 1075°C and the
B8 decreased with increasing in the
Tcr. The
Tcr was closely related with the primary grain size and it was about 1075°C when the grain size was about 15 μm. The
Tcr increased with increasing primary grain size and it was about 1100°C when the primary grain size was about 22 μm.
The same primary specimens were coated with MgO and annealed with the same heating rate in 5%H
2-N
2. The maximum
B8 obtained was almost the same as the above annealing condition; however, the primary grain size for obtaining the maximum
B8 was different in this annealing. The difference in the optimum grain size for obtaining the maximum
B8 in both annealing methods was explained on the assumption that the maximum
B8 is obtained when the
Tcr is about 1075°C in both annealing methods.
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