The Origin of Midrib in Lenticular Martensite

Abstract

In the present paper, the origin of midrib in lenticular martensite is clarified by examining the similarity between midrib and thin plate martensite in detail and studying the stress-induced growth behavior of thin plate martensite at various temperatures. Although lenticular martensite, especially midrib, exhibits a zigzag array in general, some martensite plates which are branched or kinked were also observed as thin plate martensite. The substructure of midrib is completely twinned and the orientation relationship of midrib with respect to austenite is close to Greninger-Troiano relationship. These morphology, substructure and crystallographic features of midrib in lenticular martensite are quite similar to those of thin plate martensite. Furthermore, stress-induced growth behavior of thin plate martensite changes with deformation temperature. Thermally-transformed thin plate martensite grows keeping a thin plate shape when deformed at temperature close to the Ms temperature. However, it grows into a lenticular shape accompanying a substructure with a high density of dislocations after deformation at temperature much higher than Ms temperature. Therefore, it is concluded that midrib in lenticular martensite is thin plate martensite itself. The difference between lenticular martensite and thin plate martensite is only in their growth behaviors.

Microstructural Path Analysis of Martensite Dimensions in FeNiC and FeC Alloys

“…This observation supports the view that the martensite propagation is not single-step. The midrib of lenticular-martensite is similar to thin-plate martensite that tends to grow with minimum disturbance within the surrounding austenite 15 . Moreover, sometimes a midrib is seen to penetrate an impinged unit until the boundary of the twinned zone.…”

“…These intrinsic aspects of martensite growth have been considered from different points of view [7][8][9][10][11][12][13][14][15] . However, the linkage to a formal description of the progress of martensite transformation as a function of the leading variable still deserves effort, minding the microstructural complexity of martensite, an example of which is shown in Figure 1.…”

The Effect of Ti Content on α' Martensite Phase Transformation, and Magnetic Properties by Mössbauer Spectroscopy in Fe-30%Ni-x%Ti (wt%) Alloys

“…In Fig. 1b, the martensite/austenite (M/A) interface of lenticular martensite is smoothly curved and the midrib region, where the martensitic transformation is thought to begin, has a substructure of fine transformation twins [2]. The small lenticular martensite partially fills the inside of the austenite grains in Fig.…”

“…Martensite phase transformation occurs athermally, with rapid transformation during quenching; yet, it also occurs isothermally, with a slower transformation, when Febased alloys are kept at a constant temperature and external deformation is applied [1]. In addition to kinetic differences in the transformation, there are differences in morphologies of both martensite phases [2][3][4]. As one of the most important structural materials, martensite -its morphology and substructure in Fe-Ni alloyshas been investigated widely [5][6][7][8].…”

Carbon Redistribution in Martensite in High-C Steel: Atomic-Scale Characterization and Modelling

“…Shibata et al [8] studied the mechanisms of martensite plate formation during cooling. The midribs mark the starting point of the transformation where the mechanical twins form.…”