Microstructure Evolution during Quenching and Tempering of Martensite in a Medium C Steel
The microstructural evolution of a quenched medium-C steel during tempering was analyzed by means of Orientation Imaging Microscopy (OIM). The steel was heat treated in order to develop fully martensitic microstructures after quenching with a different prior austenite grain size (AGS). Main results can be summarized as below: A very poor effect of AGS on packet size was found in comparison to bainitic steels. A finer packet was measured at mid-thickness with respect to surface after the quenching process. This phenomenon was attributed to the effect of thermal strain path on phase transformation during quenching. The through-thickness microstructural gradient remains after tempering. High-angle boundary grains do not significantly grow after tempering; on the contrary, low-angle grain boundaries (cells) move, fully justifying the hardness evolution with tempering temperature.
E.J. Palmiere and B.P. Wynne
A. di Schino et al., "Microstructure Evolution during Quenching and Tempering of Martensite in a Medium C Steel", Materials Science Forum, Vols. 715-716, pp. 860-865, 2012