Packet microstructure in Fe-0.2 pct C martensite

Abstract

The arrangement, size, and boundary area of the laths that make up a packet of martensite in a coarse-grained Fe-0.2 pct C alloy were studied by replica and thin foil electron microscopy. Frequently laths of two habit plane variants coupled to a single {111}_A plane of the parent austenite are observed in a packet. The width distribution of the laths is log normal, with the most frequently observed lath width being 0.15 microns. Larger laths between 1 and 2 microns are distributed throughout a packet. The total lath boundary area per unit volume of martensite obtained by analysis of micrographs taken from thin foils is quite high, 65,000 cm^-1, and analysis of packet structure by selected area diffraction and precision dark field techniques show that there may be five times as much low angle boundary area as high angle boundary area in a packet.