Site-specific atomic-scale characterisation of retained austenite in a strip cast TRIP steel

TLDR: In this paper, the carbon content of retained austenite (RA) with different neighboring phases is investigated by correlating electron backscattering diffraction, transmission electron microscopy and atom probe tomography.

About: This article is published in Acta Materialia.The article was published on 2017-08-01 and is currently open access. It has received 45 citations till now. The article focuses on the topics: TRIP steel & Beta ferrite.

Figures

Figure 2. (a) EBSD phase map (red = fcc and blue = bcc) overlaid on band contrast (the black region at the right lower corner corresponds to the hole in the twin-jet electropolished foil) and (b, c, d, e) correlated TEM microstructures. (b) Blocky retained austenite and martensite adjacent to the polygonal ferrite/second phase region interface (the zone axis of insets is (011)γ and (111)α, respectively); (c, d) film retained austenite between bainitic ferrite laths (the zone axis of (c) insets is and ;

Figure 11. (a) TEM showing two film retained austenite and (b) corresponding carbon profile along the dark arrow in (a) using electron energy loss spectroscopy. RA is retained austenite and BF is bainitic ferrite lath.

Figure 9. (a) A representative cylindrical region of interest perpendicular to the iso-concentration surface of 3.0 at. % carbon (Figure 4(a)), and (b) corresponding integral profiles across the interface showing the cumulative number of carbon, manganese and chromium atoms as a function of the cumulative number of all atoms; (c) interface regions for carbon, manganese and chromium determined by proximity histogram analysis. RA is retained austenite, BF is bainitic ferrite lath and GB is ferrite in granular bainite.

Table 1. The chemical composition of the studied strip cast TRIP steel.

Figure 13. (a) Dilation as a function of holding time at 400 ˚C and (b) the corresponding evolution of segregation across the interface between austenite and ferrite after completion of growth (left diagrams) and after tempering (right schematics). PE is paraequilibrium, NP is negligible partitioning, P is partitioning, F is ferrite and A is austenite.

Table 3. The relative diffusion distance of Mn/Cr segregation region with respect to C interface region and the Gibbsian interfacial excess of solutes (atoms/cm2). RA is retained austenite, BF is baintic ferrite and GB is granular bainite.