In-Situ X-Ray Diffraction Measurement During Deformation of Austenite Above the Ae_3 Temperature

摘要

Austenite has been shown to dynamically transform into ferrite during thermomechanical processing. The driving force is the softening that takes place during deformation, while the energy obstacles consist of the free energy difference between austenite and ferrite as well as the shear dilatation and shear accommodation work. Phase transformation can only take place once the driving force is greater than the energy obstacles. In this work, volume fractions of dynamically transformed ferrite from various rolling simulations were presented. The dynamic phase change was verified by performing hot compression experiment using a modified Gleeble system equipped with a synchrotron light X-ray diffraction. The X-ray diffraction measurements were carried out before and during deformation to accurately track the behavior of austenite. The results indicate that austenite indeed transforms dynamically into ferrite. This unusual metallurgical phenomenon is known to generate ultrafine grain microstructure, which translates to improved mechanical properties of steels.