The Dynamic Transformation of Deformed Austenite

The dynamic transformation behavior of deformed austenite was studied in four steels of increasing carbon contents that had been deformed over the temperature range 743 – 917°C. Strains of 0.15 – 5 were applied at strain rates of 0.4 - 4.5 s-1. The structures observed are Widmanstätten in form and appear to have nucleated displacively. The onsets of dynamic transformation and dynamic recrystallization were detected in the four steels using the double-differentiation method. Two sets of second derivative minima were found to be associated with all the flow curves. The mean flow stresses (MFS’s) pertaining to each experimental condition were calculated. The stress drop temperatures are shown to be about 40°C above the paraequilibrium. This type of behavior is ascribed to the occurrence of the dynamic transformation of austenite to ferrite during deformation. The effect of deformation on the Gibbs energy of austenite in these steels was estimated. The work should be useful for the engineers working in the hot strip mills of steel industries and also to the scientific community who are dedicated in the area of thermo-mechanical simulations in metals and materials.