Mechanical Behavior of Individual Retained Austenite Grains in High Carbon Quenched-tempered Steel

Abstract

The deformation behaviors of metastable retained austenite and martensite in a high carbon quenched-tempered steel were investigated complementarily using electron backscattered diffraction, nanoindentation and transmission electron microscopy (TEM) to determine the effect of the austenite grain size on its mechanical stability. Investigation by the nanoindentation have shown that martensite exhibits a single plastic deformation stage, i.e., a dislocation glide motion, whereas metastable retained austenite exhibits double plastic deformation stages. TEM observations of a cross-sliced foil with an indentation mark has suggested that the first stage deformation in the austenite phase is dominated by stress-induced martensite transformation, while the second stage is governed by the slip deformation of dislocations in the transformed martensite. Furthermore, we have found that the stress required for the phase transformation and for the transition from the phase transformation to the plastic deformation of transformed martensite increase with decreasing in austenite grain size, indicating that fine austenite grains are mechanically more stable than coarse austenite grains.

Schematic illustration of the cross-sectional view of the deformation behavior during indentation for a retained austenite grain surrounded by a tempered martensite phase combined with a P/h versus h plot.