Effect of deformation on the bainitic transformation

Abstract

The effect of deformation on the growth kinetics of bainitic ferrite plates was investigated under two types of conditions. In the first, deformation (ausforming) precedes the austenite-to-bainite transformation, while in the second case the phase transformation and deformation occur concurrently. The results clearly demonstrate that ausforming accelerates the nucleation of bainitic ferrite plates, leading to significant refinement of the final microstructure. When the bainite transformation takes place during deformation, the effect on nucleation was less obvious, but a clear increase in the growth rate of bainitic ferrite was observed. A modified version of the Zener-Hillert model for plate growth, with adjustments that allow for incorporating the effect of defects in the matrix and the effect of applied deformation on the movement of interfacial disconnections, was used to rationalize the effect of deformation on the growth kinetics. The calculations show that after ausforming, the stored dislocations act as a barrier to the growth of bainitic ferrite plates, resulting in a decreased lengthening rate. Conversely, when the transformation occurs concurrently with deformation, the lengthening rate of bainitic ferrite plates is accelerated due to the interaction between the applied stress and the disconnections at the tip of the bainitic ferrite plates.