Movement of γ/ε interfaces and coalescence of ε martensite variants under the tensile stress in an Fe-24 wt Pct Mn alloy

This study was pursued to investigate the movement of gamma/epsilon interfaces and the coalescence of epsilon martensite variants in an Fe-Mn binary system. An Fe-24 wt pct Mn tensile specimen was deformed with increasing tensile strain at room temperature. The microstructural changes at a fixed area of the tensile specimen were continuously observed using an optical microscope. Some of the gamma/epsilon interfaces moved forward due to gamma --> epsilon transformation, and the others moved backward due to its reverse transformation during the tensile deformation, depending on the orientation relationship between the tensile direction and each epsilon variant. The coalescence of epsilon martensite variants primarily occurs by the following three factors: (1) the reverse transformation of epsilon variants under an applied stress having a different direction from that of the epsilon variants' shape change, (2) the nucleation and growth of new epsilon variants under an applied stress having the same direction as that of the epsilon variants' shape change, and (3) the continuous growth of pre-existing epsilon variants under an applied stress having the same direction as that of the epsilon variants' shape change.