State of the retained austenite after thermomechanical processing a trip steel

Thermomechanical processing is an optimum production method to generate the desired mechanical properties of materials, since it combines deformation and heat treatment to control microstructural evolution. TRIP (Transformation-Induced-Plasticity) behavior is a powerful mechanism with which to improve in situ mechanical properties. The basis of TRIP behavior is the retention of austenite at room temperature. With this in mind, the present work concerns the effect of austenite history after TMP on the state of retained austenite. TMP was applied to a Nb bearing TRIP steel (0.22% C, 1.55% Mn, 1.55% Si and 0.035% Nb) in order to obtain statically and dynamically recrystallized, and pancaked austenite. These conditions were achieved by changing the Zener-Holloman, parameters, i.e. the strain rate and temperature of deformation. The austenite history has significant effects on substructure and properties of austenite grains. These, in turn, affect the alloying element partitioning and the ferrite formation characteristics. All these factors can influence the state of retained austenite and, accordingly, the TRIP properties.