A STUDY OF GRAIN-BOUNDARY STATISTICS IN 304-STAINLESS STEELS AND 316L-STAINLESS STEELS

The distribution of grain boundaries by misorientation parameters in two austenitic stainless steels, AISI types 304 and 316L, having different stacking fault energies, have been studied by means of transmission electron microscopy. The results obtained show that grain boundary spectrum is characterized by the dominance of SIGMA-3n boundaries and is quasi-stable in fc.c. materials with low and medium stacking fault energy that are susceptible to annealing twinning. However, the distribution of the lengths of different grain boundary types in these materials is sensitive to the stacking fault energy. Only SIGMA-3 boundaries have been found to be energetically favoured, while the observed preponderance of SIGMA-9 and SIGMA-27 is due to geometrical reasons: they are necessary for providing connection between SIGMA-3 boundaries in the process of multiple twinning.