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 ε-M plates.Thick ε 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 ε-M variants,but reduced that of α’-M variants. 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 periods. Regardless of martensite morphologies and deformation, the Kurdjumov-Sachs (KS) orientation relationships always maintained. 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 of strain .When α’-M could be formed only by deformation, it nucleated at the intersection of ε-M variants and grew mainly in thick ε-M plates. Thick ε plates promoted significantly the α’-M and weakened the influence of grain orientations. Drawing 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 ε-M variants, but reduced that of α’-M variants.