Transmission electron microscopy studies of {225} f martensite in an Fe-8%Cr-1%C alloy

Abstract

Fully grown {225}, martensite plates in an Fe-8 %Cr-1 %C alloy were examined by means of transmission electron microscopy and diffraction. (112) b twins, (011) b planar defects and (1̄12) b slip traces were observed as internal planar inhomogeneities accompanying the transformation.§ General features of the (112) b twins were considerably different from those found in ferrous martensites which exhibit the {3, 10, 15} f habit plane. The (112) b twins were usually observed only at one austenite-martensite interface and a mid-rib region of high twin density was not found in most plates. In a few instances a mid-rib was observed at the center of plates, in which cases the (112) b transformation twins were bent at this region as well as at the interface regions to which the twins extended. (1̄12) b slip resulted in fragmented (112) b twins in several cases. Internal (011) b planar defects, which are possibly twins, formed on planes parallel with the (111) f planes of the Kurdjumov-Sachs orientation relationship. In addition to the above planar inhomogeneities, lengthy dislocations nearly parallel to (112) b and (011) b were observed in untwinned regions of plates. These internal dislocations were mixed and not of screw type as observed in Fe-Ni martensites. Dislocations observed at the austenite-martensite interface were nearly parallel to [11̄2] f , which lies approximately in the habit plane. These various internal defects are considered in relation to existing crystallographic information and theory.