Influence of austenitic orientation on martensitic transformations in a compressed high manganese steel

High manganese TRIP/TWIP steels contain two types of martensite and the morphology, size, variant selection and texture of both types of martensite are influenced by the parent austenite grain orientation. In the present paper the TRIP effect was investigated in a compressed high manganese steel, focusing on the crystallographic behavior by means of X-ray diffraction and the electron back scatter diffraction (EBSD) technique. It is observed that gamma austenite oriented with < 100 > close to the compression axis (CA) transformed more easily into alpha'-martensite with only one variant, whereas the transformation in CA//< 1 1 0 > and < 1 1 1 >-oriented austenite was sluggish and often yielded several variants. This orientation dependency was ascribed to the ease of either deformation twinning or Shockley dislocation movement. Similarly, epsilon-M was also observed to transform smoothly into alpha'-M in nearly < 100 >-oriented austenite and more sluggishly in other austenite grains of other orientations. However, the number of epsilon-M variants detected by EBSD was higher than direct observation. In contrast to thermally induced martensitic transformations, the TRIP effect during compression failed to cause grain refinement in the transformed alpha'-M. The rapid formation of alpha'-M in < 100 >-oriented gamma promoted the formation of a < 100 > texture of the alpha'-M, whereas the < 100 > texture developed in the austenite at high level of compression led to a restricted transformation into martensite. The reasons for the occurrence of a < 1 0 0 > texture in the alpha'-M and for the behavior of the epsilon-M are discussed. (C) 2011 Elsevier B. V. All rights reserved.