Study of Secondary Recrystallization in Grain-oriented Steel Treated under Dynamical Heat Treatment Conditions

Grain oriented silicon steel (GO) is mainly used as the core material in transformers, and it is the only product manufactured in the steel industry that applies the secondary recrystallization phenomenon. Its magnetic properties are closely related to the secondary recrystallization texture, i.e., the sharpness of 110 (001), Goss texture 1 . This sharp texture develops due to a discontinuous or abnormal grain growth of Goss grains during high temperature annealing at the end of industrial production process. This heat treatment performed for secondary recrystallization and subsequent purification from the inhibitor elements. This high temperature annealing is conducting at low heating rate ( 25 °C/hour) up to the purification annealing temperature ( 1200 °C) 2 . This is time and power consuming process as the duration of the whole process is about several tens of hours. That is why, now nearly all producers are targeting on more compact and less expensive production routes of the GO steels. Although it is a matter of intensive basic and applied research since more than 50 years, there is no general agreement on the origin of preferred growth of the Goss grains during final box annealing. There are two similar but competing views frequently repeated in the literature of the subject. The first one originates in the suggestion that the coincidence site lattice (CSL) misorientation relationships are a factor in the secondary recrystallization in silicon steel 3 . Briefly, according to the model, the boundaries of Goss oriented grains are more frequently of the CSL-type than boundaries of other grains 3 . Moreover, in the presence of precipitates, the CSL boundaries are assumed to be more mobile than general boundaries. Thus, the Goss grains have the opportunity to grow. The second view is based on the assumption that the high mobility is a feature of the so called “high energy” (HE) boundaries defined there as boundaries between grains misoriented by the angle of 20 to 45° 4 . Again, the advantage of the Goss grains would come from the fact that they are bounded by the HE boundaries more frequently than other grains.