Thermal Stability of Retained Austenite in Bainitic Steel: an in situ study

The tempering of two–phase mixtures of bainitic ferrite and carbon–enriched retained austenite has been investigated in an effort to separate the reactions that occur at elevated temperatures from any transformation during cooling to ambient conditions. It is demonstrated using synchrotron X–radiation measurements, that the residue of austenite left at the tempering temperature partly decomposes by martensitic transformation when the sample is cooled. It is well–established in the published literature that films of retained austenite are better able to resist stress or strain–induced martensitic transformation than any coarser particles of austenite. In contrast, the coarser austenite is more thermally stable than the film form because of its lower carbon concentration.