Interaction between carbon partitioning and carbide nucleation inside austenite during a bainitic type transformation

The interaction between the displacive transformation, carbon partitioning and carbide nucleation inside austenite during a bainitic type transformation was studied using a phase field model incorporating the displacive transformation and diffusion processes. The carbide nucleation was modeled as a formation of carbon sinks inside austenite with different nucleation sequences. The results obtained with different nucleation sequences demonstrate that carbide nucleation may play a secondary role controlling the transformation kinetics and microstructure evolution after the fast transformation stage completion; however, elastic interactions can control the ferrite morphology even at a later stage, thus leading to the change of the ferrite grain shape from a rod-like to plate-like. A rate of the carbide nucleation and the number of nucleated carbides controlled the extension of the stasis period separating the fast and slow transformation stages and the rate of the transformation after the stasis or during a temporary slowdown period. Results show that the transformation can proceed through several slowdown acceleration periods.