The role of crystallographic orientation of martensitic variants on   cleavage crack propagation
  Cleavage crack propagation has been investigated in a low-carbon lath-martensitic steel using electron back-scattered diffraction technique. The ability of different martensitic boundaries within prior-austenite grain, such as sub-block, block and packet boundaries to resist cleavage crack propagation has been estimated in terms of Kurdjumov-Sachs crystallographic variants. Crystallographic study of crack path indicated that block boundaries are more effective in cleavage crack deviation as compared to packet boundaries, whilst sub-block boundaries are ineffective in that respect. Moreover, characterizing the boundaries in terms of misorientation angle (angle-axis pair) may be misleading if their effectiveness in retarding cleavage crack propagation is considered. 
Arya Chatterjee, A. Ghosh, A. Moitra, A. K. Bhaduri, R. Mitra, D.   Chakrabarti
cond-mat.mtrl-sci