Search

Abstract: This study investigated the substructures of lenticular martensites with different martensite start temperatures (Ms) by transmission electron microscopy. Observation of Fe–33Ni revealed a substructural change from fine transformation twins in the midrib and twinned region to several sets of screw dislocations in the untwinned region during growth. Tangled and curved dislocations also appeared near the martensite–austenite interface of the untwinned region, as the martensite inherited the dislocations in the surrounding austenite. In contrast, curved and tangled dislocations appeared in the entire untwinned region in Fe–31Ni and in the whole martensite plate in Fe–20.5Ni–35Co, as the higher Ms temperatures facilitated the plastic deformation of the surrounding austenite. Thermally transformed thin plate martensite in Fe–31Ni–10Co–3Ti grew into a lenticular shape accompanied by a substructure with dislocations after deformation at temperatures above the Ms temperature. The change in the substructure of lenticular martensite presumably resulted from the local temperature rise in the martensite plate. [Copyright &y& Elsevier]

Abstract: The orientation relationship of lenticular martensite (M) with respect to austenite (A) is nearly Greninger–Troiano at the midrib and twinned region but gradually deviates towards Kurdjumov–Sachs near the M/A interface. This change is related to the change in the substructure of martensite and also to the deformation in the surrounding austenite. [Copyright &y& Elsevier]

The morphology and crystallography of lath martensite in Fe-C alloys containing various carbon contents from 0.0026 to 0.61% were studied by analyzing electron back scattered diffraction patterns in scanning electron microscopy and Kikuchi diffraction patterns in transmission electron microscopy. As carbon content increases, the sizes of both packet and block decrease. In low carbon steels (0.0026–0.38%C), a block which is observed as having different contrasts under optical microscopy contains two groups (sub-blocks) of laths which are of two K-S variants with a misorientation of about 10 degrees. On the other hand, in the high carbon alloy (0.61%C), a block consists of laths of a single K-S variant. [Copyright &y& Elsevier]