Phase-Field Simulation Of Alpha Growth Stagnation During Gamma -> Alpha Transformation In Fe-X-Y And Fe-C-Mn Alloys

In multicomponent steels such as Fe-C-Mn alloys that contain substitutional alloying elements, the stagnation of ferrite (alpha) growth during the austenite-to-ferrite (gamma -> alpha) transformation has been experimentally observed under specific chemical compositions and temperatures. The purpose of this study is to investigate the alpha growth stagnation by the phase-field (PF) method. We examined the effect of the diffusivity of the substitutional alloying element on the stagnation by simulating the isothermal gamma -> alpha transformation in virtual Fe-X-Y and real Fe-C-Mn alloys. The results for the Fe-X-Y alloy showed that at a specific diffusivity of the substitutional Y element, the alpha growth stagnated without the soft impingement of the interstitial X atoms. This applied for alloys with initial compositions in the partitioning local equilibrium (PLE) and para-equilibrium (PE) regions of the phase diagram. The stagnation was demonstrated to be caused by the alpha growth mode transition from the PE to PLE mode, which was triggered by the formation of the substitutional solute spike at the alpha/gamma interface. The results for the Fe-C-Mn alloy verified that the alpha growth mode transition also caused the stagnation of a growth in the multi-component steels. (C) The Minerals, Metals & Materials Society and ASM International 2018