抄録
The substructure of thin foil martensite formed below room temperature was studied in Fe–6Mn–1C, Fe–5.5Mn–1C, Fe–3Mn–3Cr–1C and Fe–8Cr–1C steels using transmission electron microscopy and diffraction. In the thin foils, as with bulk materials, the martensite habit plane in the above alloys was found to be near {225}. Even though constraints are expected to be relaxed for thin foils (two-dimensional transformations) the observed substructure was found to be highly complex. Substantial evidence for accommodation distortion in thin foils was obtained.
Several morphologies of {112}b transformation twins, and {011}b and {123}b stacking faults were observed, in addition to dislocations. Upon examining the crystallography of {112}b twins in some detail, it was found that the previously reported deviation of the twin traces from {112} could arise from an incorrect assessment of the twin plane trace; the present work shows the long traces lying in the specimen plane are not necessarily twin plane traces.
Two types of twin-stacking fault interactions were observed. In one case, stacking faults which appear to be inherited from the austenite place crystallographic restrictions on the {112} twins. Only those twin variants form whose twinning direction lies in the fault plane. In the other type of interaction, post-transformation accommodation distortion appears to occur by the activation of only those {110} and {123} fault variants which can penetrate both orientations of the {112} twins without suffering deviation.
