2005 Volume 46 Issue 6 Pages 1407-1412
The evolution of the eutectoid decomposition, α-Fe2Si5 → β-FeSi2 + Si, in sintered α-Fe2Si5 alloys with added Mn or Co has been traced by measuring the electrical resistivity under isothermal conditions. The time-temperature-transformation (TTT) diagram was obtained for each alloy, and presents a typical C shape in the temperature range of 873–1148 K. The addition of Mn or Co decreases the overall transformation rate, prolonging both the induction and transformation periods. The kinetics of the eutectoid reaction is discussed in the theoretical framework of Johnson–Mehl–Avrami (JMA) theory. It was found that the transformation mechanism of the eutectoid reaction is not affected by the addition of Mn or Co, and the effective activation energy of the Mn- or Co-added alloy is the same as that of the non-doped alloy. The added Mn or Co causes the decrease in the pre-exponential constant K0, which decreases the overall transformation rate.
