Effects of Precipitation, Recovery and Recrystallization on the Microstructural Evolution of Microalloyed Austenite

Abstract

<p>The deformation of metals and alloys increases the energy of the system through the storage of dislocations. This stored-energy is the driving force for the processes of recovery and recrystallization. In microalloyed steels, the dislocations provide the necessary nucleation sites for the precipitation of fine dispersions of carbonitrides. Thus, the deformation of microalloyed austenite is followed by three simultaneous processes, namely, recovery, recyrstallization and precipitation. The processes are closely coupled and the progress of each is strongly influence by the evolution of the other processes. In this contribution, existing models of recovery, recrystallization and precipitation have been coupled to produce a physically-based model of the evolution of microalloyed austenite following deformation. The model's predictions are in excellent quantitative agreement with the existing experimental observations in the literature. A series of fully-austenitic model alloys was developed to examine the underlying assumptions of the above model. The model alloys are based on the Ni-Fe-Nb-C system and were designed to match the stacking-fault-energy of low carbon steels. In this way, it was possible to observe the evolution of microstructure directly in an alloy that closely resembled C-Mn steels. Precipitation in the model alloys was studied extensively, using the techniques of small angle neutron scattering and electron microscopy. In addition, mechanical testing was used to study the variation of the yield stress in deformed and annealed samples. The predictions of the model are shown to be in good agreement with the experimental observations. Both point to a strong interaction between precipitation and recovery in microalloyed steels. This interaction dominates the microstructural evolution of these steels at low-rolling-temperatures.</p>