Phase Transformation Kinetics from Ferrite to Austenite in Fe-Cr Oxide-Dispersion-Strengthened Ferrite Steels

摘要

Oxide-dispersion-strengthened (ODS) ferritic steels of Fe-9Cr-0.3Y_2O_3 and Fe-9Cr-0.2Ti-0.3Y_2O_3 (in wt%) incorporating nanoscale oxide particles were produced by mechanical milling (MM) followed by a process of hot isotropic press (HIP). The aim of this work is to study the mechanism that controls the austenitisation process in Fe-Cr ODS ferrite steels. Kinetic features of Fe-Cr ODS ferrite steels during continuous heating were investigated by fitting the volume fraction of austenite calculated on the basis of a developed ferrite to austenite transformation model to the experimental data acquired by differential thermal analysis (DTA). The fitted results indicate that the nanocaled Ti-Y bioxide particles in Fe-9Cr-0.2Ti-0.3Y_2O_3 alloy act as more effective barriers against the movement of the interface between ferrite and austenite than the single Y_2O_3 nanoparticles in Fe-9Cr-0.3Y_2O_3 alloy due to the decrease of the values of pre-exponential factor V_0. The pinning pressure exerted by nanocaled oxide particles was calculated by the modified Zener equation. The values of pinning pressure caused by Ti-Y bioxide particles in Fe-9Cr-0.2Ti-0.3Y_2O_3 alloy are greater than that of the single Y_2O_3 nanoparticles in Fe-9Cr-0.3Y_2O_3 alloy with various heating rates. That calculated results of the pinning pressure accords with the fitted ones derived by the modified model, which validates the modified JMAK model proposed for the isochronal austenite formation in ODS steels.