Precipitation kinetics and their effects on age hardening in an Fe-Mn-Si-Ti martensitic alloy

The kinetics of the phase transformations occurring during the isothermal tempering of an Fe-Mn-Si-Ti martensitic alloy are reviewed. The use of the kinetic theory of overlapping phase transformations (KTOPT) permits the characterization of the main basic processes that develop simultaneously during tempering, and which effectively compete for the same solute as they progress. The partial transformation of martensite into austenite takes place at tempering times where the metastable and isomorphous precipitates of Fe3Si are developed at the intermediate tempering temperatures. The austenite growth process overlaps the growth of the metastable precipitates of Fe3Si, resulting in a reversal of the hardening mechanisms, where the shearing of particles by dislocations predominates at long tempering times. Therefore, the coarsening of the metastable compound of Fe3Si deviates from the classical Lifshitz, Slyozov and Wagner coarsening behavior. The precipitation of the stable phase (Laves phase) does not interfere with the evolution of either of the abovementioned overlapping processes. (C) 2011 Elsevier B.V. All rights reserved.