Acoustic-emission and dilatometric investigations of the influence of Cr on the austenite decomposition kinetics

The interest of small additions of Cr (< 3 wt%) in steels for automotive and bearing applications has been recently highlighted. The microstructure of these steels is primarily based on the bainitic phase. Therefore, in order to optimize their microstructure and mechanical properties, it is of primary importance to gain a better understanding of the influence of Cr on austenite decomposition in different temperature regimes with a particular attention for the transition from ferrite to bainite and martensite formation. In the present study, the acoustic emission technique is used together with dilatometry and optical microscopy in order to obtain a full view of the transformation processes and kinetics. Specifically, acoustic emission is a technique that is capable of distinguishing a displacive from a diffusional transformation.