Magnetic properties and crystallization behavior of Fe-based nanocrystalline strips fabricated by twin-roll casting

Abstract

In this study, the Fe78.4B12.3Si7.6C1Cu0.7 MG strip with a thickness of 157 µm was produced via twin-roll casting. The increased thickness resulted in a lower colling rate, lower energy state, and smaller free volume content. Moreover, the tremendous squeezing force applied during casting caused significant residual stress. Dense atomic stacking with high stress residual suppressed the magnetic domain rotation and domain-wall movement, producing a great coercivity (Hc). Two-pass rapid annealing(TPRA) was explored to improve the soft magnetic properties. Low-temperature annealing eliminated the residual stress, reducing the stress anisotropy and magnetic domain pinning of strips. A co-existing structure of residual amorphous and α-Fe(Si) phase was produced after high-temperature annealing. Fine α-Fe(Si) grain size of 24 nm decreased the magnetocrystalline anisotropy, and a great volume fraction of 71.3 % reduced the magnetostriction coefficient from 30 to 4.33 ppm. Finally, the Hc decreased from 27.4 to 6.4 A·m−1 after TPRA.