Ductile-to-Brittle Transition Behavior of Fe-6.5 Wt%Si Alloy with Three-Point Bending Testing

Fe-6.5 wt%Si alloy is one of the attractive soft magnetic materials for making transformers and motors with low noise and low power loss. However, it has a higher ductile to brittle transition (DBT) temperature caused by ordered structures, which determines the warm rolling processing. In this work, three-point bending tests were performed to study the DBT behavior of air-cooled and water-quenched Fe-6.5 wt%Si alloy. The results showed that under different strain rates, the DBT temperature of the water-quenched specimen was about 30 °C lower than that of the air-cooled specimen. The DBT activation energies were calculated to be 0.536 eV (air-cooled specimen) and 0.473 eV (water-quenched specimen). The differences in DBT behaviors of both specimens were primarily attributed to different ordered degrees, where D03 ordered structures could only be detected in the air-cooled specimen. Compared with the air-cooled specimen, the water-quenched specimen presented a wider workable area, suggesting its better plastic deformation ability. Moreover, a numerical model regarding strain rate-temperature dependence was further fitted to predict DBT temperatures.