Martensite Nucleation at Grain Boundaries Containing Intrinsic Grain Boundary Dislocations

Abstract

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.