Influence of annealing parameters on phase evolution and recrystallization kinetics of a Mn-Al-Si alloyed duplex steel

Abstract

In this study, the phase transformation and recrystallization behavior of hot-forged Fe-Mn-Al-Si-C alloyed duplex steel has been investigated in wide ranges of annealing temperatures (973-1273K) and durations (15–150min). The recrystallization kinetics has been evaluated employing Johnson-Mehl-Avrami-Kolmogorov model. A limited extent of phase transformation (i.e. duplex to single phase) has been found to take place during annealing in the range of 973-1173K. However, during annealing at 1273K, not only the transformation from duplex to ferritic microstructure accelerates, but also recrystallization is initiated in these ferrite grains. The changes in the free energy of the austenite with the annealing temperature play a pivotal role in dictating the stabilization of the corresponding phase. Moreover, the disappearance of the austenitic phase at 1273K owing to higher free energy is compensated by the formation of Mn-Al-Si rich carbide precipitates. The phase evolution triggered by annealing at 1273K affects the recrystallization kinetics of each of the phase constituents. A sharp rise in the Avrami exponent (n) value is noticed following annealing at 1273K, which clearly denotes that the disappearing austenite-ferrite interfaces facilitate the migration of the ferrite boundaries that stimulate recrystallization. In spite of the increasing values of n with the annealing temperature, its maximum value (at 1273K) remains close to 1. This is a clear indication of the sluggish nature of the recrystallization process in the developed alloy.