3D Crystallographic Analysis of Grain Boundaries of Austenite Transformed from Ferrite on Heating in Fe-Mn-C Alloy

Abstract

To control the ferrite and martensite microstructure in dual-phase steels, the phase transformation from ferrite (α) to austenite (γ) on heating is essential. For a comprehensive understanding of the γ formation in the early stage of the α → γ phase transformation, the orientation relationships and the boundaries between α and γ grains were investigated using a 3D electron backscatter diffraction analysis. It was found that, when the orientations of the α and γ grains hold the K–S relationship or the N–W relationship, the orientation of the boundary does not correspond to the exact close-packed planes {011}α or {111}γ, but deviates within the vicinity of these crystal planes based on a variety of misorientations of up to 40 deg. Most of the boundary planes with the K–S relationship are parallel to the crystal planes between {011}α and {111}α of the α grain, and {111}γ and {012}γ of the γ grain. Focusing on the crystallographic feature of the boundary planes in austenite phase, the mechanism of the α → γ transformation is discussed.