2014 Volume 54 Issue 10 Pages 2394-2403
It is shown that grain boundaries containing intrinsic grain boundary dislocations act as preferential nucleation site for the martensitic transformation. The microstructure and crystallography of BCC α’-martensite formed in a sensitized AISI 304 stainless steel was studied in detail by means of convergent beam Kikuchi pattern analysis. The orientation relationship between martensite and austenite was determined to be Kurdjumov-Sachs type. The presence of intrinsic grain boundary dislocations was observed at a grain boundary 10.83° from the exact Σ11 CSL boundary orientation, where a martensite nucleus formed by the faulting and extension of intrinsic grain boundary dislocations. The selection of the crystallographic variant for the martensite nucleus was not related to a reduction in interfacial energy at nucleation, nor was it related to the accommodation of transformation strain by easy slip in the austenite.