The heritage of the twin microstructure in the sigma phase formed from deformed austenite

Abstract Deformation twinning is the main mechanism for the nanocrystallization of austenite and the sigma phase, which has been found to nucleate at deformation twin boundaries, especially at their intersections in over-deformed austenite stainless steel. In the present paper, deformation twin heritage is found in sigma nuclei in the early stage of sigma phase transformation, due to the continuous feature of twin boundaries. The sigma nuclei change their crystal orientation by following the symmetrical feature of deformation twin boundaries during growth. This unique nucleation and growth pattern of the sigma phase is in favour of decreasing the energy required for sigma transformation from deformed austenite.