Microstructure Evolving Behaviors of Undercooled Ultrafine Austenite Grains During Deformation

Samples with ultrafine grained austenite were prepared by repetitive rapid heating and quenching for three times and were used to investigate the dynamic microstructural evolving behaviors at different temperatures. A simultaneous development of dynamic strain-induced transformation (DSIT) and austenite grain growth was detected at the deformation temperatures above A_r3, while only DSIT happened as the deformation proceeded at lower temperatures close to and below A_r3. In addition, a reverse ferrite-to-austenite transformation was also observed. Most of the strain-induced ferrite nucleated on the boundaries of ultrafine prior austenite grains, especially at the corners and no evidence about intragranular nucleus was obviously obtained.