Formation Temperature and Growth Behavior of Thin Plate Martensite in Fe–Ni–C Alloys

Abstract

The authors have previously found that the morphology of martensite in Fe-Ni-0.25%C alloys the transition temperature from the lenticular to the thin plate and the carbon content of Fe-Ni-C alloys was examined by adjusting the carbon content up to 0.9% and the nickel content from 25 to 35%. Furthermore, some features in the progress of transformation to the thin plate martensite from austenite were observed as compared with those of lenticular martensite. The main results obtained are as follows.(1) The transition temperature at which the morphology of martensite in Fe-Ni-C alloys changes from the lenticular to the thin plate rises with increase in carbon content. For example, in (2) The following features in the progress of transformation to the thin plate martensite were observed. (a) During the subsequent cooling, the martensite plate itself thickens in addition to the formation of a new martensite plate in the other part of austenite. (b) The burst phenomenon is not observed. (c) Accommodation slip caused by martensitic transformation is hardly observed in the austenite adjacent to the martensite plate. These phenomena are entirely different from the usual lenticular.

Effect of Mo on the magnetic properties of martensitic phase in Fe–Ni–Mo alloys

“…It may be concluded that Mo element influences both on the stabilization of austenite and on the martensite start temperature (M S ) like other some alloying elements. Also Maki et al [16,17] investigated the effect of Ms temperature on martensite morphology.…”

The Origin of Midrib in Lenticular Martensite

“…16,17) Among various 0 martensite morphology, only thin plate martensite has a mobile M/A interface and exhibits a shape memory effect. [18][19][20] As mentioned above, basic characters of lenticular martensite and thin plate martensite are completely different. However, when only midrib is paid attention, substructures and habit planes of midrib and thin plate martensite are quite similar.…”

Some Observations of Ausageing Effects on the Martensitic Transformation in an Fe–Ni–Ti Alloy

“…Those were known merely to belong to two zones of the martensite, [731] and [951], away taneous appearance of such two different zonal patterns is accounted for by some elongation of reciprocal lattice points, buckling of the foil specimen and so on. Anyway, such a nottwinned structure of the "thin plate" martensite is quite different from a completely twinned one of the thin plate martensites typically observed in Fe-Ni-C alloys (17). Thus, another type of lattice invariant shear (LIS), other than twinning, should occur upon the formation of such a thin plate martensite as presently observed, in order to maintain the invariant plane (a) and (b) are obviously asymmetrical in shape, indicating the martensite crystal to be tetragonal.…”

“…Maki et al (17) previously found in Fe-Ni-C alloys that the martensite morphology changed from lenticular to thin plate even in an alloy with an identical composition if Ms temperature (or the formation temperature of martensites strain-induced) was decreased. Hence it has been known that a transition temperature exists for the morphological change of an individual alloy.…”