Grain boundary segregation in Fe-Mn-C twinning-induced plasticity steels studied by correlative electron backscatter diffraction and atom probe tomography

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We report on the characterization of grain boundary (GB) segregation in an Fe-28Mn-0.3C (wt.%) twinning-induced plasticity (TWIP) steel. After recrystallization of this steel for 24 h at 700 degrees C, similar to 50% general grain boundaries (GBs) and similar to 35% Sigma 3 annealing twin boundaries were observed (others were high-order Sigma and low-angle GBs). The segregation of B, C and P and traces of Si and Cu were detected at the general GB by atom probe tomography (APT) and quantified using ladder diagrams. In the case of the Sigma 3 coherent annealing twin, it was necessary to first locate the position of the boundary by density analysis of the atom probe data, then small amounts of B, Si and P segregation and, surprisingly, depletion of C were detected. The concentration of Mn was constant across the interface for both boundary types. The depletion of C at the annealing twin is explained by a local change in the stacking sequence at the boundary, creating a local hexagonal close-packed structure with low C solubility. This finding raises the question of whether segregation/depletion also occurs at Sigma 3 deformation twin boundaries in high-Mn TWIP steels. Consequently, a previously published APT dataset of the Fe-22Mn-0.6C alloy system, containing a high density of deformation twins due to 30% tensile deformation at room temperature, was reinvestigated using the same analysis routine as for the annealing twin. Although crystallographically identical to the annealing twin, no evidence of segregation or depletion was found at the deformation twins, owing to the lack of mobility of solutes during twin formation at room temperature. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Publisher
PERGAMON-ELSEVIER SCIENCE LTD
Issue Date
2015-01
Language
English
Article Type
Article
Keywords

AIDED CRYSTALLOGRAPHIC ANALYSIS; STRAIN-RATE SENSITIVITY; TWIP STEEL; HIGH-STRENGTH; AUSTENITIC STEEL; SOLUTE SEGREGATION; TRIP/TWIP STEELS; ALLOYS; MICROSTRUCTURE; EMBRITTLEMENT

Citation

ACTA MATERIALIA, v.83, pp.37 - 47

ISSN
1359-6454
DOI
10.1016/j.actamat.2014.09.041
URI
http://hdl.handle.net/10203/207024
Appears in Collection
MS-Journal Papers(저널논문)
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