Materials Transactions Online

Transactions of the Japan Institute of Metals, Vol. 16 No. 2 (1975) pp.73-86
© 1975 The Japan Institute of Metals

Substructure of Thin Foil (225) Ferrous Martensites

R. Oshima* and C. M. Wayman**

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.

(Received May 27, 1974)

* Department of Metallurgy and Mining Engineering, University of Illinois at Urbana-Champaign, Illinois. Present address: Faculty of Engineering Science, Osaka University, Toyonaka 560, Japan.

** Department of Metallurgy and Mining Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, U.S.A.

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