Abstract
In this contribution, the nucleation and growth mechanism of austenite during the intercritical annealing (IA) of medium Mn steels (MMSs) are reviewed. The nucleation of austenite can be enhanced due to the introduction of (sub)grain boundaries, dislocations, and carbides before austenitization. Although martensite may transform to austenite in a displacive way during flash heating, austenitic nuclei usually grow with the diffusion and partitioning of solute C/Mn atoms. The latter, however, is still difficult to be modeled because the combined influence of interface dissipation energy, defects, and carbide particles is not well understood and quantified. Next, four recent emerging processing technologies, including prior deformation for generating dislocations, additional tempering for the precipitation of carbides, additional annealing before IA, and flash heating, are also analyzed according to the above‐stated nucleation and growth mechanism. Finally, it is proposed that the targeted austenite grains for improving the mechanical properties of MMS shall be produced by enhancing both nucleation sites and growth kinetics of austenite via the deliberate design of processing routes.
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