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 γ/ε interfaces and the coalescence of ε 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 γ/ε interfaces moved forward due to γ → ε 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 ε variant. The coalescence of ε martensite variants primarily occurs by the following three factors: (1) the reverse transformation of ε variants under an applied stress having a different direction from that of the ε variants' shape change, (2) the nucleation and growth of new ε variants under an applied stress having the same direction as that of the ε variants' shape change, and (3) the continuous growth of pre-existing ε variants under an applied stress having the same direction as that of the ε variants' shape change.