A model for the competition between strain-induced precipitation and epitaxial growth in microalloyed austenite

A model has been developed for describing the competition between the formation of microalloyed carbonitrides by strain-induced precipitation (SIP) and by epitaxial growth on pre-existing TiN particles in γ-Fe. It is assumed that Nb and C/N atoms in the matrix will either feed the growth of pre-existing TiN precipitates or precipitate as new strain-induced particles. The model is successfully applied to the data set obtained by transmission electron microscopy (TEM) in a model alloy. Using this model, it is possible to estimate the effects of process parameters (T, applied strain), the number density of pre-existing TiN, and the Nb, C, N and Mn content on precipitate evolution and precipitation hardening. Notably, it is shown that the presence of a high number density of pre-existing TiN precipitates can suppress SIP. The conditions where epitaxial growth dominates and those in which strain-induced precipitation dominates are predicted and summarized in the form of processing maps.