Couplings of Thin-plate Martensites in an Fe–Ni–C Alloy

Abstract

The morphologies of couplings of thin-plate martensites in an Fe-31%Ni-0.28%C alloy were investigated by means of transmission electron microscopy and they were discussed in terms of the phenomenological martensite theory. The results obtained are as follows.(1) The morphologies of couplings such as spear, wedge, kink, diamond, composite spear and zig-zag types were observed. These couplings consisted of variants in the same plate group and some of wedge and zig-zag type couplings were found to be composed of variants in different plate groups.(3) From the average form of the shape strain matrices of the variants, it is considered that the spear, wedge, diamond and zig-zag type couplings are self-accommodating, whereas the kink type is not.(4) The diamond and composite spear type couplings were the composite of some of the three fundamental types, spear, wedge and kink ones.(5) The junction planes of couplings of variants in the same plate group could be derived from the planes of intersection of the strain ellipsoids of the variants and the sense of the shear directions of the shape strains of the variants at the junction planes.

Crystallographic Analysis of Isothermally Transformed Bainite in 0.2C–2.0Mn–1.5Si–0.6Cr Steel Using EBSD

“…Variant selection is, generally (in the absence of retained deformation), explained to be caused by steels tendency to accommodate plastic strains induced in austenite during transformation and thereby to enhance bainite transformation. For example, in the case of martensitic transformation, it is well known to have the specific combination of variants in order to accommodate the transformation strains [24] .…”

Effect of Austenite Grain Size on the Morphology and Crystallography of Lath Martensite in Low Carbon Steels

“…self-accommodation, takes place. 17) As the Ms temperature decreases and austenite/martensite are strengthened by addition of manganese, it becomes more difficult to deform austenite and/or martensite plastically. Under such circumstances, the elastic stress is larger even for the formation of block of a given size, resulting in more frequent self-accommodation.…”

The Origin of Midrib in Lenticular Martensite

“…These martensite plates consist of several variants which are selfaccommodating of transformation strain one another. 21,22) All lenticular martensite plate do not necessarily exhibit such a typical morphology and some irregular morphologies can be observed. Figures 2(a), (c) and (e) show the various kinds of irregular morphologies of lenticular martensite.…”