Effect of Electropulsing on Recrystallization of Fe-3%Si Alloy Strip

Abstract

Recrystallization and microstructural changes of an electropulsing treated (EPT) Fe-3%Si alloy strip were studied using optical microscopy and electron backscattering diffraction (EBSD) techniques. Microstructural evolution and misorientation angle distribution were detected during recrystallization in both EPT and traditional heat treated (THT) alloy specimens. The results indicate electropulsing tremendously accelerated movement of dislocation and vacancies, which is in favors of recrystallization. The temperature of recrystallization was reduced. A sufficient high temperature became a dominant factor in speeding up recrystallization. The mechanism of electropulsing induced recrystallization is discussed from the point view of dislocation dynamics, microstructural changes and electropulsing kinetics. (doi:10.2320/matertrans.M2010044) Grain-oriented Fe-3% Si steels are used as cores in electrical transformers due to their soft magnetic properties. In order to develop a new production technology for grain- oriented silicon steel heat treatment, EPT is use to cold rolling Fe-3% Si strip. As an alternative to the traditional thermal and mechanical processes, EPT has been recognized for its high efficiency and attracted attention for use in extensive studies in materials science and engineering, such as electroplasticity, 1-4) electromigation, 5) recrystallization, 6) phase transformation 7-11) and mechanism of interaction between electrons and lattice atoms and dislocation move- ment. 12,13) In our previous studies indicated that EPT enhanced rates of recrysytallization of AZ31 alloy. 14) Compared with the conventional processes, microstructure and grain size were remarkably different, and the material properties were improved. But so far little has been done on the effects of electropulsing on the microstructural evolution of the Fe-Si alloy. The material selected in the research was a commercial Fe-Si alloy with a composition of Al(0.024 mass%), N(0.026 mass%), Cu(0.10), Si(3 mass%), Fe in balance. The as-received Fe-Si alloy strip of 6 mm in width and 0.3 mm in thickness was produced after 75% final reduction of cold rolling at room temperature. The schematic view of EPT process is shown in Fig. 1. Multiple pulses current generated continuously are applied to the alloy strip directly when the Fe-Si alloy strip was moving at a speed of 1 m/min through a distance of 200 mm between the two electrodes. An electropulsing generator was applied to discharge positive- directional multiple pulses with various pulse voltage through adjusting controlling parameters. It took about 12 s to move the strip from anode to cathode. An infrared thermoscope was adopted near the cathodes to test the surface maximum temperature of material directly. The current parameters such as amplitude and root-mean-square density