|About this Abstract
||2018 TMS Annual Meeting & Exhibition
||Computational Thermodynamics and Kinetics
||Transition Process from BCT Martensite to η Phase during Tempering in Fe-C Alloy
||Yohei Osawa, Michitoshi Saeki, Masanori Enoki, Marcel H.F. Sluiter, Hiroshi Ohtani
|On-Site Speaker (Planned)
Martensitic transformation is widely used to enhance hardness of steels. During its tempering process, it is well known that martensite transforms into η (Fe<SUB>2</SUB>C) and α phases. However, the reason for η phase forming more preferentially than cementite remains unclear.
With this point as background, the Gibbs free energy of BCT martensite was evaluated using first-principles calculations combined with the cluster variation method. The activation energy from BCT lattice to η phase was calculated by means of the variable cell nudged elastic band method.
The results showed that BCT martensite has spinodal decomposition tendency between lower and higher carbon regions. Furthermore, the activation energy for formation of η phase in BCT lattice was 0.24 eV/atom, which is lower than that for carbon diffusion. Therefore, transition from BCT martensite to η phase is induced by spinodal decomposition in lower temperature region where the driving force for cementite precipitation is not sufficient.
||Planned: Supplemental Proceedings volume