Abstract: Strain-induced martensites in high manganese TRIP/TWIP steels were investigated in the presence of thermal martensites and under the influence of austenitic grain orientation by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Before deformation, the morphology of α'-M depended mainly on the number of variants and growing period. Regardless of martensite morphologies and
deformation, the Kurdjumov-Sachs (K-S) orientation relationships always maintained. The 6 α'-M variants formed from a plate of ε-M were of 3 pairs of twins with a common axis <110>_α' parallel to the normal of {111}_γ habit plane to minimize transformation strain. When α'-M could be formed only by deformation, it nucleated at the intersection of ε-M variants and grew mainly in thick "-M plates. Thick " plates promoted significantly the α'-M and weakened the influence of grain orientations. During tension, the transformation in <100>-oriented grains was observed to be slower than that in <111>-oriented grains. Deformation twins promoted ε-M formation slightly and had no apparent effect on α'-M. Deformation increased the number of "-M variants, but reduced that of α'-M variants.

Key words: High manganese steel, Martensite, TRIP effect, Orientation relationship, Electron backscattered diffraction (EBSD)