A structure created by intersecting ε martensite variant plates in a high-manganese steel

Microstructural evidence for a new intersection structure, which has been observed in grains oriented to near < 101 > in a polycrystalline Fe-30Mn-4Si-2Al TRIP/TWIP steel, was obtained by combined use of electron backscatter diffraction and transmission electron microscopy, and the responsible intersection mechanisms are discussed from crystallographic and thermodynamic viewpoints. A gamma phase with the orientation 90 degrees rotated from the matrix with respect to the intersection axis is produced at the intersection of two dense epsilon plates, whereas the twinning of the obstacle epsilon plate occurs when the incident plate is a fine gamma/epsilon lamella or a stacking fault bundle. The results are compared with various structures reported previously, and the wide variation of the intersection reactions is interpreted by their dependence on thermodynamic stability of the phases, grain orientation and shear amount.